Chapter 35 Cranial Surgery

Question 1

What is normal ICP in dogs and cats?

Answer 1

5-15 mmHg

(Chapter 29 says 8-15 mmHg, chapter 35 says 5-12 mmHg)

Question 2

What is the formula for CPP?

Answer 2

CPP = MAP - ICP

Question 3

List 3 primary homeostatic mechanisms that maintain ICP within optimal range

Answer 3

1. Volume buffering: Increase in volume of one component requires reciprocal decrease of others if ICP is to remain unchanged (Monro-Kellie doctrine). Usually CSF drainage
2. Autoregulation: Autoregulation of cerebral blood flow is the ability of brain to maintain normal cerebral perfusion. Pressure regulation, chemical autoregulation
3. Cushing reflex: response to global ischaemia and uncontrolled intracranial hypertension –> cathecholamines –> systemic vasoconstriction –> baroreceptior response –> vagally mediated bradycardia. Indicates imminent brain herniation

Question 4

List 6 groups of medication that should be considered during intracranial surgery

Answer 4

1. Anticonvulsants
2. Analgesic
3. Antibiotics
4. Pressors
5. Osmotic diuretics
6. Sedatives

Question 5

What is the optimal range of PaCO2?

Answer 5

30 - 35 mmHg

Question 6

List 5 factors to consider in management of intracranial hypertension

Answer 6

1. Reduce cerebral oedema (mannitol, hypertonic saline. Corticosteroids if neoplastic vasogenic oedema or inflammatory disease)
2. Prevent hypercapnia and hypoxia (ventilation, oxygen supplementation + blood transfusion as necessary)
3. Control central venous blood volume (head elevation, no neck wraps or jugular samples).
4. Prevent systemic hypotension
5. Control cerebral oxygen demand (pain, hyperthermia, seizures, halluconogenic drugs)

Question 7

Below what level PaCO2 can cerebral ischaemia be seen

Answer 7

<30 mmHg

Question 8

What is ideal CPP in small animals?

Answer 8

50 - 90 mmHg

(roughly speaking aim to keep MAP >80 mm Hg if unable to measure ICP (and therefore unable to calculate CPP))

Question 9

What is dose of mannitol 20%

And dose of 7.5% NaCl

Answer 9

Mannitol: 1 g/kg over 10 mins

7.5% NaCl: 4 ml/kg over 10 mins

Question 10

How is mannitol believed to affect ICP?

Answer 10

1. Plasma expanding effect –> increased cerebral blood flow and O2 delivery. Immediate
2. Delayed osmotic effect –> osmitoc gradient –> reduced brain water content. 20 - 30 minute delay

Question 11

Why is hypertonic saline less likely to cause hypotension from diuresis than mannitol?

Answer 11

Because sodium (of hypertonic saline) is reabsorbed inthe kidneys.

Question 12

How do ultrasonic aspirators work?

What are supposed benefits?

Answer 12

Ultrasonic vibration of tip –> fragmentation of tissue + simultaneous lavage + aspiration.

Advantages:

• Improved visibility with simultaneous lavage + aspiration
• Decreased haemorrhage through preservation of vasculature
• Combined, may result in improved extent of resection (improved survival times reported in dogs w meningiomas).

Question 13

What 8 factors shoudl be considered when planning appropriate surgical approach for intracranial pathology?

Answer 13

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

Question 14

Why is bipolar electrocaustery preferred over monopolar

Answer 14

Bipolar –> less widespread tissue damage

Question 15

What 4 considerations should be borne in mind when opening dura?

Answer 15

1. How to best access the pathology
2. Location of major vessels within and under the dura
3. How the dural defect will be closed (graft vs. direct closure)
4. Effect of potential brain swelling.

Question 16

The dura meter of the brain possesses two distinct layers in certain places to enclose venous sinuses. Which respective venous sinus is associated with:

Falx cerebri

Tentorium cerebelli (n.b. often mineralised)

Diaphragm sellae

Answer 16

Falx cerebri = dorsal sagittal sinus

Tentorium cerebelli = transverse sinus

Diaphragm sellae (i.e top of sella turcica) = cevernous venous sinus

Question 17

List 4 options for menigneal closure following craniotomy

Answer 17

1. Primary closure
2. Temporalis muscle fascia
3. Porcine SI submucosa
4. Prosthetic dura (GoreTex or DuraGen)

Question 18

List 5 options for craniotomy closure

(n.b. if small defect may not need to be closed)

Answer 18

1. Replacement of excised bone
2. Calvarial allografts
3. Acrylic cranioplasty i.e. PMMA
4. Metallic mesh (titanium preferred)
5. 3D printed implant

Question 19

What is the preferred material for post-craniotomy mesh and why

Answer 19

Titanium

• Resistant to biofilm formation
• Relative radiolucency/MRI compatibility
• corrosion resistant
• Rigid but malleable

Question 20

Label the diagram:

Answer 20

Question 21

What intraoperative imaging technique can be used to better visualise lesion?

