Mesothelioma in horses

Thoracic and Abdominal Mesothelioma in an Older Horse in Lazio Region

Simple Summary

Mesothelioma in the equine species is poorly described in Italy. It is important to make an early and error-free diagnosis for a correct clinical approach, as well as to establish the triggering cause of this neoplasm. The etiology, most likely of an environmental nature, would reveal a valid biological indicator in the horse, far from urbanized centers.

Abstract

A Quarter Horse, a gelding aged 22, was subjected to a clinical examination for colic syndrome. During admission to the clinic, blood counts and ultrasound examination were performed. Ultrasound revealed abdominal masses and abundant accumulation of pleural (50 L) and abdominal fluid (100 L). Cytology was performed on the aspirated fluid. The patient was euthanized. The autopsy examination revealed abundant effusion and nodular masses on the peritoneum, omentum, lungs, heart, and mediastinum. A diagnosis of epithelioid mesothelioma was made via histopathology and confirmed with immunohistochemistry; it showed positive antibodies against cytokeratin (CK) and vimentin. Mesothelioma is a rare cancer in older horses. It is important to employ the correct differential diagnostics using the available methods, providing valid ante-mortem support to the clinical veterinarian and monitoring the territory using this species as a valid biological indicator.

Concurrent thoracic mesothelioma and thyroid C-cell adenoma with amyloid deposition in an aged horse

A 21‐year‐old American Saddlebred mare died with a history of weight loss and breathing difficulties of 1 month duration. Post‐mortem examination revealed a copious pleural effusion with multifocal to coalescing numerous white to grey nodular masses on the serosal surface of the pericardium, lungs and thoracic cavity. In addition, the left thyroid gland was markedly enlarged. A thoracic mesothelioma and C‐cell adenoma with amyloid deposits of the left thyroid gland were diagnosed by histopathology and confirmed by immunohistochemistry employing antibodies against cytokeratin (CK), vimentin and calcitonin. Amyloid deposits in the thyroid tumour were confirmed by Congo red staining with apple‐green birefringence under polarized light. Mesothelioma remains an uncommon neoplasm encountered in aged horses. Discussion includes the diagnostic challenge of differentiating carcinomatosis from mesothelioma by histology and differentiating reactive and neoplastic mesothelial cells by cytology.

Cranial Mediastinal Liposarcoma in a Horse

A 23-year-old Anglo-Arabian mare was presented with tachypnea, dyspnea, and pitting edema of the ventral thoracic subcutis. On necropsy, a tan to red, friable, irregularly shaped mass (23 × 20 × 18 cm) occupied the cranial mediastinum. Histologically, the mass was classified as a liposarcoma and was composed of short interlacing bundles of spindle-shaped to irregularly rounded cells with discrete, variably sized, clear cytoplasmic vacuoles, which were stained with oil red O in frozen sections of formalin-fixed tissue.

Disseminated lipid-rich peritoneal mesothelioma in a horse

A 9-year-old Haflinger mare presented to the Liphook Equine Hospital with a history of weight loss, azotemia, and repeated episodes of ascites over a period of 10 days. The horse was euthanized after exploratory laparotomy revealed large numbers of variably sized masses distributed throughout the peritoneal cavity. Macroscopically, some masses were papillary, while others were nodular. Histologically, the masses were comprised of large to giant, variably shaped, and occasionally multinucleated neoplastic cells with marked anisokaryosis and anisocytosis and a high mitotic rate. Small to moderate numbers of neoplastic cells were swollen by 1 to several, moderately sized to large, clear, circular or ovoid vacuoles, which stained positive with oil red O. Immunohistochemically, the neoplastic cells co-expressed vimentin and cytokeratin. Electron microscopy demonstrated tumor cells with tight junctions, microvilli, and numerous intracytoplasmic lipid droplets. These findings are consistent with a lipid-rich form of mesothelioma, which should be considered as a differential diagnosis if lipid vacuoles are present in potentially neoplastic cells in equine abdominocentesis samples.

Neoplasia of the respiratory tract

Tumors of the equine respiratory tract occur infrequently. An accurate diagnosis of neoplasia of the respiratory tract is critical because the prognosis is usually grave. The clinical signs and diagnostic procedures are discussed for tumors of the nasal and paranasal sinuses, nasopharynx/larynx, guttural pouch and thorax including lung, pleura, and thymus.