Ch 35 Cranial surgery Flashcards
What is the normal intracranial pressure of dogs and cats?
5-12mmHg
Affected by arterial inflow, venous outflow and resistance of cerebral vasculature
brain is protected by the confines of the cranial cavity, where it exists in equilibrium with blood and cerebrospinal fluid
Normal function of neurons depends on an adequate supply of oxygen and glucose.
High metabolic demands + limited energy storage capacity necessitate keeping cerebral blood flow within a relatively normal range at all times.
An increase in the volume of one component requires a reciprocal decrease in one or more of the others if intracranial pressure is to remain relatively unchanged (Monro-Kellie doctrine)
How do you calculate cerebral perfusion pressure (CPP)?
CPP = MAP - ICP
ICP closely approximately venous outflow pressure
What factors can alter cerebral blood volume without altering blood flow?
Low head position
Venous outflow obstruction
Increases intrathoracic pressure
What factors alter cerebral blood volume by altering the blood flow?
CO2
O2
Lactic acid
Drugs
What three primary homeostatic mechanisms maintain intracranial pressure?
autoregulation is the ability to maintain normal cerebral perfusion
Volume buffering
- Increase in one parameter (blood volume) causing a decrease in another (CSF volume)
Autoregulation of blood flow
- Reflex vascular changes regulated by the pial arterioles at pressures between 50 - 150mmHg
Chemical autoregulation
- Cerebral vasodilation with increases PaCO2
- Cerebral vasoconstriction with decreased PaCO2
- Decreased PaO2 will eventually cause cerebral vasodilation (less then 60mmHg)
What is the Cushing’s reflex?
Uncontrolled ICP leads to reduced cerebral blood flow, ischaemia and hypercarbia
Stimulates catecholamine release leading to systemic vasoconstriction and increased cardiac output (thereby increased CPP)
Baroreceptors sense hypertensive stare and cause a vagally mediated bradycardia
Indicates imminent brain herniation
pre-op consdierations
- minimum database, concurrent health problems
- thorax/abdo rads/us
- assess for coagulopathy (no nsaid, PT/aPTT
- pre-Sx corticosteroid
anaesthetic
- all monitoring equipment
- mechanical ventilation and blood products are readily available.
- Premedication limited to an analgesic
- induction and entube: avoid increase ICP
- TIVA (prefered over GA)
- Intermittent positive pressure ventilation is important in order to maintain optimal PaCO2
What is the ideal PaCO2 which is aimed for during intracranial surgery?
30 - 35mmHg
Below 30, neuronal ischaemia can occur and exacerbate intracranial hypertension
What monitoring systems are available for monitoring ICP?
Fiber-optic based systems
miniaturised strain gauge devices
Transcranial Doppler ultrasound (indirect)
What are the anaesthetic goals for managing intracranial hypertension (7)
1.Prevent hypercapnia
2.Prevent hypoxia
(Oxygen supplementation, blood transfusions, controlled ventilation PaCO2 30)
3.Prevent systemic hypotension (maintain at or above 80mmHg to maintain a CPP of 50 - 90mmHg, use vasopressors)
4.Reduce cerebral oedema (mannitol/hypertonic saline) : Hydration status, electrolyte concentrations, and acid-base status should be determined
5.Corticosteroids (neoplasm associated oedema and primary inflammatory disease)
6.Control cerebral venous blood volume (head elevation etc)
7.Control cerebral oxygen demand (Hyperthermia, seizures, pain and ketamine all increased oxygen demand)
Mannitol is believed to have two effects on intracranial pressure: an immediate (minutes) plasma-expanding effect that reduces blood viscosity and increases cerebral blood flow and O2 delivery to the brain and a delayed, osmotic effect that occurs 20 to 30 minutes after
0.5 to 1.0 g/kg IV over 10 to 20 minutes.
