Epidemiology of Vestibular Schwannomas

Introduction: In Denmark, with a population of 5.1 to 5.2 million and a uniform public health-care system, we have, since introduction of translabyrintine surgery in 1976, been able prospectively to register all diagnosed vestibubular schwannomas (VS) in the entire country.

Material: The study is based on 1446 patients with unilateral VS, diagnosed in the period from July 1976 to December 2001.

Results: During the first 7-year period from July 1976 to June 1983, the incidence was 7.8 VS/million/year. During the second 7-year period from July 1983 to June 1990, it increased to 9.4 VS/million/year. During the third period of 5.5 years from July 1990 to December 1995, the incidence further increased to 12.4 VS/million/year. And during the fourth period of 6 years from January 1996 to December 2001, the incidence increased yet again to 17.4 VS/million/year.

Discussion and Conclusion: The most important result of this study was diagnosis of 166 intrameatal VS in the fourth period, in contrast to a diagnosis of 1 VS in the first period, 1 VS in the second period, and 28 VS in the third period. The high number of the intrameatal VS, found mostly in older patients, correlates significantly with the increase of MRI scanners in Denmark during this period. The study illustrates that most intrameatal VS diagnosed in the last period already existed in the first two periods, but they were not diagnosed before MRI scan became available. This epidemiological study also strongly indicates that many intrameatal VS do not grow or grow so slowly that they will remain intrameatal VS for many years or even an entire lifetime. For this reason we do not operate on intrameatal VS, instead preferring to wait and scan.

Another interesting problem is: what is the real incidence of VS? In 1976 the incidence was 6 VS∕million/year, and in 2001 it was 19 VS/million/year. The mean incidence for the entire 25.5 years period was 11.5 VS/million/year. The increasingly high incidence during recent years reveals the problem of tumor growth, that is, what happened with the previously undiagnosed VS. We believe that patients died with the tumor not because of the tumor, but exact proofs have yet to be provided.