Sarcoma of possible nerve sheath origin in a captive muskrat

A captive adult female muskrat (Ondatra zibethicus) was found dead without previous signs of disease. At necropsy, abdominal organs were infiltrated w ith a poorly demarcated, soft, tan tissue. Microscopically this tissue was composed of neoplastic cells assuming two distinct growth characteristics c onsistent with Antoni A and B patterns. Ultrastructurally, the neoplastic c ells were pleomorphic, lacked junctional devices, had abundant mitochondria and ergastoplasm, and frequently were closely associated with extracellula r collagen. Immunocytochemical examination of tumor cells demonstrated spor adic expression of neuron specific enolase. Microscopic tumor metastases to the myocardium, ascending aorta, lungs and visceral pleura were present. T his is the first report of a sarcoma compatible with a malignant peripheral nerve sheath tumor in a muskrat.