[A Rare Case of Radiation-Induced Meningioma that Occurred Only 3 Years and 6 Months after Radiation Therapy for Oligodendroglioma].

We describe an adult case of radiation-induced meningioma(RIM)that was identified within a short interval from the initial treatment for brain tumor. A 45-year-old woman, who had tumor resection followed by radiation therapy for right frontal oligodendroglioma, showed a small enhanced lesion on the right frontal region 3 years and 6 months after the initial radiation therapy. The pathological diagnosis was meningioma(World Health Organization(WHO)grade I)and the Ki-67 labeling index was 3.2%. Most RIMs occur after a long period of time(18.7-24.0 years on average)following radiation therapy. Several studies have suggested that the period before the occurrence of RIM is correlated with both the age of a patient and the radiation dose at the time of radiation therapy. A patient that receives a higher dose of radiation at a younger age has a higher risk of RIM occurrence. In this case, the patient was middle aged;however, she was exposed to a high dose of radiation(54 Gy). High-dose radiation might induce the early onset of RIM. Recently, treatments for glioma have been developed, thus resulting in an increased long-term survival rate among patients. Physicians must pay attention not only to the recurrence of gliomas but also to the occurrence of RIMs.