De novo formation of cavernoma after radiosurgery for adult cerebral arteriovenous malformation--case report.

A 47-year-old male underwent stereotactic radiosurgery (25 Gy) for a cerebral arteriovenous malformation located in the right caudate nucleus, using a linear accelerator. Complete obliteration of nidus was confirmed 20 months after radiosurgery. However, a hypointense mass on T(2)-weighted magnetic resonance imaging developed in the area adjacent to the nidus after approximately 80 months. The mass gradually increased in size and induced severe perifocal edema over 2 years. The mass was successfully excised. Histological examination revealed that the mass consisted of dilated sinusoid vessels attached to the hematoma capsule, and the hematoma included clots in various stages of organization encapsulated by dense collagenous tissue. The histological diagnosis was cavernoma. De novo formation of cavernoma is well known to occur after radiation surgery for intracranial tumor, especially in pediatric patients, but is rare in adults. Based on the radiological and histological findings in the present case, the radiation-induced cavernoma underwent repeated bleedings resulting in chronic encapsulated expanding hematoma.