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Ischaemic foot: an unusual cause

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Q1: What do the Duplex scans show?

Duplex of right leg arteries show triphasic flow in the superficial femoral artery (fig 1, see p501). Flow in the popliteal artery is low resistance, low velocity, and monophasic (fig 2, see p501).

Q2: What does the MRA show?

The MRA shows occlusion of the right popliteal artery segment at the knee level with three vessels run-off in the leg (fig 3, see p501).

Learning points

  • PAES should be included in the differential diagnosis of ischaemic foot, claudication, or bizarre leg pains in young men, especially men.

  • MRA appears to be the most useful single investigation in the diagnosis of PAES.6

  • Prompt diagnosis enables treatment before arterial occlusion.

  • A missed diagnosis may have serious long term consequences in a young patient.

Q3: What are the causes of ischaemic foot?

Ischaemic foot is caused by atherosclerotic occlusive arterial disease, embolism, vascular injury caused by trauma, radiation, burns, and compression including popliteal artery entrapment syndrome (PAES), small artery obliteration caused by Raynaud’s disease, cystic degeneration of arterial wall, Buerger’s disease, diabetes mellitus, and scleroderma.

Discussion

PAES is a rare, under-diagnosed but eminently curable cause of intermittent claudication and lower limb ischaemia in young adults. It is much more common in males and the median age at presentation is 29 years (14–45).1 The male preponderance is possibly because of superior muscular development, and a similar syndrome is seen in athletes who are over trained.2 The anatomical abnormality leading on to the syndrome is essentially that of compression of the popliteal artery by the medial head of the gastrocnemius muscle in the popliteal fossa. This is due to the aberrant course of the artery, an atypical insertion of the muscle, or a combination of these two factors.3 Typically patients present with a long history of intermittent claudication, though occasionally they can present with acute leg ischaemia. Clinical examination demonstrates absence of pedal pulses if the popliteal artery is occluded resulting in a low ankle systolic pressure. Popliteal entrapment can be bilateral and it is essential that the contralateral side be screened if the condition is diagnosed in one limb.1 The diagnosis of PAES has traditionally been made on history, clinical examination, and angiography. Duplex imaging is now increasingly being used for diagnosis and screening but is considered to have a high false positive result.4 MRA demonstrates the abnormal anatomy clearly and the avoidance of radiation makes it preferable to computed tomography.5 Operative intervention and decompression is straightforward and involves freeing the artery from the entrapping muscle. Interposition vein grafting and femoropopliteal bypass grafting gives better results than simple thromboendarterectomy and vein patch if the popliteal artery is occluded.1

Final diagnosis

Popliteal artery entrapment causing ischaemia of the right leg.

References

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