How to evaluate lower extremity aneurysms on ultrasound

Click here to read how to find and assess a lower extremity aneurysm on duplex ultrasound.
Last update26th Feb 2021

During the ultrasound evaluation of a patient, it’s important to check for aneurysms. Lower extremity arterial aneurysms are seen more often in the popliteal artery and less often in the common femoral artery (CFA).

Genetic disorders (such as Marfan’s syndrome) increase the chance of an aneurysm in other vessels. In patients without a genetic predisposition, the popliteal artery and the CFA are the most commonly affected vessels. This is believed to be because these two vessels are located in joint creases. So, they undergo frequent compression and can incur wall damage from repetitive microtrauma.

If a patient is found to have an abdominal aortic aneurysm, you’ll also want to spot check the CFA and popliteal artery for any evidence of aneurysms.

Figure 1. The two most common locations where a lower extremity arterial aneurysm can occur are within the popliteal artery and the common femoral artery (CFA).

Guidelines for defining an aneurysm on ultrasound

Aneurysms can be defined in two different ways on ultrasound:

  1. Comparison
  2. Direct measurement

The most important way to define an aneurysm is by comparison. In the lower extremities, arteries are considered aneurysmal if the vessel’s diameter increases by 1.5 times compared to the segment proximal to the suspected aneurysm.

With the direct measurement method, 10 mm is considered aneurysmal for the popliteal artery and 15 mm is considered mildly aneurysmal for the CFA.

Figure 2. Aneurysms can be identified on ultrasound by comparison or direct measurement. With the comparison method, a bulge is considered an aneurysm if it is 1.5 times greater in diameter than the proximal segment. With direct measurement, a bulge is considered an aneurysm if it is greater than or equal to 10 mm in the popliteal artery or 15 mm in the common femoral artery.

Steps for measuring an aneurysm on ultrasound

There are four steps for measuring an aneurysm on ultrasound:

  1. Make the aneurysm as circular as possible in the transverse view.
  2. Place the calipers from the outer wall to the opposite outer wall and include all of the mural thrombus. Measure the diameter of the aneurysm from anterior to posterior.
  3. Measure the nearest normal proximal segment for comparison.
  4. Switch to a longitudinal view and measure the aneurysm to confirm the transverse measurement.
Figure 3. When measuring an aneurysm on ultrasound in a transverse view, measure anterior to posterior from outer wall to outer wall and include the mural thrombus, if present.

When an artery has a stent graft placed to exclude a thrombotic aneurysm, you should still measure the aneurysm from the outer wall to the opposite outer wall in the transverse view. Also, check for an endoleak (a leak through the graft or at the graft end), which allows blood flow into the excluded aneurysm sac. An endoleak continually increases the size of the aneurysm and the risk of rupture.

Figure 4. An artery with a stent graft that has been placed to exclude a thrombotic aneurysm should be checked with ultrasound for an endoleak. Endoleaks allow blood flow into the aneurysm sac and increase the chance of rupture.

When taking measurements in a longitudinal view, also take anterior to posterior measurements (e.g., from the top of the screen to the bottom). The measurements should be taken as perpendicular as possible to the vessel walls to get the most accurate diameter.

Figure 5. When measuring an aneurysm in a longitudinal view, measure from top to bottom (e.g., anterior to posterior) and take the measurement as perpendicular to the vessel walls as possible.

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Recommended reading

  • Aboyans, V, Criqui, MH, Abraham, P, et al. 2012. Measurement and interpretation of the ankle-brachial index: a scientific statement from the American Heart Association. Circulation126: 2890–2909. PMID: 23159553
  • Cervin, A, Wanhainen, A, and Björck, M. 2020. Popliteal aneurysms are common among men with screening detected abdominal aortic aneurysms, and prevalence correlates with the diameters of the common iliac arteries. Eur J Vasc Endovasc Surg59: 67–72. PMID: 31757587
  • Cleveland Clinic. 2021. Leg and foot ulcers. Cleveland Clinic
  • Cleveland Clinic. 2021. Marfan syndrome. Cleveland Clinic
  • Cleveland Clinic. 2021. Popliteal artery entrapment syndrome (PAES). Cleveland Clinic
  • Cleveland Clinic. 2021. Statin medications & heart disease. Cleveland Clinic
  • Collins, L and Seraj, S. 2010. Diagnosis and treatment of venous ulcers. Am Fam Physician81: 989–996. PMID: 20387775
  • Høyer, C, Sandermann, J, and Peterson, LJ. 2013. The toe-brachial index in the diagnosis of peripheral arterial disease. J Vasc Surg58: 231–238. PMID: 23688630
  • Jaoude, WA. 2010. Management of popliteal artery aneurysms. SUNY Downstate Department of Surgery
  • Johns Hopkins Medicine. 2021. Aneurysm. Johns Hopkins Medicine
  • Kassem, MM and Gonzalez, L. 2020. “Popliteal artery aneurysm”. In: StatPearls [Internet]. Treasure Island (FL): StatPearls Publishing.
  • Moxon, JV, Parr, A, Emeto, TI, et al. 2010. Diagnosis and monitoring of abdominal aortic aneurysm: current status and future prospects. Curr Probl Cardiol35: 512–548. PMID: 20932435
  • Richert, DL. 2016. Gundersen/Lutheran Ultrasound Department Policy and Procedure Manual. Gundersen Health System
  • Rivera, PA and Dattilo, JB. 2020. “Pseudoaneurysm”. In: StatPearls [Internet]. Treasure Island (FL): StatPearls Publishing.
  • Stanford Medicine 25. 2021. Measuring and understanding the ankle brachial index (ABI). Stanford Medicine 25
  • Teo, KK. 2019. Acute peripheral arterial occlusion. Merck Manuals Professional Edition
  • The Regents of the University of California. 2020. Diabetic foot ulcers. UCSF Department of Surgery
  • Zwiebel, WJ and Pellerito, JS. 2005. Introduction to Vascular Ultrasonography. 5th edition. Philadelphia: Elsevier Saunders. (Zwiebel and Pellerito 2005, 254–259)

About the author

Elizabeth Tenny, BS RVT RDCS
Registered Vascular Technologist in the Department of Vascular Surgery, Stanford Health Care, USA.
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