Discoid Lateral Meniscus-MRI

Discoid lateral menisci is a common problem. The normal configuration of a meniscus is that of a matured crescent moon, whereas that of a discoid meniscus generally is a thickened, very early crescent moon. Children with discoid meniscus usually present with a snapping knee joint, this snapping increases the chance of tearing the lateral meniscus as seen in this case. MRI is the modality of choice to evaluate a discoid meniscus before surgery.



Teaching Points :

Discoid meniscus is fairley common in children on clinical examination to come with snapping sounds of the knees.Clinical examination shows a senstivity of 88 % v/s an MRI sensitivity of only 38 % in various series.

There are 3 varieties – complete, incomplete and wrisberg variant.

Normal lateral meniscus covers approximately 70 % of the tibial plateau as compared to 50 % in case of medial meniscus.

The most acurate Radiological criteria is  a ratio of minimal meniscal width to the maximal tibial width exceeding 20 %. The others include squaring of the lateral tibial border, presence of osteochondritis dessicans at times, widening of the lateral joint space on X-ray.

The relative MRI criteria include minimal meniscal width on coronal of more than 15 mm, ratio of sum of both lateral  horns to the meniscal diameter of more than 75 %, absence of menico-capsular attachment and coronary ligaments on MRI.Discoid meniscus by its biomechanics, is more susceptible for shearing forces leading to tears more often. Treatment varies from conservasion to complete meniscectomy

Case by-

Dr.Sumer K Sethi, MD
Consultant Radiologist ,VIMHANS
CEO-Teleradiology Providers
Editor-in-chief, The Internet Journal of Radiology
Director, DAMS (Delhi Academy of Medical Sciences)