Medial collateral ligament ganglion cyst: a rare cause of medial knee pain.

Ganglion cysts are commonly found in areas of constant mechanical stress such as the joints and tendons of the wrist or hand as well as the anterior aspect of the ankle. In the knee, parameniscal cysts are often encountered secondary to meniscal tears or articular degeneration. Intra-articular ganglion cysts are uncommon and often arise from the cruciate ligaments and are found in the intercondylar notch. However, ganglion cysts arising from collateral ligaments are very rare. We present a rare case of a boy in early childhood with non-specific medial joint line swelling and discomfort and was diagnosed with a medial collateral ligament ganglion cyst after multimodality imaging. To our knowledge, this is the first case documented in children.