Enlargement of the Internal Auditory Canal and Hearing Preservation in the Middle Fossa Approach for Intracanalicular Vestibular Schwannomas

Abstract

The middle fossa (MF) approach is one of the treatment options for patients with intracanalicular vestibular schwannomas. This study investigated whether enlargement of the internal auditory canal (IAC) represents a risk factor for hearing loss in the MF approach. Participants comprised 48 patients who underwent resection of intracanalicular vestibular schwannoma using the MF approach at Nagoya City University Hospital. In this retrospective case review, the shape of the IAC on the affected side was compared with the normal side by coronal reconstruction computed tomography images. A difference of > 1 mm was judged as IAC enlargement. Patients were classified into 4 groups: NE, no enlargement; SE, superior enlargement; IE, inferior enlargement; and BE, both superior and inferior enlargement. In addition, pure-tone average (PTA) and speech discrimination score (SDS) were estimated before and after surgery to evaluate hearing. Hearing preservation (PTA ≤ 50 dB; SDS ≥ 50%) was seen in 96% (21/22), 100% (3/3), 50% (8/16), and 29% (2/7) in the NE, SE, IE, and BE groups, respectively. A significant difference in hearing preservation was seen between cases without IE (NE and SE) and cases with IE (IE and BE) (P < 0.0001). IE of the IAC was identified as an independent risk factor for hearing loss by logistic regression analysis (odds ratio, 32.0; 95% confidence interval, 4.2-783.6). Enlargement of the IAC on coronal reconstruction computed tomography scan before surgery can predict hearing preservation using the MF approach. Patients without IE may represent good surgical candidates for the MF approach.