7.5% NaCl solution 4 mL/kg IV administered over 10 minutes.
frusemide 0.7 to 2 mg/kg IV.
pre-op imaging
(MRI) is generally the imaging modality of choice; however, the additional data provided by computed tomography (CT) imaging may be particularly useful where bony lesions such as fractures, skull-based multilobular tumors of bone, or osteo/chondrosarcomas are present or for surgical localization in hypophysectomy procedures
Positron emission tomography (PET) imaging has potential to define both the extent of intracranial disease and the functional characteristics of neoplasms; however, its use is very limited in veterinary patients to date.
surgical instruments
magnification
Gelatin foam, oxidized regenerated cellulose, and bone wax are ideal products for control of hemorrhage
Ultrasonic aspirators are particularly useful for resection or debulking of extra- and intraparenchymal neoplasm
Intraoperative ultrasonography often facilitates removal of intraparenchymal lesions,
What is unique about burring for cranial surgery?
Smallest burr size allows a secure fit if planning to replace bone
Inner cortical bone has highly irregular undulations with marked differences in bone thickness
Dorsal calvaria is considerably thicker
Cutting at angle of 30 degree allows for almost complete apposition
Cancellous bone is called diploe
What electrosurgical device is preferred when working on dural and parenchymal tissues?
irrigation-coupled bipolar device
Standard bipolar on minimum effective setting with constant slow, steady saline drip sufficient
What can be used to make the initial dura cut?
If wanting to close the dura, what needs to be done intraop?
11 Bard Parker blade, the tip of a needle or microscissors
It must be kept stretched during the procedure to prevent shrinkage - attach to surrounding tissues using suture, skin staples or mosquito forceps
what consdierations for durotomy?
The dura should be opened with the following considerations in mind:
(1) how to best access the pathology;
(2) the location of major vessels within and under the dura—hemorrhage early on will obscure the view and potentially lead to brain swelling;
(3) how the dural defect will be closed (graft vs. direct closure); and
(4) the effect of potential brain swelling.
What can be used to close a dural defect?
Fascia of temporalis muscle (surface of fascia facing towards brain)
Porcine SISM
Sutured with 4-0 PDS or tissue glue
haemorrhage control
If meningeal or parenchymal > locate and coagulate the vessel rather than “chase” a vessel under a bony ledge
large venous sinuses (dorsal sagittal sinus, transverse sinus). Light bleeding > gelatin foam or other hemostatic agent placed over the tear in the sinus. Heavier bleeding may require that the sinus be packed with gelatin foam or bone wax
excising brain mass
extraparentchymal
- Craniectomies should be large enough to allow dissection
- electrosurgical coagulation of all visible blood vessels that appear to be supplying the mass prior to removal
- dentifying a plane of dissection between the mass and normal brain
- cotton nibs or paddies are helpful to aid in gentle retraction
- Keep the brain surface moist at all times
intraparenchymal
- Intraparenchymal lesions require incision into a gyrus of the cerebrum
- surface vessels in the region of the proposed incision should be gently coagulated
- mass excised using an ultrasonic aspirator
What are some options for cranioplasty?
Replacement with excised bone
allograft
Acrylic cranioplasty (PMMA)
Metallic mesh with low profle self-tapping screws
Smaller-sized defects that are well covered by a protective layer of temporalis muscle
Avoid placing foreign material where is may become contaminated by air from paranasal sinuses
What fluorescent dyes can be used intra-op to aid in lesion localisation?
5-aminolevulinic acid
Indocyanine green
Transfrontal craniotomy
olfactory bulbs and rostral portion of frontal lobe
- Modified transfrontal approach increased visibility and surgical access
- achieved by removing additional bone overlying the frontal sinus than is noted in the standard description.
Because the frontal sinus is in direct communication with the outside environment via the nasal cavity, a watertight closure of the graft over the surface of the brain is of prime importance for preventing various surgical complications (
The rostral and middle cranial fossae contain the cerebral hemispheres, thalamus, hippocampus, and olfactory system, whereas the caudal cranial fossa contains the cerebellum, pons, medulla, and fourth ventricle. The midbrain is located at the junction of the two compartments.
