eng Science and Education Publishing American Journal of Medical Case Reports 2374-216X 2025-08-12 13 7 37 40 10.12691/ajmcr-13-7-1 AJMCR20251371 article Jorge L車pez Villegas jlopezv@ccss.sa.cr 1 Leonardo Granados Altamirano 1 Jos谷 Rojas Rodr赤guez 1 Betzab谷 Rojas Mena 2 Hematology Department, Dr. Rafael 芍ngel Calder車n Guardia Hospital, Caja Costarricense de Seguro Social, San Jos谷, Costa Rica 1Hematology Department, Dr. Rafael 芍ngel Calder車n Guardia Hospital, Caja Costarricense de Seguro Social, San Jos谷, Costa Rica Myeloid sarcoma (MS), also known as granulocytic sarcoma or chloroma, is a rare extramedullary manifestation of acute myeloid leukemia (AML). Mediastinal presentation is exceedingly uncommon and may lead to misdiagnosis, particularly when hematologic parameters are preserved. We report the case of a 44-year-old male who presented with constitutional symptoms and an isolated anterior mediastinal mass without peripheral blood abnormalities. Diagnosis was established through flow cytometry, histopathology, and immunohistochemistry. Molecular profiling revealed a complex mutational landscape including PHF6, TP53, WT1 mutations, and a PICALM每MLLT10 fusion. The patient was treated with AML-directed chemotherapy and remains under close surveillance. This case highlights the diagnostic challenges and prognostic implications of extramedullary AML with rare genetic alterations. https://pubs.sciepub.com/ajmcr/13/7/1/ajmcr-13-7-1.pdf Myeloid sarcoma acute myeloid leukemia mediastinal mass extramedullary leukemia