Surgical Technology and Practice

Question 1

You use a 2-0 coated vicryl suture to close the galea during closure of a craniotomy. Which one of the following statements is correct?
a. It is a synthetic, braided absorbable suture
b. It is a synthetic, braided non-absorbable suture
c. It is a synthetic, monofilament absorbable suture
d. It is a natural, braided absorbable suture
e. It is a synthetic, monofilament nonabsorbable suture

Answer 1

a. It is a synthetic, braided absorbable suture

Suture choice will depend on tensile strength
required, local availability and surgeon preference. Size varies from 5 (largest; not the same
as 5-0) to 11-0 (smallest). Needle shape (e.g.
straight, half curved, ½ circle) and point geometry
(e.g. cutting needle, taper, reverse cutting) also
vary. Natural sutures include silk and catgut,
while the remainder are synthetic and have different structure (braided vs. monofilament) and
absorption (absorbable vs. non-absorbable) properties. Absorbable suture breaks down over time
in the body. The amount of time it takes a suture
to break down in the body depends on a few factors such as suture type, size and the location it is
placed. Suture absorption rates can increase in
patients with fever, infection or protein deficiency. Also, the strength to a suture will decrease
significantly prior to its complete breakdown
time. Therefore a suture with higher tissue tension will have a greater chance of failure prior
to the amount of time listed above. Braided suture
have a number of strands woven together like a
string. It is thought that non-braided sutures
cause less reactivity in the body and are not as
prone to becoming infected because they lack
the grooves and rough surface for things to
adhere. However non-braided sutures can have
a greater tendency to loosen at the surgical knot
with the lack of grip

Suture choice will depend on tensile strength
required, local availability and surgeon preference. Size varies from 5 (largest; not the same
as 5-0) to 11-0 (smallest). Needle shape (e.g.
straight, half curved, ½ circle) and point geometry
(e.g. cutting needle, taper, reverse cutting) also
vary. Natural sutures include silk and catgut,
while the remainder are synthetic and have different structure (braided vs. monofilament) and
absorption (absorbable vs. non-absorbable) properties. Absorbable suture breaks down over time
in the body. The amount of time it takes a suture
to break down in the body depends on a few factors such as suture type, size and the location it is
placed. Suture absorption rates can increase in
patients with fever, infection or protein deficiency. Also, the strength to a suture will decrease
significantly prior to its complete breakdown
time. Therefore a suture with higher tissue tension will have a greater chance of failure prior
to the amount of time listed above. Braided suture
have a number of strands woven together like a
string. It is thought that non-braided sutures
cause less reactivity in the body and are not as
prone to becoming infected because they lack
the grooves and rough surface for things to
adhere. However non-braided sutures can have
a greater tendency to loosen at the surgical knot
with the lack of grip.

Question 2

During the resection of an intracranial tumor your boss asks the scrub nurse to prepare the ultrasonic aspirator. Which one of the following statements are correct regarding this piece of equipment?
a. Composed of an ultrasound generator, a sucker, and an irrigator
b. Ultrasonic dissector/aspirator that is selective for tissue with high water and low collagen content
c. Fragmentation of solid tissues, relative sparing of vessels
d. It could induce false-negative results during motor brain mapping with direct electrical stimulation
e. Aspiration, ultrasonic dissection and irrigation properties can be controlled individually

Answer 2

d. It could induce false-negative results during motor brain mapping with direct electrical stimulation

CUSA is commonly used during surgical removal
of gliomas, meningiomas, schwannomas, craniopharyngiomas, and spinal cord neoplasms.
Briefly, it is composed of an ultrasound generator a sucker, and an irrigator that, together, form an
ultrasonic dissector/aspirator that is selective for
tissue with high water and low collagen content.
Its usefulness and widespread use are attributable
to several advantages, comprising fragmentation
of solid tissues, relative sparing of vessels, reduction of surgical time (by combining aspiration,
ultrasonic dissection, and irrigation in a single
operation), improved safety (by adjusting settings) and supposed minimal trauma to surrounding neural brain structures. On the other hand,
the use of ultrasonic dissection also has some disadvantages, primarily related to the inadequate
and unknown control of its energy, which may
lead to sudden and sometimes unexpected events
(vascular injuries and/or neural tissue damages)
and its possible interaction with intraoperative
brain mapping. In motor testing performed
through direct electrical stimulation a positive
response is given by the active movement (or by
its recording), whereas in language testing a positive response is actually a negative event (e.g.
inability to name objects). If CUSA use negatively
interferes with electrical conduction in adjacent
tissue it could lead to the misdetection of a motor
site, reducing the sensitivity of the technique (if
CUSA and DES are used simultaneously) by
causing false-negative results and increasing the
risk of motor deficit. Equally, when the CUSA
is used during intraoperative language testing,
through its negative interference with neurological function it could show true-positive
eloquent sites.

CUSA is commonly used during surgical removal
of gliomas, meningiomas, schwannomas, craniopharyngiomas, and spinal cord neoplasms.
Briefly, it is composed of an ultrasound generator, a sucker, and an irrigator that, together, form an
ultrasonic dissector/aspirator that is selective for
tissue with high water and low collagen content.
Its usefulness and widespread use are attributable
to several advantages, comprising fragmentation
of solid tissues, relative sparing of vessels, reduction of surgical time (by combining aspiration,
ultrasonic dissection, and irrigation in a single
operation), improved safety (by adjusting settings) and supposed minimal trauma to surrounding neural brain structures. On the other hand,
the use of ultrasonic dissection also has some disadvantages, primarily related to the inadequate
and unknown control of its energy, which may
lead to sudden and sometimes unexpected events
(vascular injuries and/or neural tissue damages)
and its possible interaction with intraoperative
brain mapping. In motor testing performed
through direct electrical stimulation a positive
response is given by the active movement (or by
its recording), whereas in language testing a positive response is actually a negative event (e.g.
inability to name objects). If CUSA use negatively
interferes with electrical conduction in adjacent
tissue it could lead to the misdetection of a motor
site, reducing the sensitivity of the technique (if
CUSA and DES are used simultaneously) by
causing false-negative results and increasing the
risk of motor deficit. Equally, when the CUSA
is used during intraoperative language testing,
through its negative interference with neurological function it could show true-positive
eloquent sites.

Question 3

Which one of the following statements regarding transcranial Doppler ultrasound is LEAST accurate?
a. Doppler effect is the apparent change in frequency of a wave as the source moves relative to the observer
b. Transcranial Doppler takes advantage of reflection of sound waves off blood vessel walls
c. May be useful in distinguishing vasospasm from hyperemia
d. A Lindegaard ratio (LR) of >3 suggests vasospasm
e. Middle cerebral artery (MCA) vasospasm is suggested by a Vmean of >180 cm/s

Answer 3

b. Transcranial Doppler takes advantage of reflection of sound waves off blood vessel walls

Doppler effect (shift) is the apparent change in
frequency of a wave as the source moves towards
or away from the observer. According to this
principle, ultrasound waves emitted from the
Doppler probe are transmitted through the skull
and reflected by moving red blood cells within the
intracerebral vessels. The difference in the frequency between the emitted and reflected waves
(Doppler shift frequency) is directly proportional
to their speed. Physiological variables affecting
TCD measured mean blood velocity are age, gender, hematocrit, viscosity, carbon dioxide,
temperature, blood pressure, and mental or
motor activity. Four main acoustic windows have
been described: transtemporal, transorbital, submandibular and the suboccipital windows.
Although each window has unique advantages
for different arteries and indications, a complete
TCD examination should include measurements
from all four windows and the course of blood
flow at various depths within each major branch
of the circle of Willis should be assessed. Specific
arteries of the circle of Willis are identified using
the following criteria: relative direction of the
probe within a specific acoustic window, direction
of blood flow relative to the probe, depth of ultrasound (insonation), and response to carotid compression or vibration (when difficult to
differentiate anterior from posterior circulation).
The LR, defined as the ratio between the time
mean average (Vmean) velocity of the MCA to
ICA, is the most established of such ratios and
helps differentiate hyperemia from vasospasm.
Hyperemia would result in flow elevations in
both the MCA and ICA and result in an
LR<3, whereas vasospasm would preferentially
elevate the MCA flow velocity over the ICA with
LR>6. LR between 3 and 6 is a sign of mild VSP
and >6 is an indication of severe VSP. TCD flow
velocity criteria appear to be most reliable for
detecting angiographic MCA and basilar artery
vasospasm. Findings in MCA vasospasm include
MCA Vmean 180 cm/s, a sudden rise in MCA
Vmean by >65 cm/s or 20% increase within 24 h
during days 3-7 post-subarachnoid hemorrhage,
LR6, and abrupt increase in Pulsatility index
>1.5 in two or more arteries suggesting increases
in ICP and/or vasospasm. TCD is most useful in
monitoring the temporal course of angiographic
vasospasm following SAH to help guide the timing
of diagnostic and therapeutic angiographic
interventions.

Doppler effect (shift) is the apparent change in
frequency of a wave as the source moves towards
or away from the observer. According to this
principle, ultrasound waves emitted from the
Doppler probe are transmitted through the skull
and reflected by moving red blood cells within the
intracerebral vessels. The difference in the frequency between the emitted and reflected waves
(Doppler shift frequency) is directly proportional
to their speed. Physiological variables affecting
TCD measured mean blood velocity are age, gender, hematocrit, viscosity, carbon dioxide,
temperature, blood pressure, and mental or
motor activity. Four main acoustic windows have
been described: transtemporal, transorbital, submandibular and the suboccipital windows.
Although each window has unique advantages
for different arteries and indications, a complete
TCD examination should include measurements
from all four windows and the course of blood
flow at various depths within each major branch
of the circle of Willis should be assessed. Specific
arteries of the circle of Willis are identified using
the following criteria: relative direction of the
probe within a specific acoustic window, direction
of blood flow relative to the probe, depth of ultrasound (insonation), and response to carotid compression or vibration (when difficult to
differentiate anterior from posterior circulation).
The LR, defined as the ratio between the time
mean average (Vmean) velocity of the MCA to
ICA, is the most established of such ratios and
helps differentiate hyperemia from vasospasm.
Hyperemia would result in flow elevations in
both the MCA and ICA and result in an
LR<3, whereas vasospasm would preferentially
elevate the MCA flow velocity over the ICA with
LR>6. LR between 3 and 6 is a sign of mild VSP
and >6 is an indication of severe VSP. TCD flow
velocity criteria appear to be most reliable for
detecting angiographic MCA and basilar artery
vasospasm. Findings in MCA vasospasm include
MCA Vmean 180 cm/s, a sudden rise in MCA
Vmean by >65 cm/s or 20% increase within 24 h
during days 3-7 post-subarachnoid hemorrhage,
LR6, and abrupt increase in Pulsatility index
>1.5 in two or more arteries suggesting increases
in ICP and/or vasospasm. TCD is most useful in
monitoring the temporal course of angiographic
vasospasm following SAH to help guide the timing
of diagnostic and therapeutic angiographic
interventions.

