The incidence of primary central nervous system neoplasms before and after computerized tomography availability

The observed incidence of primary intracranial neoplasms has increased dramatically among the elderly over the past several years. It is unclear to what extent this increase can be attributed to improved detection by new imaging technology and what portion might represent a true increase in incidence. The first computerized tomography (CT) scanner was operative in Norway in 1975 and became available in all geographical regions within 4 years. The author analyzed incidence data from the population-based Cancer Registry of Norway, placing particular emphasis on the basis for diagnosis (histological, imaging, or clinical findings) for the registrations. In the decade from 1983 to 1992, when the use of CT was widespread, incidence rates of primary intracranial neoplasms for individuals aged 55 to 74 and above 74 years were, respectively, 1.76 (95% confidence interval (CI), 1.63-1.90) and 3.35 (95% CI, 2.70-4.15) times the rates in 1963 to 1972 before CT was available. For persons older than 74 years, the relative incidence increase was 1.98-fold (95% CI, 1.53-2.56) for histologically verified tumors; 15.20 (95% CI, 7.80-29.61) when based on imaging (without histological evidence); and 3.33 (95% CI, 1.93-5.76) when based on clinical diagnosis (without imaging or histological evidence). In this age group, the increase for gliomas was 1.77 (95% CI, 1.18-2.65) and 2.28 (95% CI, 1.53-3.39) for meningioma patients. The present study demonstrates that new imaging technology has improved the diagnostic yield of primary intracranial neoplasms. For those older than 74 years, a large part of the three-fold incidence increase from the pre-CT decade 1963 to 1972 to the post-CT decade 1983 to 1992 can be attributed to improved tumor detection.