Eosinophilic myelocytoma in an owl monkey (Aotus trivirgatus)

A mass found in the anterior mediastinum at necropsy of an adult female owl monkey (Aotus trivirgatus) was morphologically consistent with an eosinophilic myelocytoma. Lymph nodes, kidneys, bone marrow, and other tissues were diffusely infiltrated by neoplastic cells. Intracellular and extracellular Charcot-Leyden crystals were present in the neoplasm.