Prevalence of unsuspected acoustic neuroma found by magnetic resonance imaging

OBJECTIVES: Acoustic neuromas (ANs) comprise 6% of intracranial tumors. Pop ulation and autopsy studies have widely divergent estimates of AN incidence . With widespread use of MRI, asymptomatic ANs will be identified, which sh ould improve estimates of the prevalence of this tumor. METHODS: The reports of all brain MRI scans during a 5-year period were ret rospectively searched for the diagnosis of AN. MRIs obtained because of a s uspicion of AN were discarded, leaving only the unsuspected ANs. RESULTS: A total of 24,246 MRI studies were performed during this time peri od. Seventeen patients had unsuspected ANs. Eight tumors were smaller than 1 cm, 6 were between 1 and 2 cm, and 3 were 2 cm or larger. For all MRI sca ns, we found 7.0 unsuspected ANs per 10,000 brain MRI studies (0.07%). CONCLUSION: The true prevalence of AN is likely greater than the 10 per mil lion per year previously reported. This implies that there may be a larger number of asymptomatic ANs than previously suspected.