What is a popliteal aneurysm and its typical features?

Popliteal Artery Aneurysm: Definition and Clinical Features

A popliteal aneurysm is a localized dilation of the popliteal artery to at least twice its normal diameter, characterized by high risk of thromboembolic complications rather than rupture, and requiring surgical intervention when reaching 2.0 cm or larger to prevent limb loss. 1, 2

Epidemiology and Demographics

• Account for 70% of all peripheral aneurysms in the lower extremities 1
• Estimated incidence of 0.1% to 2.8% 1, 3
• Predominantly affects men 1
• Approximately 50% are bilateral 1
• Approximately 50% are associated with other aneurysms, particularly abdominal aortic aneurysms 1, 4

Natural History and Pathophysiology

• Unlike abdominal aortic aneurysms, the natural history is one of thromboembolism or thrombosis rather than expansion and rupture 1
• Progression pattern:
  • Asymptomatic popliteal aneurysms have a high rate of becoming symptomatic
  • 50% become symptomatic within 2 years of discovery
  • 75% become symptomatic within 5 years 1
• Growth rate:
  • Aneurysms >2.0 cm: average growth of 1.5 mm per year
  • Aneurysms <2.0 cm: average growth of 0.7 mm per year 1

Clinical Presentation

• At least 40% are symptomatic at discovery 1
• Presentation patterns:
  • Asymptomatic pulsatile mass in the popliteal fossa
  • Acute limb ischemia due to thrombosis-in-situ (accounts for approximately 10% of acute arterial occlusions in elderly men) 1
  • Distal emboli to the calf or foot causing chronic ischemia
  • Pressure symptoms in the popliteal fossa 3, 5
  • Rarely, neurological symptoms like foot drop 5
  • Rupture is distinctly unusual 1, 3

Diagnostic Features

• Symptomatic popliteal aneurysms typically:
  • Exceed 2.0 cm in diameter
  • Often contain substantial mural thrombus on ultrasound imaging
  • Frequently associated with distal tibioperoneal arterial occlusions suggesting previous emboli 1
• Diagnostic workup:
  • Ultrasound is the initial diagnostic test of choice 1, 2
  • Patients with palpable popliteal mass should undergo ultrasound examination 1
  • Patients with confirmed popliteal aneurysm should be screened for contralateral popliteal aneurysms and abdominal aortic aneurysms 1, 2

Management Recommendations

• Surgical indications:
  • All symptomatic popliteal aneurysms 1, 2, 3
  • Asymptomatic popliteal aneurysms ≥2.0 cm in diameter 1, 2, 3
• Management of asymptomatic aneurysms <2.0 cm:
  • Annual ultrasound monitoring is recommended 1, 2
• Acute thrombosis management:
  • In patients with acute ischemia and absent runoff, catheter-directed thrombolysis or mechanical thrombectomy should be considered to restore distal runoff 1, 2, 6

Treatment Outcomes and Prognosis

• Complications of untreated popliteal aneurysms:
  • 36% of patients with observed aneurysms develop complications 1
  • Cumulative incidence of ischemic complications can reach 70% during 5-10 years of follow-up 1
• Post-treatment outcomes:
  • Even after surgical repair of symptomatic aneurysms, 56% of patients may continue to experience distal ischemia 1
  • Amputation rates of 19% have been reported after repair of symptomatic aneurysms 1
  • Open repair shows better patency rates than endovascular repair, particularly for acute ischemia (86.8% vs 47.6% at 1 year) 7
  • Vein grafts demonstrate superior patency compared to prosthetic grafts 7

Common Pitfalls

• Mistaking thrombosed popliteal aneurysm for an embolic event, often discovered during attempted embolectomy 1
• Failing to screen for contralateral popliteal aneurysms and abdominal aortic aneurysms 1, 2
• Delaying treatment of asymptomatic aneurysms ≥2.0 cm, which have high risk of complications 1, 2, 3
• Not considering popliteal aneurysm in the differential diagnosis of a popliteal mass 2