Cyst formation after stereotactic radiosurgery for intracranial meningioma

The authors report 2 cases of delayed cyst formation after gamma knife radiosurgery for 3 meningioma lesions. All 3 lesions reported here had a distinctive feature before gamma knife treatment of small and spotty intratumoral cysts. One patient experienced an intriguing clinical course of spontaneous regression of the enlarged cyst, and 2 of the 3 lesions became symptomatic requiring surgical interventions. Cyst formation as a postradiosurgical complication is relatively rare in meningioma patients in the literature, and its pathogenesis is unclear. We describe herein the clinical courses of these 2 patients and review the relevant literature in this report. From our experience of these 2 cases, we suggest that we should be aware of the possible development of spotty intratumoral cysts into larger cysts after stereotactic radiosurgery and that we should carefully observe such patients after the treatment.