[Case of venous angioma with chronic encapsulated hematoma]. 
We would like to report a rare case of a venous angioma with a chronic encapsulated hematoma, in a 31-year-old woman who was admitted to our hospital in November, 2005.  Her neurological examination was noted to be normal.  A CT was performed which showed an isodense mass in the left cerebellar hemisphere.  This finding was confirmed on MR imaging, which showed a hyperintense mass on T1-weighted imaging, and a hypo to isointense area on T2-weighted images.  T1-weighted images with Gd-DTPA enhancement revealed a dilated vein and, as a result, an angiogram was obtained.  The venous phase demonstrated medullary veins converging on a central vein, which is usually known as a caput medusae.  Follow up T1-weighted images with Gd-DTPA enhancement showed peripheral ring enhancement and expansion of the capsulated hematoma.  Total removal of the hematoma and its capsule was performed in July, 2006.  The hematoma was seen both inside and outside the tough capsule.  A histological examination revealed that the capsule consisted of an outer collagenous layer and an inner granulated layer with deposits of hemosiderin.  The hemorrhage rate of a venous angioma has been reported as between 0.22-0.61% per year.  We thought that the initial small hemorrhage from the venous angioma resulted in the development of an encapsulated hematoma, and the total hematoma had expanded not only inside due to the hemorrhage of the capsule, but also outside because of the venous angioma.