MR diagnosis of discoid lateral menisci of the knee.

OBJECTIVE

To establish explicit criteria for MR imaging diagnosis of discoid lateral menisci of the knee.

SUBJECTS

Materials included surgically proved 38 discoid lateral menisci and 36 normal lateral menisci of adult patients. A discriminant analysis was used to identify the optimal cut-off points of the following eight parameters: (1) transverse width of a lateral meniscus on the coronal image at the midportion of a meniscal body; (2) ratio of transverse width between a lateral meniscus and a tibia; (3) height of the lateral margin of a lateral meniscus; (4) difference in height between lateral and medial menisci; (5) transverse area of a lateral meniscus; (6) the number of consecutive sagittal slices demonstrating continuity of the meniscus between the anterior and posterior horns (bow tie appearance); (7) height of the anterior horn of a lateral meniscus on the sagittal image; (8) height of the posterior horn of a lateral meniscus on the same sagittal image.

RESULTS

The transverse width of a lateral meniscus on the coronal image was the best parameter, with a cut-off point of 14 mm. Using this criterium, 33 knees of 38 discoid lateral menisci and all 36 normal menisci were correctly identified, yielding an overall accuracy of 93%.

CONCLUSION

A discoid lateral meniscus should be present if the transverse width of a lateral meniscus at the midportion of a meniscal body exceeds 14 mm, independent of the tibial width.