Chapter 35 Cranial Surgery Flashcards
What is normal ICP in dogs and cats?
5-15 mmHg
(Chapter 29 says 8-15 mmHg, chapter 35 says 5-12 mmHg)
What is the formula for CPP?
CPP = MAP - ICP
List 3 primary homeostatic mechanisms that maintain ICP within optimal range
- 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
- Autoregulation: Autoregulation of cerebral blood flow is the ability of brain to maintain normal cerebral perfusion. Pressure regulation, chemical autoregulation
- Cushing reflex: response to global ischaemia and uncontrolled intracranial hypertension –> cathecholamines –> systemic vasoconstriction –> baroreceptior response –> vagally mediated bradycardia. Indicates imminent brain herniation
List 6 groups of medication that should be considered during intracranial surgery
- Anticonvulsants
- Analgesic
- Antibiotics
- Pressors
- Osmotic diuretics
- Sedatives
What is the optimal range of PaCO2?
30 - 35 mmHg
List 5 factors to consider in management of intracranial hypertension
- Reduce cerebral oedema (mannitol, hypertonic saline. Corticosteroids if neoplastic vasogenic oedema or inflammatory disease)
- Prevent hypercapnia and hypoxia (ventilation, oxygen supplementation + blood transfusion as necessary)
- Control central venous blood volume (head elevation, no neck wraps or jugular samples).
- Prevent systemic hypotension
- Control cerebral oxygen demand (pain, hyperthermia, seizures, halluconogenic drugs)
Below what level PaCO2 can cerebral ischaemia be seen
<30 mmHg
What is ideal CPP in small animals?
50 - 90 mmHg
(roughly speaking aim to keep MAP >80 mm Hg if unable to measure ICP (and therefore unable to calculate CPP))
What is dose of mannitol 20%
And dose of 7.5% NaCl
Mannitol: 1 g/kg over 10 mins
7.5% NaCl: 4 ml/kg over 10 mins
How is mannitol believed to affect ICP?
- Plasma expanding effect –> increased cerebral blood flow and O2 delivery. Immediate
- Delayed osmotic effect –> osmitoc gradient –> reduced brain water content. 20 - 30 minute delay
Why is hypertonic saline less likely to cause hypotension from diuresis than mannitol?
Because sodium (of hypertonic saline) is reabsorbed inthe kidneys.
How do ultrasonic aspirators work?
What are supposed benefits?
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).
What 8 factors shoudl be considered when planning appropriate surgical approach for intracranial pathology?
- General location of the lesion
- Size and extent of the lesion relative to the size of 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)
Why is bipolar electrocaustery preferred over monopolar
Bipolar –> less widespread tissue damage
What 4 considerations should be borne in mind when opening dura?
- How to best access the pathology
- Location of major vessels within and under the dura
- How the dural defect will be closed (graft vs. direct closure)
- Effect of potential brain swelling.
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
Falx cerebri = dorsal sagittal sinus
Tentorium cerebelli = transverse sinus
Diaphragm sellae (i.e top of sella turcica) = cevernous venous sinus
List 4 options for menigneal closure following craniotomy
- Primary closure
- Temporalis muscle fascia
- Porcine SI submucosa
- Prosthetic dura (GoreTex or DuraGen)
List 5 options for craniotomy closure
(n.b. if small defect may not need to be closed)
- Replacement of excised bone
- Calvarial allografts
- Acrylic cranioplasty i.e. PMMA
- Metallic mesh (titanium preferred)
- 3D printed implant
Label the diagram:
What intraoperative imaging technique can be used to better visualise lesion?
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).
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
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
How does modified transfrontal approach differ from usual transfrontal approach?
- 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
Label the diagram
What structures limit the lateral and dorsal extent of sub-occipital approach?
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.
Describe the imaging abnormalities/post op complications (different patients)
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.
List 4 indications for surgical intervention in brain trauma cases
- 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.
