Large subependymal giant cell astrocytoma in a young adult with no evidence of Tuberous Sclerosis Complex: A case report of recurrence and complex course

Subependymal giant cell astrocytoma (SEGA) is most associated with tuberous sclerosis complex (TSC); however, its occurrence in adults lacking TSC stigmata presents a considerable diagnostic challenge. A 22-year-old male with a prior subtotal resection of an intraventricular tumor presented with a six-week history of progressive headaches, nausea, vomiting, and visual impairment. Clinical examination identified bilateral papilledema without systemic or cutaneous features of TSC. Contrast-enhanced MRI showed a large (5.2 cm), heterogeneously enhancing, calcified intraventricular mass in the right lateral ventricle and foramen of Monro, causing obstructive hydrocephalus. Near-total resection was achieved via an interhemispheric transcallosal craniotomy. Histopathological evaluation demonstrated large polygonal cells with abundant eosinophilic cytoplasm. Immunohistochemistry (IHC) confirmed SEGA, showing positive glial fibrillary acidic protein (GFAP) and S-100, focal synaptophysin, and a low Ki-67 index. Molecular analysis of tumor tissue identified a pathogenic TSC2 alteration, whereas peripheral-blood testing was negative for a pathogenic germline TSC1 or TSC2 variant. Persistent hydrocephalus required postoperative placement of a ventriculoperitoneal shunt. At 18-month follow-up, surveillance MRI detected a recurrent enhancing nodule. Given the recurrent lesion and multidisciplinary assessment of resectability, everolimus was initiated. After 12 months of therapy, substantial tumor reduction and near-baseline functional recovery were achieved. This case demonstrates that mTOR inhibition can effectively control recurrent SEGA in the absence of TSC and points out the possibility of spontaneous SEGA development in individuals without TSC.