Imaging diagnosis--Enostosis-like lesion in the femur of a horse

An enostosis-like lesion was diagnosed in the left femur of a Swedish Warmblood horse that had a left hindlimb lameness of 3 weeks duration. With scintigraphy using technetium 99m-hydroxymethylene diphosphonate (⁹⁹m Tc-HDP) a marked regional focal increase in radioactivity was identified in the medullary cavity of the left femur. Radiographically there was a corresponding focal increase in bone opacity in the middiaphysis of the left femur. Histopathologically, a 5 cm area of bone matrix was present in the diaphysis of the left femur and confirmed as an enostosis-like lesion. Enostosis-like lesions should be considered as a source of pain in horses with difficult to localize, moderate to severe chronic lameness.