Cystic arteriovenous malformation. A case report.

The authors report on a rare case of arteriovenous malformation (AVM) associated with cyst formation. Only five similar cases have been reported. CT findings of the cyst are divided into two types: 1) slit-like low density and 2) round one. Three patients showing slit-like cysts had experienced sudden severe headaches, probably due to haemorrhage. In contrast, two patients showing round cystic lesions had not experienced such sudden headaches and they revealed a nodule in the cyst at surgery. These facts suggest that there may be two different mechanisms for cyst formation in AVM's: haemorrhage and exudation. Slit-like cysts may result from old haemorrhage from the AVM nidus. Round cystic lesions may be due to exudation from the AVM nidus.