Perineal sarcoid in a Caspian miniature horse

An 8-year-old stallion male Caspian miniature horse was acquired by the Veterinary Teaching Hospital, Islamic Azad University from a commercial source for teaching veterinary students. One year later, during an annual health screen, a mass was noted in the perineal region. The mass was surgically removed. Histologic examination revealed that the mass was a relatively well-demarcated, unencapsulated neoplasm composed of streams, bundles, and whorls of neoplastic spindle cells that had oval to fusiform nuclei with stippled chromatin, variably distinct nucleolus, and moderate amounts of eosinophilic cytoplasm. Based on the morphologic and histologic findings, a diagnosis of equine sarcoid was made. Results of bacteriologic tests and fungal culture of the mass were negative. By re-examining the horse 3 weeks after surgery, the affected site was completely healed. To the authors’ knowledge, this is the first report of sarcoid in a Caspian miniature horse.