Question 4

Which one of the following statements regarding intraoperative ultrasound is most accura
a. It is highly useful in the brain but not spinal cord due to anatomical constraints
b. It can aid in adjusting for intraoperative brain shift and in detection of intraoperative hemorrhage or hydrocephalus
c. Its utility in identification of critical tumor margins during surgery and unintentional residual has not been shown
d. Contrast-enhanced intraoperative ultrasound cannot be performed in those with a known allergy to iodinated contrast
e. Intraoperative Doppler angiography can be used to improve accuracy of functional mapping during eloquent tumor surgery

Answer 4

b. It can aid in adjusting for intraoperative
brain shift and in detection of intraoperative hemorrhage or hydrocephalus

Intraoperative US offers real-time information
about the location, size, vascular relationships
and adjacent structures of brain and spinal cord
lesions. This allows adjustment for brain shift,
detection of untoward intraoperative events such
as hemorrhage or hydrocephalus, critical tumor
margins and residual tumor. It is easily available,
convenient, fast and easy to use and may provide
a more practical alternative to intraoperative MRI. Furthermore, newer technologies such as
contrast-enhanced US (i.e. microbubble contrast), or the integration of US with navigation
systems, or with functional navigation systems
as a method of assessing and adjusting for brain
shift may add additional benefits. In particular,
navigable 3D ultrasound (3D iUS) is a novel tool
that combines navigation technology with a dedicated cranial insonation probe capable of generating 2D/3D images that can be superimposed on
preoperative MR imaging and repeatedly updated
to provide a more accurate anatomic orientation,
as well as be used independently without preoperative imaging to improve gross total resection
levels to those seen with 5-ALA and intraoperative MRI. intraoperative doppler-angiography
enabled the delineation of vascular anatomy in
real-time. The specific limitations include concerns regarding image quality and difficulties
with orientation of the 2D ultrasound plane,
learning curve, artifacts during resection may
compromise image accuracy, and in particular,
hemorrhage and tissue handling have been shown
to decrease the specificity and positive predictive
value of iUS. Furthermore, there is no functional
information provided and electrophysiological
functional monitoring must still be considered
when dealing with lesions involving eloquent
structures.

Intraoperative US offers real-time information
about the location, size, vascular relationships
and adjacent structures of brain and spinal cord
lesions. This allows adjustment for brain shift,
detection of untoward intraoperative events such
as hemorrhage or hydrocephalus, critical tumor
margins and residual tumor. It is easily available,
convenient, fast and easy to use and may provide
a more practical alternative to intraoperative MRI. Furthermore, newer technologies such as
contrast-enhanced US (i.e. microbubble contrast), or the integration of US with navigation
systems, or with functional navigation systems
as a method of assessing and adjusting for brain
shift may add additional benefits. In particular,
navigable 3D ultrasound (3D iUS) is a novel tool
that combines navigation technology with a dedicated cranial insonation probe capable of generating 2D/3D images that can be superimposed on
preoperative MR imaging and repeatedly updated
to provide a more accurate anatomic orientation,
as well as be used independently without preoperative imaging to improve gross total resection
levels to those seen with 5-ALA and intraoperative MRI. intraoperative doppler-angiography
enabled the delineation of vascular anatomy in
real-time. The specific limitations include concerns regarding image quality and difficulties
with orientation of the 2D ultrasound plane,
learning curve, artifacts during resection may
compromise image accuracy, and in particular,
hemorrhage and tissue handling have been shown
to decrease the specificity and positive predictive
value of iUS. Furthermore, there is no functional
information provided and electrophysiological
functional monitoring must still be considered
when dealing with lesions involving eloquent
structures.

Question 5

Which one of the following statements regarding high frequency focused ultrasound (HIFU) is LEAST accurate?
a. It is a minimally invasive technique
b. It utilized a piezoelectric ultrasound transducer
c. A single treatment volume can be >5 cm3
d. Tissue response is assessed by MRI at 6 weeks
e. Intraprocedural ultrasound provides better temperature mapping than

Answer 5

a. It is a minimally invasive technique

High-intensity focused ultrasound (HIFU) ablation is a non-invasive technique that uses a beam
generated by a piezoelectric ultrasound transducer
propagates through tissue as a high-frequency
(0.5-4 MHz) pressure wave. The beam is focused
on to the targeted tissue, and each treatment
volume is approximately 0.80.20.2 cm3
. The
energy from the beam raises the temperature of
the focused area to 60-95 °C within a few seconds
without causing damage to the adjacent tissues,
thereby leading to very localized protein denaturation and coagulative necrosis. The available
HIFU devices are generally integrated with either
MRI or ultrasound imaging in order to plan treatment and monitor response in real time. MRI has
the advantage of excellent anatomical resolution,
high sensitivity for lesion detection but temperature mapping is challenging; ultrasonography
offers real-time visualization of the targeted volume (compensates for movement) and guidance
of energy deposition within the treated area
through a hyper-echogenic cross visible during
pulse application. In addition, ultrasonography
provides a rapid real-time assessment of the volume of coagulative necrosis/temperature during
treatment by visualization of a hyper-echogenic
spot on the screen. HIFU ablation provides a completely non-invasive therapy, thus avoiding
potential complications associated with general
anesthesia and surgery. It has been used for the
treatment of liver, kidney, prostate, brain, bone
and breast cancer.

High-intensity focused ultrasound (HIFU) ablation is a non-invasive technique that uses a beam
generated by a piezoelectric ultrasound transducer
propagates through tissue as a high-frequency
(0.5-4 MHz) pressure wave. The beam is focused
on to the targeted tissue, and each treatment
volume is approximately 0.80.20.2 cm3
. The
energy from the beam raises the temperature of
the focused area to 60-95 °C within a few seconds
without causing damage to the adjacent tissues,
thereby leading to very localized protein denaturation and coagulative necrosis. The available
HIFU devices are generally integrated with either
MRI or ultrasound imaging in order to plan treatment and monitor response in real time. MRI has
the advantage of excellent anatomical resolution,
high sensitivity for lesion detection but temperature mapping is challenging; ultrasonography
offers real-time visualization of the targeted volume (compensates for movement) and guidance
of energy deposition within the treated area
through a hyper-echogenic cross visible during
pulse application. In addition, ultrasonography
provides a rapid real-time assessment of the volume of coagulative necrosis/temperature during
treatment by visualization of a hyper-echogenic
spot on the screen. HIFU ablation provides a completely non-invasive therapy, thus avoiding
potential complications associated with general
anesthesia and surgery. It has been used for the
treatment of liver, kidney, prostate, brain, bone
and breast cancer.

Question 6

Which one of the following statements regarding the WHO surgical safety checklist is most accurate?
a. If there is a risk of >250 mL of blood loss it must be formally discussed during the signin
b. It is designed to reduce the number of surgical never events by increasing
c. Surgical site should be marked during the time out
d. VTE prophylaxis should be decided before leaving the operating room
e. Essential imaging must be displayed during the time out

Answer 6

e. Essential imaging must be displayed during the time out

To assist operating teams to reduce the number
of patient safety events in the surgical environment, a core set of standards have been identified
by the WHO that can be applied universally
within any healthcare setting to address issues
including correct site surgery, hemorrhage risk,
antibiotic prophylaxis, airway management and
the risk of allergies. WHO surgical safety checklist is designed to reduce the number of errors and
complications resulting from surgical procedures
by improving team communication and by verifying and checking essential care interventions. It
consists of sign in, time out and sign out stage
assessments below:

To assist operating teams to reduce the number
of patient safety events in the surgical environment, a core set of standards have been identified
by the WHO that can be applied universally
within any healthcare setting to address issues
including correct site surgery, hemorrhage risk,
antibiotic prophylaxis, airway management and
the risk of allergies. WHO surgical safety checklist is designed to reduce the number of errors and
complications resulting from surgical procedures
by improving team communication and by verifying and checking essential care interventions. It
consists of sign in, time out and sign out stage
assessments below:

Question 7

The Leksell stereotactic frame is most accurately described as which one of the following types of stereotactic system?
a. Polar coordinate
b. Arc-radius (arc-quadrant)
c. Burr-hole mounted
d. Arc-phantom target
e. Cartesian coordinate

Answer 7

b. Arc-radius (arc-quadrant)

Stereotactic frame-based guidance systems have
generally been based on four systems: polar coordinate, arc-radius, focal point, and phantom target. The polar coordinate system is based on
the necessity that guidance of the probe be
described with regard to the angle relative to a
skull entry point. Usually, a minimum of two
angles (in planes orthogonal to each other) is
required to characterize a unique trajectory; in
addition to these angles, the distance of the probe
to the target lesion needs to be calculated (e.g.
Spiegel-Wycis, Horsley-Clarke). The arc-radius
system (e.g. Leksell frame) is based on the concept that a probe equivalent to the radius of a
semicircular arc will reach the center of the arc
when introduced perpendicular to any point
along the arc. Adjustment of the arc (vertically
and anterior-posterior) permits targeting of different points; the base of the arc is attached to a
rigid head frame on the patient’s head which
defines the corners of a cube visible on CT. After
the geometric center of the cube is defined, the
relative location of the target can be calculated
and the semicircular arc manipulated accordingly
to place that lesion at the center of the arc. Arcphantom systems (e.g. CRW frame) allow
mounting of the arc onto a phantom base frame
to check the accuracy of the trajectory immediately before transferring it to the patient. A burr
hole-mounted system provides a limited range of
possible intracranial target points with a fixed
entry point (usually over non-eloquent brain):
provided two angular degrees of freedom (horizontal plane, vertical plane) and a depth adjustment. Cartesian geometry is the underpinning
for all frame types, and describes the location of
a point in space with three coordinates (x, y, z).

Stereotactic frame-based guidance systems have
generally been based on four systems: polar coordinate, arc-radius, focal point, and phantom target. The polar coordinate system is based on
the necessity that guidance of the probe be
described with regard to the angle relative to a
skull entry point. Usually, a minimum of two
angles (in planes orthogonal to each other) is
required to characterize a unique trajectory; in
addition to these angles, the distance of the probe
to the target lesion needs to be calculated (e.g.
Spiegel-Wycis, Horsley-Clarke). The arc-radius
system (e.g. Leksell frame) is based on the concept that a probe equivalent to the radius of a
semicircular arc will reach the center of the arc
when introduced perpendicular to any point
along the arc. Adjustment of the arc (vertically
and anterior-posterior) permits targeting of different points; the base of the arc is attached to a
rigid head frame on the patient’s head which
defines the corners of a cube visible on CT. After
the geometric center of the cube is defined, the
relative location of the target can be calculated
and the semicircular arc manipulated accordingly
to place that lesion at the center of the arc. Arcphantom systems (e.g. CRW frame) allow
mounting of the arc onto a phantom base frame
to check the accuracy of the trajectory immediately before transferring it to the patient. A burr
hole-mounted system provides a limited range of
possible intracranial target points with a fixed
entry point (usually over non-eloquent brain):
provided two angular degrees of freedom (horizontal plane, vertical plane) and a depth adjustment. Cartesian geometry is the underpinning
for all frame types, and describes the location of
a point in space with three coordinates (x, y, z).

