Intratracheal Leiomyosarcoma in a 13-Year-Old German Riding Pony Mare.

A 13-year-old German Riding Pony mare was referred for evaluation of progressive respiratory noise and mixed dyspnoea, which rapidly deteriorated to respiratory distress. Clinical examination revealed marked rattling inspiratory and expiratory tracheal sounds and severe, rattling, vesicular lung sounds. Arterial blood gas analysis demonstrated moderate hypoxaemia (partial pressure of arterial oxygen 76 mmHg at rest). Upper airway endoscopy identified a pink, cauliflower-like pedunculated mass originating from the dorsal tracheal wall approximately 15 cm cranial to the tracheal bifurcation, causing an estimated 60% luminal obstruction. The mass was successfully removed via transendoscopic electrosurgical excision. However, complete tumour-free margins were not achieved. Histopathological examination revealed the diagnosis of leiomyosarcoma. Following surgery, the mare exhibited rapid clinical improvement. Peri-operative treatment included antimicrobial, anti-inflammatory, and bronchodilatory therapy. A follow-up endoscopy one month after surgery showed adequate healing of the surgical site. A small, vascularized tissue structure within the scar tissue, considered suspicious for residual tumour growth, was identified. However, no significant progression was observed during a follow-up examination seven months postoperatively. This case highlights tracheal leiomyosarcoma as a rare differential diagnosis in horses with respiratory distress and describes transendoscopic electrosurgical excision as a feasible therapeutic option.