Auditory brainstem response (ABR) testing is less sensitive in detecting small vestibular schwannomas than medium-size tumors. Magnetic resonance imaging (MRI) is more sensitive than ABR alone for small and large tumors, but it carries with it increased cost and issues of unavailability and patient discomfort. We conducted a prospective pilot study of 7 patients with untreated MRI-proven, unilateral vestibular schwannoma to determine if we could increase the sensitivity of ABR testing in detecting small tumors. Our method involved the use of a new ABR index that is based on threshold differences. All patients underwent pure-tone audiometry followed by a determination of behavioral threshold and neurodiagnostic threshold ABR in the normal ear, which was used as a control, and in the diseased ear. Analysis of results revealed that all 7 patients had an abnormal ABR threshold difference, and 5 patients displayed abnormal traditional ABR indices. The mean difference between the ABR and behavioral click thresholds was 41.4 dB in the diseased ears (with the ABR threshold being higher than the click threshold) and 15.8 dB in the normal ears. None of the control ears had a threshold difference >30 dB.
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