Audiovestibular Characteristics of Small Cochleovestibular Schwannomas in Neurofibromatosis Type 2

Abstract

Objective Describe the relationship between cochleovestibular schwannoma (CVS) volume, audiovestibular characteristics, and magnetic resonance imaging (MRI) findings in patients with neurofibromatosis type 2 (NF2). Study Design Subgroup analysis of NF2 prospective natural history study from 2008 to 2011. Setting Quaternary medical research institute. Subjects and Methods NF2 patients with small treatment-naive CVSs (volume <1000 mm3) by ear; N = 49 ears (32 patients). Cross-sectional analysis of the following parameters was performed: tumor size, auditory brainstem response (ABR), 4-frequency pure-tone average (4f-PTA; 0.5, 1, 2, and 4KHz), cervical vestibular evoked myogenic potential (cVEMP), caloric testing, 240° velocity step test (VST), and MRI findings. Results For all physiologic measures but the 4f-PTA, larger tumors correlated with abnormal responses ( P < .05). For abnormal ABR, mean tumor volume was 405 vs 151 mm3 ( P = .0007) for normal ABR. Similarly, larger tumors correlated with weak caloric responses (mean 521 vs 165 mm3; P = .0007) and weak cVEMP (mean 357 vs 192 mm3; P = .0262). Tumor volume was not significantly correlated with 4f-PTA. Elevated intralabyrinthine protein on MRI fluid-attenuated inversion recovery sequences was correlated with larger tumor volume (mean 333 vs 55 mm3; P = .001) and abnormal ABR and 4f-PTA ( P < .05) but did not correlate with cVEMP, VST, or caloric responses. Conclusion In our cohort, ABR, caloric response, cVEMP, and elevated intralabyrinthine protein correlated with tumor volume, but 4f-PTA did not. Abnormal ABR and 4f-PTA correlated with elevated intralabyrinthine protein. These findings may provide insight on the effect of small CVS on the inner ear and cochleovestibular nerves, which may aid in their optimal management.