Middle Fossa Approach for Vestibular Schwannoma (Acoustic Neuroma) Resection

Hearing preservation approach for small tumors (< 15 mm) Patient preference with reasonable expectations

Medium to large tumors with extension into the cerebellopontine angle (CPA)
No Hearing

Relative Contraindications: age > 65 years, no fundal cap (tumor abuts the cochlea in the lateral internal auditory canal), poor hearing (pure-tone average worse than 50 dB or speech discrimination worse than 70%), seizure disorder

Operative surgeon is at the head of the bed. Patient is in the supine position with head rotated so the operative ear is facing up.
Intraoperative monitoring of cranial nerves 7 and 8.

MRI with and without gadolinium
Audiogram

Anatomy Pearls
- Create large craniotomy (5 cm x 5 cm)
- Arcuate eminence only predicts the superior semicircular canal 50% of the time, therefore we advocate blue-lining the canal to create a definitive landmark
- Geniculate ganglion is dehiscent 5 - 15% of the time, therefore elevate dura in posterior to anterior direction
- There are multiple ways to identify the internal auditory canal (IAC). After blue-lining the superior semicircular canal, we advocate for finding the IAC medially at the porus because there is more room to dissect. Other approaches include:
1. House (1961) —> Retrograde dissection from the GSPN to the labyrinthine segment of facial nerve
2. Fisch (1970) —> Dissect in a 60-degree angle from a blue-lined semicircular canal
3. Garcia-Ibanez (1972) —> IAC bisects the angle formed between the superior semicircular canal and the GSPN
- Medial IAC dissection allows 270-degrees of exposure while the lateral IAC dissection only allows 90-degrees
- After exposing the porus, release CSF from the posterior fossa to relax the dura and possible allow withdrawal of the retractor
- Try to dissect tumor in a lateral to medial direction to prevent cochlear nerve avulsion from the lamina cribrosa

Advantages:
- Provides complete exposure of the IAC and possibly allows tumor resection with hearing preservation

Disadvantages:
- Technically challenging because of the limited exposure and often nebulous surgical landmarks along the floor of the middle fossa
- Facial nerve is positioned between the dissection approach and the tumor, therefore potentially higher rates of facial nerve weakness.
- Requires retraction of the temporal lobe.

CSF leak (2-7%), facial nerve weakness/paralysis (15% immediate, 5% long-term), hearing loss (outcomes dependent on tumor size, location, nerve of origin, and pre-operative hearing), seizure, stroke, meningitis, death

None

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