CHRONIC ENCAPSULATED EXPANDING HEMATOMA IN ASSOCIATION WITH GAMMA-KNIFE STEREOTAXIC RADIOSURGERY FOR A CEREBRAL ARTERIOVENOUS MALFORMATION

The authors report a rare case of a patient with a chronic encapsulate d expanding hematoma and progressive neurological deterioration who pr esented 2 years after gamma knife radiosurgery for a cerebral arteriov enous malformation (AVM). A tough capsule containing multiple layers o f organized hematoma resulting from previous bleeding was confirmed su rgically. Histological examination revealed that the capsule consisted of a dense collagenous outer layer and a granulomatous newly vascular ized inner layer with marked fibrosis. Hemosiderin deposits were frequ ently observed in the inner layer, which suggested recurrent minor ble eding from fragile vessels in this layer. An AVM was found in the hema toma, which had degenerated as the result of radiosurgery. A cross-sec tion of the abnormal vessels showed various stages of obliteration due to intimal hypertrophy. The clinical course, radiological features, a nd histological findings in this case were compatible with those of pr eviously reported chronic encapsulated hematomas. A possible mechanism of hematoma formation and its expansion are discussed.