My calf suddenly swelled and hurts. Is it a burst Baker's cyst or a blood clot?

Why the two look alike

When a Baker's cyst leaks or bursts, joint fluid tracks down between the calf muscles. That causes sudden pain, tightness and swelling in the calf, sometimes with a feeling of warm fluid running down the leg and, days later, a bruise-like discolouration near the ankle.

A deep vein thrombosis, a clot in a deep calf vein, causes very similar swelling, warmth and aching. A clot can travel to the lungs, which is why doctors always rule it out first rather than assume the cyst is to blame. A cyst can also press on the veins and sit alongside a clot.

Go now if

• The calf is suddenly swollen, tight or painful, with or without a known cyst
• You have recently had a long flight, surgery, a plaster cast or a long period of immobility
• You feel short of breath, have chest pain or cough up blood: call 999 in Qatar
• The leg becomes very tense, pale, numb or difficult to move

What happens at the hospital

An ultrasound of the leg veins is the key test. It shows whether there is a clot and often shows fluid from a leaked cyst at the same time. Blood tests may be added. If there is a clot, it is treated with blood-thinning medicine under medical supervision.

If the scan confirms a leaked cyst without a clot, the calf usually settles over one to a few weeks with rest, elevation, ice, compression and simple pain relief. The fluid is gradually reabsorbed by the body.

After it settles

A burst cyst is a sign that the knee is producing too much fluid. Once the calf has calmed, book a knee assessment to find and treat the cause, such as arthritis or a meniscus tear, so the cyst is less likely to refill and leak again. At Aman Hospital in Doha, Dr. Gelber examines the knee and uses MRI or X-ray where needed to plan treatment.