Baker's cyst, or popliteal cyst, is a fluid-filled mass that is a distention of a preexisting bursa in the popliteal fossa, most commonly the gastrocnemio-semimembranosus bursa. This bursa is unique in that it communicates with the knee joint, unlike other periarticular bursae, via an opening in the joint capsule posterior to the medial femoral condyle. Many have theorized that this opening creates a valve-like mechanism in the presence of effusion that contributes to the formation of these cysts in adults. Popliteal cysts rarely manifest alone and are most often found in conjunction with other intra-articular pathologies and inflammatory conditions, such as osteoarthritis, meniscus tears, and rheumatoid arthritis. In children, popliteal cysts are only occasionally associated with these conditions and are more often an incidental finding discovered during a routine physical examination. Popliteal cysts may present as either a chronically persistent or relapsing condition or as an acute and dramatic condition that can occur in the case of cyst rupture presenting as pseudothrombophlebitis. Ultrasound and magnetic resonance imaging have proven to be consistent and accurate in the confirmation of popliteal cysts, with magnetic resonance imaging becoming the modern imaging modality of choice. This review discusses the anatomy and etiology of popliteal cysts, describes the common clinical presentations, reviews the differential diagnoses, and provides guidance for proper diagnostic imaging. It also provides a comparison of current conservative, minimally invasive, and invasive treatment options, along with a discussion of results. Postoperative rehabilitation depends largely on the condition associated with the popliteal cyst.

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