Fat Embolism Secondary to Yellow Fat Disease in an Appaloosa Horse

A 4-year-old female Appaloosa horse was referred to the Department of Comparative Pathology, Veterinary Faculty, with a history of colic and acute respiratory distress. At necropsy, gross lesions consisted of extensive firm, multinodular, hemorrhagic foci in fat tissues with yellow-brown discoloration. The most affected areas were peritoneal fat and perirenal, epicardial, and subcutaneous adipose tissues. Other findings were hepatic lipidosis and multiple 1–1.5 cm hemorrhagic foci scattered in both lungs. Histopathological examination revealed severe degeneration and necrosis of adipose tissue with dystrophic calcification. The necrotic fat was infiltrated by abundant foamy macrophages and multinucleated giant cells. Based on these histopathological changes, yellow fat disease, also called nutritional panniculitis, was diagnosed. In addition, the microscopic examination of lung and kidney sections stained with osmium tetroxide and oil red O revealed numerous lipid droplets within glomerular and alveolar septal capillaries. To the authors' knowledge, this is the first description of the development of fat embolism in horses affected by yellow fat disease.