Question 8

Which one of the following statements regarding frameless stereotaxy is most accurate?
a. Does not require manual mapping of coordinate space of preoperative image onto surgical field
b. Point-pair registration is generally less reliable than point-pair registration
c. Accurate optical tracking requires the patient’s head to be immobilized in a clamp
d. Surface-contour registration usually requires fiducial markers
e. Electromagnetic frameless stereotaxy is not suitable in pediatric neurosurgery

Answer 8

c. Accurate optical tracking requires the patient’s head to be immobilized in a clamp

For both frame-based and frameless systems the
relationship between the coordinate space for
the preoperative images and that for the surgical
field must be established. In frame-based systems,
by using the same frame for both preoperative
image acquisition and performing the surgery,
the relationship between the two coordinate systems is known and no further transformation is
required. For frameless systems, point-pair registration or surface contour registration can be used to establish the relationship between the preoperative images and that for the surgical field.
Point-pair matching requires a set of at least three
non-colinear points to be defined in the coordinates of the images. These ‘fiducial points’ can
consist of either natural anatomic landmarks
(i.e. nasion, lateral canthus, or tragus), skinapplied markers, or bone-implanted markers.
These same fiducial points are defined again
within the coordinate system of the surgical field
in the operating room. Software is then used to
establish the relationship between the coordinates of the fiducial points in the image space
and their counterpart in the surgical space.
In surface contour registration, mapping a
radiographic surface can be achieved by touching
a number of multiple random points (termed
cloud of points) or by scanning a surface with
laser registration. These surface-based algorithms allow the use of imaging obtained before
the intent to operate, but are less accurate compared to the combination of natural landmarks
and skin-applied fiducial markers. Once the
spatial relationship is established with either
point-pair registration or surface contour registration, it is used throughout the remainder of
the operation to map anatomic targets of the
patient to that of the preoperative images. This
thus requires that the patient’s head be immobilized with a head clamp and the operating table
not be moved during surgery. To overcome the
error that may be induced with patient or operating table movement, tracking units attached to
the patient’s head or a surgical head clamp can
be used. Electromagnetic (rather than optical)
tracking is the latest development in frameless
stereotaxy and is used in pediatric neurosurgery as it avoids the need for head clamping (not possible in those without fused skull sutures).

For both frame-based and frameless systems the
relationship between the coordinate space for
the preoperative images and that for the surgical
field must be established. In frame-based systems,
by using the same frame for both preoperative
image acquisition and performing the surgery,
the relationship between the two coordinate systems is known and no further transformation is
required. For frameless systems, point-pair registration or surface contour registration can be used to establish the relationship between the preoperative images and that for the surgical field.
Point-pair matching requires a set of at least three
non-colinear points to be defined in the coordinates of the images. These ‘fiducial points’ can
consist of either natural anatomic landmarks
(i.e. nasion, lateral canthus, or tragus), skinapplied markers, or bone-implanted markers.
These same fiducial points are defined again
within the coordinate system of the surgical field
in the operating room. Software is then used to
establish the relationship between the coordinates of the fiducial points in the image space
and their counterpart in the surgical space.
In surface contour registration, mapping a
radiographic surface can be achieved by touching
a number of multiple random points (termed
cloud of points) or by scanning a surface with
laser registration. These surface-based algorithms allow the use of imaging obtained before
the intent to operate, but are less accurate compared to the combination of natural landmarks
and skin-applied fiducial markers. Once the
spatial relationship is established with either
point-pair registration or surface contour registration, it is used throughout the remainder of
the operation to map anatomic targets of the
patient to that of the preoperative images. This
thus requires that the patient’s head be immobilized with a head clamp and the operating table
not be moved during surgery. To overcome the
error that may be induced with patient or operating table movement, tracking units attached to
the patient’s head or a surgical head clamp can
be used. Electromagnetic (rather than optical)
tracking is the latest development in frameless
stereotaxy and is used in pediatric neurosurgery
as it avoids the need for head clamping (not possible in those without fused skull sutures).

Question 9

Which one of the following statements regarding airflow systems in operating suits is most accurate?
a. Laminar air flow has been consistently shown to reduce surgical infections
b. Positive pressure ventilation is usually used in isolation rooms
c. Negative pressure ventilation is usually used in operating suites
d. Bacterial contamination of surgical wounds is most commonly from shedding
e. Bacterial content of air in laminar flow systems is lower than in conventional ventilation systems

Answer 9

e. Bacterial content of air in laminar flow systems is lower than in conventional ventilation systems

The goals of the ventilation system are comfort of
patient and staff, removal of pollutants/aerosols,
temperature and humidity control, and control
air movement to minimize the transfer of airborne contaminants from less clean to clean areas.
Airborne contaminants may enter an operating
room via the following routes: (a) through the
supply air; (b) shed by operating staff; (c) through
surgical activities; and (d) transferred from adjacent spaces. A recirculating system is one that
recirculates some or all of the inside air back to
the OR suites or some other part of hospital,
whereas in a non-recirculating system, all air
brought to the room is conditioned, outside air. When a recirculating system is used, the air
return duct should have a high efficiency particulate air (HEPA) filter built into the system. In
an OR where inhalational anesthetics are used,
there should be separate systems for ventilation,
vacuum (patient and surgical suction), and waste
anesthetic gas disposal. Studies have demonstrated that most of the causes of wound contamination in the operating suite are the result of the
patient’s skin flora and bacteria shed on airborne
particles from the personnel. Room ventilation
affects the distribution of these airborne particles
in four ways: total ventilation (dilution), air distribution (directional airflow), room pressurization
(infiltration barrier), and filtration (contaminant
removal). As the air flows of the room increases,
the greater the dilutional effect on airborne particles. However, resultant turbulent flow also
increases microbial distribution throughout the
room. Low-velocity unidirectional (laminar) flow
minimizes the spread of microbes in the room.
Directional flow can be from the outside into
the OR (negative pressure), or from the OR to
the outside (positive pressure). Negative pressure
ventilation is used for highly infective rooms in
the hospital (e.g. isolation rooms for tuberculosis
patients) and positive pressure ventilation is used
for protective environments (e.g. ORs and rooms
with immunocompromised patients). This is
described as an entire body of air within a designated space (theatre suite) moving with uniform
velocity in a single direction along parallel
flow lines. True laminar flow is only achieved
when approximately 100% HEPA filter coverage
occurs. Laminar flow ventilation comprises a
continuous flow of air with bacteria less than 10
colony-forming units/m3
. Despite this, infection
rates for joint replacement surgery have actually
been show to increase in laminar flow versus conventional theatre ventilation (reasons remain
unclear).

The goals of the ventilation system are comfort of
patient and staff, removal of pollutants/aerosols,
temperature and humidity control, and control
air movement to minimize the transfer of airborne contaminants from less clean to clean areas.
Airborne contaminants may enter an operating
room via the following routes: (a) through the
supply air; (b) shed by operating staff; (c) through
surgical activities; and (d) transferred from adjacent spaces. A recirculating system is one that
recirculates some or all of the inside air back to
the OR suites or some other part of hospital,
whereas in a non-recirculating system, all air
brought to the room is conditioned, outside air.
When a recirculating system is used, the air
return duct should have a high efficiency particulate air (HEPA) filter built into the system. In
an OR where inhalational anesthetics are used,
there should be separate systems for ventilation,
vacuum (patient and surgical suction), and waste
anesthetic gas disposal. Studies have demonstrated that most of the causes of wound contamination in the operating suite are the result of the
patient’s skin flora and bacteria shed on airborne
particles from the personnel. Room ventilation
affects the distribution of these airborne particles
in four ways: total ventilation (dilution), air distribution (directional airflow), room pressurization
(infiltration barrier), and filtration (contaminant
removal). As the air flows of the room increases,
the greater the dilutional effect on airborne particles. However, resultant turbulent flow also
increases microbial distribution throughout the
room. Low-velocity unidirectional (laminar) flow
minimizes the spread of microbes in the room.
Directional flow can be from the outside into
the OR (negative pressure), or from the OR to
the outside (positive pressure). Negative pressure
ventilation is used for highly infective rooms in
the hospital (e.g. isolation rooms for tuberculosis
patients) and positive pressure ventilation is used
for protective environments (e.g. ORs and rooms
with immunocompromised patients). This is
described as an entire body of air within a designated space (theatre suite) moving with uniform
velocity in a single direction along parallel
flow lines. True laminar flow is only achieved
when approximately 100% HEPA filter coverage
occurs. Laminar flow ventilation comprises a
continuous flow of air with bacteria less than 10
colony-forming units/m3
. Despite this, infection
rates for joint replacement surgery have actually
been show to increase in laminar flow versus conventional theatre ventilation (reasons remain unclear).

Question 10

Which one of the following statements about operating microscope optics is most accurate?
a. The higher the magnification, the smaller the width of field
b. The higher the magnification, the smaller the depth of field
c. The higher the magnification, the smaller the working distance
d. The higher the magnification, the smaller the interpupillary distance
e. The higher the magnification, the higher the focal length of the objective lens

Answer 10

a. The higher the magnification, the smaller
the width of field

Resolving power of an optical system is its ability
to make clear and distinguishable two separate
entities. The resolving power of the unaided
human eye is only 0.2 mm. Most people who view
two points closer than 0.2 mm will see only 1
point. Moving closer to an object increases
resolution up to a point, but objects closer than
10-12 cm go out of focus. Optical aids (e.g.
loupes, OMs, surgical headlamps, fiberoptic
handpiece lights) can improve resolution by many
orders of magnitude. For example, a common
OM can raise the resolving limit from 0.2 to
0.006 mm (6 μm), a dramatic improvement Stereopsis, or 3D perception, is critical to achieving precision surgery, and is an advantage over
2D endoscopes. Several factors are important
for increasing resolution without compromising
ergonomics, eyestrain, head/neck fatigue:

Resolving power of an optical system is its ability
to make clear and distinguishable two separate
entities. The resolving power of the unaided
human eye is only 0.2 mm. Most people who view
two points closer than 0.2 mm will see only 1
point. Moving closer to an object increases
resolution up to a point, but objects closer than
10-12 cm go out of focus. Optical aids (e.g.
loupes, OMs, surgical headlamps, fiberoptic
handpiece lights) can improve resolution by many
orders of magnitude. For example, a common
OM can raise the resolving limit from 0.2 to
0.006 mm (6 μm), a dramatic improvement. Stereopsis, or 3D perception, is critical to achieving precision surgery, and is an advantage over
2D endoscopes. Several factors are important
for increasing resolution without compromising
ergonomics, eyestrain, head/neck fatigue:

Question 11

Which of the labels in the picture of an operating microscope shown below is the beam splitter?

