Audiovestibular Characteristics of Small Cochleovestibular Schwannomas in Neurofibromatosis Type 2

Abstract

Objectives: Describe the relationship between cochleovestibular schwannoma (CVS) volume, audiovestibular changes, and magnetic resonance imaging (MRI) findings in patients with neurofibromatosis Type 2 (NF-2). Methods: Subgroup analysis of NF-2 prospective natural history study from June 2008 to June 2011. Subjects: NF-2 patients with small treatment- naïve CVS (volume < 1cm3) by ear. N = 49 ears, 32 patients. Setting: Quaternary medical research institute. Intervention: None. Outcome Measurements: Tumor size, auditory brainstem response (ABR), audiogram (4-frequency PTA - 0.5, 1, 2, 4KHz), vestibular evoked myogenic potential (VEMP), caloric videonystagmography (VNG), rotary chair testing (240°/sec velocity step test), and magnetic resonance imaging (MRI) findings. Results: Larger tumor volume (mean 0.489cm3; 95% confidence interval [CI] 0.313-0.664) correlated with abnormal ABR findings, compared to smaller tumors with normal ABR (mean 0.151cm3; 95%CI 0.89-0.213). Larger tumors also correlated with weak caloric response (mean 0.520cm3; 95%CI 0.300-0.741 vs. mean 0.199cm3; 95%CI 0.102-0.296). Tumor volume was not significantly correlated with PTA, VEMP, or rotary chair testing. Elevated intralabyrinthine protein on MRI fluid-attenuated inversion recovery sequences was correlated with larger tumor size (mean volume 0.331cm3; 95%CI 0.246-0.419 vs. 0.055cm3; 95%CI 0.008-0.103) and abnormal ABR and PTA ( P < 0.05), but it did not correlate with VEMP or caloric responses. Conclusions: In our sample, ABR, caloric response, and intralabyrinthine protein correlated with tumor volume, but PTA, VEMP, and high velocity step testing did not. Abnormal ABR and PTA were correlated with elevated protein. These findings may provide insight on the effect of small CVS on the inner ear and cochleovestibular nerves, which may aid in their management.