Answer 21

US

Flourescence guided techniques under investigation:

• Intra-operative IV fluoroscein sodium had agreement with pre-op gadolinium MRI enhancement (Nakano, VetSurg, 2018)

A, On the transverse plane, T2-weighted image, a large hyperintense intraparenchymal, high-grade glioma can be seen displacing the right lateral ventricle that appears crescent shaped and hyperintense (black arrow).

B, Intraoperative ultrasonography clearly defines the location and depth of the mass, and the overlying ventricle is seen as an anechoic rim dorsal to the mass (white arrow).

Question 22

List 4 approaches to the cranial cavity and the areas accessed with each

N.B. cranial cavity is compartmentalized into rostrotentorial compartment (i.e. cranial to tenorium cerebelli) and caudotentorial compartment.

Cranial compartment contains:

• Cerebral hemispheres
• Thalamus
• Hippocampus
• Olfactory system

Caudal compartment contains:

• Cerebellum
• Pons
• Medulla
• 4th ventricle

Answer 22

Transfrontal (and modified transfrontal)

• Olfactory bulb
• Rostral frontal lobe

Rostrotentorial (depending on where approach made - can be bilateral)

• Frontal lobe
• Parietal lobe
• Temporal lobe
• Occipital lobe
• Lateral ventricles
• Falx cerebri
• Corpus callosum

Sub-occipital aka occipital

• Caudal cerebellum
• Dorsal medulla
• Fourth ventricle
• Cranial cervical SC

Caudal cranial fossa approach with transverese venous sinus occlusion

​Most commonly in conjunction with rostrotentorial or sub-occipital approach

• Enter at level of tentorium cerebelli

Question 23

List 2 approaches to the pituitary gland

Answer 23

Trans-sphenoidal

Ventral paramedian

Question 24

Which vessel might cause bleeding from ventral olfactory/rostral lobe

Answer 24

Ethmoidal artery

Question 25

How does modified transfrontal approach differ from usual transfrontal approach?

Answer 25

* Increased visibility and access * Rostral portions of temporal muscles are elevated bilaterally. * Lateral osteotomy extended (caudolaterally) beyond attachment of orbital ligament to zygomatic process of frontal bone Rostral (A) and lateral (B) views respectively showing the approximate outline of frontal sinus osteotomy (dotted lines). C, The midsagittal bony bridge connecting the outer table of the frontal bone to the inner table is osteotomized using an osteotome and mallet. The location and angle of this cut are based on imaging because there is enough individual variation between dogs that landmarks alone are not reliable. D-E, Illustrations showing the approach before (D) and after (E) the inner table of the frontal bone is removed. In panel D, the midline bony bridge (arrowhead) is visible, and the location of the olfactory bulbs (arrow) can be approximated. The osteotomized bridge connecting the cribriform plate can be partially resected to access ventrally located masses or masses extending caudally into the region of the thalamus. Incision into the dura (dotted lines) should be made in such a way that the dorsal sagittal sinus is not violated if it is patent. At the rostral-most extent, the dorsal sagittal sinus may be ligated or controlled with electrosurgical coagulation if bilateral access to the brain is needed

Question 26

Label the diagram

Answer 26

Question 27

How can a rostrotentorial approach be modified to improve access ventrally?

Answer 27

Osteotomy of zygomatic process temporal bone

Question 28

Which two venous structures may cause bleeding during sub-occipital apprach?

Answer 28

Occipital emissary vein or condyloid vein Vertebral venous plexus may be present circumfrentially around Sc at this level

Question 29

What structures limit the lateral and dorsal extent of sub-occipital approach?

Answer 29

Transverse sinus laterally Confluens sinuum dorsally Approaches to the caudal fossa. A, An illustration of the caudolateral aspect of the skull. The occipital lobe of the cerebrum (arrow) and the cerebellum (arrowhead) are visible using the caudal cranial fossa approach with occlusion of the transverse sinus. B, An illustration of the caudal to rostral view of the skull. The caudal aspect of the cerebellar vermis and cranial cervical spinal cord via (sub)occipital craniectomy are visible; this approach is typically used in decompressive surgery for Chiari-like malformation. The limits of this approach are defined by the location of the confluens sinuum and the transverse sinuses. C, Combined approaches to the caudal cranial fossa are used for removing masses from the cerebellopontine angle.