Answer 11

A. Light fiber;
B. objective lens;
C. magnification changer;
D. teaching binoculars;
E. eyepiece;
F. main binoculars;
G. beam splitter

The surgical microscope is a complicated system
of lenses that allows stereoscopic vision at a
magnification of approximately 4-40 with an
excellent illumination of the working area. The
separation of the reflected light into two beams
within a microscope is what produces the stereoscopic effect that allows the clinician to see depth
of field. The light beams fall parallel onto the retinas of the observer so that no eye convergence is
necessary and the demand on the lateral rectus
muscles is minimal. The optical unit consists of:
* Eyepieces—magnify the interim image
generated in the binocular tubes. Eyepiece
selection not only determines the magnification, but also the size of the field of view.
* Binoculars—the precise adjustment of the
interpupillary distance (by adjusting the distance between binocular tubes holding the
eyepieces) is the basic pre-requisite for the
stereoscopic view of the operation area.
Longer the focal length of binoculars, the
greater the magnification and narrower
the field of view. Many microscopes now
include a beam splitter and a second set of
teaching binoculars (non-stereoscopic as
they split light from a single objective).
* Magnification changer (binocular objectives)—one cylinder, into which two
Galilean telescope systems with various
magnification factors are built. The combination of the magnification changer with
varying objective lenses and eyepiece yields
an increasing magnification line when the
control is adjusted.
* Objective lens—its focal length determines
the working distance between the lens and
the surgical field.
* Lighting unit as optimal illumination is
necessary with high magnifications. Surgical microscope uses coaxial fiber-optic illumination producing an adjustable, bright,
uniformly illuminated, shadow-free, circular spot of light that is parallel to the optical
viewing axis.

Question 12

Which one of the following statements regarding fluorescein sodium is LEAST accurate?
a. It emits light in the 600-700 nm range
b. It is preferentially taken up by neoplastic cells
c. It relies on breakdown of the blood-brain barrier
d. It can guide where laser scanning confocal microscope should be focused
e. It can assess patency of EC-IC bypass and at risk vessels during aneurysm surgery

Answer 12

a. It emits light in the 600-700 nm range

Fluorescein sodium has an excitation maximum of
494 nm and an emission maximum of 521 nm. It
readily crosses capillaries, provides fluorescent
contrast in the extracellular matrix, and has a urine
clearance of 24-36 h after intravenous injection.
The amount of fluorescein delivered to a tumor
site is increased by the breakdown of the normal
blood-brain barrier. Fluorescein has been used
in cerebral angiography to detect arteriovenous
malformations, assess superficial temporal arteryMCA anastomoses patency, and to aid in treating
cerebral aneurysms. Fluorescein is not a tumorspecific agent, but it is excellent for visualizing
regions of compromised neurovasculature. The
presumption in its use for neuro-oncology is
that these areas correspond to the enhancing
regions, which also correspond to bulk tumor.
Rates of 100% GTR have been achieved for
non-eloquent tumors using microscope was developed equipped with dichroic mirrors specific
for fluorescein-guided resection of malignant gliomas. Fluorescein-guided laser scanning confocal
microscopy in humans had been able to provide
assessment of tumor grade, tumor histology, and
tumor margins for a variety of tumor subtypes.
The results from these two studies demonstrate
the feasibility of this technology as a diagnostic
and therapeutic tool, as it can help identify many
of the pathognomonic cytoarchitectural features
of various brain tumors and aid in the intraoperative diagnosis and resection of various central nervous system tumors. Fluorescein in this case can
both guide the operator grossly to areas to be
viewed with LSCE and provide the contrast to
allow cellular visualization. Fluorescein is FDA
approved and is widely used in the field of ophthalmology as well as in GI studies. Most fluorescein
clinical studies in neurosurgery report no serious
adverse effects with use of the fluorophore.

Fluorescein sodium has an excitation maximum of
494 nm and an emission maximum of 521 nm. It
readily crosses capillaries, provides fluorescent
contrast in the extracellular matrix, and has a urine
clearance of 24-36 h after intravenous injection.
The amount of fluorescein delivered to a tumor
site is increased by the breakdown of the normal
blood-brain barrier. Fluorescein has been used
in cerebral angiography to detect arteriovenous
malformations, assess superficial temporal arteryMCA anastomoses patency, and to aid in treating
cerebral aneurysms. Fluorescein is not a tumorspecific agent, but it is excellent for visualizing
regions of compromised neurovasculature. The
presumption in its use for neuro-oncology is
that these areas correspond to the enhancing
regions, which also correspond to bulk tumor.
Rates of 100% GTR have been achieved for
non-eloquent tumors using microscope was developed equipped with dichroic mirrors specific
for fluorescein-guided resection of malignant gliomas. Fluorescein-guided laser scanning confocal
microscopy in humans had been able to provide
assessment of tumor grade, tumor histology, and
tumor margins for a variety of tumor subtypes.
The results from these two studies demonstrate
the feasibility of this technology as a diagnostic
and therapeutic tool, as it can help identify many
of the pathognomonic cytoarchitectural features
of various brain tumors and aid in the intraoperative diagnosis and resection of various central nervous system tumors. Fluorescein in this case can
both guide the operator grossly to areas to be
viewed with LSCE and provide the contrast to
allow cellular visualization. Fluorescein is FDA
approved and is widely used in the field of ophthalmology as well as in GI studies. Most fluorescein
clinical studies in neurosurgery report no serious
adverse effects with use of the fluorophore.

Question 13

Which one of the following statements regarding indocyanine green (ICG) is LEAST accurate?
a. It emits light in the 700-850 nm range (far red/infrared)
b. It has better cellular penetration than 5-ALA
c. It has higher levels of non-specific binding in tumor surgery
d. It can be used for intraoperative cerebral angiography
e. Tumor visualization is most specific between 1 and 2 h post injection

Answer 13

e. Tumor visualization is most specific between 1 and 2 h post injection

ICG is a near-infrared fluorescent agent with
maximal excitation at 778 nm and emission
spectra range of 700-850 nm in serum. It is fairly
water-soluble, which allows it to be given intravenously and cleared through renal and bile excretion. ICG concentration within a tumor site is
enhanced by breakdown of the normal bloodbrain barrier. ICG has a greater tissue penetrance
than visible-wavelength fluorophores, such as 5-
ALA and fluorescein. ICG is an anionic, amphiphilic, tricarbocyanine probe, which allows it to
have a high affinity for proteins, such as albumin,
and allows visualization of solid tumors, but may
also cause higher levels of nonspecific binding.
Similar to fluorescein, ICG provides nonspecific
contrast in areas of permeable neurovasculature.
ICG has been given intravenously for blood vessel
angiography, identifying extrahepatic bile ducts
and detecting liver metastases. It can also be given
subcutaneously for sentinel lymph node mapping
for breast, anal, and GI cancer as well as assessing
lymphatic drainage for lymphedema. ICG was able
to contrast the fluorescent glioma tumor tissue
within 1 mm of the histological tumor margins
in an animal model. However, this technique is
not effective in distinguishing between malignant
cells and other areas of the brain that may incidentally uptake the injected dye. Cellular visualization
using ICG contrast with an infrared LSCE may overcome these limitations. In contrast, macroscopic detection is more subjective to the surgeon.
Intravenously administered ICG is immediately
localized to a tumor site, and the fluorescent signal
remains in the tumor up to 1 h after injection, with
constant imaging, demonstrating limited photobleaching and clearance. The delivery of the dye
to the site of the tumor relies on binding to serum
proteins and the damaged vasculature primarily
located at the site of the tumor. However, with
time the dye will diffuse into surrounding tissue.
These properties allow real-time, in vivo assessment that differentiates glioma tissue and normal
brain. In contrast to visible wavelength fluorophores, ICG provides visualization of deeper tissue
structures due to its infrared excitation and emission spectra. However, depth of imaging still
remains limited to a few hundred microns deep
to the imaging surface. ICG is considered to have
fewer risks than other FDA approved intravenous
fluorophores

ICG is a near-infrared fluorescent agent with
maximal excitation at 778 nm and emission
spectra range of 700-850 nm in serum. It is fairly
water-soluble, which allows it to be given intravenously and cleared through renal and bile excretion. ICG concentration within a tumor site is
enhanced by breakdown of the normal bloodbrain barrier. ICG has a greater tissue penetrance
than visible-wavelength fluorophores, such as 5-
ALA and fluorescein. ICG is an anionic, amphiphilic, tricarbocyanine probe, which allows it to
have a high affinity for proteins, such as albumin,
and allows visualization of solid tumors, but may
also cause higher levels of nonspecific binding.
Similar to fluorescein, ICG provides nonspecific
contrast in areas of permeable neurovasculature.
ICG has been given intravenously for blood vessel
angiography, identifying extrahepatic bile ducts
and detecting liver metastases. It can also be given
subcutaneously for sentinel lymph node mapping
for breast, anal, and GI cancer as well as assessing
lymphatic drainage for lymphedema. ICG was able
to contrast the fluorescent glioma tumor tissue
within 1 mm of the histological tumor margins
in an animal model. However, this technique is
not effective in distinguishing between malignant
cells and other areas of the brain that may incidentally uptake the injected dye. Cellular visualization
using ICG contrast with an infrared LSCE may
overcome these limitations. In contrast, macroscopic detection is more subjective to the surgeon.
Intravenously administered ICG is immediately
localized to a tumor site, and the fluorescent signal
remains in the tumor up to 1 h after injection, with
constant imaging, demonstrating limited photobleaching and clearance. The delivery of the dye
to the site of the tumor relies on binding to serum
proteins and the damaged vasculature primarily
located at the site of the tumor. However, with
time the dye will diffuse into surrounding tissue.
These properties allow real-time, in vivo assessment that differentiates glioma tissue and normal
brain. In contrast to visible wavelength fluorophores, ICG provides visualization of deeper tissue
structures due to its infrared excitation and emission spectra. However, depth of imaging still
remains limited to a few hundred microns deep
to the imaging surface. ICG is considered to have
fewer risks than other FDA approved intravenous
fluorophores.

Question 14

Which one of the following statements regarding 5-ALA is most accurate?
a. It emits light in the 400-500 nm range
b. It is normally produced from protoporyphyrin IX in the heme synthesis pathway
c. 5-ALA based fluorescence does not occur
in red blood cells
d. Neoplastic cells preferentially take up 5-ALA
e. Photosensitivity is a recognized side effect

Answer 14

c. 5-ALA based fluorescence does not occur
in red blood cells

Produced in the mitochondria, 5-ALA is a natural
precursor for the production of protoporphyrin
IX (PpIX) in the heme synthesis pathway found
in all cells. PpIX is a fluorescent molecule that
binds membrane lipids and has an excitation
range of 375-440 nm and emission range of
640-710 nm in vivo. Overloading this pathway
with exogenous 5-ALA causes the collection of
PpIX to fluorescently detectable levels in cells.
As the production of PpIX occurs in situ in mitochondria, fluorescence is limited to cells.
This decreases fluorescent signal in blood or
edematous regions of the operative field. Furthermore, neoplastic cells demonstrate preferential
uptake of exogenous 5-ALA and increased collection of PpIX, making the fluorescent signal more
robust in these abnormal tissues and making
intraoperative visualization feasible, especially in
intracranial tumors of higher grades. Photobleaching occurs with PpIX fluorescence level
dropping to 36% after 25 min under violet light
or 87 min under white light. It can be limited
by allowing excitation and white light to penetrate as small an area as possible in the surgical
field. Phototoxicity is limited with 5-ALA, since
fluorescent microscopes do not produce sufficient energy for significant ROS production.
Currently, the FDA has approved 5-ALA and its derivatives for research diagnostic applications
in endoscopic, photodynamic detection of bladder cancer and residual glioma, as well as the
treatment of basal cell carcinoma and actinic
keratosis. 5-ALA macrofluorescence predicts
malignant glioma tissue with 90% accuracy,
showing residual tumor better than post-op
MRI, and the level of residual solid tissue fluorescence was shown to correlate with patient survival. In an RCT, its use improved gross total
resection rates and overall progression-free
survival time. In low-grade glioma, macroscopically detectable fluorescence does not occur but
hand held intraoperative confocal microscope
allowed visualization of 5-ALA-induced fluorescence of low-grade glioma tumor and tumor
margins in vivo that corresponded with standard
histopathology. Some controversy still exists as to
the biology of 5-ALA metabolism in low-grade
gliomas and the need for complete resection by
MRI. Though 5-ALA administration is considered
safe,minor systemic side effects have been reported,
including nausea, vomiting, and hypotension as
well as increased sensitivity to sunlight up to 48 h
after administration. As with other fluorophores,
these side effects are limited with lower dosing.

