Baker Cyst on MRI: Imaging Findings

What your report says: “Baker's cyst” or “popliteal cyst”

Report wording you may see

• “Small popliteal (Baker's) cyst”
• “Distended gastrocnemius-semimembranosus bursa”
• “Ruptured Baker's cyst with fluid tracking into the calf”
• “Septated popliteal cyst with internal debris”

What it does and doesn't mean

• It is common. In one MRI study of older adults with knee osteoarthritis, a popliteal cyst was found in about a third of those with knee pain and in over a quarter of those without pain.
• It goes with effusion, meniscal tears and degenerative change: the more of these a knee has, the more likely a cyst is.
• “Ruptured” or “leaking” means fluid has escaped into the calf, which can cause sudden calf pain and swelling that looks like a blood clot.

When it tends to matter

Because the cyst is usually secondary, care tends to focus on the joint problem behind it. New calf swelling should be checked by a doctor promptly, as a ruptured cyst and a blood clot can look alike.

Questions for your doctor

• How large is the cyst, and does it connect to the joint?
• What inside my knee is likely feeding it: effusion, a meniscal tear or arthritis?
• Is there any sign of rupture or leakage into the calf?
• If my calf swells suddenly, what should I do?

A Baker's cyst (popliteal cyst) is a fluid-filled swelling behind the knee that typically communicates with the joint through a valvular mechanism between the semimembranosus tendon and the medial gastrocnemius. Baker's cysts are often secondary to intra-articular pathology such as meniscal tears, cartilage damage, or inflammatory arthritis.