This patient had a parrot-beak tear at surgery. It is not known if it is congenital or acquired, but most are found in children or young adults. A discoid meniscus is felt to be more prone to a tear than a normal meniscus, and can be symptomatic even without being torn. Although they are easily identified on coronal images by noting meniscal tissue extending into the tibial spines at the intercondylar notch, they are most reliably diagnosed by noting more than two consecutive sagittal images that show the meniscus with a bowtie appearance. Figure 23 Figure 23 is an example in the coronal plane.
Meniscal tissue is seen going all the way into the notch.
This was a large discoid lateral meniscus. Two bowties is normal, fewer than two should suggest a bucket-handle tear, and more than two should suggest a discoid meniscus. The pitfalls are fairly straightforward, but unfortunately they are somewhat plentiful. First, there is small menisci in a child or a small adult. Also, the ratio will be normal.