Kapitel 35 – cranial surgery

Question 1

What is the normal cranial pressure in cats and dogs?

Answer 1

5-12 mmhg

Question 2

What is CPP and how do you calculate it?

Answer 2

Cerebral perfusion pressure
CPP = MAP-ICP

Question 3

What are the three primary mechanism maintaining ICP?

Answer 3

Volume buffering - refers to the ability of the intracranial contents to resist a change in pressure with the addition of intracranial volume

Autoregulation - is the ability of the brain to maintain normal cerebral perfusion. Pressure autoregulation describes a vascular reflex that occurs in response to changes in transmural pressure of cerebral vessels. This reflex serves to keep blood flow constant over a range of systemic blood pressures by altering the resistance of the cerebral vessels. In the normal brain, this mechanism operates primarily in the pial arterioles at perfusion pressures between 50 and 150 mm Hg.

Cushing reflex (vasopressor response) - is a physiological response to global brain ischemia and severely increased intracranial pressure. This stimulates release of catecholamines, leading to systemic vasoconstriction and increased cardiac output. In the extreme, baroreceptors, sensing this systemic hypertensive state, cause a vagally mediated bradycardia

Question 4

What factors should be considered during the pre-operatoive planning of the craniectomy/craniotomy?

Answer 4

• General location of the lesion
• Size and extent of the lesion relative to the size of the head/brain
• Vital structures in the vicinity that will limit craniectomy size
• Suspected type of lesion (neoplastic vs. inflammatory vs. infectious) and need obtain a complete resection
• Purpose for approaching the lesion (biopsy vs. excision)
• Potential for complications with the approach, especially if more than one approach may be used
• Instruments available to the surgeon (e.g., endoscopic vs. classical instruments)
• Suspected nature of the lesion (e.g., fluid vs. solid, friable vs. fibrous, vascular vs. nonvascular)

Question 5

Name some cranioplasty techniques used in small animals

Answer 5

• Replacement of the excised skull bone or Calvarial allograft
• Acrylic cranioplasty - polymethylmethacrylate being the most frequently reported
• Metallic mesh - titanium is considered superior for the purpose of skull reconstruction.

Question 6

Name the standard approaches to the canine brain access to the olfactory frontal region.

Answer 6

• Transfrontal craniotomy
• Modified transfrontal approach (removing of additional bone overlying the frontal sinuses giving increased
• Rostrotentorial approach
• (sub) Occipital craniectomy or caudotentorial craniectomy
• Transverse sinus occlusion

Question 7

What are some indications for transfrontal craniotomy?

Answer 7

Lesions involving the olfactory bulbs and rostral portion of the frontal lobes of the brain are best approached through a transfrontal craniotomy. Olfactory bulb/frontal lobe neoplasms, abscesses or granulomas secondary to foreign body migration, and fungal granulomas and neoplasms invading through the cribriform plate are the most common conditions in which this approach is indicated.

Question 8

Which approach is typically used for Chiari-like malformations?

Answer 8

(sub) occipital cranioectomy

Question 9

What is the approach to reach the pituitary gland?

Answer 9

Transorally (transsphenoidally) or via a ventral paramedian approach.

Question 10

Cranial surgical procedures and neurological disease has shown to be a major postanasthetic risk factor of what?

Answer 10

Aspiration pneumonia due to altered mentation, decreased gag reflex, vomiting, regurgitation or megaesophagus.