Popliteal artery aneurysms account for 70% of peripheral arterial aneurysms. Like aortic aneurysms, they are silent until critically symptomatic. However, unlike aortic aneurysms, they rarely rupture. The presenting manifestations are due to peripheral embolization and thrombosis. Popliteal aneurysms may embolize over time and occlude distal arteries. Due to the redundant parallel arterial supply to the foot, ischemia does not occur until a final embolus occludes flow. Acute ischemia caused by popliteal aneurysms has a poor prognosis due to the chronicity of the process. Approximately one-third of patients will require an amputation. The results of both chemical and mechanical thrombolysis may be disappointing because of clot age and adherence to the artery wall.
Pseudoaneurysms of the femoral artery following arterial punctures for arteriography and cardiac catheterization occur with an incidence ranging from 0.05% to 6%. Thrombosis and embolization are the main risks of femoral true or false aneurysms and should be repaired when greater than 2 cm in diameter.
These same complications can occur in a rare anomaly, persistence of the sciatic artery. In this anomaly, the large embryonic sciatic artery originates from the internal iliac artery and communicates directly with the popliteal artery. Persistent sciatic arteries have a propensity for aneurysmal degeneration, presenting as painful, pulsatile buttock masses. There is no femoral artery. The diagnosis of a persistent sciatic artery is suggested by the absence of a femoral pulse with intact popliteal and pedal pulses. The prevalence is 0.25:1000 patients studied by angiography.
Symptoms and Signs
Until progressive stenosis or thrombosis occurs, peripheral artery aneurysms are usually asymptomatic. The patient may be aware of a pulsatile mass when the aneurysm is in the groin, but popliteal aneurysms are often undetected by the patient and physician. Peripheral aneurysms may produce symptoms by compressing the local vein or nerve, but this is unusual. In most patients, the first symptom is due to ischemia. The pathologic findings range from rapidly developing gangrene to moderate ischemia that slowly lessens as collateral circulation develops. Symptoms from recurrent embolization to the leg are often transient if they occur at all. Sudden ischemia may appear in a toe or part of the foot, followed by slow resolution, and the true diagnosis may be elusive. The onset of recurrent episodes of pain in the foot or hand, particularly if accompanied by cyanosis, suggests embolization and requires investigation of the heart and proximal arterial tree.
Because popliteal pulses are somewhat difficult to palpate even in normal individuals, a particularly prominent or easily felt pulse is suggestive of aneurysmal dilation and should be confirmed by ultrasound. Since popliteal aneurysms are bilateral in 60% of cases, the diagnosis of thrombosis of a popliteal aneurysm is often aided by the palpation of a pulsatile aneurysm in the contralateral popliteal space.
Arteriography may not demonstrate aneurysms accurately, because mural thrombus reduces the apparent diameter of the lumen. Nevertheless, arteriography is advised—especially when operation is considered—to define the status of the arteries distal to the aneurysm.
Duplex color ultrasound is the most efficient investigation to confirm the diagnosis of peripheral aneurysm, to measure its size and configuration, and to demonstrate mural thrombus.
Treatment of Peripheral Arterial Aneurysms
Early operation is indicated for any peripheral embolization, size greater than 2 cm or an aneurysm with mural thrombus. Immediate or urgent operation is indicated when acute embolization or thrombosis has caused acute ischemia. Intra-arterial thrombolysis may be done in the setting of acute ischemia, if examination (light touch) suggests that immediate surgery is not imperative. Bypass with saphenous vein may include either excision or exclusion, by proximal and distal ligation, depending upon location. If exclusion rather than resection is performed, the geniculate “feeder” arteries within the aneurysm must be ligated or progressive enlargement can still occur.
Acute pseudoaneurysms of the femoral artery due to arterial punctures can be successfully treated using ultrasound-guided compression. Open surgery with prosthetic interposition grafting is preferred for primary aneurysms of the femoral arteries, popliteal arteries. Endovascular repair with small stent-grafts has been done but is reserved for high-risk patients.
Persistent sciatic artery aneurysms are treated by exclusion of the aneurysm by surgical techniques or endovascular techniques and a femoral-popliteal bypass.