Question 30

What are the two most common, life-threatening complicatioons during brain surgery

Answer 30

Brain swelling and uncontrolled haemorrhage

Question 31

List 3 intra-op methods to control brain swelling What additional step can be performed

Answer 31

Osmotic diuretics Cool saline lavage Meticulous control of haemorrhage Can perform wide decompressive craniectomy (+ alleviate sourve of swelling)

Question 32

List 7 possible complications following intracranial surgery

Answer 32

1. Apiration pneumonia 2. Intracranial haemorrhage 3. Meningitis/infection 4. Tension pneumocephalus 5. Seizures 6. Elevated ICP (brain swelling) 7. Compression of brain secondary to fibrous tissue/muscle (like laminectomy membrane)

Question 33

Describe the imaging abnormalities/post op complications (different patients)

Answer 33

Potential complications associated with cranial surgical procedures. A, Transverse plane postcontrast T1-weighted image with extensive suppurative meningoencephalitis and myositis associated with a rostrotentorial craniectomy and polymethylmethacrylate (asterisk) reconstruction. Staphylococcus pseudointermedius was isolated from the suppurative inflammation. B, Transverse CT image post stereotactic biopsy. Clinically insignificant air pockets are present; however, a large hyperattenuating lesion is present over the left temporal and parietal lobes, causing marked mass effect and displacement of the falx cerebri. Surgical exploration by craniotomy revealed an epidural hemorrhage from a lacerated meningeal vessel. C, On transverse plane T1-weighted MR images, the hyperintensity (arrowhead) represents hemorrhage, potentially from involvement of the middle meningeal artery following a rostrotentorial craniectomy. Secondary swelling of brain and increased intracranial pressure resulted in transcraniectomy herniation of parietal lobe. D, Sagittal plane postcontrast T1-weighted image with contrast-enhancing mass (oligodendroglioma) extending into the nasal cavity. Extension of the neoplasm followed a stereotactic biopsy tract created 3 months previously, probably secondary to seeding of the neoplasm along the tract.

Question 34

List 10 steps in post-op craniectomy monitoring

Answer 34

1. Temperature 2. Respiration 3. ECG 4. MAP 5. Blood gases + electrolytes 6. Neuro status (MDGS) 7. Hydration status (aim for normovolaemia) 8. Avoid neck compression 9. Head elevated at 30º 10. ?Sedation 11. Analgesia 12. ?Anticonvulsant 13. Urinary/oral care 14. Turning

Question 35

When shoudl brain biopsy be considered

Answer 35

If presentation atypical or when ddx have widely differign tx (eg lymphoma/histiocytic sarcoma vs meningioma)

Question 36

Name a common intraparenchymal neoplasm

Answer 36

Oligodendroglioma

Question 37

What type of biopsy needle is used for brain biopsy?

Answer 37

Nashold (side cutting guillotine biopsy, blunt tip)

Question 38

What % of stereotactic brain biopsies are diagnostic?

Answer 38

90%

Question 39

List 2 potential benefits to brain neoplasm resection

Answer 39

Increased MST Improved neuro status (decreased tumour burden may improve efficacy of adjuvant therapy) (Diagnosis reached)

Question 40

List 4 indications for surgical intervention in brain trauma cases

Answer 40

* Severely depressed skull fractures * Ongoing haemorrhage * Presence of FBs * Deteriorating neuro status CT image (A) and three-dimensional reconstruction (B) from a 13-year-old Rat Terrier presenting comatose after being stepped on by a horse. Bilateral craniectomy and fragment removal revealed severely malacic cerebral tissues resulting in euthanasia. Ventrodorsal skull radiograph (C) and transverse T1-weighted postcontrast MR image of a Doberman Pinscher presenting for progressive deterioration in mentation with a bullet lodged in the left parietal bone. Removal of the bullet via craniectomy revealed a bleeding meningeal vessel and subdural hematoma. The dog recovered well following intensive care for 3 weeks.

Question 41

list 4 congenital anomalies that may require surgical intervention

Answer 41

* Intracranial arachnoid diverticula * Dermoid/epidermoid cysts (usually arise in caudal fossa) * Congenital hydrocephalus * Chiari-like malformation

Question 42

List 6 complications of VP shunt placement

Answer 42

1. Blockage 2. Migration 3. Infection 4. Undershunting 5. Control valve fracture 6. Seizure

Question 43

List the three components of a VP shunt

Answer 43

Ventricular catheter = control valve + abdominal catheter _Ventricular catheter:_ A fenestrated section of silicone rubber tubing with a tip (distal end) that will be positioned in the lateral ventricle, and a proximal end that will be attached to the control valve. _Control valve_: Mechanism for regulating the flow of cerebrospinal fluid through the shunt that is designed to simulate normal cerebrospinal fluid drainage. The valve is either made of or covered with silicone rubber and sits between the skull and the temporalis muscle. More sophisticated shunts are programmable to maintain ventricular pressures within preset ranges. Some shunts also have siphon control valves that prevent the shunt from overdraining a ventricle and producing too low an intracranial pressure. _Abdominal catheter:_ Attaches to the control valve and runs subcutaneously to enter the abdominal (peritoneal) cavity.

Question 44

Where in the ventricles should ventricular catheter for VP shunt be placed and why?

Answer 44

Lateral ventricle. Frontal horn or temporal horn to avoid irritating vascular choroid plexus

Question 45

What is the name of the area where the pituitary is located

Answer 45

Sella turcica (meaning is "turkish seat" in latin - depression looks like a saddle)