A Sudden Expansion: Acute Subdural Hematoma From Extramedullary Acute Myeloid Leukemia.

Chloromas are extramedullary agglomerations of malignant myeloid blast cells, also known as myeloid sarcoma. Myeloid sarcoma of the central nervous system (CNS) is a very rare presentation of extramedullary leukemic mass infiltration. This may be seen as an intracranial mass due to invasion of the brain parenchyma or as leukemic infiltration of the meninges. Such infiltration may present as a subdural hematoma (SDH), particularly in coagulopathic or immunocompromised patients undergoing chemotherapy. We present a 63-year-old male with acute myeloid leukemia (AML), previously treated with azacitidine/venetoclax induction and intrathecal methotrexate, who was admitted with abdominal thromboses and started on therapeutic anticoagulation. The patient later developed acute encephalopathy, and imaging demonstrated a large left-sided acute-on-subacute SDH with mass effect. Despite anticoagulation reversal and surgical intervention, the patient experienced recurrent hemorrhage. Histopathology of the subdural membrane tissue confirmed AML with monocytic differentiation. The clinical course was further complicated by tumor lysis syndrome, metabolic acidosis, and acute liver failure. The patient expired following withdrawal of life-sustaining treatment. This case highlights a rare, catastrophic CNS manifestation of AML in the form of a dural-based chloroma inducing a subacute-chronic SDH. Dural metastasis should be considered in patients with hematologic malignancies and subacute SDH. Although SDHs can typically be treated with good outcomes following surgical evacuation, those due to leukemic infiltration from AML - especially high-risk phenotypes - may portend less favorable outcomes, due to concomitant coagulopathy and being a marker for more aggressive hematologic disease.