How to assess and treat lower extremity arterial aneurysms
When peripheral arterial disease (PAD) occurs in the lower extremities, the causes can include atherosclerosis, aneurysm, or trauma. Let’s review the risk factors of lower extremity arterial aneurysms as well as symptoms and potential treatments for this type of PAD.
With true aneurysms, the artery wall layers become weak and balloon out. A vessel is considered aneurysmal when it is dilated at least 1.5 times the size of the proximal segment.
Figure 1. A bulge in a vessel is considered to be an aneurysm if it measures 1.5 times the size of the proximal segment.
Risk factors for lower extremity arterial aneurysms
There are seven known risk factors for lower extremity aneurysms:
- Male sex
- Disorders involving weak connective tissue
- Congenital vessel wall weakness
- Nicotine use
- Repetitive arterial compression
True aneurysms are more prevalent in biological males but can develop in anyone with weak connective tissue, such as Marfan’s syndrome. It can also occur in weak vessel walls, which is largely due to congenital disorders.
Hypertension and nicotine use are risk factors for aneurysms that develop over time. As well, repetitive compression, such as popliteal artery entrapment, can increase the risk of aneurysms. Aneurysms can also acutely occur from trauma.
Figure 2. Risk factors for a lower extremity aneurysm include male sex, disorders involving weak connective tissue, congenital vessel wall weakness, hypertension, nicotine use, repetitive arterial compression, and trauma.
Signs and symptoms of a lower extremity aneurysm
Signs and symptoms of a lower extremity arterial aneurysm can vary, depending on the patient’s situation:
- Pain and bulging or no symptoms
- Blue toe syndrome or acute ischemia
Pain and bulging or no symptoms
A patient with a lower extremity arterial aneurysm can present with pain and / or bulging in the area of the aneurysm. Aneurysms are usually painful if thrombotic or ruptured but are often otherwise asymptomatic.
Even if the patient is asymptomatic, a thorough and routine exam of the common femoral artery (CFA) and the popliteal artery can reveal a pulsating mass in the groin or behind the knee. Aneurysms can also be found incidentally on imaging of the CFA and the popliteal artery areas that was ordered for unrelated indications.
Asymptomatic aneurysms will likely have a normal ankle pedal pulse check and a normal ankle-brachial index (ABI) test. Normal pedal pulse checks and ABI results indicate that the aneurysm is not disrupting blood flow (yet).
Blue toe syndrome or acute ischemia
Occasionally, mural thrombus can occur with a true aneurysm. Mural thrombus, a coagulation of blood along the inner wall of an aneurysm, is associated with an increased risk of rupture and an embolism.
Aneurysms become symptomatic when a mural thrombus lodges in any number of toe arteries. This is referred to as blue toe syndrome, which is very painful and reflects sudden cyanosis.
Large embolic showers can block runoff arteries, causing acute limb ischemia of the calf and foot. A mural thrombus can also expand to occlude the aneurysm and completely block blood flow to the lower leg. These symptoms are emergencies, not only because of the risk of aneurysmal rupture but also because the lower extremities are at risk of irreparable damage that could result in amputation.
Figure 3. Blood coagulation along the inner wall of an aneurysm is called a mural thrombus, and is associated with an increased risk of rupture and embolism.
How to assess a lower extremity arterial aneurysm
If you palpate a pulsating mass or encounter blue toe syndrome, order an arterial duplex ultrasound rather than an ABI test. An ABI will show you the overall circulation in the lower extremities by providing waveforms and calculations. If a large aneurysm exists but is patent and allows normal blood flow to the ankles, it will not be detected by an ABI.
The arterial duplex ultrasound will obtain images of the artery and locate the aneurysm, which can then be examined and measured. For example, if a patient with a history of AAA was found to have a CFA aneurysm when they were scanned with a duplex ultrasound, the ABI for that patient would be normal.
Figure 4. An arterial duplex ultrasound can be used to locate an arterial aneurysm, which can then be examined and measured.
When and how to treat a lower extremity aneurysm
Asymptomatic lower extremity aneurysms smaller than 2 cm can be followed on serial duplex ultrasounds. When the aneurysm becomes larger than 2 cm, elective treatment is an option. If the aneurysm becomes symptomatic, treatment is necessary.
Table 1. Treatment recommendations for lower extremity arterial aneurysms based on size and symptoms.
Once a diagnosis has been made, three treatment options exist for true lower extremity aneurysms:
- Tie off the aneurysm and create a bypass.
- Cut the aneurysm out of the vessel and insert a bypass graft to reconnect the artery.
- Place a stent-graft through the arterial aneurysm so that blood directs through the stent only (e.g., excluding the aneurysm).
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