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Tracheal mastocytosis in a horse.

Upper airway obstruction in the horse may occur due to a number of different causes, including neoplasia, foreign bodies, anaphylaxis, trauma, inflammation, pharyngeal cysts, and polyps (1,2). These may be differentiated by physical, radiographic, and endoscopic examination, or by biopsy or exploratory surgery. Neoplastic lesions of the trachea are rarely reported in any species, including man (3). In this report, we describe the clinical features and surgical treatment of intratracheal mastocytosis in a horse. A 21-year-old, Arabian-cross gelding was examined by a staff member of the Herd Medicine and Theriogenology Department of the Western College of Veterinary Medicine (WCVM) for the complaint of inspiratory dyspnea of three days duration. The gelding was normal at rest. Tracheal palpation elicited a mild cough and wheezing. When fed, the horse had severe, progressive inspiratory stridor which abated when the feed was removed. There had been no recent changes in the animal's environment or feeding management. Respiratory distress was not reported during exercise. Three months previously, the gelding had a cutaneous mastocytoma diagnosed by excisional biopsy. Endoscopic examination of the upper respiratory tract revealed a 1 cm nodular mass in the caudal aspect of the right nasal cavity, a similar mass in the right nasopharynx, and a large intraluminal tracheal mass 5 cm caudal to the larynx (Figure 1). The mass was smooth and pink, with a broad-based attachment to the dorsolateral aspect of the trachea. It was 4-5 cm in diameter and occupied 70-75% of the crosssectional area of the trachea. The horse was referred to the Veterinary Teaching Hospital for further evaluation. Lateral cervical radiographs revealed a 9 x 6 cm intraluminal soft tissue mass originating from the dorsum of the trachea 5 cm caudal to the larynx (Figure 2). The dorsal aspect of the tracheal shadow was depressed where the mass was attached, attenuating the tracheal lumen. The horse was prepared for a ventral laryngotomy. He was premedicated with xylazine (Rompun, Bayvet, Mississauga, Ontario) and general anesthesia was