A cystic or a "cyst-like" lesion represents a common finding in a MRI examination of the knee. They are ususally fluid-filled bursae, synovial cysts of the popliteal space, meniscal cysts, ganglionic cysts or other fluid collections. The learning objective of this presentation is the description of above abnormalities and make the radiologist familiar and confident with their imaging features.

The cystic lesions of the knee represent a common clinical problem. Histologically they are divided in two types: ganlgia and synovial cysts (bursae). Ganglia are benign cystic lesions lined by a dense fibrous capsule containing internal viscous material. Ganglia may arise from joint capsules, ligaments, tendon sheaths, bursae or subchondral bone and generally do not communicate directly with the joint1. Sometimes ganglia may undergo process of synovialization. Synovial cysts are lined by synovial cells and ususally contain viscous fluid. Bursae are located between surfaces, where...

According to the location of a cystic or "cyst-like" lesion they can be categorised in posterior, anterior, medial, lateral and other cystic lesions. POSTERIOR KNEE Popliteal or "Baker" cysts are seen in 10-41% of the knee and the prevalence increases with the age and the presence of arthritis or knee effusions2.They are located in the medial gastrocnemius-semimembranosus bursa, which is composed by two parts, the gasstrocnemius and the semimembranosus bursa, that maybe partially separated by a central septum3(Fig.1). The typical location of a popliteal cyst...

Cysts and "cyst-like" lesions are a common finding inside and around the knee joint. MRI can demonstrates excellent all these lesions. The radiologists must be familiar about their appearances and differentiation, guiding thus specific treatment and avoiding unwarranted interventional procedures.

1. Haller J, Resnick D, Greenway G, et al. Juxtaacetabular ganglionic (or synovial) cysts: CT and MR features. J Comput. Assist. Tomogr. 1989;13:976-983. 2. Fielding JR, Franklin PD, Kustan J. Popliteal cysts: a reassessment using magnetic resinance imaging. Skeletal Radiol 1991;20:433-435. 3. Lee KR, Cox GG, Neff JR et al. Cystic masses of the knee: arthrographic and CT evaluation. AJR 1987;148:329-334. 4. Wigley RD. Popliteal cysts: variations on a theme of Baker. Semin. Arthritis Rheum. 1982;12:1-10. 5. Zidorn T. Classification of the suprapatellar septum considering...