Association of parameniscal cysts with underlying meniscal tears as identified on MRI and arthroscopy.
Although patients with parameniscal cysts usually have underlying meniscal tears, we noted that this association was less common with anterior lateral cysts. We wished to determine whether the frequency of a meniscal tear underlying a parameniscal cyst varied with cyst location. We reviewed a database of 7,771 knee MR examinations and identified 134 patients with an MR diagnosis of 138 parameniscal cysts and correlative arthroscopy in 78 patients. We reviewed their medical records and MR studies to determine the location of the cysts and presence of an underlying meniscal tear as determined by MRI or arthroscopy. There were 50 lateral and 88 medial parameniscal cysts. Medial meniscal tears were found underlying a cyst in 96% of arthroscopy patients and 86% of patients who had only MR examinations without a location difference in tears (p = 0.68). Meniscal tears were found on MRI or arthroscopy in all 28 patients with a lateral cyst overlying the body or posterior horn of the lateral meniscus, whereas a tear was found on MRI or arthroscopy in only 14 (64%) of 22 patients with cysts adjacent to or extending to the lateral meniscus anterior horn (p = 0.006). Anterior lateral cysts extended medially either into the root or into Hoffa fat-pad, but the type of extension did not correlate with the presence of an underlying meniscal tear. In contrast to medial parameniscal cysts or cysts at other locations adjacent to the lateral meniscus, anteriorly located lateral parameniscal cysts are less likely to have underlying meniscal tears.