Intracranial extramedullary relapse of acute myeloid leukemia presenting as myeloid sarcoma mimicking meningioma: a case report and literature review.

Background: Myeloid sarcoma (MS) is a rare extramedullary tumor of immature myeloid cells. Intracranial MS occurring as an extramedullary relapse without concurrent systemic acute myeloid leukemia (AML), is exceptionally rare and poses a considerable diagnostic challenge due to its non-specific clinical and radiological features, often mimicking more common intracranial neoplasms like meningioma. Case presentation: We report a case of isolated intracranial MS in a 61-year-old female with a prior history of FLT3-ITD mutated AML (M2), who had been in sustained complete hematologic remission for four years. She presented with a two-week history of diminished responsiveness and apathy. Cranial MRI revealed a well-defined, homogenously enhancing left frontal mass with a dural tail sign and significant peritumoral edema, initially suggestive of a meningioma. However, diffusion-weighted imaging (DWI) demonstrated restricted diffusion. The tumor was resected. Histopathological examination revealed diffuse sheets of immature myeloid cells. Immunohistochemistry was positive for CD117, CD34, and CD68, with weak MPO expression, confirming the diagnosis of MS. Post-operatively, the patient was referred for systemic chemotherapy. Conclusion: This case illustrates that intracranial MS can be a form of extramedullary relapse in AML patients even during long-term remission and can closely mimic a meningioma radiologically. Key diagnostic clues include a prior history of AML and radiographic features such as restricted diffusion on DWI and prominent peritumoral edema. However, these findings are non-specific, and a definitive diagnosis relies on histopathological and immunohistochemical analysis. The management of MS should be based on systemic AML therapy principles rather than surgery alone. This report highlights the necessity of considering MS in the differential diagnosis of new intracranial masses in patients with a history of AML to ensure timely and appropriate treatment.