Rostrotentorial approach
frontal, parietal, temporal and occipital lobes of the cerebrum
- Lateral ventricles, falx cerebri and corpus callosum also approached through gyrotomy
- Can be extended caudally to expose tentorium cerebelli following occlusion of transverse sinus
Suboccipital craniectomy or Caudotentorial craniectomy
Caudal cerebellum, dorsal aspect of medulla, 4th ventricle, cranial cervical spinal cord
> enlarging the foramen magnum
Significant bleeding from the occipital emissary vein (exiting from the skull near the mastoid foramen) or condyloid vein (adjacent to the condyle) can be encountered.
the internal vertebral venous plexus may be present circumferentially around the spinal cord (interarcuate branch).
Approach to pituitary gland
ranssphenoidally (transorally) or via ventral paramedian approach
gland itself lies in the sella turcica of the sphenoid bone, which forms the base of the cranial cavity and the roof of the nasopharynx
Transverse Sinus Occlusion
Dorsal cerebellopontine angle, cerebellum, lateral aspect of tentorium cerebello
- Usually combined with suboccipital or rostrotentorial approach
Why is it extra important to close dural defects after a transfrontal approach?
To prevent infection and pneumocephalus due to communication with the paranasal sinuses
What may cause significant haemorrhage in a transfrontal approach?
Dorsal sagittal sinus
internal ethmoid artery (ventral aspect of olfactory-rostral frontal lobe region)
If you need to remove part of cribiform plate
What external nerves need to be avoided during the rostrotentorial approach?
Auriculotemporal nerve/temporal nerve supplying the temporalis muscle . Exit and course ventrally at the level of the zygomatic process
Palpebral branch or auriculopalpebral nerve if combining with osteotomy of zygomatic arch
post-op imaging
and monitoring
Brain healing/recovery from acute injury is ongoing for weeks to months
MRI > imaging requirements for adjunctive therapies such as radiation therapy.
systemic blood pressure support using fluid therapy and vasopressive drugs while preventing increases in intracranial pressure/brain oedema
Ventilatory support may be indicated to maintain PaCO2 in the range between 28 and 32 mm Hg
recumbency care, nutrition
Physiologic monitoring (BP, T, blood gas, electrolyte etc)
Mental state and level of consciousness
Brainstem reflexes
Pupillary size and reactivity
Resting eye position
Corneal reflexes
Abnormal respiratory patterns
Motor responses and gait
Abnormal posturing (decerebrate/decerebellate)
elevated 30 degree, analgesia, antiseizure,
What vessels can cause significant bleeding during the suboccipital craniectomy?
occipital emissary vein (exits near mastoid foramen)
Condyloid vein (adjacent to the condyle)
Internal venous plexus/interarcuate branch or dura
Limited laterally by the transverse sinus and dorsally by the confluens sinuum
intra-op complications
minimized by appropriate and adequate surgical exposure and minimal handling of brain tissues.
brain swelling
- osmotic diuretics
- cool saline lavage
- meticulous control of hemorrhage
- Wide decompressive craniectomy (if herniation)
widespread ischemia secondary to electrosurgical coagulation or thrombosis of major venous
uncontrolled hemorrhage
hematomas can form quickly and are not easily seen or identified, resulting in brain swelling, ischemia, and herniation.
post-op complications (8)
aspiration pneumonia
seizures
hemorrhage
increased ICP > secondary to brain swelling with associated risk of brain herniation.
subcutaneous emphysema with incomplete sealing of transfrontal craniotomy
infection
pneumocephalus
compression of brain secondary to fibrous tissue
What are the broad options for brain biopsy?
What kind of needles are recommended?
Freehand-guided aspiration through small burr holes
Larger craniotomy approaches guided by advanced imaging
Procedure specific, minimally traumatic, side-cutting guillotine biopsy needles eg, Nashold needle
What are the reported rates of diagnostic yield with stereotactic brain biopsy?
Morbidity?
Mortality?
Diagnostic yield over 90%
Morbidity 27% (generally less then 5% with experience and avoiding high risk areas such as brain stem)
Mortality is rare
What are the benefits of brain neoplasia resection?
