Rare encounter of spinal atypical teratoid/rhabdoid tumor in an adult: A case report and review of clinicopathological diagnostic pitfalls.

Atypical teratoid/rhabdoid tumor (AT/RT) is a highly aggressive embryonal tumor that most commonly affects young children, with primary spinal involvement being exceedingly rare in adults. We highlight a rare case of a 26-year-old female who presented with paraparesis and was found to have a well-defined, homogeneously enhanced intradural extramedullary lesion at the D9 - D10 level on magnetic resonance imaging (MRI), initially suggestive of a benign nerve sheath tumor. Surgical excision followed by histopathological evaluation revealed undifferentiated tumor cells arranged in nests and cords within a hyalinized stroma. Immunohistochemistry demonstrated strong glial fibrillary acidic protein (GFAP) and focal epithelial membrane antigen (EMA) positivity, CD99 positivity, and complete loss of SWI/SNF-related matrix-associated actin-dependent regulator of chromatin, subfamily B, member 1 (SMARCB1) integrase interactor 1 (INI1) expression in tumor cells, confirming the diagnosis of AT/RT. The lesion lacked hemorrhage or necrosis, adding to its benign radiological mimicry. This case highlights the diagnostic pitfalls in adult spinal AT/RT, especially when radiological findings overlap with benign tumor and histological features overlap with other small round cell tumors such as Ewing sarcoma, metastatic carcinoma, or CIC-rearranged sarcomas. The distinct nested and cord-like architecture observed in this case broadens the familiar histopathological spectrum of AT/RT. The patient received postoperative radiotherapy, and emerging data suggest potential benefit from multimodal approaches including surgery, radiotherapy, chemotherapy, and targeted therapies such as mechanistic target of rapamycin (mTOR), enhancer of zeste homolog 2 (EZH2), and cyclin dependent kinase 4/6 (CDK4/6) inhibitors. This report stresses the need to consider AT/RT in the differential diagnosis of adult intradural extramedullary spinal lesions and reinforces the diagnostic utility of SMARCB1 (INI1) immunohistochemistry. Molecular subtyping may further guide therapeutic decisions and improve prognostication in this rare and challenging tumor.