Atypical Extraventricular Cystic Subependymal Giant Cell Astrocytoma in a Child Who Did Not Fulfil Clinical Criteria for Tuberous Sclerosis Complex: A Diagnostic Pitfall—A Case Report

Subependymal giant cell astrocytoma (SEGA) usually arises near the foramen of Monro in patients with tuberous sclerosis complex (TSC). A 14-year-old boy presented with headache and a 6.2 × 5.8 cm extraventricular, cyst-dominant hemispheric lesion containing a mildly enhancing mural nodule. Microsurgical excision was performed. Histology demonstrated mixed spindle and polygonal epithelioid/ganglioid cells in a fibrillary, microvascular stroma. Tumor cells were positive for glial fibrillary acidic protein (GFAP) and cluster of differentiation 56 (CD56); epithelial membrane antigen (EMA), inhibin, and thyroid transcription factor-1 (TTF-1) were negative, and the Ki-67 labeling index was approximately 1%. No additional major or minor feature of TSC was identified using the 2021 International TSC Consensus criteria. At 12 months, the patient was neurologically intact and headache-free. Germline or tumor TSC1/TSC2 testing and postoperative contrast-enhanced magnetic resonance imaging (MRI) were unavailable. This case highlights the integrated assessment required for pediatric cystic tumors with mural nodules.