Increased survival times and immediate improvement
Improve efficacy of adjuvent radiation and chemotherapy
Allow introduction of therapies directly into the neoplasm or resection cavity
Brain tumor removal considerations?
The benefits of surgical resection (with or without adjunctive therapy) compared to radiation therapy alone have not been demonstrated in veterinary patients
evidence-based data in human beings support surgical resection of gliomas and meningiomas
survival outcomes following surgery for neoplasms such as meningioma vary widely from 1 month to 6 years depending on study location and surgical technique
likelihood of short-term improvement in quality of life
Value of obtaining diagnostic material
Location of the neoplasm and likelihood of surgical morbidity
Availability of surgical expertise
Availability of alternative therapeutic options (radiation therapy, chemotherapy)
Owner preferences relating to short-term and long-term risk/benefit assessment
brain truam sx indications
severely displaced skull fractures,
suspected ongoing hemorrhage,
foreign bodies such as bullets or missiles
deteriorating neurological status in the face of appropriate medical management of intracranial hypertension.
List some congenital or developmental diseases which may benefit from surgical intervention (4)
Intracranial arachnoid diverticula
Dermoid and epidermoid cysts
congenital hydrocephalus
malformation of the caudal cranial fossa and craniocervical junction (Chiari-like malformation)
Where in the ventricles should a ventriculoperitoneal shunt be placed?
What is the function of the control valve?
frontal horn or temporal horn of the lateral ventricle
(avoid irritating the vascular choroid plexus)
Control valve helps to maintain physiological ventricular pressures by controlling the siphoning effect. Simulates normal CSF drainage
Paralumbar skin incision caudal to last rib for placement of abdominal catheter
Results of oral prednisolone administration
or ventriculoperitoneal shunt placement in dogs
with congenital hydrocephalus: 40 cases (2005–2016)
Sabrina Gillespie 2019
DESIGN
Retrospective case series.
ANIMALS
40 client-owned dogs
Of 12 medically treated dogs, 6 improved and 6 deteriorated. Of
26 surgically treated dogs with data available, 14 (54%) improved, 1 (4%)
stabilized, and 11 (42%) deteriorated; 4 (15%) had known postoperative complications.
Overall, 10 of 26 (38%) surgically treated dogs with known outcomes were euthanized because of unresolved clinical signs or complications
associated with VPS placement.
Incidence of and risk factors for major complications
or death in dogs undergoing cytoreductive surgery
for treatment of suspected primary intracranial masses
Rickard J. Kohler 2018
paucity of objective
information about optimal treatment for dogs
with intracranial tumors, and data that are available
are limited to results of retrospective studies
Retrospective cohort study.
ANIMALS
160 client-owned dog
reviewed for complications occurring within 30 days after surgery
13.1) dogs died
18.8% developed major complications other than death
- seizures 11.3%]
- worsening of neurologic status (6 [3.8%])
- aspiration pneumonia (6 [3.8%]).
Dogs with abnormal preoperative neurologic
examination findings were more likely to develop complications or die.
Dogs undergoing a suboccipital approach were more likely to die.
Radiation treatment for intracranial tumors has been
associated with a median survival time of 351 days
(range, 139 to > 900 days)
surgical treatment
has been associated with a median survival time
of 312 days (range, 27 to 2,104 days)
However, reported
median survival times vary substantially dt tumor type/surgery/skill etc
Indications,
complications, and mortality rate
following craniotomy or craniectomy in dogs and cats: 165 cases (1995–2016)
Bridget A. Morton 2022
150 dogs and 15 cats.
PROCEDURES
For this multi-institutional retrospective case series
The most common indication: meningioma (75/142 [52.8%]).
Complications
(35.2%) cases within 24 hours (52.1%) cases 1 to 10 days
Perioperative: hypotension and anemia
postoperative period: neurologic deficits, seizures, postoperative anemia, and aspiration pneumonia.
The mortality rate with death ≤ 10 days postoperatively was 14.5% (24/165).
