Incidental discovery of acoustic neuromas.

Our objective is to report 4 cases of incidentally discovered acoustic neuromas (ANs) and to determine the incidence of asymptomatic ANs. A prospective study of 161 consecutive patients undergoing gadolinium-enhanced MRI (Gd-MRI) at a tertiary-care university-affiliated medical center was carried out from September 1994 to April 1995. The Gd-MRI scans were performed for tentative diagnoses other than AN or sensorineural hearing loss. In 161 consecutive patients examined, no ANs were found incidentally on Gd-MRI scans. Previous studies have suggested that the incidence of occult ANs is as high as 1%. On the basis of our results, we suggest that the actual incidence may be lower. However, our study is limited by its small size and the low incidence of ANs in the general population. Also reported are the clinical and MRI characteristics of 4 patients with incidentally diagnosed ANs.