When Marrow Mimics Malignancy: Tumefactive Hepatic Extramedullary Hematopoiesis Presenting as a Hypervascular Liver Mass.

Extramedullary hematopoiesis (EMH) is the production of blood cells outside the bone marrow, usually occurring as a compensatory response to hematologic stress or marrow dysfunction. Although EMH most commonly presents as diffuse tissue infiltration, it can rarely manifest as a localized solid mass, known as tumefactive EMH, creating a significant diagnostic challenge by mimicking benign or malignant lesions on non-invasive imaging. We report the case of a 47-year-old male with cirrhosis secondary to autoimmune hepatitis, receiving mycophenolic acid, who presented with severe symptomatic anemia, profound jaundice, hepatosplenomegaly, and markedly elevated carbohydrate antigen 19-9 (CA 19-9) levels. Dynamic abdominal CT revealed a 63-mm hypervascular ovoid mass in hepatic segment VIII, showing heterogeneous arterial-phase enhancement and relatively decreased attenuation on the delayed/parenchymal phase, raising strong suspicion for hepatocellular carcinoma or intrahepatic cholangiocarcinoma. Given the suspicious radiological and biochemical findings, a percutaneous liver biopsy was performed. Histopathological evaluation demonstrated sinusoidal and perisinusoidal hematopoietic elements with megakaryocytic and erythroid differentiation. Immunohistochemistry demonstrated CD61-positive megakaryocytic elements and glycophorin A-positive erythroid precursors, supporting hepatic EMH and ruling out hepatocellular carcinoma, cholangiocarcinoma, or metastatic malignancy in the analyzed tissue. Subsequent bone marrow evaluation showed mild reticulin fibrosis and findings suggestive of a possible early-stage myeloproliferative neoplasm; however, definitive molecular and cytogenetic characterization could not be completed, and diagnostic criteria for a definitive hematologic disorder were not fulfilled. This case highlights that tumefactive hepatic EMH can radiologically and biochemically simulate hepatobiliary malignancy, particularly in patients with chronic liver disease, cholestasis, and elevated CA 19-9. It underscores the essential role of histopathological confirmation in preventing inappropriate oncological management and illustrates that focal hepatic EMH should prompt evaluation for a possible underlying hematologic disorder without assuming a definitive myeloproliferative neoplasm.