Abstract
BACKGROUND: Supratentorial ependymoma, ZFTA fusion-positive, CNS WHO grade 3, is a rare pediatric brain tumor characterized by brisk mitotic activity and sometimes microvascular proliferation and/or necrosis. Typical treatment includes a combination of resection, chemotherapy, and radiation therapy. These tumors often present at age 3 or 4 years and have a poor prognosis. OBSERVATIONS: The authors present the case of a 4-year-old girl who presented asymptomatically with recurrence of a supratentorial ependymoma, ZFTA fusion-positive, CNS WHO grade 3, of the right parietal lobe with a homozygous CDKN2A deletion through chemotherapy after an initial gross-total resection. Tumor recurrence presented with a traditional intraparenchymal cystic component that initially appeared to invade through the dura mater, diploë, and outer table of the skull. On closer examination of the calvaria and dura in the operating room, a trabeculated and soft tissue mixed with invasion into the outer table contiguous with calcifications on the native dura was observed. Histopathological analysis confirmed that the recurrent tumor was confined intradurally with treatment effect, and the dural and calvarial findings represented a reactive inflammatory process likely related to prior surgery, chemotherapy, and possibly the neoplasm itself. LESSONS: This case illustrates an atypical presentation of a recurrent supratentorial ependymoma, ZFTA fusion-positive, CNS WHO grade 3, where reactive inflammatory changes of the dura and calvaria mimicked dural and calvarial invasion. These findings demonstrate the importance of histopathological evaluation in distinguishing true tumor recurrence from atypical inflammatory responses to prior surgery, chemotherapy, or the neoplasm itself and close postoperative follow-up. https://thejns.org/doi/10.3171/CASE25146.