Discoid Meniscus

This MRI study of knee joint depicts discoid lateral meniscus.

No obvious associated meniscal tear or para meniscal cyst.

Discoid meniscus

This is a congenital condition and is bilateral in about 50% of the cases. Usually encountered as an incidental finding on MRI examination in about 5% of the cases, typically affecting lateral meniscus. Discoid medial meniscus is very rare.

The pathology behind  this discoid shape is loss of normal orientation of collagen fibres of meniscus.

Frequently this is an asymptomatic condition however the discoid meniscus has propensity for pressure, wear and tear leading early cystic degeneration, meniscal tear and para meniscal cyst formation. In such cases patient may present with knee pain with or without locking. 

MRI is the investigation of choice. 

The width of the body of meniscus, if 15 mm or more on coronal section is diagnostic of discoid meniscus. The body of the lateral meniscus is normally has bowtie configuration on sagittal section and seen only on two consecutive slices. If the meniscal body is seen on three or more consecutive slices while scrolling the sagittal sections, instead of normal bowtie tie should alarm of discoid morphology. 

The observation is usually managed conservatively if patient is not symptomatic. 

Partial or total resection is the option kept in front of patient if accompanied with complications like tear.