Hearing Preservation in the Middle Fossa Approach for Vestibular Schwannoma

  Objective  To discuss the middle fossa approach (MFA) for vestibular schwannoma (VS) and hearing preservation (HP).

  Methods  Retrospectively analyze the database of HP in patients that underwent MFA for intracanalicular VS from May 2006 to May 2021. Examinations of preoperative hearing and craniocerebral imaging were performed to evaluate whether the patients met the criterion of HP. The function of the cochlear nerve was evaluated with American Academy of Otolaryngology-Head and Neck Surgery (AAO-HNS) hearing classification; the facial nerve function was evaluated with House-Brackmann (HB) grading. Different clinical characteristics regarding HP were summarized.

  Results  A total of 22 patients with VS that met the inclusion and exclusion criteria were included in this study. Facial nerve function was HB grade Ⅰ in 21 patients, grade Ⅲ in 1 patient. The preoperative serviceable and usable HP rate were 77.3%(17/22, 95% CI: 58.3%-96.3%) and 86.4%(19/22, 95% CI: 70.8%-100%), respectively. Seventeen patients met the criterion of hearing preservation, and the other 5 got their residual hearing reserved. The tumor was completely removed in 22 patients with VS and without postoperative complications, such as cerebrospinal fluid (CSF) leakage, epidural hematoma or infection. The rates of postoperative serviceable and useful HP were 52.9%(9/17, 95% CI: 26.5%-79.4%) and 73.7%(14/19, 95% CI: 51.9%-95.5%), respectively. In the patients present and those absent of CSF cap, the rates of postoperative serviceable HP were 60.0% (3/5, 95% CI: 23.1%-96.9%), 50.0% (6/12, 95% CI: 16.8%-83.2%), and the rates of useful HP were 80.0% (4/5, 95% CI: 24.5%-100%), and 71.4% (10/14, 95% CI: 44.4%-98.5%), respectively. In the tumor originating from the superior vestibular nerve, the rates of postoperative serviceable HP and useful HP were 33.3% (2/6, 95% CI: 0-87.5%) and 57.1% (4/7, 95% CI: 7.7%-100%), respectively. Whereas in patients with tumors originating from the inferior vestibular nerve, the rates of serviceable HP and useful HP were 55.6% (5/9, 95% CI: 14.0%-96.1%) and 80.0% (8/10, 95% CI: 49.8%-100%), respectively. For the patients in the presence and those in the absence of adhesion between the tumor and the cochlear nerve, the rates of serviceable HP were 41.7%(5/12, 95% CI: 8.9%-74.4%), 80.0% (4/5, 95% CI: 24.5%-100%), and the rates of useful HP were 66.7% (8/12, 95% CI: 35.4%-98.0%), 85.7% (6/7, 95% CI: 50.8%-100%), respectively. The median follow-up was 4.9 years. None of the patients had tumor recurrence. Postoperatively, the facial nerve function was HB grade Ⅰ in 21 patients and grade Ⅳ in 1 patient.

  Conclusions  The preoperative hearing classification and the features of imaging should be considered for complete excision of the tumor with the middle fossa approach and HP. As well, sufficient surgical skills need to be grasped in the condition of different nerve origin and the degree of adhesion between the tumor and cochlear nerve to preserve the anatomy and function of the cochlear nerve.