Long-term complications (39.4%)
Surgical techniques used in the
management of intra-arachnoid
diverticula in dogs across four referral
centres and their immediate outcome
B. Jones 2022
existence of multiple techniques is suggestive that,
currently, no one surgery can be concluded to be superior. The
personal experience and preference of the individual surgeon
Retrospective multi-centre case series across four referral centres.
Results: Fifty-seven dogs with spinal
most common type of surgery was durectomy
(28 dogs) followed by marsupialisation (11 dogs), durotomy alone (seven dogs), shunt placement (six
dogs) and stabilisation (five dogs)
Dogs with a thoracolumbar intra-arachnoid diverticulum that undergo a shunt placement are
likely to deteriorate neurologically in the immediate 24-hour postoperative period but appear to improve
by 3 to 5 weeks after surgery. Further work is required to evaluate whether one surgical technique
is superior for preventing or reducing long-term relapse.
All 27 dogs reported to be incontinent presurgery had followup
data at 3 to 5 weeks. Nineteen of 27 (70%) resolved
Overall, 84% of dogs improved in the 3- to 5-week
Anaesthetic management
and complications during
hypophysectomy in 37 cats
with acromegaly
Traditionally, these cases have been managed medically
or with radiation therapy,5 but more recently, surgical
removal of the tumour is being offered by some
veterinary hospitals. This involves an intraoral approach through the soft palate and skull base to expose and resect the pituitary gland
death rate 8- (14%).
Intraoperative complications identified during the
cases reviewed here included hypothermia, bradycardia,
hypotension and airway obstruction.
Clinical characteristics and outcome in 15 dogs treated
with transsphenoidal hypophysectomy for nonfunctional
sellar masses
Study design: Multi-institutional retrospective study
Perioperative mortality was 33% (5/15).
The median survival for all dogs was 232 days (0–1658). When dogs that did
not survive to discharge were excluded, the median survival time was 708 days
Dogs with NFPA that survived to
discharge and received adjunctive therapy had good to excellent outcomes
Prolonged survival after craniectomy with skull reconstruction
and adjuvant definitive radiation therapy in three dogs with
multilobular osteochondrosarcoma
Holmes 2019
This retrospective case series, 3 dogs
All dogs were treated surgically with a modified craniectomy,
repaired with a titanium mesh—polymethyl methacrylate bone cement implant or a low prolife
titanium mesh plate and followed by adjuvant definitive radiation therapy
Survival times from surgery were 387, 422, and 730 days
Multilobular osteochondrosarcoma is an uncommon canine primary
bone tumor that can arise from bone, connective tissue, or cartilage.
These tumors are typically slow-growing, locally invasive tumors that
most commonly affect the cranium, orbit, mandible, and maxilla.
Complete surgical excision with histologically clean margins can
offer long-term local tumor control and is the treatment of choice, However, complete
histologic margins can be a surgical challenge.
Presumed complete margins were achieved
in nine of the dogs but local recurrence was documented in five of
the nine dogs with a median disease free interval of approximately
6 months.9 For calvarial multilobular osteochondrosarcomas, local
tumor recurrence occurred at 6 months in one of two dogs following
incomplete excision
Local
recurrence has been reported to be 42% following complete surgical
resection and as high as 77% in dogs with incompletely resected
multilobular osteochondrosarcomas
An expanded study, however, found adjuvant
therapies did not improve control when compared to surgery alone
and reported a high percentage of dogs developing local recurrence
and/or metastatic disease when receiving adjuvant therapy.
Outcome and quality of life after
intracranial meningioma surgery in cats
Lydia Koch 2023
The study included 14 cases
Thirteen questionnaires were completed. Three cats were evaluated twice owing to revision surgery. Owners
reported a statistically significant (P <0.001) improvement from immediately after the operation to 240 days after
surgery. Preoperative clinical signs resolved in 95% of cases
limitations, such as small sample size, recall bias, lack of a control group and validation of
the questionnaire, need to be kept in mind when interpreting the results
The median (range) survival time was 861 (15–2064) days
Three cats (27%) had recurrence
