Intra-articular lipomatous lesion in the stifle in a dog

A seven-year-old, female Labrador retriever was presented with chronic and intermittent left hindlimb lameness, deteriorating over the previous three weeks. Radiographs showed an avoid mass with a fat opacity, at the craniomedial aspect of the left distal femur, with craniomedial displacement of the patella and marked degenerative joint disease. Computed tomography (CT) scans revealed an ovoid, well-defined, mildly heterogeneous, non-enhancing, septated fat attenuating mass (-70HU). On ultrasound (US), the mass had smooth regular margins and was slightly hyperechoic to adjacent muscles with a mildly heterogeneous aspect. Cytology revealed well-differentiated adipocytes. The findings were consistent with intra-articular lipomatous lesion, most likely a true intra-articular lipoma.