Delayed cyst formation after radiosurgery for arteriovenous malformation: A case report and critical review.

Background: Stereotactic radiosurgery (SRS) is a validated treatment option for cerebral arteriovenous malformations (AVMs), even if a greater knowledge of its potential delayed complications is still being acquired. Case Description: A 49-year-old man suffered multiple episodes of cerebral hemorrhage in an approximate 10-year follow-up interval in the context of a left central core AVM with deep venous drainage into the internal cerebral veins (Spetzler Martin Grade 4) despite being treated with gamma knife radiosurgery at two separate timepoints, and with an almost complete obliteration confirmed. Approximately 10 years after the first radiosurgery treatment, he developed severe motor aphasia, Grade 3 right hemiparesis, progressive confusion, and memory deficits. Cerebral imaging revealed cystic degeneration in the AVM's periphery. Cyst fenestration and cystoperitoneal shunt were attempted. The treatments were temporarily effective, but a progressive cyst enlargement recurred with clinical deterioration. The patient was therefore proposed for surgical mass and cyst excision through an interhemispheric transcallosal approach. The postoperative magnetic resonance imaging showed complete removal of the lesion, and an uneventful post-operative course ensued. At the 6-month follow-up, our patient experienced a noticeable improvement in his speech, power, dexterity and was able to walk autonomously. Conclusion: Cystic degeneration of AVMs is a possible long-term complication after SRS. Long-term follow-up and data on such patients remain crucial, even with evidence of complete nidal obliteration.