Giant Cell Tumour of Knee Popliteus Muscle Synovial Sheath.

The giant cell tumour of the tendon sheath (GCTTS) is the second most common soft tissue benign tumour and rarely presents in the knee. We report a rare presentation of a GCTTS in the knee with corresponding magnetic resonance imaging (MRI), an arthroscopic picture, and histological presentation. It is a rare occurrence but should be considered as a differential in atraumatic knee pain presentation. This case report gives a classic picture of its presentation, diagnosis, and histopathology.