A prospective study of ABR and MRI in the screening for vestibular schwannomas

The advent of magnetic resonance imaging (MRI) has significantly increased the clinician's ability to detect small vestibular schwannomas. This had led to controversy in the evaluation of patients with asymmetric sensorineural hearing loss, as some recent studies have suggested that the auditory brainstem response (ABR) does not adequately detect small tumors of the internal auditory canal and cerebellopontine angle. As these studies evaluated ABR results in patients already diagnosed with vestibular schwannomas, they could not determine the epidemiologic accuracy (validity) of the ABR as a screening test for retrocochlear pathology. We report on the preliminary results of an ongoing prospective study on the evaluation of patients with asymmetric sensorineural hearing loss. All patients with asymmetry in two or more pure-tone thresholds of > or = 15 decibels or asymmetry in speech discrimination scores of > or 15% or both entered the study and underwent both an ABR examination and an enhanced MRI scan. Based on preliminary results obtained from the first 47 patients entered in this study, the ABR screening test for retrocochlear pathology was determined to have a sensitivity of 63%, a specificity of 64%, a positive predictive value of 26%, and a negative predictive value of 89%. All patients in whom ABR failed to diagnose a vestibular schwannoma had unilateral hearing los. These results bring into question the validity of ABR as a screening test for retrocochlear pathology, particularly in cases of unilateral hearing loss. Continued patient enrollment in this study will allow the confirmation of these results.