Radiotherapy for Refractory Cystic Progression in Basal Ganglia Pilocytic Astrocytoma: A Case Report.

Pilocytic astrocytoma (PA) is a common low-grade pediatric glioma that often exhibits cystic components. Although cyst-related symptoms are usually controlled by gross-total resection or cerebrospinal fluid (CSF) diversion procedures, management can be challenging when tumors arise in deep or eloquent locations and are associated with highly proteinaceous cyst fluid. We report a case of a 14-year-old girl with PA arising in the basal ganglia who developed recurrent and refractory cystic enlargement following chemotherapy. Despite multiple interventions, including Ommaya reservoir placement, repeated cyst aspirations, endoscopic cyst fenestrations, and cystoperitoneal and ventriculoperitoneal shunts, cyst control was repeatedly compromised due to obstruction associated with extremely high cyst fluid protein levels. Although cyst-ventricle communication resulted in a marked reduction in protein concentration, recurrent obstruction and cyst re-expansion persisted. Given the refractory nature of the cystic lesion and the absence of endocrine dysfunction, fractionated radiotherapy was selected. Following radiotherapy (60 Gy in 30 fractions), magnetic resonance imaging revealed reduced contrast enhancement and stabilization of the cystic component. The patient remained clinically stable without treatment-related adverse events or cyst enlargement during the two-year follow-up. This case highlights the limitations of conventional surgical and CSF diversion strategies for cystic PA with high proteinaceous content. Radiotherapy may be a viable therapeutic option for refractory cystic progression in patients with PA, even in the absence of solid tumor growth.