Ch 35 - Cranial Surgery Flashcards

1
Q

What is the normal intracranial pressure of dogs and cats?

A

5-12mmHg

Affected by arterial inflow, venous outflow and resistance of cerebral vasculature

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2
Q

How do you calculate cerebral perfusion pressure (CPP)?

A

CPP = MAP - ICP

ICP closely approximately venous outflow pressure

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3
Q

What factors can alter cerebral blood volume without altering blood flow?

A
  • Low head position
  • Venous outflow obstruction
  • Increases intrathoracic pressure
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4
Q

What factors alter cerebral blood volume by altering the blood flow?

A
  • CO2
  • O2
  • Lactic acid
  • Drugs
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5
Q

What three primary homeostatic mechanisms maintain intracranial pressure?

A

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)

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6
Q

What is the Cushing’s reflex?

A
  • 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

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7
Q

What is the ideal PaCO2 which is aimed for during intracranial surgery?

A

30 - 35mmHg

Below 30, neuronal ischaemia can occur and exacerbate intracranial hypertension

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8
Q

What monitoring systems are available for monitoring ICP?

A
  • Fiber-optic based systems
  • miniaturised strain gauge devices
  • Transcranial Doppler ultrasound (indirect)
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9
Q

What are the anaesthetic goals for managing intracranial hypertension

A
  • Prevent hypercapnia and hypoxia
  • Prevent systemic hypotension (maintain at or above 80mmHg to maintain a CPP of 50 - 90mmHg)
  • Reduce cerebral oedema (mannitol/hypertonic saline)
  • Corticosteroids (neoplasm associated oedema and primary inflammatory disease)
  • Control cerebral venous blood volume (head elevation etc)
  • Control cerebral oxygen demand (Hyperthermia, seizures, pain and ketamine all increased oxygen demand)
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10
Q

What is unique about burring for cranial surgery?

A
  • 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
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11
Q

What electrosurgical device is preferred when working on dural and parenchymal tissues?

A

Irrigation-coupled bipolar device

Standard bipolar on minimum effective setting with constant slow, steady saline drip sufficient

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12
Q

What can be used to make the initial dura cut?

If wanting to close the durs, what needs to be done intraop?

A
  • # 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
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13
Q

What can be used to close a dural defect?

A
  • Fascia of temporalis muscle (surface of fascia facing towards brain)
  • Porcine SISM

Sutured with 4-0 PDS or tissue glue

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14
Q

What are some options for cranioplasty?

A
  • Replacement of excised bone
  • Acrylic cranioplasty (PMMA)
  • Metallic mesh with low profle self-tapping screws

Avoid placing foreign material where it may become contaminated by air from paranasal sinuses

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15
Q

What fluorescent dyes can be used intra-op to aid in lesion localisation?

A
  • 5-aminolevulinic acid
  • Indocyanine green
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16
Q

List the main approaches to the brain and the area of the brain which they are best used for

A

Transfrontal craniotomy
- olfactory bulbs and rostral portion of frontal lobe
- Modified transfrontal approach increased visibility and surgical access

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

Transverse Sinus Occlusion
- Dorsal cerebellopontine angle, cerebellum, lateral aspect of tentorium cerebello
- Usually combined with suboccipital or rostrotentorial approach

Approach to pituitary gland
- transsphenoidally (transorally) or via ventral paramedian approach

17
Q

Why is it extra important to close dural defects after a transfrontal approach?

A

To prevent infection and pneumocephalus due to communication with the paranasal sinuses

18
Q

What may cause significant haemorrhage in a transfrontal approach?

A
  • Dorsal sagittal sinus
  • internal ethmoid artery (ventral aspect of olfactory-rostral frontal lobe region)
  • If you need to remove part of cribiform plate
19
Q

What external nerves need to be avoided during the rostrotentorial approach?

A
  • 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
20
Q

What vessels can cause significant bleeding during the suboccipital craniectomy?

A
  • 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
21
Q

Where is the pituitary gland located?

A

In the sella turcica of the sphenoid bone

22
Q

What are the broad options for brain biopsy?
What kind of needles are recommended?

A
  • 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

23
Q

What are the reported rates of diagnostic yield with stereotactic brain biopsy?
Morbidity?
Mortality?

A
  • Diagnostic yield over 90%
  • Morbidity 27% (generally less then 5% with experience and avoiding high risk areas such as brain stem)
  • Mortality is rare
24
Q

What are the benefits of brain neoplasia resection?

A
  • Increased survival times and immediate improvement
  • Improve efficacy of adjuvent radiation and chemotherapy
  • Allow introduction of therapies directly into the neoplasm or resection cavity
25
Q

List some congenital or developmental diseases which may benefit from surgical intervention

A
  • Intracranial arachnoid diverticula
  • Dermoid and epidermoid cysts
  • congenital hydrocephalus
  • malformation of the caudal cranial fossa and craniocervical junction (Chiari-like malformation)
26
Q

Where in the ventricles should a ventriculoperitoneal shunt be placed?
What is the function of the control valve?

A
  • Placed in the frontal horn or temporal horn of the lateral ventricle to 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