Chondromatosis within a meniscal cyst of the knee.

A 32-year-old man complained of left gonalgia for 2 years and noticed a soft part tumor on the lateral side of his left knee. Roentgenograms showed some small calcified shadows at the same site of the tumor. Arthroscopy revealed a lateral meniscus to be an incomplete discoid with degenerative tears. At the operation, a multilocular soft part tumor was noticed in continuity with the lateral meniscus macroscopically. Small, loose bodies and gelatinous fluid were found in the cavity of the tumor. Histologically loose bodies were chondroma and the soft part tumor was meniscal cyst. The meniscal cyst wall contained hyaline cartilagenous tissue. Therefore it was thought that chondroma originated from the cyst wall.