Produced in the mitochondria, 5-ALA is a natural
precursor for the production of protoporphyrin
IX (PpIX) in the heme synthesis pathway found
in all cells. PpIX is a fluorescent molecule that
binds membrane lipids and has an excitation
range of 375-440 nm and emission range of
640-710 nm in vivo. Overloading this pathway
with exogenous 5-ALA causes the collection of
PpIX to fluorescently detectable levels in cells.
As the production of PpIX occurs in situ in mitochondria, fluorescence is limited to cells.
This decreases fluorescent signal in blood or
edematous regions of the operative field. Furthermore, neoplastic cells demonstrate preferential
uptake of exogenous 5-ALA and increased collection of PpIX, making the fluorescent signal more
robust in these abnormal tissues and making
intraoperative visualization feasible, especially in
intracranial tumors of higher grades. Photobleaching occurs with PpIX fluorescence level
dropping to 36% after 25 min under violet light
or 87 min under white light. It can be limited
by allowing excitation and white light to penetrate as small an area as possible in the surgical
field. Phototoxicity is limited with 5-ALA, since
fluorescent microscopes do not produce sufficient energy for significant ROS production.
Currently, the FDA has approved 5-ALA and
19 SURGICAL TECHNOLOGY AND PRACTICE e27
its derivatives for research diagnostic applications
in endoscopic, photodynamic detection of bladder cancer and residual glioma, as well as the
treatment of basal cell carcinoma and actinic
keratosis. 5-ALA macrofluorescence predicts
malignant glioma tissue with 90% accuracy,
showing residual tumor better than post-op
MRI, and the level of residual solid tissue fluorescence was shown to correlate with patient survival. In an RCT, its use improved gross total
resection rates and overall progression-free
survival time. In low-grade glioma, macroscopically detectable fluorescence does not occur but
hand held intraoperative confocal microscope
allowed visualization of 5-ALA-induced fluorescence of low-grade glioma tumor and tumor
margins in vivo that corresponded with standard
histopathology. Some controversy still exists as to
the biology of 5-ALA metabolism in low-grade
gliomas and the need for complete resection by
MRI. Though 5-ALA administration is considered
safe,minor systemic side effects have been reported,
including nausea, vomiting, and hypotension as
well as increased sensitivity to sunlight up to 48 h after administration. As with other fluorophores,
these side effects are limited with lower dosing.

Question 15

You are setting up the stereotactic frame in
the operating room. Your consultant asks
you to adjust the anterior-posterior measurement using the Vernier scale for submillimeter accuracy. What reading is currently shown in the example below?
a. 3.0 mm
b. 2.1 mm
c. 2.0 mm
d. 3.1 mm
e. 1.1 mm

Answer 15

b. 2.1 mm

The top scale is a simple rule scale in cm and mm,
the other is a Vernier scale with ten divisions.
Whilst one of these scales is fixed, the other is able
tomovewith the stage.The Vernier scale’s ten divisions are equal to nine small divisions on the rule
scale. Therefore each Vernier division is equal to
0.9 mm. The difference between a rule scale division and a Vernier division is thus: 19/10¼
0.1 mm. Hence, the instrument can be read to an
accuracy of approximately 0.1 mm. To take a
reading, note the division on the rule scale immediately prior to the 0 of the Vernier scale (this will
provide your first decimal place), then look along
the Vernier scale until you find a mark on it
which is in line with a mark on the rule scale-this
provides your second decimal place. As such, the
reading is 2.1 mm in the example. Vernier scales
are seen on stereotactic frame axes and inaccuracies
in set up can significantly alter targeting in
3D space

The top scale is a simple rule scale in cm and mm,
the other is a Vernier scale with ten divisions.
Whilst one of these scales is fixed, the other is able
tomovewith the stage.The Vernier scale’s ten divisions are equal to nine small divisions on the rule
scale. Therefore each Vernier division is equal to
0.9 mm. The difference between a rule scale division and a Vernier division is thus: 19/10¼
0.1 mm. Hence, the instrument can be read to an
accuracy of approximately 0.1 mm. To take a
reading, note the division on the rule scale immediately prior to the 0 of the Vernier scale (this will
provide your first decimal place), then look along
the Vernier scale until you find a mark on it
which is in line with a mark on the rule scale-this
provides your second decimal place. As such, the
reading is 2.1 mm in the example. Vernier scales
are seen on stereotactic frame axes and inaccuracies
in set up can significantly alter targeting in
3D space.

Question 16

Which one of the following statements
regarding image-guided neurosurgery in
pediatric patients is most accurate?
a. Optical frameless stereotactic navigation
is ideal for children with unfused skull
sutures
b. Electromagnetic frameless stereotactic
navigation is more appropriate for neuroendoscopy in children
c. Reference array for electromagnetic navigation must be fixed to bone
d. Surface contour registration is not required in electromagnetic navigation
e. Electromagnetic navigation requires a clear visual line of sight between the tracker and the stylet

Answer 16

e. Electromagnetic navigation requires a clear visual line of sight between the tracker and the stylet

Both frame-based and frameless optical neuronavigation have been limited in their use in young
pediatric patients, largely due to the hazards of
fixing young patients’ heads in pinned cranial fixation. The recent development of electromagnetic neuronavigation techniques has led to the
greater use of stereotactic navigation in patients
in whom cranial fixation would not be tolerated.
Endoscopic surgery in pediatric patients is well
described for a variety of intracranial pathologies.
The use of stereotactic navigation as an adjunct to
neuroendoscopy is similarly a recognized and
growing technique. The improved accuracy and
safety afforded the surgeon by stereotaxy has
allowed the development of neuroendoscopic
techniques for biopsy or resection of intraventricular and periventricular lesions, the fenestration
of cysts, cerebrospinal fluid diversion procedures
and the placement of catheters, even in the presence of abnormal or difficult anatomy. However,
due to the restrictions imposed by the risks of
rigid pinned cranial fixation, these techniques
were not always suitable for very young patients.
The equipment required for the procedures comprised the StealthStation AxiEM Neuronavigation System (Medtronic, Louisville, CO, USA),
which utilizes a coil to generate an electromagnetic field around the patient’s head. Navigation
stylets within this field are accurately localized
with reference to a small array, which is secured
to the patient’s head (either adhesive-based scalp
or fixed to the cranial bone). Previous optical
technology necessitates the immobilization of
the patient’s head with rigid cranial fixation in
pins and a visible reference frame with an unimpeded line of sight and utilized probes that attach
to the endoscope, and these can hinder the free
manipulation of the instrument by the surgeon.
We found that the electromagnetic stereotactic
system afforded the desired degree of navigational accuracy with a number of advantages over
optical systems. The navigation stylets were less
cumbersome than the equivalent optical probes,
and the placement of the navigation stylets within
the channel of the endoscope did not affect the
system’s accuracy.

Both frame-based and frameless optical neuronavigation have been limited in their use in young
pediatric patients, largely due to the hazards of
fixing young patients’ heads in pinned cranial fixation. The recent development of electromagnetic neuronavigation techniques has led to the
greater use of stereotactic navigation in patients
in whom cranial fixation would not be tolerated.
Endoscopic surgery in pediatric patients is well
described for a variety of intracranial pathologies.
The use of stereotactic navigation as an adjunct to
neuroendoscopy is similarly a recognized and
growing technique. The improved accuracy and
safety afforded the surgeon by stereotaxy has
allowed the development of neuroendoscopic
techniques for biopsy or resection of intraventricular and periventricular lesions, the fenestration
of cysts, cerebrospinal fluid diversion procedures
and the placement of catheters, even in the presence of abnormal or difficult anatomy. However,
due to the restrictions imposed by the risks of
rigid pinned cranial fixation, these techniques
were not always suitable for very young patients.
The equipment required for the procedures comprised the StealthStation AxiEM Neuronavigation System (Medtronic, Louisville, CO, USA),
which utilizes a coil to generate an electromagnetic field around the patient’s head. Navigation
stylets within this field are accurately localized
with reference to a small array, which is secured
to the patient’s head (either adhesive-based scalp
or fixed to the cranial bone). Previous optical
technology necessitates the immobilization of
the patient’s head with rigid cranial fixation in
pins and a visible reference frame with an unimpeded line of sight and utilized probes that attach
to the endoscope, and these can hinder the free
manipulation of the instrument by the surgeon.
We found that the electromagnetic stereotactic
system afforded the desired degree of navigational accuracy with a number of advantages over
optical systems. The navigation stylets were less
cumbersome than the equivalent optical probes,
and the placement of the navigation stylets within
the channel of the endoscope did not affect the
system’s accuracy.

