The incidence of sporadic vestibular schwannoma (VS) has increased significantly over recent decades. The rising incidence of VS has been largely attributed to the increasing use of magnetic resonance imaging (MRI), especially with regard to incidentally diagnosed tumors. However, no study to date has directly investigated this supposed etiology beyond the observation that VS incidence rates have risen in the post-MRI era. Therefore, the primary objective of the current study was to characterize the incidence of head MRIs over the previous two decades in Olmsted County, Minnesota and compare this trend to the incidence of asymptomatic, incidentally diagnosed VS over the same time period.
Population-based incidence study.
Using the unique resources of the Rochester Epidemiology Project, procedure codes for head MRIs and diagnostic codes for VS among residents of Olmsted County, Minnesota between Jan 1, 1995 and Dec 31, 2016 were retrieved. Incidence rates of head MRI and incidentally diagnosed VS were calculated on a per-year basis.
A total of 43,561 head MRIs among 30,002 distinct persons were identified from 1995 to 2016. The incidence of head MRI significantly increased between 1995 and 2003 (p < 0.001), but remained stable between 2004 and 2016 (p = 0.14). Over the same time interval, 25 cases of incidentally diagnosed VS were identified. The incidence of asymptomatic VS increased over time from 0.72 per 100,000 person-years between 1995 and 1999 to 1.29 between 2012 and 2016 (p = 0.058). No plateauing of incidence rates was observed in incidental tumors over the study period. The size of incidentally diagnosed tumors did not change over the study period (p = 0.93), suggesting that the increasing incidence of asymptomatic tumors is not explained by improved diagnostic capability of more recent MRI studies.
Despite the plateauing of head MRI incidence rates after 2004, the incidence of asymptotic, incidentally diagnosed VS continued to increase. Our findings suggest that there may be additional contributory etiologies for the rising incidence of VS beyond greater detection alone.