Prevalence of unsuspected acoustic neuroma found by magnetic resonance imaging.

OBJECTIVES

Acoustic neuromas (ANs) comprise 6% of intracranial tumors. Population and autopsy studies have widely divergent estimates of AN incidence. With widespread use of MRI, asymptomatic ANs will be identified, which should improve estimates of the prevalence of this tumor.

METHODS

The reports of all brain MRI scans during a 5-year period were retrospectively searched for the diagnosis of AN. MRIs obtained because of a suspicion of AN were discarded, leaving only the unsuspected ANs.

RESULTS

A total of 24, 246 MRI studies were performed during this time period. 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 scans, 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 million per year previously reported. This implies that there may be a larger number of asymptomatic ANs than previously suspected.