Question 17

Which one of the following statements regarding cranioplasty materials is LEAST accurate?
a. Autologous bone flaps in children may
undergo resorption
b. MMA use can cause an exothermic burn
reaction
c. PEEK implants require 3D planning CT
d. Titanium mesh is associated with a higher
infection rate
e. Ceramic plates are prone to shattering

Answer 17

d. Titanium mesh is associated with a higher
infection rate

Question 18

In the UK, which of the statements about
neurosurgical management of patients at risk
of latent Creutzfeldt-Jacob Disease (CJD) is
LEAST accurate?
a. Assume that anyone born before 1st
January 1997 and was eating beef before
then could potentially have latent CJD
b. Adult neurosurgery departments have had
to keep a separate set of instruments only
to be used on those at high risk of CJD
since 2006
c. There is no effective way of decontaminating surgical instruments of CJD
d. Screening questionnaires should be conducted in all adult patients to assess their
risk of having CJD
e. Single use instruments should be used
where possible in those patients with high
risk of CJD

Answer 18

b. Adult neurosurgery departments have had
to keep a separate set of instruments only
to be used on those at high risk of CJD
since 2006

Two main issues dominate the management of
CJD in neurosurgical patients in the UK:
1. Implementation of CJD screening questions and quarantining of neurosurgical
instruments. These questions were
designed to reduce the risk of spread of sporadic CJD, from patients who suffer from
the disease, have received a human dural
graft or those that have had human derived
hormone treatments, as well as individuals
who have had massive blood transfusions
from multiple donors.
2. Since it has been causally proven that eating
beef with bovine spongiform encephalopathy (BSE) can cause vCJD in humans, the
assumption has been that anyone who has
had beef in the 1980s can be harboring latent
vCJD. Since BSE has been eliminated in
the food chain by 1997, patients born after
1997 are thought to have no risk of developing vCJD. NICE have therefore recommended a new set of instruments be used
on these patients, lest they contract the disease from neurosurgical instruments used on
older patients who may have been harboring
vCJD. The requirement to have (i) a whole
set of instruments to be kept completely
separate and used on a specific cohort of
patients presents huge financial and
logistical challenges (e.g. tracking systems,
single use instruments in high risk patients).
This was temporary advice based on the assumption that effective methods for
removing CJD infectivity from instruments
was likely to be available within 5 years.
However, this has not occurred and the
patients born in 1997 are now coming to
the adult neurosurgical centers which will
now have to keep two separate pools of
instruments or risk them being potentially
being infected with the vCJD agent. As such,
some are now arguing that the costs are disproportionate to the risks (which have been
revised down) and guidance should change

Two main issues dominate the management of
CJD in neurosurgical patients in the UK:
1. Implementation of CJD screening questions and quarantining of neurosurgical
instruments. These questions were
designed to reduce the risk of spread of sporadic CJD, from patients who suffer from
the disease, have received a human dural
graft or those that have had human derived
hormone treatments, as well as individuals
who have had massive blood transfusions
from multiple donors.
2. Since it has been causally proven that eating
beef with bovine spongiform encephalopathy (BSE) can cause vCJD in humans, the
assumption has been that anyone who has
had beef in the 1980s can be harboring latent
vCJD. Since BSE has been eliminated in
the food chain by 1997, patients born after
1997 are thought to have no risk of developing vCJD. NICE have therefore recommended a new set of instruments be used
on these patients, lest they contract the disease from neurosurgical instruments used on
older patients who may have been harboring
vCJD. The requirement to have (i) a whole
set of instruments to be kept completely
separate and used on a specific cohort of
patients presents huge financial and
logistical challenges (e.g. tracking systems,
single use instruments in high risk patients).
This was temporary advice based on the
assumption that effective methods for
removing CJD infectivity from instruments
was likely to be available within 5 years.
However, this has not occurred and the
patients born in 1997 are now coming to
the adult neurosurgical centers which will
now have to keep two separate pools of
instruments or risk them being potentially
being infected with the vCJD agent. As such,
some are now arguing that the costs are disproportionate to the risks (which have been
revised down) and guidance should change.

Question 19

In the UK, which one of the following groups would you not consider high risk of potentially carrying CJD?
a. Individuals receiving blood components from a person who later developed variant CJD
b. Individual who received human-derived pituitary hormones in 1972
c. Individuals who underwent intradural brain/spinal cord surgery or received human-derived dural graft before August 1992
d. Individuals who have had surgery using instruments that had been used on someone who was at high risk of CJD
e.Individuals who have been identified as having received blood or blood components from 300 or more donors since January 2000

Answer 19

e.Individuals who have been identified as having received blood or blood components from 300 or more donors since January 2000

CJD is a progressive, fatal neurological disease that
belongs to a wider group of neurodegenerative disorders known as transmissible spongiform
encephalopathies (TSEs) or prion diseases. Prions
are infectious particles composed of abnormally
folded forms of the prion protein that are thought
to cause TSEs, including CJD. They resist complete inactivation by conventional hospital decontamination techniques. Individuals undergoing
surgery may therefore be infected by prioncontaminated instruments previously used on
patients with CJD. Sporadic CJD (85-90% of
cases) is of unknown etiology with a worldwide
annual incidence of about 1 in 1 million people.
Inherited CJD (10-15% of cases) is associated with
coding mutations, insertions or deletions in the prion protein gene. Iatrogenic CJD (less than 1%
of cases) arises from accidental exposure to human
prions through surgical or medical procedures. A
novel form of human prion disease, variant CJD,
was first recognized in the UK in 1996 and is
believed to result from consumption of food
derived from cattle with BSE. There have been
seven cases of iatrogenic transmission of (presumed sporadic) CJD via contaminated neurosurgical instruments or intracerebral electrodes. Five
cases resulted from neurosurgical instruments:
four in the UK and one in France. All of the
UK cases occurred over 30 years ago.
Increased risk of CJD
1. Recipients of hormone derived from
human pituitary glands, e.g. growth hormone, gonadotrophin, are “at increased
risk” of transmission of sporadic CJD. In
the UK the use of human-derived gonadotrophin was discontinued in 1973, and use
of cadaver-derived human growth hormone was banned in 1985. However, use
of human-derived products may have continued in other countries after these dates.
2. Individuals who underwent intradural brain
or intradural spinal surgery before August
1992 who received (or might have received)
a graft of human-derived dura mater are “at
increased risk” of transmission of sporadic
CJD (unless evidence can be provided that
human-derived dura mater was not used).
3. Individuals who have had surgery using
instruments that had been used on someone
who went on to develop CJD, or was “at
increased risk” of CJD;
4. Individuals who have been identified as
having received blood or blood components from 300 or more donors since
January 1990.
5. Individuals who have given blood to someone who went on to develop vCJD.
6. Individuals who have received blood from
someone who has also given blood to a
patient who went on to develop vCJD,
7. Individuals who have been treated with certain implicated UK sourced plasma products between 1990 and 2001
Increased risk of vCJD
Individuals who have received labile blood
components (whole blood, red cells, white cells
or platelets) from a donor who later went on to
develop vCJD.
Individuals who have received an organ or tissue from a donor infected with CJD or “at
increased risk” of CJD.

CJD is a progressive, fatal neurological disease that
belongs to a wider group of neurodegenerative disorders known as transmissible spongiform
encephalopathies (TSEs) or prion diseases. Prions
are infectious particles composed of abnormally
folded forms of the prion protein that are thought
to cause TSEs, including CJD. They resist complete inactivation by conventional hospital decontamination techniques. Individuals undergoing
surgery may therefore be infected by prioncontaminated instruments previously used on
patients with CJD. Sporadic CJD (85-90% of
cases) is of unknown etiology with a worldwide
annual incidence of about 1 in 1 million people.
Inherited CJD (10-15% of cases) is associated with
coding mutations, insertions or deletions in the
Analysis of the Advantages and Disadvantages of Common Cranioplasty Materials
Material Advantages Disadvantages
Autologous bone Accepted by host, low rate of fracture Bone resorption, infection
MMA Strong, heat resistant, inert, low cost,
ease of use
Infection, fracture, exothermic burn
reaction, inflammation, lack of incorporation
Hydroxyapatite Noninflammatory, decent chemical bonding
to bone, excellent cosmesis and contouring
ability
Low tensile strength, brittle, infection,
fragmentation, lack of osteointegration
Titanium mesh Noninflammatory, noncorrosive, strong,
malleability, low infection rate, good cosmesis
Expensive, image artifact on imaging
Alumina
ceramics
Hard, chemically stable, tissue compatible,
low infection rate
Expensive, prone to shatter
PEEK implant Radiolucent, chemically inert, strong, elastic,
does not create artifacts on imaging,
comfortable, does not conduct temperature
Cost, need for additional 3D planning and
imaging, difficult to bond to other materials,
infection
Table with permission from Shah A, et al. Materials used in cranioplasty: a history and analysis. Neurosurg Focus
2014;36(4):E19.
19 SURGICAL TECHNOLOGY AND PRACTICE e29
prion protein gene. Iatrogenic CJD (less than 1%
of cases) arises from accidental exposure to human
prions through surgical or medical procedures. A
novel form of human prion disease, variant CJD,
was first recognized in the UK in 1996 and is
believed to result from consumption of food
derived from cattle with BSE. There have been
seven cases of iatrogenic transmission of (presumed sporadic) CJD via contaminated neurosurgical instruments or intracerebral electrodes. Five
cases resulted from neurosurgical instruments:
four in the UK and one in France. All of the
UK cases occurred over 30 years ago.
Increased risk of CJD
1. Recipients of hormone derived from
human pituitary glands, e.g. growth hormone, gonadotrophin, are “at increased
risk” of transmission of sporadic CJD. In
the UK the use of human-derived gonadotrophin was discontinued in 1973, and use
of cadaver-derived human growth hormone was banned in 1985. However, use
of human-derived products may have continued in other countries after these dates.
2. Individuals who underwent intradural brain
or intradural spinal surgery before August
1992 who received (or might have received)
a graft of human-derived dura mater are “at
increased risk” of transmission of sporadic
CJD (unless evidence can be provided that
human-derived dura mater was not used).
3. Individuals who have had surgery using
instruments that had been used on someone
who went on to develop CJD, or was “at
increased risk” of CJD;
4. Individuals who have been identified as
having received blood or blood components from 300 or more donors since
January 1990.
5. Individuals who have given blood to someone who went on to develop vCJD.
6. Individuals who have received blood from
someone who has also given blood to a
patient who went on to develop vCJD,
7. Individuals who have been treated with certain implicated UK sourced plasma products between 1990 and 2001
Increased risk of vCJD
Individuals who have received labile blood
components (whole blood, red cells, white cells
or platelets) from a donor who later went on to
develop vCJD.
Individuals who have received an organ or tissue from a donor infected with CJD or “at
increased risk” of CJD.

Question 20

Which one of the following LEAST accurately describes how surgeons interact with
currently available surgical robots?
a. Master-slave
b. Supervisory controlled
c. Telesurgical
d. Shared-control
e. Augmented reality

Answer 20

e. Augmented reality

Surgical robots can be broadly classified into
three categories on the basis of how surgeons
interact with them: supervisory-controlled robot
systems in which the surgeon plans the operation,
and the robot then carries it out autonomously
under the supervision of the surgeon; telesurgical
(master-slave) systems in which the surgeon
(master) remotely controls the robots actions
(slave); and handheld shared-controlled systems
in which the surgeon and robot share control of
the instrument. Augmented reality systems refer
to fusion of virtual 3D brain models and the actual
operating field, may enhance the operating room
workflow and improve safety by eliminating the
need for surgeons to repeatedly interrupt operations and look away from the surgical field at
image guidance. Such systems are already commercially available for use with surgical microscopes, but have not yet been widely applied to
neuroendoscopy.

Surgical robots can be broadly classified into
three categories on the basis of how surgeons
interact with them: supervisory-controlled robot
systems in which the surgeon plans the operation,
and the robot then carries it out autonomously
under the supervision of the surgeon; telesurgical
(master-slave) systems in which the surgeon
(master) remotely controls the robots actions
(slave); and handheld shared-controlled systems
in which the surgeon and robot share control of
the instrument. Augmented reality systems refer
to fusion of virtual 3D brain models and the actual
operating field, may enhance the operating room
workflow and improve safety by eliminating the
need for surgeons to repeatedly interrupt operations and look away from the surgical field at
image guidance. Such systems are already commercially available for use with surgical microscopes, but have not yet been widely applied to
neuroendoscopy.

