Ch 35 Cranial surgery

Question 1

What three primary homeostatic mechanisms maintain intracranial pressure?

autoregulation is the ability to maintain normal cerebral perfusion

Answer 1

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)

Question 2

pre-op consdierations

Answer 2

• 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

Question 3

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

Answer 3

30 - 35mmHg

Below 30, neuronal ischaemia can occur and exacerbate intracranial hypertension

Question 4

What are the anaesthetic goals for managing intracranial hypertension (7)

Answer 4

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)

Question 5

pre-op imaging

Answer 5

(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.

Question 6

surgical instruments

Answer 6

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,

Question 7

What is unique about burring for cranial surgery?

Answer 7

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

Question 8

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

Answer 8

irrigation-coupled bipolar device

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

Question 9

What can be used to make the initial dura cut?

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

Answer 9

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

Question 10

what consdierations for durotomy?

Answer 10

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.

Question 11

What can be used to close a dural defect?

Answer 11

Fascia of temporalis muscle (surface of fascia facing towards brain)
Porcine SISM
Sutured with 4-0 PDS or tissue glue

Question 12

haemorrhage control

Answer 12

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

Question 13

excising brain mass

Answer 13

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

Question 14

What are some options for cranioplasty?

Answer 14

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

Question 15

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

Answer 15

5-aminolevulinic acid
Indocyanine green

Question 16

Transfrontal craniotomy

Answer 16

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 (

Question 17

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.

Question 18

Rostrotentorial approach

Answer 18

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

Question 19

Suboccipital craniectomy or Caudotentorial craniectomy

Answer 19

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).

Question 20

Approach to pituitary gland

Answer 20

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

Question 21

Transverse Sinus Occlusion

Answer 21

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

Question 22

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

Answer 22

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

Question 23

What may cause significant haemorrhage in a transfrontal approach?

Answer 23

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

Question 24

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

Answer 24

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

Question 25

post-op imaging and monitoring | Brain healing/recovery from acute injury is ongoing for weeks to months

Answer 25

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,

Question 26

What vessels can cause significant bleeding during the suboccipital craniectomy?

Answer 26

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

Question 27

intra-op complications

Answer 27

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.

Question 28

post-op complications (8)

Answer 28

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

Question 29

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

Answer 29

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**

Question 30

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

Answer 30

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

Question 31

What are the benefits of brain neoplasia resection?

Answer 31

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

Question 32

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

Answer 32

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

Question 33

brain truam sx indications

Answer 33

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.

Question 34

List some congenital or developmental diseases which may benefit from surgical intervention (4)

Answer 34

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

Question 35

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

Answer 35

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

Question 36

Results of oral prednisolone administration or ventriculoperitoneal shunt placement in dogs with congenital hydrocephalus: 40 cases (2005–2016) Sabrina Gillespie 2019

Answer 36

Retrospective, oral prednisolone administration vs VP shunt placement in dogs with congenital hydrocephalus: 40 cases 12 medically > 6 improved and 6 deteriorated (50%) 26 surgically > 14 (54%) improved, 1 (4%) stabilized, and 11 (42%) deteriorated; 4 (15%) had known postoperative complications. (38%) surgically treated dogs with known outcomes were euthanized because of unresolved clinical signs or complications associated with VPS placement.

Question 37

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

Question 38

Indications, complications, and mortality rate following craniotomy or craniectomy in dogs and cats: 165 cases (1995–2016) Bridget A. Morton 2022

Answer 38

craniotomy or craniectomy 150 dogs and 15 cats. retrospective case series indication: meningioma [52.8%] Complications (35.2%) cases within 24 hours (52.1%) cases 1 to 10 days The mortality rate shor-term 14.5% Long-term complications (39.4%)

Question 39

Surgical techniques used in the management of intra-arachnoid diverticula in dogs across four referral centres and their immediate outcome B. Jones 2022

Answer 39

Spinal intra-arachnoid diverticula in dogs. 57. Retrospective Durectomy (28 dogs) followed by marsupialisation (11 dogs), durotomy alone (seven dogs), shunt placement (six dogs) and stabilisation (five dogs) shunt placement are likely to deteriorate 24-hour but then improve. incontinent presurgery > Nineteen of 27 (70%) resolved Overall, 84% of dogs improved in the 3- to 5-week

Question 40

Anaesthetic management and complications during hypophysectomy in 37 cats with acromegaly Neilson 2019 | JFMS

Answer 40

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.

Question 41

Clinical characteristics and outcome in 15 dogs treated with transsphenoidal hypophysectomy for nonfunctional sellar masses Hyde 2022

Answer 41

Retrospective. transsphenoidal hypophysectomy for sellar masses Perioperative mortality 33% (5/15). MST 232 days (0–1658) survive to discharge > MST 708 days received adjunctive therapy had good to excellent outcomes

Question 42

Prolonged survival after craniectomy with skull reconstruction and adjuvant definitive radiation therapy in three dogs with multilobular osteochondrosarcoma Holmes 2019

Answer 42

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

Question 43

Multilobular osteochondrosarcoma

Answer 43

- bone, connective tissue, or cartilage. - slow-growing, locally invasive (cranium, orbit, mandible, and maxilla) - Complete surgical excision with histologically clean margins can offer long-term local tumor control - Complete histologic margins can be a surgical challenge. local recurrence in 5/9 dogs with DFI 6mths 42% following complete surgical 77% in dogs with incomplete Adjuvant therapies did not improve control when compared to surgery alone Modified craniotomy with mesh closure > Survival times from surgery were 387, 422, and 730 days

Question 44

Outcome and quality of life after intracranial meningioma surgery in cats Lydia Koch 2023

Answer 44

intracranial meningioma surgery in cats. 14 cases Preoperative clinical signs resolved in 95% of cases MST 861 (15–2064) days Three cats (27%) had recurrence