Enostosis‐like lesions in the long bones of 10 horses: scintigraphic and radiographic features

Ten horses admitted for lameness evaluation including bone scintigraphy had enostosis-like lesions, described scintigraphically as focal or multifocal areas of intense increased radioisotope uptake within the medullary cavity of one or more long bones, and radiographically as one or multiple round to irregularly shaped radiopacities within the medullary cavity, often in close proximity to the nutrient foramen. There were 6 Thoroughbreds, one male, one female and 4 geldings, 3 Standardbreds, all geldings and one Appaloosa gelding; age 3-10 years. Enostosis-like lesions were seen in the tibia (5 horses), radius (3 horses), humerus (one horse) and third metatarsal bone (MT-III) (4 horses). The number of affected bones in each horse was 1-3. Of 16 affected limbs, there were 9 hindlimbs and 7 forelimbs. Enostosis-like lesions were considered a possible cause of lameness in 5 horses, but were considered incidental findings in the other horses. Lesions thought to cause lameness were seen in the tibia (2 horses), MT-III (one horse) and in the radius (4 horses). Lameness resolved after horses were rested (2-6 months) and given nonsteroidal anti-inflammatory drugs (4 horses). Follow-up scintigraphic examination in 3 horses (2, 6 and 9 months later, respectively) revealed normal radioisotope uptake in the affected areas.