[A chronic encapsulated expanding hematoma with cyst formation caused by rupture of arteriovenous malformation: a case report].

A 57-year-old male was admitted to our hospital complaining of a headache with disturbance of consciousness on November 7, 1994. CT scans revealed an intracerebral hematoma of 25ml in volume in the left frontal lobe with adjacent spotty calcification. An arteriovenous malformation (AVM) with a nidus of 2.0 x 2.0cm in size was found to be the cause of the hematoma by cerebral angiography. Since the patient complained of mild right hemiparesis 10 days after the onset, CT scans were taken and a slightly enlarged hematoma with capsule formation was observed. On the 31st day after the onset, the hematoma had liquefied and the surrounding capsule was clearly visible on CT. Since the patient's only symptom was a slight headache, and he displayed no other serious conditions, a palliative operation was planned. The AVM was removed and the capsule was resected 41 days after the onset. The capsule or cyst wall of the liquefied hematoma was composed of three layers: a granulation layer with a neovascular system on the inside, a collagenous layer in the middle, and a reactive brain tissue layer on the outside. The structure of the capsule was the same as the structure of the cyst wall in chronic hematomas that have been reported as cystic AVM or encapsulated expanding hematoma in the literature. We would therefore like to propose that chronic encapsulated expanding hematomas form with time due to intermittent bleeding or exudation form the neovascular system of a cyst wall.