Management of cysts arising after radiosurgery to treat intracranial arteriovenous malformations

OBJECTIVE: The proper treatment for patients with cyst formation after arteriovenous malformation radiosurgery is unknown. METHODS: The treatment of six patients who developed cysts after arteriovenous malformation radiosurgery is described. Four patients had undergone gamma knife radiosurgery (two patients developed cysts after repeat procedures), and two patients had undergone linear accelerator-based radiosurgery. The median prescription isodose volume at the time of the first radiosurgical procedure was 13.2 cm³ (range, 8.0-28.7 cm³). RESULTS: The cysts were discovered a median of 48 months (range, 24-89 mo) after radiosurgery. Three patients were originally without symptoms, and observation with serial imaging was performed; two of those patients developed symptoms 13 and 40 months later, whereas one patient has remained without symptoms for 51 months. Initial treatments for patients with symptomatic cysts included cyst aspiration (n = 3) and placement of a cystoperitoneal shunt (CPS) (n = 2). The median cyst volume was 14 cm³ (range, 4-63 cm³). Cyst recurrence occurred within 2 months for patients who underwent aspiration alone, necessitating placement of a CPS. Shunt placement eliminated the cysts for four patients, at a median follow-up time of 16 months (range, 9-27 mo). One patient's cyst persisted despite CPS placement, and cyst excision was performed. No morbidity occurred with any of the cyst treatments. CONCLUSION: Cyst formation after arteriovenous malformation radiosurgery may occur many years after the procedure. Although most symptomatic cysts can be effectively treated with CPSs, cyst excision may be necessary if the mass effect is not relieved with the less invasive approach.