Vestibular schwannomas

Introduction

Vestibular schwannomas (VS) are also called acoustic neuromas and are benign primary intracranial tumors that form along the vestibulocochlear nerve from Schwann cells that are responsible for the myelin sheath around the nerve axons. The incidence is 6 to 9 per million persons per year; however, this number is increasing as a result of widespread availability of neuroimaging. Although they only account for 6% of primary intracranial tumors, they account for 85% of tumors in the cerebellopontine angle (CPA). As a result of increasing diagnoses, the treatment algorithms for patients who present with VS is becoming more refined, with the goals of quality of life, facial nerve function, and hearing preservation. These treatment options include observation, surgical resection, and/or radiation therapy. Surgical resections vary in goal from gross total resection to planned subtotal resection, and approaches vary from retrosigmoid, middle fossa, and translabyrinthine, among others. In this chapter, we present a case of a patient with VS.

Example case

Chief complaint: tinnitus and imbalance

History of present illness

A 53-year-old, right-handed woman with a history of diabetes, hypertension, and hypercholesterolemia presented with left-sided tinnitus and imbalance. Approximately 6 months prior, she started developing ringing in her left ear and felt as though her hearing was worse on the left side to the point in which she could not use that ear while on the telephone. In addition, she complained of progressive imbalance in which she had constant falls. Her primary care physician ordered brain imaging ( Fig. 68.1 ).

Medications : Aspirin, hydrochlorothiazide, simvastatin, metformin.
Allergies : No known drug allergies.
Past medical and surgical history : Diabetes, hypertension, and hypercholesterolemia.
Family history : No history of intracranial malignancies.
Social history : Secretary, no smoking or alcohol.
Physical examination : Awake, alert, oriented to person, place, time; Cranial nerves II to XI except left V1 to V3 facial numbness, left House-Brackmann 2/6; Moves all extremities with good strength; Cerebellar: Left to right finger-to-nose dysmetria, truncal ataxia.
Audiogram : Left ear discrimination 25%, pure tone audiogram 75 dB (Gardner-Robertson class III).

