Intraoperative cochlear nerve monitoring in vestibular schwannoma surgery--does it really affect hearing outcome?

OBJECTIVE: The objective of this study was to examine the usefulness of intraoperative cochlear nerve monitoring (ICNM) in the preservation of normal and social hearing in vestibular schwannoma (VS) removal. METHODS: A retrospective chart review was conducted. Of 1315 patients operated for VS between June 1988 and December 2005, 150 patients were subjected to hearing preservation surgery. Among these, 99 patients with preoperative normal and social hearing (class A and B in the modified Sanna classification) and with a small tumor <1.5 cm in size were included in the analysis. The difference in hearing preservation rates between patients operated with and without ICNM was statistically examined using Fisher's exact test. An initial analysis was conducted for the total group. Patients were then divided into two subgroups according to the surgical approach (middle cranial fossa and retrosigmoid-retrolabyrinthine). The effectiveness of ICNM in each subgroup was analyzed. RESULTS: The hearing preservation rate was 26.7% in cases operated with ICNM and 20.8% in cases without ICNM. The difference did not reach statistical significance (p = 0.79). In subgroup analyses, the ICNM did not prove to contribute to the significantly higher hearing preservation rate. CONCLUSIONS: ICNM did not increase the ratio of patients with postoperative normal and social hearing in VS surgery.