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Findings: Coronal T1-weighted and sagittal turbo spin density-weighted images of the knee from an 0.2T open scanner are present.

Diagnosis: Discoid lateral meniscus with a tear.

Discussion: A discoid meniscus is an abnormally enlarged meniscus. The abnormal shape may range from generalized enlargement to a diffuse slab of meniscal tissue which fills the entire compartment. Discoid menisci occur most commonly within the lateral meniscus. Patients present in their teens or twenties with symptoms of a meniscal tear. At the time of MR imaging a discoid meniscus is recognized by the enlarged shape. Continuous meniscal signal is seen on three or more sagittal images that are 5 mm thick. On coronal images meniscal tissue extends closer to the notch than a normal meniscus and the height of the discoid meniscus may be 2 mm or greater than the opposite meniscus. Criteria for tear within a discoid meniscus are the same as for tear within any other meniscus.

References:
Silverman JM, Mink JH, Deutsch AL. Discoid Menisci of the Knee:
MR Imaging Appearance. Radiology 1989;173-351-354.

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