	Franco DeMonte, MD, MD Anderson Cancer Center, Houston, TX, United States	Gerardo D. Legaspi, MD, Philippine General Hospital, Manila, Philippines	Robert E. Wharen, MD, Larry B. Lundy, MD, Mayo Clinic, Jacksonville, FL, United States	Gelareh Zadeh, MD, PhD, Farshad Nassiri, MD, Toronto Western Hospital, Toronto, Canada
Preoperative
Additional tests requested	Audiogram (BAERs) Neuro-otology evaluation	None	Vestibular testing Facial EMG CT of temporal bones	CTA
Surgical approach selected	Left retrosigmoid craniotomy with opening of foramen magnum and posterior lip of IAC	Left retrosigmoid craniotomy	Left translabyrinthine with possible abdominal fat graft	Left retrosigmoid craniotomy
Other teams involved during surgery	Neuro-otologist	None	Neuro-otologist	None
Anatomic corridor	Left retrosigmoid	Left retrosigmoid	Left translabyrinthine	Left retrosigmoid
Goal of surgery	Gross total resection pending adhesion to brainstem and facial nerve	Gross total resection	Brainstem decompression, preservation of cranial nerve V and VII	Maximal safe resection with facial nerve preservation and brainstem decompression
Treatment of asymptomatic lesions surgically	Conservatively followed to assess for growth	Lesions over 2 cm adjacent to the brainstem	Lesions compressing MCP or fourth ventricle	Lesions over 3 cm and not insolated to porous
Treatment using SRS	All but largest tumors, young patients, Koos IV tumors	Patients who refuse surgery, elderly	Growth of asymptomatic lesions, tumors <2.5 cm	Lesions <3 cm that are growing on serial imaging
Perioperative
Positioning	Left lateral, head flexed laterally to right	Left supine with right head rotation	Left supine with right head rotation	Left park bench
Surgical equipment	Surgical navigation Surgical microscope IOM (facial EMG) Nerve stimulator Ultrasonic aspirator	Lumbar drain IOM (facial nerve EMG) Surgical microscope Ultrasonic aspirator	Surgical microscope IOM (facial and trigeminal EMG) Nerve stimulator Cardiac pacer leads	Surgical microscope IOM (cranial nerve stimulator) Doppler Ultrasonic aspirator
Medications	Steroids	None	Steroids	Steroids Mannitol
Anatomic considerations	Transverse and sigmoid sinuses, petrosal vein, cranial nerves IV–XII, SCA, AICA, PICA, VA, petrous surface of cerebellum, brainstem	Cranial nerves V–XI, AICA, PICA, lateral cerebellum and pons	Cranial nerves IV–XI, posterior fossa vessels and brainstem perforators	Transverse and sigmoid sinuses, cranial nerves especially facial nerve, mastoid air cells, vertebral artery
Complications feared with approach chosen	Injury to cerebellum, facial nerve and other cranial nerve, vasculature, brainstem	Facial nerve injury	Cranial neuropathy especially facial paralysis, cerebellar and brainstem compression, CSF leak	Cranial neuropathy, venous sinus injury, brainstem injury
Intraoperative
Anesthesia	General	General	General	General
Skin incision	Midline posterior cervical down to C2 and laterally to EAM above left ear	Sigmoid incision 1.5 cm lateral to mastoid extending 1 cm above transverse sinus and 5 cm below	Postauricular C-shaped incision	Sigmoid incision based on transverse-sigmoid junction
Bone opening	Occipital craniotomy exposing lower part of transverse sinus and posterior sigmoid sinus, foramen magnum	Occipital craniotomy exposing lower part of transverse sinus and posterior sigmoid sinus, IAC	Mastoidectomy and bone overlying sigmoid sinus, labyrinthectomy, removal of bone overlying middle and posterior dura	Occipital craniotomy exposing lower part of transverse sinus and posterior sigmoid sinus, foramen magnum
Brain exposure	Retrosigmoid, left cerebellar hemisphere	Retrosigmoid, left cerebellar hemisphere	Translabyrinthine, cerebellopontine angle	Retrosigmoid, left cerebellar hemisphere
Method of resection	Occipital craniotomy up to sinus margins, removal of foramen magnum and bone beneath anterior curve of sigmoid sinus, dura opened in midline over cisterna magna, CSF drained, dural incision extended to transverse-sigmoid junction, tumor exposed and queried for facial nerve with stimulator, tumor incised and centrally debulked, inferior debulking to identify flocculus/choroid plexus/lower cranial nerves, origin of facial nerve, continual debulking to identify cerebellar interface/petrosal vein/fifth nerve/upper pole of tumor, posterior IAC is drilled after cisternal portion of tumor removed, distal portion of tumor is removed to expose facial nerve in porous, removal of intermediary tumor dependent on adherence to facial nerve, watertight dural closure	Lumbar drain placement, incision carried down to periosteum, muscle flap retracted to sigmoid sinus and paramedian area, retraction held down by silk stay sutures and anchored with rubber bands, burr hole on asteroid, 3-cm keyhole craniotomy with craniotome exposing transverse and sigmoid sinuses, additional drilling down to maximize sinus exposure, air cells plugged with morselized muscle and bone wax, 5–10 cc drainage from lumbar drain, curvilinear dural opening 5 mm from edge of sigmoid sinus to transverse-sigmoid sinus, dural edge tacked up, drill 1 cm of IAC, debulk tumor if needed to visualize IAC, start IAC tumor debulking to identify location of facial nerve, arachnoid lifting before cauterization, dissect arachnoid away from tumor surface, dissect inferior pole of tumor and drain CSF as much as possible, isolate lower cranial nerves and protect with cottonoids, debulk tumor to level of IAC and test for facial nerve, superior dissection and test for facial nerve, intramural guttering in the midportion all the way to the IAC, dissect capsule from cerebellum and pons medially then laterally from the meatus, wax IAC, close in layers	Mastoidectomy with bone removal posterior to sigmoid sinus, removal of incus, amputation of malleus head, transect tensor tympani tendon, obliterate Eustachian tube with fascia and bone wax, labyrinthectomy, removal of bone overlying middle and posterior fossa dura, skeletonize IAC and identification of jugular bulb, open dura along posterior fossa and IAC, identify tumor capsule and absence of facial nerve with stimulation, protect lower cranial nerves, intratumoral debulking, identify cranial nerves VII and VIII, remove as much tumor as possible without compromising nerve function, drape bony defect with temporalis fascia, use abdominal fat to fill defect	Pericranial harvest, divide subcutaneous tissue and muscles, map transverse and sigmoid sinus based on navigation, burr hole placed inferomedial to the sinus junction, 3-cm craniotomy to level of foramen magnum and up to edge of transverse and sigmoid sinus, remove foramen magnum with rongeurs, wax mastoid air cells, Y-shaped dural opening, open cisterna magna to relax cerebellum, gentle retraction of cerebellum with telfa until superior-inferior extent of tumor identified, stimulate posterior aspect in case facial nerve present (start at 1 mA and decrease to 0.1 mA), safe entry zone identified, tumor entered, sequential debulking with internal decompression with ultrasonic aspirator and dissection of capsule from arachnoid, stimulate for facial nerve identification, remove intracanalicular portion by using diamond drill to expose dura over canal, open dura sharply, stimulate to find facial nerve, divide vestibular and cochlear nerve, roll tumor from medial to lateral and inferior to superior with direct visualization of facial nerve, reconstruct porous with fat and Tisseel, watertight dural closure with pericranium
Complication avoidance	Large bony opening, early drainage of CSF, identify inferior pole of tumor and lower cranial nerves, proximal and distal facial nerve identification, removal of tumor along facial nerve depends on adherence and monitoring feedback	Lumbar drain placement and drainage, avoidance of retractors, early identification of facial nerve at IAC, inferior to superior dissection	Large bone removal for exposure, stimulate to confirm absence of facial nerve, intratumoral debulking, leaving remnant on facial nerve to minimize injury	Large bone removal for exposure, drain CSF, stimulate for facial nerve, keep arachnoid plane to protect cranial nerves
Postoperative
Admission	ICU	Floor	ICU or intermediate care	ICU
Postoperative complications feared	CSF leak, facial paralysis especially with corneal anesthesia, swallowing difficulties	Facial weakness, CSF leak	Facial nerve palsy, cranial nerves V/IX/X/XI neuropathy, brainstem stroke, CSF leak	Cranial nerve palsies namely facial, venous sinus injury, CSF leak, hydrocephalus, brainstem injury
Follow-up testing	MRI within 24 hours after surgery Ophthalmology consult if any facial weakness	MRI 6 months after surgery	CT within 48 hours after surgery Swallowing evaluation MRI 3 months after surgery	CT within 12 hours after surgery MRI within 48 hours after surgery Audiogram 12 weeks after surgery
Follow-up visits	10–14 days after surgery	1 week after surgery	2 weeks after surgery	4–6 weeks after surgery 6 months after surgery
Adjuvant therapies recommended	SRS only for clear evidence of growth	SRS only for clear evidence of growth	SRS only for clear evidence of growth	SRS or repeat resection for clear evidence of growth