What Is a Popliteal Cyst?

A popliteal cyst, also called a Baker's cyst, is an accumulation of synovial fluid in the back of the knee in an area called the popliteal bursa, according to Mayo Clinic. It can form as a result of joint inflammation, knee injury, arthritis or a cartilage tear.

When symptoms occur, physical activity usually aggravates them. Symptoms can include swelling behind the knee or the leg, knee stiffness and pain, explains Mayo Clinic. In rare cases a popliteal cyst can burst and cause a leak of synovial fluid into the calf region. This may cause sharp knee pain, swelling, redness, and the sensation of water running down the calf area. A burst popliteal cyst requires immediate medical attention to rule out other potential medical problems.

A doctor usually diagnoses a popliteal cyst by completing a thorough physical exam and conducting an ultrasound and magnetic resonance imaging, states Mayo Clinic. He also uses these diagnostic methods to rule out other potential knee problems that cause similar symptoms, such as a blood clot, tumor or an aneurysm. The treatment of a popliteal cyst includes medications that reduce joint inflammation, fluid drainage and physical therapy. A cyst that continues to refill with synovial fluid after drainage may require removal.