Intracranial Extramedullary Hematopoiesis: a Rare Entity

Abstract Introduction/Objective Extramedullary hematopoiesis (EMH) is characterized by ectopic proliferation and differentiation of hematopoietic precursor cells outside the bone marrow. In postnatal life, EMH occurs due to hematopoietic disorders, infection or advanced tumors and is usually seen in the spleen, liver, and lymph nodes. Intracranial EMH is an extremely rare entity that has been reported to be associated with hematological disorders, meningioma, subdural hematoma and pilocytic astrocytoma. Methods/Case Report To highlight the significance of identifying EMH as one of the differential diagnoses of brain lesions, we present a 67-year-old female with a history of headaches and generalized malaise. Her past medical history was significant for hypertension and mild anemia. As part of the headache workup, magnetic resonance imaging (MRI) of the brain showed a 3.7cm cystic mass in the right inferomedial parietal lobe with medial mural enhancement, associated with edema and mass effect. A similar 3mm left parietal lobe enhancing focus was also noted. These findings were suggestive of a hemangioblastoma. Resection of the larger mass showed a benign vascular lesion with endothelial hyperplasia without the appearance of cavernous hemangioma or vascular malformation. Foci of erythroid and myeloid precursors, and megakaryocytes were seen. Immunohistochemical stains were negative for GFAP, CK AE1/AE3 and inhibin ruling out glial neoplasms, metastatic carcinoma and hemangioblastoma. Hematopoietic cells were positive for CD45, while immature red cells were positive for E-cadherin and endothelial cells were positive for CD31, consistent with EMH. Further workup was negative for any underlying hematological disorders, resulting in the diagnosis of idiopathic intracranial EMH. The patient received intensity- modulated radiation therapy (IMRT) for her remaining left parietal lesion. After 3 months of regular follow-up, her headache and malaise significantly improved. Results (if a Case Study enter NA) NA. Conclusion To our knowledge, this is the first reported case of idiopathic intracranial EMH.