Abstract
A 57‐year‐old male complained of a painful sensation on the medial joint line of the right knee for about 5 years. A palpable soft mass measuring about 5.5 × 4.0 × 2.0 cm was found on the medial joint line. Plain roentgenography showed bulging soft tissue over the medial aspect of the right knee. Sonography revealed a hypoechoic intra‐articular soft tissue mass. Magnetic resonance imaging revealed a multilobulated homogeneous cystic lesion originating from the medial collateral ligament, with hypointensity on T1‐weighted images and hyperintensity on T2‐weighted images. We performed an arthroscopic examination before surgical excision of the tumor to rule out a parameniscal cyst, and no meniscal tear was found. Microscopic examination proved that the excised tumor was a ganglion cyst. The patient was free of his previous symptoms and had no recurrence at 2‐year follow‐up.