Disseminated hemangiosarcoma in a horse.

A 6.5-year-old horse with a history of exercise-induced pulmonary hemorrhage was admitted because of acute onset of epistaxis, dyspnea, high respiratory rate, pale mucous membranes, and dark feces. There was no clinical or laboratory evidence of a bleeding disorder, and the horse's anemia was considered to be secondary to pulmonary hemorrhage. The cause of the hemorrhage was not found on thoracic sonograms or from cytologic examination of transtracheal aspirates. Despite supportive care, the horse's health deteriorated, and it was euthanatized. Necropsy revealed blood in the thoracic and peritoneal cavities and reddish black masses in many tissues. Histologic examination confirmed a diagnosis of hemangiosarcoma. Hemangiosarcoma is a rare tumor in horses; however, as this case demonstrates, it can cause pulmonary hemorrhage and respiratory distress and may be difficult to diagnose before death.