Pictorial case study

THE CASE

A 68-year-old man presented in the surgery with slight discomfort in his right knee and an intermittent swelling behind the knee which caused a sensation of tightness. He did not recall any injury to his knee. He was otherwise well and on no medication.

Examination of his knee revealed a soft fluctuant swelling in the popliteal fossa which was tender to touch. Otherwise examination of the knee was normal. X-ray revealed the outline of a swelling in the popliteal fossa and mild degenerative changes in the knee. What is the diagnosis, management and differential diagnoses?

DIAGNOSIS AND MANAGEMENT

The diagnosis is a Baker's or popliteal cyst, which is a collection of fluid behind the knee. It is most commonly due to arthritis but can be caused by other knee injury such as a meniscal tear.

The cyst is continuous with the joint and indicates some knee joint pathology.

The cyst might be asymptomatic or might be painful. If very tense it may rupture.

Treatment of the cyst is not usually necessary but the underlying joint condition may need treatment with analgesia or referral to an orthopaedic surgeon if a meniscal lesion is suspected. If the cyst is very large it might rarely require aspiration or surgery.

POSSIBLE DIFFERENT DIAGNOSIS

- Lipoma.

- Sebaceous cyst.

- Anterior cruciate ligament tear or ganglion.

DIFFERENTIAL DIAGNOSIS

Lipoma

- Usually situated on the posterior area of the knee.

- Soft, benign tumour located superficially under the skin.

- It does not usually require treatment.

- Painless.

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