Popliteal cysts in adults: A review*,**

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Abstract

Objective: To review the epidemiology, clinical presentation, pathogenesis, imaging, differential diagnosis, complications, and treatment of popliteal cysts. Methods: References were taken from MEDLINE from 1985 to 1998 under the subject “Popliteal Cyst” with subheadings of Radiography, Ultrasonography, and Radionuclide Imaging. Other pertinent references were used. Childhood cysts were excluded. Results: Depending on the studied population and the imaging technique, 5% to 32% of knee problems may have these cysts, with 2 age-incidence peaks of 4 to 7 years and 35 to 70 years. In older patients there is usually coexistent joint pathology. Symptoms may arise in the popliteal fossa from the cyst itself or be dominated by knee pain from coexisting knee pathology. Many cysts are asymptomatic. Physical examination will miss one half of these cysts. Pathogenesis depends on the connection between the joint and bursa, with a valvelike effect allowing passage of fluid from the joint into the bursa with subsequent distention producing these cysts. Some bursae have no such joint-bursal communication, and the cysts arise primarily as bursitis of the gastrocnemio-semimembranosus bursa. Imaging is performed by plain x-ray, ultrasound, arthrography, computerized axial tomography, magnetic resonance imaging, or nuclear scan; sonography is the method of choice. Complicated cysts with extension or rupture into the calf mimic phlebitis, an important differential diagnosis. Asymptomatic cysts found incidentally need no treatment; most symptomatic cysts respond to intra-articular corticosteroid injections. Surgical excision is rarely necessary. Conclusions and Relevance: Popliteal cysts are fairly common, may not be found on physical examination, require imaging (preferably sonography) to be identified, mimic phlebitis when extending into the calf, and often respond to intra-articular steroid or, rarely, surgical resection. Semin Arthritis Reheum 31:108-118. Copyright © 2001 by W.B. Saunders Company

Section snippets

Epidemiology

The presence of popliteal cysts varies depending on the technique of investigation and the studied population. Of 400 consecutive magnetic resonance imaging (MRI) studies from patients referred for knee problems to an orthopedic clinic, 77 (19%) popliteal cysts were found (4). Of 1,113 MRI studies (5) of knees evaluated for internal derangement, 55 (5%) had cysts. Using arthrography (6) to find internal derangement, 58 of 247 (23%) knees from military aircrews and 64 of 202 (32%) knees from a

Clinical presentation

The usual patient complaints resulting from popliteal cysts are swelling, a mass, pain, or stiffness, often aggravated by activity. There may be a bulge and tightness in the back of the knee on walking (2) or vague posterior knee pain (1). A mass was the chief concern in 68 of 82 patients with surgically treated cysts (3). Forty-six of the 82 had local “aching” and 13 were stiff. Nine of the 82 had knee swelling; 7 of these 9 had no recognized joint pathology. One third of the 82 had no

Pathogenesis

The pathogenesis of popliteal cysts is explained by the interconnection between the knee joint and the bursae, as well as fluid mechanics. Such a connection was found in 30% to 50% of cadaveric dissections 1, 21, 22, 23, 55% of surgically proven cysts (7), 37% of arthroscopically examined knees (24), and in 50% of arthrograms of normal knees (25). By injecting dye into the knee joint as well as directly into the cysts, a valvelike mechanism has been shown (26). During flexion the communication

Cysts: Pathologic or physiologic?

The presence of G-S bursal filling, even large distentions, does not necessarily indicate disease (25). Arthrographically, clinically evident cysts are no different than nonclinically appearing (6). Of 940 arthrograms for suspected meniscal tears, 234 cysts were found of which 179 were asymptomatic (32). The author believed these were normal variations of the G-S bursa. Of 62 patients with cysts shown by arthrography, 56% had no palpable mass and only 35% had popliteal fossa pain (17). The 10

Imaging

Figures 1 to 3 show some arthrogram characteristics of popliteal cysts.

. Arthrogram of an uncomplicated knee cyst after intra-articular injection of air and positive contrast dye. (Reproduced with permission (6).)

. Arthrogram showing filling of a popliteal cyst dissecting into the calf. Cyst contour is smooth. (Reproduced with permission (77).)

. Arthrogram dye flowed into the smoothly contoured dissecting cyst in this calf (arrowhead). Note the feathery contour of the ruptured cyst (arrow).

Associated conditions and differential diagnosis

Knee pathology associated with popliteal cysts includes OA, RA, and torn meniscus, with rarer associations including tuberculosis, Charcot joint, pigmented villonodular synovitis, Reiter's syndrome, gonococcal arthritis, and Still's disease (2). Medial meniscal posterior horn lesions may cause cysts by producing synovitis 49, 69. The differential diagnosis of popliteal cysts 2, 48 includes popliteal artery aneurysm, venous thrombosis, lipoma, liposarcoma, popliteal varices, hematoma, ganglionic

Complications: Pseudothrombophlebitis

The imperative consideration in the differential diagnosis is to distinguish DVT from ruptured popliteal cyst 17, 71, 72, 73, 74. Missed thrombophlebitis risks pulmonary embolism, and anticoagulants, given for a dissecting cyst falsely diagnosed as thrombophlebitis and perhaps requiring hospitalization, may cause cyst hemorrhage with prolonged convalescence (75).

The enlarged cyst, compressing an adjacent vein, may cause lower leg and ankle swelling, mimicking venous thrombosis (71).

Cyst complications

Dissecting cysts are more common than ruptured cysts (17). Crescentic violaceous discoloration inferior to the malleolus, not seen in venous thrombosis, is occasionally present in cyst rupture, as the bloody synovial fluid dissects inferiorly and is strong evidence against thrombosis (83), although the ecchymosis may be on the dorsum of the foot (84). A hemorrhagic ruptured cyst produces an ecchymosis of the posterior calf from the popliteal fossa to the ankle (85). Arthrographically, a

Treatment

Asymptomatic popliteal cysts found incidentally need no treatment. Symptoms may require bed rest, although no details of bed rest (eg, duration, frequency, or benefit) could be found in the literature. If knee effusion is present, joint aspiration with intra-articular corticosteroids usually is beneficial. If necessary, contrast dye can be instilled into the joint through the same needle (2). There are numerous descriptions of rapid improvement of popliteal cysts, with or without calf

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    Address reprint requests to John R. Handy, MD, 2916 Sussex Rd, Augusta, GA 30909.

    **

    John R. Handy, MD: Associate Clinical Professor of Medicine, Division of Rheumatology, Department of Medicine, Medical College of Georgia, Augusta, GA.

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