CASE 51

By: Dr. Subramaniyan Ramanathan MD and Dr. Mahmoud Alheidous

HISTORY: 17-year-old male with history of trauma 3 months back and now presenting with pain and locking.

What are your findings?

What is the differential diagnosis?

What are the causes?

FINDINGS:

Sagittal and coronal MRI shows abnormally wide body of lateral meniscus suggesting discoid meniscus. Diffuse intrameniscal signal changes with horizontal tear in body and posterior horn.

DIAGNOSIS:

Discoid lateral meniscus with horizontal tear.

PEARLS AND DISCUSSION:

A discoid meniscus is a common variant describing an abnormally enlarged meniscal body and reported to be seen incidentally found in 3-5% of knee MRI examinations. Discoid menisci are almost uniformly lateral and frequently bilateral (up to 50%) with a two to one female to male predominance.

The discoid meniscus can be asymptomatic or associated with degeneration and tearing because of its abnormal shape and altered mechanics. Children with lateral discoid meniscus may present with snapping knee syndrome in which the knee snaps with flexion and extension, more commonly seen with Wrisberg variant. Isolated tears of the lateral meniscus, particularly in younger children, should raise suspicion for an underlying discoid meniscus.

Radiographs can suggest the diagnosis with the widening of the lateral joint space and cupping of the lateral tibial plateau, which is normally flat or even slightly convex. MRI is definitive and the criteria for diagnosis include visualization of the meniscal body on at least three or more 4- to 5-mm contiguous sagittal images, at least 2 mm or greater measurable height difference between the discoid and normal meniscus on the coronal plane, or greater than 12 mm in width. Discoid meniscus can have associated anomalies like hypoplasia of the lateral tibial femoral condyle and tibial spine, and lateral joint space widening.

FURTHER READING:

1. Stark JE, Siegel MJ, Weinberger E, Shaw DW. Discoid menisci in children: MR features. J Comput Assist Tomogr 1995; 19:608 –611

2. Ryu KN, Kim IS, Kim EJ, et al. MR imaging of tears of discoid lateral menisci. AJR 1998; 171:963–967

3. Singh K, Helms CA, Jacobs MT et-al. MRI appearance of Wrisberg variant of discoid lateral meniscus. AJR. 2006;187 (2): 384-7