DOI: https://doi.org/10.36347/sjmcr.2026.v14i05.071

Pages: 1166-1170

Embryonal tumors with multilayered rosettes (ETMR) are rare, highly aggressive WHO grade 4 embryonal tumors of the central nervous system, usually arising intracranially. Extra-axial and extracranial presentations are exceptional and may mimic more common pediatric sacrococcygeal tumors. We report the case of a 3-year-old girl presenting with a presacral and subcutaneous sacrococcygeal mass. MRI and CT demonstrated a large heterogeneous solid-cystic lesion with marked diffusion restriction, pelvic extension, and regional lymphadenopathy, initially suggesting a malignant sacrococcygeal teratoma. Histopathologic and immunohistochemical evaluation confirmed the diagnosis of ETMR. After neoadjuvant chemotherapy, follow-up MRI revealed a marked partial response with significant tumor shrinkage, decreased enhancement and vascularity, and regression of lymphadenopathy. Therapeutic response was assessed using both RECIST 1.1 and RANO criteria, demonstrating a significant partial response. This case emphasizes the diagnostic value of diffusion-weighted MRI in identifying hypercellular pediatric tumors in unusual extracranial locations and expands the differential diagnosis of aggressive sacrococcygeal masses in young children to include ETMR.