A Baker cyst, also called a popliteal cyst, is a fluid-filled swelling that develops in the popliteal fossa, the space behind the knee. It typically forms when excess fluid from the knee joint, often caused by arthritis, a meniscus tear, or cartilage damage, herniates through a weak point in the joint capsule. On ultrasound, a Baker cyst appears as a well-defined, anechoic or hypoechoic fluid collection with a characteristic neck connecting it to the knee joint, often located between the medial head of the gastrocnemius and the semimembranosus tendon. Ultrasound is also important for detecting complications such as cyst rupture, which can mimic deep vein thrombosis by causing sudden calf swelling and pain.
Sonography Term