Myeloid Sarcoma Involving the Central Nervous System: A Rare Entity Mimicking Meningioma (P3.159)

Objective: To report a very rare neoplasm, myeloid sarcoma of the CNS, which may mimic meningioma on imaging. Background: Myeloid sarcoma (MS) is a neoplasm consisting of myeloid blasts, with or without maturation, occurring at extramedullary sites. MS can involve many sites, however, occurrences in the central nervous system (CNS) are very rare and may arise prior to, during or upon remission of acute myelocytic leukemia (AML). We are reporting a case of MS involving the CNS to add one more case to the limited literature (12 cases). Design/Methods: A 30 year-old male presented with one month of headaches, nausea, vomiting, and blurry vision. Cranial MRI showed multiple extra-axial hyperintense masses, presumed to be meningiomas, predominantly in the right cerebellopontine angle and left cranial fossa with associated mass effect. The patient underwent craniotomy for the posterior fossa mass. Results: Intraoperative cytological imprints showed abundant non-cohesive neoplastic cells with a high nuclear-to-cytoplasmic ratio, with some cells having an eccentrically placed nucleus and basophilic cytoplasm. Permanent sections showed sheets of tumor cells with scant cytoplasm that was basophilic and faintly granular. The nuclear morphology was predominantly myeloid with a subset of cells appearing lymphoid. Immunohistochemistry showed strong cytoplasmic staining for lysozyme, rare scattered positivity for CD3, and many with moderate immunoreactivity to CD68. The cells were negative for CD20, CD79a, OSCAR, and EMA. A final diagnosis of MS was rendered, and the patient disclosed in retrospect, that he had been treated for AML nine years previously. Conclusions: MS in AML patients is well described, but CNS involvement is rare. The hematolymphoid neoplasms mimicking meningioma are primary CNS lymphoma, mucosa associated lymphoid tissue (MALT) lymphoma, and MS. In our case, the immunohistochemical profile was characteristic of MS. This report highlights that though rare, it is important to keep MS on the differential diagnosis of dural based masses. Disclosure: Dr. Goodman has nothing to disclose. Dr. Agudo MD has nothing to disclose.