Dyspnea Caused by an Obstructive Tracheal Leiomyoma in a Horse: A Rare Case

Tracheal leiomyoma is a rare neoplasm of the respiratory tract in animals. This primary benign tumor arises from smooth muscle cells of the trachea. We report a 13-year-old female horse with clinical signs of severe airways obstruction. It had dyspnea, exercise intolerance, chronic progressive respiratory noises, and cyanosis in mucosa membranes. Radiography revealed a foreign body obliterating the luminal trachea. Endoscopic biopsy showed a 3 × 3-cm ovoid mass attached to the dorsal aspect of the trachea. Hematoxylin and eosin and Masson's trichrome stains showed dense spindle cells forming irregular bundles disposed in short interlacing fascicles. Nuclei were elongated with blunt ends, eosinophilic cytoplasm with indistinguishable cell borders, and low mitotic activity. This study is considered the first reported case of an obstructive intratracheal leiomyoma in the horse.