In a study by Morton 2022 in JAVMA, what was the most common indication for craniotomy or craniectomy in dogs and cats? What were the most common post-operative complications? What were the most common long term complications?
Meningioma was the most common indication.
Post-operatively seizures, anemia, neurologic deficits, and aspiration pneumonia were most frequent. Seizures and neurologic deficits were most common long-term.
Overall mortality rate was 15%.
In a study by Tichenor 2024 in JAVMA, what were the median survival times for cats undergoing surgery as compared to steriotactic radiotherapy as a treatment for intracranial meningioma?
MST for surgery 1345 days, for radiotherapy 340 days. Good survival was also achieved with radiotherapy following recurrence of tumour (700 days).
In a study by Glamann 2023 in VRU, what sign on MRI can be used to differentiate between intracranial intra-axial gliomas and extra-axial meningiomas?
The claw sign (85% sensitive and 80% specific).
In a study by Parker 2022 in JVIM, what percentage of dogs undergoing surgery for a rostrotentorial brain tumour developed early post-operative seizures? Were these related to outcome?
13% developed seizures.
Dogs with seizures had longer hospitalization, were more likely to have neurologic complications, and were less likely to survive to discharge.
The presence of previous epilepsy or use of anticonvulsant medications were not associated with the risk of early post-operative seizures.
What determines cerebral perfusion pressure?
CPP = MAP - ICP
What mechanisms maintain intracranial pressure within a range in which the brain functions best?
- Volume buffering: primarily accomplished through CSF drainage in response to fluctuations in ICP.
- Autoregulation of cerebral blood flow: keeps blood flow constant between systemic blood pressures of 50-150 mmHg. Chemical autoregulation is affected predominantly by PaCO2.
- Cushing reflex: increased ICP leads to cerebral ischemia, this stimulates a release of catecholamines that causes systemic vasoconstriction. Baroreceptors detect this change and induce a vagally mediated bradycardia. Indicates imminent brain herniation.
What are some mechanisms of secondary brain injury?
- Gross movements of neural tissue between compartments secondary to intracranial hypertension, causing distortion and fracture.
- Unregulated glutamate release causing cytotoxic damage to cells.
- Loss of the blood brain barrier with reaction toward the brain tissue as a foreign entity, upregulating the inflammatory response.
Should perilesional edema be treated prior to surgery for intracranial neoplasia?
Yes, corticosteroids are used.
A thorough work-up for any coagulation abnormalities should also be performed pre-op.
What are some measures by which increased ICP can be managed?
- Prevent hypercapnia and hypoxia. PaO2 should be maintained above 60 mmHg. PaCO2 should be maintained between 30-35 mmHg.
- Prevent systemic hypotension: fluid resuscitation and pressors. Should be maintained between 50-90 mmHg (ideally above 80mmHg if ICP monitoring not possible).
- Reduce cerebral edema: mannitol (1g/kg IV) and hypertonic saline (4 ml/kg IV).
- Corticosteroids, for neoplasm induced cerebral edema and primary inflammatory diseases.
- Control cerebral venous blood volume: head elevation (30 degrees).
- Control cerebral oxygen demand.
What is the mechanism of action of mannitol?
- Has an immediate plasma expanding effect increasing cerebral blood flow and oxygen delivery.
- Delayed (20-30 minutes) osmotic effect causing a reduction in brain water content and reduced ICP.
What is the benefit of hypertonic saline over mannitol for use with elevated ICP?
Less likely to cause diuresis induced hypotension (due to reabsorption in the kidneys). May be more appropriate for patients with hypotension and increased ICP.
What are some surgical instruments that should be considered when performing neurosurgery?
- Magnification.
- Head mounted fiber optic light source.
- Monopolar and bipolar electrocautery.
- Gelatin foam, oxidized regenerative cellulose, and bone wax.
- High speed pneumatic drills.
- Ultrasonic aspirators.
What is the benefit of use of ultrasonic aspirators during cranial surgery?
Allow for more aggressive removal of neoplastic tissue with reduced damage to low-water content structures such as vasculature.
What is the safest method of entry into the cranial cavity?
Use of a high-speed pneumatic burr.
What are some methods of dural closure following craniectomy?
- Direct suturing.
- Use of the fascia of the temporalis muscle as an autologous dural replacement.
- Porcine small intestinal submucosa.
What are some options for reconstruction of the skull following craniectomy?
- Replacement of the excised skull bone or calvarial allografts.
- Acrylic cranioplasty (PMMA most common). Most common complication is infection. Should not be used in approaches which result in exposure to contaminated air from the paranasal sinuses (such as the transfrontal approach).
- Metallic mesh. Titanium preferred due to its relative radiolucency, MRI compatability, low density, and corrosion resistance.
What are some options for navigation during neurosurgical procedures?
- Intraoperative neuronavigation based off pre-operative MRI (may be limited by brain shift and alterations in structure after the surgery is started).
- Intraoperative MRI.
- Intraoperative ultrasound.
- Use of nanoparticles, such as ICG.
What are the two anatomic compartments of the cranial cavity (for surgical purposes)?
Refer to the division created by the tentorium cerebelli:
- Rostrotentorial (rostral and middle): cerebral hemispheres, thalamus, hippocampus, olfactory system.
- Caudotentorial (caudal cranial fossa): cerebellum, pons, medulla, fourth ventricle.
The midbrain is located at the junction of the two compartments.
What are some surgical approaches to the cranial cavity?
- Transfrontal craniotomy.
- Modified transfrontal approach.
- Unilateral rostrotentorial approach.
- Suboccipital craniectomy or caudotentorial craniectomy +/- transverse sinus occlusion.
- Approach to the pituitary gland.
What is the primary indication for a transfrontal craniotomy?
Access to the rostral portion of the frontal lobes and olfactory bulb.
Due to the direct communication with the outside environment a watertight closure over the surface of the brain is required.
What is the primary indication for a modified transfrontal craniotomy?
Increased exposure to the olfactory region. Accomplished through removal of additional bone overlying the frontal sinus.
What is the primary indication for a unilateral rostrotentorial craniotomy?
Access to various portions of the frontal, parietal, temporal, and occipital lobes the cerebrum. Entry is via the frontal, parietal, temporal, or sphenoid bones.
Can be extended caudally to exposure the tentorium cerebellum with occlusion of the transverse venus sinus.
Can also be performed bilaterally and jointed on midline to approach midline lesions, large bilateral lesions, or to achieve extensive cerebral decompression.
During a bilateral midline rostrotentorial approach to the brain, which venous structure should be avoided?
Dorsal sagittal sinus.
Control of hemorrhage can be performed using gently pressure, flushing with cool saline, and use of hemostastic agents. Electrocoagulation typically worsens hemorrhage.
What can be performed in conjunction with a rostrotentorial craniotomy to increase exposure of the ventrolateral aspect of the skull?
Ostectomy of the zygomatic arch, which allows retraction of the temporalis muscle rostrolaterally.