Question 21

Which one of the following statements regarding neuroendoscopy is LEAST accurate?
a.Image guidance systems are not currently
compatible with neuroendoscopes
b. Generally do not provide stereoscopic
vision
c. Single anatomic corridor can result in
instrument clashing
d. Usually requires an assistant to hold scope
if the primary surgeon wishes to bimanually manipulate a lesion
e. There is an operator learning curve

Answer 21

a.Image guidance systems are not currently
compatible with neuroendoscopes

In minimally invasive neurosurgical procedures,
the relative paucity of anatomic landmarks often
necessitates more frequent use of image guidance,
which may have a considerable impact on surgical
performance. Second, while endoscopes do
provide an extended viewing angle compared with
operating microscopes, some deliver lower-quality
imaging, and most lack stereoscopy, limiting the
appreciation of complex spatial relationshipswithin
the brain. Third, the use of endoscopes makes
bimanual manipulation difficult or impossible.
Within the brain, which is incompatible with gas
insufflation, debris quickly clouds the endoscopic
field unless a sucker is concurrently used; a single
surgeon can therefore not easily view and manipulate tissue simultaneously. Although an additional
surgeon may assist, the use of a single anatomic
corridor makes it difficult to do so without the
operating surgeons obstructing each other or their
instruments clashing. Instrument holders have
recently been developed but can again lead to
crowding of instruments, and inevitably interrupt
the operative workflow, because they must be
repeatedly repositioned. Moreover, even when
specially designed tube-shaft instruments are
used, manipulation through uniportal keyhole neurosurgical approaches is almost coaxial, to the
major detriment of surgical dexterity. Advances in
augmented reality, intraoperative imaging, stereoendoscopy (3D HD), and bimanual manipulation/
jointed wrist instruments will be required to
overcome these issues

In minimally invasive neurosurgical procedures,
the relative paucity of anatomic landmarks often
necessitates more frequent use of image guidance,
which may have a considerable impact on surgical
performance. Second, while endoscopes do
provide an extended viewing angle compared with
operating microscopes, some deliver lower-quality
imaging, and most lack stereoscopy, limiting the
appreciation of complex spatial relationshipswithin
the brain. Third, the use of endoscopes makes
bimanual manipulation difficult or impossible.
Within the brain, which is incompatible with gas
insufflation, debris quickly clouds the endoscopic
field unless a sucker is concurrently used; a single
surgeon can therefore not easily view and manipulate tissue simultaneously. Although an additional
surgeon may assist, the use of a single anatomic
corridor makes it difficult to do so without the
operating surgeons obstructing each other or their
instruments clashing. Instrument holders have
recently been developed but can again lead to
crowding of instruments, and inevitably interrupt
the operative workflow, because they must be
repeatedly repositioned. Moreover, even when
specially designed tube-shaft instruments are
used, manipulation through uniportal keyhole
e30 PART II CARE OF THE NEUROSURGICAL PATIENT
neurosurgical approaches is almost coaxial, to the
major detriment of surgical dexterity. Advances in
augmented reality, intraoperative imaging, stereoendoscopy (3D HD), and bimanual manipulation/
jointed wrist instruments will be required to
overcome these issues.

Question 22

Which one of the following statements
regarding electrocautery and electrosurgery
are incorrect?
a. Flow of electrons produces current
b. Potential difference must exist for electrons to flow against resistance in a circuit
c. Impedance is the resistance to the flow of
current
d. Heat generated is governed by Joule’s
first law
e. In the isolated circuit used in diathermy
machines, loosening of the dispersive electrode will result in thermoelectric burn

Answer 22

e. In the isolated circuit used in diathermy
machines, loosening of the dispersive electrode will result in thermoelectric burn

The source voltage is created by the diathermy
generator, which converts mains 50 Hz current
into a high-frequency current of 0.2-3 MHz. At
these radiofrequencies there is minimal risk of
muscle or nerve stimulation. Instead, electrical
energy is converted to heat as the electrons overcome the impedance of the body. The heat generated is governed by Joule’s first law: Q (heat in
joules)¼I
2 (current density)R (resistance)t
(time). Current density is the current per unit
cross-sectional area. If the current is concentrated
at a single point such as the active electrode (e.g.
tip of monopolar), the effect will be greater than if
spread out over a large area (the dispersive electrode plate). Tissue temperature at the active
electrode tip is 1000°C, but 1 cm away from the
tip it only reaches 38°C. For a given voltage the
current is the same, but if the area through which
the current flow falls, resistance increases and
more heat is produced. Historically, diathermy
used mains voltage referenced to earth and the
dispersive electrode was earthed. If this pad
became loose, was incorrectly applied, or the current found an alternative path to earth (e.g. via a
limb in contact with the table), burns would result
but modern diathermy generators use an isolated
circuit (loosening of dispersive electrode would
break the circuit)

The source voltage is created by the diathermy
generator, which converts mains 50 Hz current
into a high-frequency current of 0.2-3 MHz. At
these radiofrequencies there is minimal risk of
muscle or nerve stimulation. Instead, electrical
energy is converted to heat as the electrons overcome the impedance of the body. The heat generated is governed by Joule’s first law: Q (heat in
joules)¼I
2 (current density)R (resistance)t
(time). Current density is the current per unit
cross-sectional area. If the current is concentrated
at a single point such as the active electrode (e.g.
tip of monopolar), the effect will be greater than if
spread out over a large area (the dispersive electrode plate). Tissue temperature at the active
electrode tip is 1000°C, but 1 cm away from the
tip it only reaches 38°C. For a given voltage the
current is the same, but if the area through which
the current flow falls, resistance increases and
more heat is produced. Historically, diathermy
used mains voltage referenced to earth and the
dispersive electrode was earthed. If this pad
became loose, was incorrectly applied, or the current found an alternative path to earth (e.g. via a
limb in contact with the table), burns would result
but modern diathermy generators use an isolated
circuit (loosening of dispersive electrode would
break the circuit).

Question 23

Which one of the following statements
regarding bipolar diathermy is most accurate?
a.Cutting setting uses a pure continuous
sine wave of low voltage
b. Coagulation setting uses a pure continuous sine wave of high voltage
c. Dessication requires avoidance of tissue
contact with the diathermy probe
d. Blended waveforms should be avoided
e. Coagulation requires a waveform with a
high duty cycle

Answer 23

a.Cutting setting uses a pure continuous
sine wave of low voltage

There are two types of diathermy circuits: monopolar and bipolar. In monopolar mode, current
flows from the diathermy device through the surgical active electrode, through the body, and back
to the diathermy device via the dispersive electrode. The current density is greatest at the
active electrode and heating occurs here. In bipolar mode the surgical tool is a pair of forceps
where one blade represents the active electrode
and the other the return electrode. The current
flows at high current densities from one tip to
the other via the bite of tissue between, rather
than through the body; this eliminates the need
for a dispersive pad. Modern devices are capable
of sealing vessels up to 7 mm in diameter by a
combination of mechanical pressure and diathermy. Microprocessors use tissue response generators to adjust current and voltage based on the
sensed tissue impedance, so vessels can be reliably
sealed to withstand three times normal systolic
pressure. The surgeon has the ability to alter
the power setting, the waveform, the diathermy
tool and how it is applied:

There are two types of diathermy circuits: monopolar and bipolar. In monopolar mode, current
flows from the diathermy device through the surgical active electrode, through the body, and back
to the diathermy device via the dispersive
electrode. The current density is greatest at the
active electrode and heating occurs here. In bipolar mode the surgical tool is a pair of forceps
where one blade represents the active electrode
and the other the return electrode. The current
flows at high current densities from one tip to
the other via the bite of tissue between, rather
than through the body; this eliminates the need
for a dispersive pad. Modern devices are capable
of sealing vessels up to 7 mm in diameter by a
combination of mechanical pressure and diathermy. Microprocessors use tissue response generators to adjust current and voltage based on the
sensed tissue impedance, so vessels can be reliably
sealed to withstand three times normal systolic
pressure. The surgeon has the ability to alter
the power setting, the waveform, the diathermy
tool and how it is applied:

Question 24

Which one of the following statements
regarding complications of diathermy is most
accurate?
a. Surgical smoke does not contain any toxic
substances
b. Electromagnetic interference of cardiac
pacemakers is higher with short, low
power bursts of diathermy
c. Capacitive coupling may cause thermoelectric burns even in an isolated diathermy
circuit
d. Burns at tissue pedicles are due to the low
current density passing through the
narrow point
e. Pools of alcohol-based skin prep are not a
fire risk

Answer 24

c. Capacitive coupling may cause thermoelectric burns even in an isolated diathermy
circuit

Fires can occur when pools of flammable, alcoholbased skin preparations are ignited. Thermoelectric burns occur where the current density rises
inadvertently, such as where tissue in a pedicle
burns, at the dispersive electrode if it is applied
incorrectly or not of sufficient size, so the site
should be well perfused, be distant to any metal
implants that may become heated, and be free
from hair. Burns have also been reported from
insulation failure at the active electrode or accidental contact between the active electrode and
another conductor. Dispersive electrode contact
monitoring pads have a dual foil design that allows
measurement of skin impedance to ensure adequate skin contact. An audible alarm alerts staff
to electrode failure. The isolated circuit reduces
the risk of burns from contactwith earthed objects,
as the current must return to the generator to complete the circuit; however, burns can still occur due
to capacitive coupling. Diathermy can interfere
with both electroencephalography and electrocardiography monitoring electrodes. Of greater consequence is the interaction between EMI and
cardiac pacemakers or implantable defibrillators.
Bipolar is safer than monopolar, but can still cause
EMI. The effects are unpredictable and include
inappropriate pacing, damage to the device, inappropriate defibrillation, and myocardial heat damage. Modern pacemakers have a titanium shell and
interference monitor to protect them from EMI.
The use of a magnet to reset pacemakers to asynchronous continuous pacing is not predictable.
Current advice suggests limiting the use of diathermy to short low power bursts and avoiding
monopolar where possible. Placement of the dispersive electrode away from the device increases
safety. Where appropriate the device should be
checked and reprogrammed to monitoring mode
prior to surgery. Diathermy smoke consists of
95% steam and 5% cellular debris, containing a
variety of toxic mutagenic chemicals including
hydrogen cyanide and benzene. Viruses and viable
cancer cells can be transmitted in surgical smoke
and diathermy machines now contain a surgical
smoke evacuator with a 0.1 m filter, attached to
the diathermy pencil<2 cm from the site of smoke
production.

