Mesothelioma is a rare mesodermal neoplasm arising from pleura, pericardium and peritoneum or tunica vaginalis. Primary tumours arising from mesothelial cells lining the peritoneal cavity have been recorded in the abdominal cavity of cattle⁵, dogs¹ and cats³, ⁴. In the present paper, a rare case of peritoneal mesothelioma encountered in a cat is reported.

A 12 years old female cat carcass was brought to the Department of Veterinary Pathology, Madras Veterinary College, Chennai-600 007 for postmortem examination with a history of swelling in right thoracic region for the past one month. Necropsy examination revealed numerous fleshy irregularly shaped masses ranging from approximately 1x 1x1 to 2 × 2 × 1 cm in size in the visceral peritoneum (Fig.1). Scattered multifocal haemorrhages on epicardium and endocardium, pulmonary emphysema, hepatomegaly and congested spleen were also noticed.

Fig. 1:Cat- Peritoneum, mesothelioma - Variable sized nodules.

Fig. 2:Section showing stroma and islands of neoplastic components. HE ×40

Histopathological examination of peritoneal masses revealed cells of varying proportions of arboriform neoplastic components. Finger like projections contained delicate stromal tissue having elongated fibroblasts and capillaries. Abundant stromal connective tissue separated the neoplastic areas as small islands (Figs.2,3). Many small blood vessels were also seen. The proliferating mesothelial cells showed squamoid, cuboidal and short columnar cells with eosinophilic cytoplasm containing pleomorphic round to elongated nuclei (Fig. 4). A few mitotic figures were seen. Stromal tissue contained abundant collagen, blood vessels, fibrocytes and scattered infiltration of lymphocytes, plasma cells and eosinophils. There was no metastasis. At some places lining neoplastic cells were pseudostratified. Some cells showed one or two nucleoli. Microscopical feature of epithelial and stromal components suggested the biphasic nature of mesothelioma².

Fig. 3:Mesothelioma: Arboriform pattern. HE ×100

Fig. 4:Mesothelioma: Cuboidal to columnar neoplastic cells arranged on a stroma. HE ×320

Mesothelioma in a cat