What are the characteristics of popliteal artery aneurysms?

Characteristics of Popliteal Artery Aneurysms

Popliteal artery aneurysms are the most common peripheral arterial aneurysms, with their natural history characterized primarily by thromboembolic complications rather than rupture. 1

Key Characteristics

• Popliteal aneurysms account for 70% of all aneurysms in the lower extremities, with an estimated incidence of 0.1% to 2.8% 1
• They occur predominantly in males (95-99% of cases) 2
• Approximately 50% are bilateral, and about 50% are associated with other aneurysms, particularly abdominal aortic aneurysms 1, 3
• They are true aneurysms (not false/pseudoaneurysms) involving all layers of the arterial wall 2
• Unlike abdominal aortic aneurysms, the natural history is one of thromboembolism or thrombosis rather than expansion and rupture 1

Clinical Presentation and Complications

• At least 40% of popliteal aneurysms are symptomatic at discovery due to thrombosis-in-situ or distal emboli 1
• Rupture is distinctly unusual, occurring in only about 7% of untreated cases 1
• Thrombosis accounts for approximately 10% of acute arterial occlusions in elderly men 1
• Limb ischemia is a common complication, with up to 36% of untreated popliteal aneurysms developing ischemic complications 1
• The cumulative incidence of ischemic complications can reach 70% during 5-10 years of follow-up 1

Natural History and Risk Factors

• Up to 50% of previously asymptomatic popliteal aneurysms become symptomatic within 2 years and 75% within 5 years 1, 3
• Symptomatic popliteal aneurysms generally exceed 2.0 cm in diameter 1
• Larger aneurysms have a higher risk of thrombosis, with a 39% thrombosis rate reported in one series, occurring most often in larger aneurysms 1
• Mural thrombus is often present and can be a source of distal embolization 1

Diagnosis

• Ultrasound is the recommended initial diagnostic test for patients with a palpable popliteal mass 1, 3
• Imaging should evaluate for contralateral popliteal aneurysms and abdominal aortic aneurysms, which frequently coexist 1, 3
• The presence of a prominent popliteal pulse in the opposite leg may suggest bilateral popliteal aneurysms 1, 3

Management Recommendations

• Patients with popliteal aneurysms 2.0 cm in diameter or larger should undergo repair to reduce the risk of thromboembolic complications and limb loss 1, 3, 4
• For asymptomatic aneurysms smaller than 2.0 cm, annual ultrasound monitoring is reasonable 1, 3
• In patients with acute ischemia and popliteal artery aneurysms with absent runoff, catheter-directed thrombolysis or mechanical thrombectomy is recommended to restore distal runoff 1, 3
• Without proper treatment, up to 19% of patients with symptomatic popliteal aneurysms may require amputation despite surgical repair 3

Common Pitfalls

• Popliteal aneurysm thrombosis is commonly mistaken for an embolic event, with the diagnosis often made intraoperatively during attempted embolectomy 1
• Severe ischemia usually occurs because thrombosis happens suddenly without collateral enhancement and because the popliteal artery is the sole axial artery traversing the knee 1
• Even after surgical repair of symptomatic popliteal aneurysms, 56% of patients may continue to experience distal ischemia due to prior emboli with thrombosis of downstream outflow vessels 1
• Delaying treatment of asymptomatic aneurysms can lead to significantly worse outcomes when they become symptomatic 1

Based on the evidence presented, the correct answer to the original question is (c) popliteal artery aneurysms are the most common peripheral arterial aneurysms.