Fires can occur when pools of flammable, alcoholbased skin preparations are ignited. Thermoelectric burns occur where the current density rises
inadvertently, such as where tissue in a pedicle
burns, at the dispersive electrode if it is applied
incorrectly or not of sufficient size, so the site
should be well perfused, be distant to any metal
implants that may become heated, and be free
from hair. Burns have also been reported from
insulation failure at the active electrode or accidental contact between the active electrode and
another conductor. Dispersive electrode contact
monitoring pads have a dual foil design that allows
measurement of skin impedance to ensure adequate skin contact. An audible alarm alerts staff
to electrode failure. The isolated circuit reduces
the risk of burns from contactwith earthed objects,
as the current must return to the generator to complete the circuit; however, burns can still occur due
to capacitive coupling. Diathermy can interfere
with both electroencephalography and electrocardiography monitoring electrodes. Of greater consequence is the interaction between EMI and
cardiac pacemakers or implantable defibrillators.
Bipolar is safer than monopolar, but can still cause
EMI. The effects are unpredictable and include
inappropriate pacing, damage to the device, inappropriate defibrillation, and myocardial heat damage. Modern pacemakers have a titanium shell and
interference monitor to protect them from EMI.
The use of a magnet to reset pacemakers to asynchronous continuous pacing is not predictable.
Current advice suggests limiting the use of diathermy to short low power bursts and avoiding
monopolar where possible. Placement of the dispersive electrode away from the device increases
safety. Where appropriate the device should be
checked and reprogrammed to monitoring mode
prior to surgery. Diathermy smoke consists of
95% steam and 5% cellular debris, containing a
variety of toxic mutagenic chemicals including
hydrogen cyanide and benzene. Viruses and viable
cancer cells can be transmitted in surgical smoke
and diathermy machines now contain a surgical
smoke evacuator with a 0.1 m filter, attached to
the diathermy pencil<2 cm from the site of smoke production.

Question 25

Which one of the following dural sealants is
made from human fibrinogen and thrombin
only?
a. DuraSeal (Confluent Surgical Inc, Waltham, MA, USA)
b. Bioglue (Cryolife, Kennesaw, GA, USA)
c. Tissucol (Baxter International Inc, Westlake Village, CA, USA)
d. Tisseel (Baxter International Inc, Westlake Village, CA, USA)
e. Evicel (Johnson & Johnson Wound Management, Ethicon Inc, Somerville, NJ,USA)

Answer 25

e. Evicel (Johnson & Johnson Wound Management, Ethicon Inc, Somerville, NJ,USA)

Dural sealants, including DuraSeal (polyethylene
glycol hydrogel [Confluent Surgical Inc., Waltham, MA, USA]), Bioglue (glutaraldehyde bovine albumin [Cryolife, Kennesaw, GA,
USA]), Tissucol (human fibrinogen, thrombin,
albumin, and animal aprotinin), Tisseel (human
fibrinogen, thrombin, and aprotinin [Baxter International Inc., Westlake Village, CA, USA]), and
Evicel (human fibrinogen and thrombin [Johnson
and Johnson Wound Management, Ethicon Inc.,
Somerville, NJ, USA]). These products are used
alone to reinforce primarily repaired dura or as
adjuncts to dural substitutes

Dural sealants, including DuraSeal (polyethylene
glycol hydrogel [Confluent Surgical Inc., Waltham, MA, USA]), Bioglue (glutaraldehyde,
bovine albumin [Cryolife, Kennesaw, GA,
USA]), Tissucol (human fibrinogen, thrombin,
albumin, and animal aprotinin), Tisseel (human
fibrinogen, thrombin, and aprotinin [Baxter International Inc., Westlake Village, CA, USA]), and Evicel (human fibrinogen and thrombin [Johnson and Johnson Wound Management, Ethicon Inc., Somerville, NJ, USA]). These products are used alone to reinforce primarily repaired dura or as adjuncts to dural substitutes.

Question 26

1. Oxidized cellulose

Hemostatic agents in neurosurgery:
a. Arista (Davol, CR Bard Inc, Rhode
Island, USA)
b. Avitene (Davol, CR Bard Inc, Rhode
Island, USA)
c. Floseal (Baxter International Inc, Westlake Village, CA, USA)
d. Hydrogen peroxide
e. Spongostan (Johnson & Johnson)
f. Surgicel (Ethicon, Johnson & Johnson)
g. Surgiflo (Ethicon, Johnson & Johnson)
h. TachoSil (Takeda Nycomed AS, Baxter
International)

Answer 26

f. Surgicel (Ethicon, Johnson & Johnson)

Adequate hemostasis is a prerequisite in neurosurgery, to prevent dramatic postoperative bleedings and their consequences. Different sorts of
local hemostatic agents have been developed,
with a variable efficacy. Some of them have been
used for years, none being perfect. The residual
presence of these agents may behave as foreign
bodies and induce inflammation, infection, and
even delayed bone growth. Safety is another concern since most of modern agents contain more
or less human and animal components.

Question 27

2. Microfibrillar collagen

Hemostatic agents in neurosurgery:
a. Arista (Davol, CR Bard Inc, Rhode
Island, USA)
b. Avitene (Davol, CR Bard Inc, Rhode Island, USA)
c. Floseal (Baxter International Inc, Westlake Village, CA, USA)
d. Hydrogen peroxide
e. Spongostan (Johnson & Johnson)
f. Surgicel (Ethicon, Johnson & Johnson)
g. Surgiflo (Ethicon, Johnson & Johnson)
h. TachoSil (Takeda Nycomed AS, Baxter
International)

Answer 27

b. Avitene (Davol, CR Bard Inc, Rhode Island, USA)

Adequate hemostasis is a prerequisite in neurosurgery, to prevent dramatic postoperative bleedings and their consequences. Different sorts of
local hemostatic agents have been developed,
with a variable efficacy. Some of them have been
used for years, none being perfect. The residual
presence of these agents may behave as foreign
bodies and induce inflammation, infection, and
even delayed bone growth. Safety is another concern since most of modern agents contain more
or less human and animal components.

Question 28

3. Human derived thrombin and bovine derived gelatin matrix

Hemostatic agents in neurosurgery:
a. Arista (Davol, CR Bard Inc, Rhode
Island, USA)
b. Avitene (Davol, CR Bard Inc, Rhode
Island, USA)
c. Floseal (Baxter International Inc, Westlake Village, CA, USA)
d. Hydrogen peroxide
e. Spongostan (Johnson & Johnson)
f. Surgicel (Ethicon, Johnson & Johnson)
g. Surgiflo (Ethicon, Johnson & Johnson)
h. TachoSil (Takeda Nycomed AS, Baxter
International)

Answer 28

c. Floseal (Baxter International Inc, Westlake Village, CA, USA)

Adequate hemostasis is a prerequisite in neurosurgery, to prevent dramatic postoperative bleedings and their consequences. Different sorts of
local hemostatic agents have been developed,
with a variable efficacy. Some of them have been
used for years, none being perfect. The residual
presence of these agents may behave as foreign
bodies and induce inflammation, infection, and
even delayed bone growth. Safety is another concern since most of modern agents contain more
or less human and animal components.

Question 29

1. Human thrombin and fibrinogen with
   equine collagen

Dural substitutes:
a. DuraGen (Integra Life Sciences, Plainsboro, NJ, USA)
b. DuraGuard (Synovis Surgical Innovations, St Paul, MN, USA)
c. DuraMatrix (Stryker, Cambridge, MA,
USA)
d. Durepair (TEI Biosciences, Medtronic
Neurosurgery, MN, USA)
e. Durasis (Cook Biotech Inc, Bloomington,
IN, USA)
f. Fascia lata
g. TachoSil (Takeda Nycomed AS, Baxter
International)
h. TissuDura (Baxter International Inc,
Westlake Village, CA, USA)
i. Neuro-Patch (B. Braun, Melsungen,
Germany)
j. Pericranium

Answer 29

g. TachoSil (Takeda Nycomed AS, Baxter
International)

Dural substitutes are designed to be either placed
as an onlay over dural defects or sutured into
place. These could be autologous tissues, such
as pericranium or fascia lata, or artificial dural
substitutes. The latter are generally derived from
bovine tendon [DuraGen, DuraGen Plus (Integra LifeSciences, Plainsboro, NJ, USA), DuraMatrix (Stryker, Cambridge, MA, USA),
TissuDura (Baxter Healthcare S.A., Opfikon,
Switzerland)], fetal bovine skin [Durepair (Medtronic Inc., Minneapolis, MN, USA), bovine
pericardium/dura [Dura-Guard (Synovis Surgical
Innovations, St. Paul, MN, USA)] or porcine collagen [Durasis (Cook Biotech Inc., Bloomington,
IN, USA)] sources, polyurethane [Neuro-Patch
(B. Braun, Melsungen AG, Melsungen,
Germany)], polyglactin (Ethisorb Dura Patch
[Johnson & Johnson, New Brunswick, NJ,
USA)], polytetrafluoroethylene-based sheets
[Preclude, Gore-Tex (W.L. Gore and Associates
Inc., Flagstaff, AZ, USA)], human acellular dermis [AlloDerm (LifeCell Corporation, Branchburg, NJ, USA)] grafts, and TachoSil [human
fibrinogen and thrombin with equine collagen
(Takeda Pharmaceutical Company, Osaka,
Japan)].

Question 30

2. Bovine pericardium cross linked with gluteraldehyde

Dural substitutes:
a. DuraGen (Integra Life Sciences, Plainsboro, NJ, USA)
b. DuraGuard (Synovis Surgical Innovations, St Paul, MN, USA)
c. DuraMatrix (Stryker, Cambridge, MA,
USA)
d. Durepair (TEI Biosciences, Medtronic
Neurosurgery, MN, USA)
e. Durasis (Cook Biotech Inc, Bloomington,
IN, USA)
f. Fascia lata
g. TachoSil (Takeda Nycomed AS, Baxter
International)
h. TissuDura (Baxter International Inc,
Westlake Village, CA, USA)
i. Neuro-Patch (B. Braun, Melsungen,
Germany)
j. Pericranium

Answer 30

b. DuraGuard (Synovis Surgical Innovations, St Paul, MN, USA)

Dural substitutes are designed to be either placed
as an onlay over dural defects or sutured into
place. These could be autologous tissues, such
as pericranium or fascia lata, or artificial dural
substitutes. The latter are generally derived from
bovine tendon [DuraGen, DuraGen Plus (Integra LifeSciences, Plainsboro, NJ, USA), DuraMatrix (Stryker, Cambridge, MA, USA),
TissuDura (Baxter Healthcare S.A., Opfikon,
Switzerland)], fetal bovine skin [Durepair (Medtronic Inc., Minneapolis, MN, USA), bovine
pericardium/dura [Dura-Guard (Synovis Surgical
Innovations, St. Paul, MN, USA)] or porcine collagen [Durasis (Cook Biotech Inc., Bloomington,
IN, USA)] sources, polyurethane [Neuro-Patch
(B. Braun, Melsungen AG, Melsungen,
Germany)], polyglactin (Ethisorb Dura Patch
[Johnson & Johnson, New Brunswick, NJ,
USA)], polytetrafluoroethylene-based sheets
[Preclude, Gore-Tex (W.L. Gore and Associates
Inc., Flagstaff, AZ, USA)], human acellular dermis [AlloDerm (LifeCell Corporation, Branchburg, NJ, USA)] grafts, and TachoSil [human
fibrinogen and thrombin with equine collagen
(Takeda Pharmaceutical Company, Osaka,
Japan)].