my right knee is swollen around the entire knee and behind. It feels like something is inside that is causing an ever increasin feeling of pressure and an ache deep inside. my doctor examined it and said he thought it was a cyst behind the knee about the size of an egg. this condition has been going on since October, but in nov. i twisted it coming down a sttep hill of stairs, and since then it has slowly began to swell more and the whole knee became involved. i had ex-rays done of the knee and am seeing a specialist thurs. Could it be a tumor?