A Case of Visceral T Cell Lymphoma with Prominent Histiocyte Infiltration in a Dog

A 13-year-old intact male English Springer Spaniel presented with anorexia. Physical examination revealed a palpable abdominal mass without peripheral lymphadenopathy. Ultrasonography revealed hepatosplenomegaly and a markedly enlarged hepatic lymph node. Fine-needle aspiration of the splenic and nodal lesions revealed atypical round cells admixed with numerous histiocytes. The dog was euthanized owing to deteriorating condition despite a month of chemotherapy with lomustine. Histopathology revealed obliteration of the normal architecture of the liver, spleen, kidney, and hepatic and mesenteric lymph nodes by CD3⁺ neoplastic lymphocytes, accompanied by extensive F4/80⁺ histiocytic infiltration. This report describes a rare presentation of T-cell lymphoma with prominent histiocytic infiltration that may initially be misdiagnosed as histiocytic neoplasia in a dog.