Correlating vestibular schwannoma size with vestibular-evoked myogenic potential results.

Abstract

The maximum size of the vestibular schwannoma (VS) that is compatible with preservation of the function of the vestibular nerve in performing stereotactic radiosurgery remains unclear. This study utilized ocular vestibular-evoked myogenic potential (oVEMP) and cervical VEMP (cVEMP) test results to correlate with the size of VS. Fifty patients with unilateral VS underwent audiometry, and caloric, oVEMP and cVEMP tests. Tumor size from magnetic resonance imaging was measured on the axial plane, and the relationships between tumor size and each test result were analyzed. The pure-tone average from four frequencies did not significantly predict tumor size. Alternatively, oVEMP and cVEMP responses remained significant predictors for tumor size in the regression model, namely, tumor size (cm) = 0.62 × (oVEMP response) + 1.39 × (cVEMP response), where oVEMP and cVEMP responses were regarded as binary variables, in which 1 and 0 reflect abnormal and normal responses, respectively. This model explained 76% of the variance. Accordingly, the estimated VS size exhibiting abnormal oVEMPs and cVEMPs is >2.01 (0.62 +1.39) cm. When VS size is <2.0 cm, preservation of the function of superior/inferior vestibular nerve indicated by the oVEMP/cVEMP test is achievable. Therefore, both oVEMP and cVEMP tests may serve as supplementary tools for determining treatment option in VS patients.