Cochlear Origin of Early Hearing Loss in Vestibular Schwannoma

OBJECTIVE: To test whether early hearing loss (HL) is cochlear in origin in patients with vestibular schwannoma (VS). STUDY DESIGN: Retrospective case review in an academic tertiary referral center. METHODS: A group of 19 VS patients with normal/symmetrical hearing and a group of 20 VS patients with mild HL (threshold at any tested frequency better than 45 dB HL) on the tumor ear side. Differences of the amplitudes of the distortion products of otoacoustic emissions (DPOAEs) between the tumor ear and the nontumor ear were studied at frequencies of 1, 1.4, 2, 2.8, and 4 kHz. The Wilcoxon test was used to compare the ears for both groups and to test for possible differences in tumor size between groups. RESULTS: DPOAE amplitudes do not differ strongly between the ears in VS patients with normal/symmetrical hearing (two-sided P values: .050 at 1 kHz, .182 at 1.4 kHz, .378 at 2 kHz, .293 at 2.8 kHz, and .238 at 4 kHz) but are decreased compared with the nontumor ear at frequencies 1, 1.4, 2, and 2.8 kHz in VS patients with even mild HL (two-sided P values: .013 at 1 kHz, .007 at 1.4 kHz, .033 at 2 kHz, .010 at 2.8 kHz, and .156 at 4 kHz). Tumor size did not differ significantly between the two groups (P = .436). CONCLUSION: Amplitudes of DPOAEs begin to decrease even at the early stages of HL in VS patients, which suggests a cochlear origin of early HL in these patients. DPOAEs may be used in a clinical setting to monitor progression of cochlear damage at the early stages of hearing impairment in VS patients.