Pleural lipoma in a horse

Lipoma is a benign neoplasia originating from adipocytes. It is frequently diagnosed in veterinary medicine and usually presents as cutaneous nodules but can also occur inside body cavities in less common cases. There are several reports of abdominal cavity neoplasia in horses, an important cause of colic in these animals. No cases of neoplasia in the thoracic cavity have been reported for this species. Therefore, the aim of this study was to report an intrathoracic lipoma located in the visceral pleura of an American Quarter Horse. The equine was euthanized after relapses of surgically resolved colic and unresponsive visceral pain. At necropsy, we observed fibrinous peritonitis, adherence of intestinal loops in its abdominal cavity, and hemomelasma ilei in several intestine segments. In the thoracic cavity, a whitish, firm, pendulous structure with a regular surface measuring approximately 4.0 cm x 3.0 cm was observed in the pleura of the right caudal lung lobe–and diagnosed by histopathology as lipoma. Due to the rarity of this type of lipoma presentation and considering the absence of reports of its occurrence in horses, this report is essential to list this neoplasia as a differential in pleural masses in the species.