True incidence of vestibular schwannoma?

BACKGROUND: The incidence of diagnosed sporadic unilateral vestibular schwannomas (VS) has increased, due primarily to more widespread access to magnetic resonance imaging.
OBJECTIVE: To present updated epidemiological data on VS incidence, as well as patient age, hearing acuity, tumor size, and localization at diagnosis for the last 4 decades in an unselected population, with emphasis on developments in recent years.
METHODS: From 1976 to 2008, 2283 new cases of VS were diagnosed and registered in a national database covering 5.0 to 5.5 million inhabitants. Incidence during the period, patient sex and age, data on hearing (pure tone average and speech discrimination), and tumor size at diagnosis were retrieved from the database.
RESULTS: The incidence increased from 3.1 diagnosed VS per million per year in 1976 to a peak of 22.8 VS per million per year in 2004, which was followed by a decrease to 19.4 VS per million per year in 2008. Mean tumor size at diagnosis decreased from 30 mm in 1979 to 10 mm in 2008, whereas hearing acuity at diagnosis has improved over the years.
CONCLUSION: After a steady increase over the last 4 decades, the incidence of vestibular schwannomas appears to have peaked and decreased in recent years, stabilizing at about 19 tumors per million per year. Whereas the sex ratio and age at diagnosis have remained grossly unchanged over the years, hearing has improved, and tumor size has decreased considerably.