32 Infratentorial Cavernous Malformations
♦ Preoperative
Operative Planning
Review Imaging
- Computed tomography (CT) scan: low yield with respect to operative planning, unless patient has had a previous craniotomy, then might be helpful with understanding bone anatomy
- Magnetic resonance imaging (MRI)
- Location
- For brain stem cavernous malformation, T1 with thin slices to see if and where the lesion comes to the surface
- Size and age of clot, if previous hemorrhage
- Proximity to adjacent eloquent structures/nuclei and to the pial surface (in the case of brain stem cavernous malformation)
- Presence of multiple lesions
- Presence of venous angioma
- Stereotactic sequences for use of frameless imaging guidance intraoperatively
- Location
- Angiogram
- Only useful if an associated venous malformation or arteriovenous malformation (AVM) is suspected
- Will rule out other vascular pathology, indicated in patients presenting with spontaneous intracerebral hemorrhage; this could change operative planning (i.e., presence of true AVM could lead to surgical management with radiosurgery)
Neurophysiology
- Electroencephalogram
- Not necessary in infratentorial cavernous malformations. In case of multiple lesions, including supratentorial lesions, will identify and confirm which lesion is indeed the epileptogenic focus
- Somatosensory evoked potential (SSEP) and brain stem auditory evoked responses (BAERs)
- To guide surgeon with respect to brain stem tracts and nuclei preoperatively and intraoperatively
Special Equipment for Operating Room
- As for acoustic neuroma
Operating Room Set-up
- Operating microscope
- Frameless stereotaxy
Anesthetic Issues
- Hyperventilation; optimize pCO2 to 30 to 35 mm Hg
- Intravenous (IV) steroids (dexamethasone 10 mg IV or methylprednisolone 150 mg IV)
- Antibiotics (cefazolin 1 gm IV every 6 hours, oxacillin 2 gm every 6 hours, or vancomycin 1 gm every 12 hours); all antibiotics should be given at least 30 minutes prior to incision
- Diuresis with mannitol (0.5 to 1 g/kg) or mannitol + furosemide at time of skin incision
- Anticonvulsants continued if patient already on medications; not necessary in infratentorial lesions
- Blood pressure as per routine with any intracranial surgery
- If neurophysiology (SSEP, BAERs) is to be used, limitations to use of muscle relaxants and paralytics similar to acoustic neuroma
♦ Intraoperative
Preparation of Frameless Stereotaxy
- Load images onto system
- Perform patient coregistration
- Check accuracy of instruments and probes
Positioning
- Highly variable depending on location of lesion and approach used
Shave Patient
- Clip hair with electric razor, do not shave
- Approximately 3 cm width along length of incision
Incision, Craniotomy, Dural Opening
- Approaches
- Suboccipital: midline cerebellar or cerebellar hemisphere lesions; transvermian modification for midline pontine lesions, consider velotelar approach
- Infratentorial supracerebellar: collicular lesions
- Occipital transtentorial
- Retrosigmoid or presigmoid: lateral pontine lesions
- Far lateral
- Transtemporal
- Frontotemporal/subtemporal transtentorial: lesions of the cerebral peduncle
- Velotelar: fourth ventricle lesions
- Pial Incision
Resection of Lesion
- Dissection of glial plane
- Empty caverns within lesion of clot to internally debulk (internal decompression) then roll lesion on itself to resect away from glial plane
♦ Postoperative
- Intensive care unit monitoring for at least 24 to 48 hours, rule out postoperative hydrocephalus
- Blood pressure: systolic control below 120 mm Hg (140 if patient with poorly controlled hypertension preoperative) for first 24 to 48 hours
- Antibiotics continued for 24 hours, longer if ventriculostomy catheter in place
- Steroids tapered slowly
- CT scan in 12 to 18 hours
- MRI eventually
- Sutures removed in 7 to 10 days
