Is cyst in the knee joint harmful?

I am 17 years old, studying in school. I have been diagnosed (after a MRI scan) with a parameniscal cyst in anterior and posterior horns of lateral meniscus of my left knee joint. Mild fluid collection has also been detected. I underwent an operation and got the cyst removed. The doctor said that this kind of thing is not possible at such a young age. Please cite the reasons for this diagnosis. Is it a serious problem? Is it some kind of cancer?

 

A meniscus is a soft cushioning structure in the knee. A cyst implies a collection of fluid within the structure and is always associated with a tear in the meniscus. In other words it follows some kind of injury which may go unnoticed. It can definitely occur at your age. It is not a cancer like condition and you need not have anxiety on this score. Usually it does not recur, even though it sometimes does.