Epidemiological study of primary intracranial tumors: a regional survey in Kumamoto prefecture in southern Japan-20-year study

Background The increased use of neuro-imaging techniques, as well as various environmental factors, has been changing the incidence and the proportions of types of intracranial tumors. However, no accurate population-based epidemiological study of intracranial tumors in Japan has been reported. We evaluated recent trends in the occurrence of primary intracranial tumors among residents of Kumamoto prefecture, Japan. Methods and results We surveyed 5,448 new cases of primary intracranial tumors that were diagnosed in Kumamoto prefecture between 1989 and 2008. The overall age-adjusted incidence rate was 14.09 (11.59 for males, 16.38 for females) per 100,000 population per year. The most common tumors were meningiomas (36.8%), followed by gliomas (19.5%), adenomas (17.8%), schwannomas (9.9%), and malignant lymphomas (3.6%). The number of cases of primary brain tumors, especially meningiomas and malignant gliomas, among the elderly has steadily increased and the incidence of asymptomatic intracranial tumors also increased. The number of asymptomatic meningiomas diagnosed per year was higher than that of symptomatic meningiomas in the years between 1997 and 2008. Furthermore, the incidence rate of brain lymphoma in Kumamoto prefecture is approaching that recorded in Western countries. On the other hand, the incidence rate of germ cell tumors is on the decline, approaching that recorded for children in Western countries. Conclusion Even though we adjusted the population in Kumamoto prefecture based on the Japanese population, increasing rates of several types of intracranial tumors were observed. These incidence rates are approaching those in Western countries.