Report of a Rare Case of Intracranial Extramedullary Hematopoiesis Mimicking a Brain Tumor.

Failure of the bone marrow to maintain adequate blood cell production to match blood metabolic demand incites the production of cell lines outside the bone marrow, which is known as extramedullary hematopoiesis. Herein, we are reporting an 80-year-old male patient who presented with two weeks of worsening headaches and behavioral changes. Labs showed thrombocytosis and imaging showed a large right-sided hemorrhagic brain mass. No evidence of malignancy was seen elsewhere. Brain mass biopsy showed intracranial extramedullary hematopoiesis (IEMH) and bone marrow biopsy confirmed the diagnosis of essential thrombocythemia (ET)/myelofibrosis. This case adds to a few reported cases of IEMH, and to the best of our knowledge, this is the first reported case of IEMH in association with ET. It helps remind clinicians to keep IEMH in the differential diagnosis of those presenting with signs and symptoms of elevated intracranial pressure (ICP) and a newly found brain mass on the background of previously diagnosed or suspected myeloproliferative neoplasms.