DELAYED CYST FORMATION AFTER RADIOSURGERY FOR CEREBRAL ARTERIOVENOUS MALFORMATION - 2 CASE-REPORTS

Two patients who underwent gamma knife radiosurgery for ruptured cereb ral arteriovenous malformations (AVM) developed cystic lesions at 78 a nd 111 months after undergoing treatment. Both patients presented init ially with intracerebral hemorrhage. In one patient, the cystic lesion was discovered during routine follow-up imaging and clinical examinat ion revealed homonymous hemianopsia; the second patient presented with seizure and the lesion was identified more than 9 years after radiosu rgery. One patient underwent resection of the nidus and histologic ana lysis of the resected specimen showed vessels in various stages of obl iteration. The present paper discusses the possible mechanism for the delayed development of cystic lesions, and the possibility that radiat ion-induced vascular changes may continue in a nidus even when angiogr aphy shows complete obliteration of the nidus.