Vestibular schwannoma volume as a predictor of hearing outcome after surgery.

OBJECTIVES: To validate the prognostic capacity of several preoperative and intraoperative parameters of hearing preservation after vestibular schwannoma surgery.

STUDY DESIGN: A retrospective study of a consecutive series of 29 patients treated with the enlarged middle cranial fossa approach. Quantitative parameters were tumor volume, linear tumor size, pure-tone and speech audiometry, pure-tone average, speech discrimination score, speech reception threshold, auditory brainstem response (ABR; intra-aural interpeak latency I-V, interaural wave V latency difference), and the vestibular caloric test (speed and frequency). Qualitative parameters were fundus involvement by the tumor (in magnetic resonance imaging and surgical record), nerve of tumor origin (in magnetic resonance imaging and surgical record), ABR parameters (well-shaped ABRs: waves I, III, and V present; presence of wave V).

METHODS: All patients were divided into 2 groups on the basis of postoperative hearing: preserved hearing (55%) or nonpreserved hearing (45%). The Kolmogorov-Smirnov test was used to evaluate normality of distribution for continuous data. The t test was applied for normally distributed continuous data and the Mann-Whitney test for nonnormally distributed continuous data. The chi2 test was used for comparisons of categoric data.

RESULTS: Tumor volume was found to be the only statistically significant prognostic parameter for hearing preservation (p = 0.007). The cutoff point for the "critical" tumor volume for hearing preservation was calculated to 0.20 cm. None of the other parameters reached statistical significance.

CONCLUSION: Tumor size is a predictive factor for hearing preservation after vestibular schwannoma surgery, and patients with smaller tumors, based on volume measurement, have significantly better chances for retaining hearing. This has an impact on decision making and timing of surgery.