Subependymal giant cell astrocytoma (SEGA) is a rare, slow-growing tumor with a dual (neuroglial) component that is typically associated with tuberous sclerosis complex (TSC). We present the case of a healthy 19-year-old man with mild occipital trauma followed by two weeks of intense headache, with no response to analgesics. Imaging studies revealed a well-defined tumor in the left paraventricular zone. A biopsy showed a SEGA (GFAP+, NF+, nestin+, CK-EA3/EA4+, and TTF1+). TSC was ruled out. An immunohistochemistry (IHC) panel showed aberrant cytoplasmic expression of octamer-binding transcription factor 4 (OCT-4) in endothelial cells, pericytes, and some astrocyte-type cells; integrase interactor 1 (INI-1) expression was observed in the cytoplasm of neoplastic cells; SEGA was not associated with TSC; the expression of nestin and OCT-4 suggested their origin in neuroepithelial stem cells; thyroid transcription factor 1 (TTF-1) expression supported its origin in diencephalic structures. Tuberin expression was decreased. An aberrant pattern of INI-1 was observed, which, together with OCT-4 findings, has not been previously described.