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Q1: What is the likely diagnosis?
The differential diagnosis of calf swelling includes deep vein thrombophlebitis, a popliteal cyst, popliteal varices or artery aneurysm, ganglia, neural tumours, sarcoma, and haemangioma.
When the swelling is associated with tenderness, diagnostic considerations should include tear of medial head of gastrocnemius or plantaris muscles, cellulitis, fasciitis, compartment syndrome, venous insufficiency, and ruptured popliteal cyst.1
One of the most common and clinically important diagnosis is DVT. Since it leads to pulmonary embolism, prompt anticoagulation is indicated. On the other hand, anticoagulation after ruptured Baker's cyst can cause bleeding and posterior compartment syndrome.2
Q2: WHAT PHYSICAL EXAMINATION SIGN WAS THE CLUE FOR THE FINAL DIAGNOSIS?
Ruptured Baker's cyst simulates DVT of the calf veins, both causing painful, swollen calf with overlying skin erythema. Homan's sign, an accepted but non-sensitive sign,3 may also appear in both. Ecchymosis of the foot, especially in a malleolar region, termed the haemorrhagic crescent sign, has been reported after this rupture.4 Although this is a relatively rare finding, it is not found in DVT, and its presence should lead the clinician to the diagnosis of ruptured Baker's cyst.
Q3: WHAT ARE THE DIAGNOSTIC MODALITIES YOU WOULD USE TO CONFIRM THE DIAGNOSIS?
Ultrasound (duplex scan) is the method of choice for evaluation of posterior calf disease, although it may be difficult to diagnose Baker's cyst after its rupture. Recently, with improvement of ultrasonic images, this method can simultaneously confirm ruptured Baker's cyst and exclude DVT. Alternative imaging modalities are magnetic resonance imaging and computed tomography. Previously, the gold standard diagnostic method for ruptured Baker's cyst was an arthrogram. In this procedure the knee joint is injected with contrast material, and after mobilisation of the extremity, the radiographic dye can be demonstrated in the cyst and extravasating to the surrounding calf structures.5
Q4: WHAT TREATMENT IS INDICATED?
Ruptured Baker's cyst is treated by elevating the affected extremity, local heating, and intra-articular corticosteroid injection after aspiration of the synovial fluid from the knee.
In our patient diagnosis of ruptured Baker's cyst was confirmed by ultrasonic examination obtained during his visit to the rheumatology clinic. A fluid collection along the intermuscular fascia layers of the calf (fig 1 below) was demonstrated. The patient was treated as described above, with disappearance of the symptoms within two weeks.
Popliteal cyst is usually caused by tear of the knee joint capsule, allowing a communication between the joint space and gastrocnemius or semimembranous bursa. It was named after the British surgeon William Morton Baker, who described an association of this cyst with knee synovitis. Popliteal cysts are secondary to degenerative (osteoarthritis) or inflammatory arthritis with increased synovial fluid production. The most common complication of Baker's cyst is a rupture. This is usually caused by a rise in intra-articular pressure during powerful knee extension.
Extravasation of inflammatory and proteolytic content of synovial fluid leads to inflammation of surrounding calf structures. The patient with a ruptured cyst will therefore present with a hot, red, tender and swollen posterior calf, while the cyst is no longer palpable, and the knee is less swollen. Homan's sign may be positive in both DVT of the calf and ruptured Baker's cyst. Thus the two entities are almost indistinguishable by physical examination.
The only clinical sign differentiating ruptured Baker's cyst from DVT is bruising below the malleolus. This results from drainage of inflamed synovial fluid dissecting the calf structures to the foot. Discoloration of the malleolus area should therefore alert the physician to the diagnosis of ruptured Baker's cyst.3
Finally, DVT and Baker's cyst are not mutually exclusive diagnoses as the cyst pressure on a calf vein may cause stasis and thrombosis.6
Ruptured Baker's cyst.