Epithelioid cells in mediastinal lymph nodes of cattle without cancer

Epithelioid cells are found in lymph nodes in cases of metastatic carcinoma; however, epithelioid cells with benign features have also been discovered incidentally in lymph nodes. Epithelioid cells were observed in mediastinal lymph nodes of cattle without cancer during routine diagnostic necropsy. To explain this finding, the authors evaluated the prevalence and histopathologic, immunohistochemical, and ultrastructural features retrospectively using mediastinal lymph nodes from 110 cattle and found that 66 of the lymph nodes contained epithelioid cells. In all 66 nodes, most of the epithelioid cells were individual or aggregated in nodal sinuses; in 21 nodes, some epithelioid cells formed tubular structures. The individual and aggregated epithelioid cells were mostly considered to be mesothelial in origin by immunohistochemical and ultrastructural examination; presumably, they entered the lymph nodes via lymphatic vessels, because they were found in afferent lymphatic vessels and nodal sinuses. Although the presence of epithelioid cells in lymph nodes prompts suspicion of metastatic carcinoma, the epithelioid cells in these bovine lymph nodes did not disrupt nodal architecture, lacked atypia or mitotic figures, and did not invade nodal parenchyma.