Parameniscal cysts are a very common finding on a knee MRI. The word parameniscal means “next to the meniscus”. A cyst is simply a fluid-filled space or sack. These are different than the more common Bakers Cyst we tend to get in the back of our knee.
The meniscus is a c-shaped cartilage disc inside the knee. The meniscus helps to absorb stress to minimize the risk of developing arthritis. Meniscus tears are very common. In this popular post, we talk about whether or not a meniscus tear can heal on its own.
What is a parameniscal cyst?
If a meniscus tear has been present for a while then the fluid in our knee joint can leak out through the tear. The fluid will form a cyst. That fluid filled area is now called a “parameniscal cyst”. Sometimes these cysts can become quite large. Cysts that form on the inner part of the knee tend to be larger than cysts on the outer or lateral aspect of the knee.
Lateral meniscus cysts tend to be smaller than medial meniscus cysts because the very tight ITB tendon limits the growth of the cysts on the outside of our knee.
Lateral meniscus cysts also tend to hurt more than medial meniscus cysts because of the pressure they put on the ITB tendon.
Are parameniscal cysts dangerous?
A parameniscal cyst is not dangerous. They rarely need to be removed. In some patients, a parameniscal cyst will become very large. In those cases, the way to treat the cyst is to repair the meniscus tear. If the tear is repaired then fluid from within the knee can no longer enter the cyst. Surgery to remove a parameniscal cyst is very rarely needed. Once the tear is treated the cyst will usually go away on its own.