Acoustic Neuroma Resection

Indications

Patients with a Clinical Presentation (history of symptoms [hearing loss, tinnitus (ringing in the ears), etc.] and signs [decreased acuity or discrimination of audiogram, decreased corneal reflex, etc.]) consistent with a tumor of the vestibular component of the vestibulocochlear nerve AND a diagnostic study confirming the presence of a cerebellopontine angle tumor extending into the internal auditory (ear) canal (vestibular schwannoma on MRI) consistent with vestibular schwannoma (acoustic neuroma) are candidates for surgery.

Objectives

Preservation of hearing: The translabyrinthine approach destroys part of the inner ear necessary for hearing. This approach is reserved for patients with absent or non-serviceable hearing on the side of their vestibular tumor.
Preservation of facial nerve function is most likely to be preserved with smaller tumors (nearly 100% for tumors smaller than 2 cm in diameter).
The prognosis following acoustic neuroma (vestibular schwannoma resection) depends on the condition of the patient at the time of surgery.

Considerations
The larger the tumor the less likely the surgeon will be to preserve during resection of a vestibular schwannoma.
Commonly used approaches for removal of vestibular schwannoma (acoustic neuroma) are: translabyrinthine (“translab”), retromastoid, and subtemporal.

Translabyrinthine approach
SUBOCCIPITAL CRANIECTOMY exposes the temporal bone for drilling for the translabyrinthine approach.
The vestibular nerve enters the temporal bone at the internal auditory meatus which is the site of transition from the central to peripheral portions of the nerve and also the site of origin of vestibular schwannoma (acoustic neuroma). With a high-speed drill the surgeon can remove the temporal bone surrounding the internal auditory canal and thereby expose a tumor of the vestibular nerve.
Retrosigmoid approach
SUBOCCIPITAL CRANIECTOMY exposes the sigmoid sinus and the dura medial to it for the retrosigmoid approach.
The dura over the lateral portion of the cerebellar hemisphere is opened medial to the sigmoid sinus. A retractor is placed between the cerebellar hemisphere and the medial border of the sinus and the cerebellum is retracted medially away from the sinus, exposing the space between the cerebellum and the petrous portion of the temporal bone which is followed anteriorly until the complex of seventh and eighth cranial nerve — and attached acoustic neuroma are seen.
Middle fossa approach
CRANIOTOMY technique is used to expose the floor of the middle (temporal) fossa and the superior portion of the petrous temporal bone for drilling to expose the vestibular nerve in the internal auditory canal.
An acoustic neuroma can also be approached anteriorly from above by retracting the temporal lobe upwards to expose the petrous portion of the temporal bone. Drilling away the petrous bone exposes the vestibular nerve (and a tumor growing in it).

Exposure
acoustic neuroma (vestibular schwannoma resection)
Cerebellopontine angle exposure

Approach
Retromastoid approach
Translabyrinthine approach
Subtemporal approach

Landmarks
Inion
Tragus
Mastoid process

Hazards
Structures along the course of the approach that might be injured during the exposure during acoustic neuroma resection: the internal auditory artery lies in proximity to the complex of vestibulocochlear and facial nerves and can be injured by the manipulations required to dissect and remove the acoustic tumor. Injury to this artery can result in infarction (stroke) of the cochlear nerve with deafness.
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Hazards
Structures along the course of the approach that might be injured during the exposure during acoustic neuroma resection: the internal auditory artery lies in proximity to the complex of vestibulocochlear and facial nerves and can be injured by the manipulations required to dissect and remove the acoustic tumor. Injury to this artery can result in infarction (stroke) of the cochlear nerve with deafness.
Instruments
Mayfield pins
Kerrison ronguer
Greenberg retractor
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Anesthesia
General anesthesia is used for resection of acoustic neuroma.

Monitoring
Facial nerve monitoring gives the surgeon an indication of the effect on the facial nerve of manipulations of and around the vestibular nerve from which the tumor arises.

Position
Sitting position
Prone position
Lateral position

Prep and drape

Hemostasis
Some vestibular schwannomas (acoustic neuromas) are extensively vascularized (filled with numerous tiny, even microscopic, arteries and veins) that persist in bleeding despite focal bipolar coagulation, application of hemostatic surgical cellulose, and extended tamponade. Hemostasis problems, especially with large complex tumors, may require stopping what then becomes a first attempt at resection planning a second for another day after coagulum and scar have formed that hopefully will decrease the bleeding encountered on the second go-round.

Incision Suboccipital paramidline incision

Dissection
The most difficult aspect of surgery for resection of an acoustic neuroma is dissection of the tumor away from the facial and cochlear nerves. Too much manipulation of these structures can injure or destroy them (leaving the patient with a partial or complete neurologic deficit — facial nerve injury: inability to move the face, cochlear nerve injury: inability to hear). Large tumors frequently are sufficiently large that they abut against. may displace, and perhaps even deform, the brainstem. Dissection to develop and extend a plane between tumor and brainstem must be deliberate and meticulous to avoid the potentially grave morbidities of injury to the latter most essential of central nervous system structures..
Facial nerve monitoring helps the surgeon know what manipulations are causing damage.
The tumor is often visibly different from the nerves adjacent to it. Its capsule is usually smooth, uniform in color, and rounded or lobular. Removal of the tumor requires a combination of internal debulking with capsular dissection.

Closure
It is essential that the dura is closed “water tight” or there will be a cerebrospinal fluid (CSF) leak.
A fat graft may help prevent CSF leak.
Complications
Risks and complications of acoustic neuroma (vestibular schwannoma resection) include: facial nerve injury, cerebrospinal fluid leak, and meningitis.
NeuroSurgery InfoNet

Operations

Duration
A surgery for resection of an acoustic neuroma can take many hours:
anesthesia: placement of lines, induction, intubation: 30 minutes
positioning (for required exposure): 15 minutes
prep: 10 minutes
exposure: retromastoid – 1 hour, subtemporal – 1 hour, translabyrinthine – 1 1/2 hour
dissection and removal of tumor – 1 to 6 or more hours
closure: translab, retromastoid, subtemporal – 45 minutes
extubation – 15 minutes
preparation for transport – 10 minutes

Post Op
After surgery for resection of an acoustic neuroma the patient is usually taken to Recovery. Immediately post-operatively the patient is monitored for facial nerve weakness or neurologic deterioration for an hour or so prior to transfer to the Intensive Care Unit (ICU) for 24 to 48 hours of observation and care and then transfer to a regular ward bed.

Recovery
Most patients are up and about by the second day following acoustic neuroma (vestibular schwannoma) resection. Most can return to work at 2 to 3 weeks post op.

Rehabilitation
Most patients will not require rehabilitation following acoustic neuroma (vestibular schwannoma) resection.

Follow up
acoustic neuroma (vestibular schwannoma resection)

Reoperation
Restoration of facial movement in patients with facial nerve weakness (Post-operative weakness of the facial nerve can be quantified and followed over time using the House-Brackmann Grading system ) may require re-operation:
Facial muscle reanimation procedures
Eyelid closure – facial nerve weakness can result in inability to close the eye which can result in drying out and injury to the cornea and eye. Blepharoplasty is the name of the procedure used to suture the eyelids shut.
Revision of fat graft and closure – CSF leakage or infection of a fat graft are among complications that can require re-operation with revision of closure or debridement, respectively.
Repeat resection may be required if early follow up imaging shows incomplete resection or if long term serial images show recurrence.