Relative incidence and morphology of lateral and medial meniscal cysts detected by magnetic resonance imaging.

It is likely that meniscal cysts of the knee are a complication of meniscal tears which extend to the capsular attachment. They are reported as occurring three times more commonly on the lateral than the medial side. We reviewed 50 cases of meniscal cysts diagnosed on magnetic resonance imaging in patients with suspected internal derangement of the knee. Twenty-eight cysts involved the medial and 22 the lateral meniscus. The most common sites were the posterior third of the medial meniscus and the mid-third of the lateral meniscus. Fifteen cysts were suspected clinically, five on the medial side and 10 on the lateral side. Small cysts were only clinically predicted on the lateral side. We conclude that menial cysts are more common than previously thought and are more difficult than lateral cysts to detect clinically.