What is Popliteal Artery Aneurysm?

A popliteal artery aneurysm happens when the width of the popliteal artery, a significant blood vessel in your leg, expand more than 50% from its usual size. Usually, the diameter of this artery is between 0.7 and 1.1 cm. These aneurysms can look like fusiform, where the dilation is spread out, or like saccular, where the dilation is unequal. In fact, they make up 85% of all peripheral aneurysms, which are abnormal widenings in a blood vessel.

Something to be aware of is that popliteal artery aneurysms are often found together with abdominal aortic aneurysms, a condition where the aorta, the main blood vessel supplying blood to your body, expands abnormally. About 40% to 50% of people with a popliteal artery aneurysm also have an abdominal aortic aneurysm.

For a bit of context, the popliteal artery is actually an extension of the superficial femoral artery, which is the blood vessel running along your thigh. This artery continues down your leg, passing through an opening in the adductor magnus, a large muscle in your thigh. The artery then goes through the popliteal fossa, the hollow at the back of your knee, next to a vein. It finally ends by splitting into two arteries, the anterior tibial artery and the tibioperoneal trunk, at the bottom border of the popliteus muscle, a small muscle at the back of your knee, around the level of your shinbone’s bump.

What Causes Popliteal Artery Aneurysm?

Certain lifestyle choices and health conditions can increase your chances of developing an aneurysm. Modifiable risk factors – ones that can be changed or managed – include smoking, atherosclerosis (a condition where the arteries thicken and harden), and connective tissue disorders such as Marfan syndrome or Ehlers-Danlos syndrome.

Some factors we cannot change are also associated with a higher risk of aneurysms. These non-modifiable risk factors include getting older, being male, being of White ethnicity, and having a family history of aneurysmal diseases. These are factors we can’t modify but knowing about them can help in early diagnosis and treatment.

Risk Factors and Frequency for Popliteal Artery Aneurysm

The number of people affected by popliteal artery aneurysms (an abnormal widening of the popliteal artery) isn’t exactly known because no broad studies have been conducted. However, several reports from various institutions indicate that its prevalence increases with age and is most common in one’s 60s or 70s. Those with abdominal aortic aneurysms, a condition that also involves abnormal artery enlargement, seem to be more likely to also have popliteal or femoral (thigh) aneurysms. A study involving 225 patients showed varying degrees of popliteal artery aneurysms:

About 28% (or 63 people) had an aneurysm that was 10.5 mm or larger.
Approximately 19% (or 43 people) had an aneurysm that was 12 mm or larger.
About 11% (or 25 people) had an aneurysm that was 15 mm or larger.

Signs and Symptoms of Popliteal Artery Aneurysm

Popliteal artery aneurysms often don’t present with symptoms. However, if symptoms do arise, they might be due to the aneurysm’s size putting pressure on neighboring body parts. For instance, it may press against the tibial nerve leading to leg pain or numbing sensations. Similarly, compression of the popliteal vein may result in swelling in the calf. Additionally, the popliteal artery may narrow due to a clot formation, causing an onset of pain while walking. Noteworthy is that about half of the patients have aneurysms on both sides.

When an aneurysm suddenly forms a clot, it might result in symptoms of acute lower extremity ischemia. This condition can cause sudden pain, numbing sensations, paralysis, pale skin, and irregular temperature in the affected area. And this can be due to either the clot formation within the aneurysm or the clot that travels and blocks downstream vessels. A manifestation of the latter might include “blue toe syndrome” or bluish discoloration of the fingers or toes. Without treatment, about 30% of patients may experience acute clot formation and clot migration, running the risk of possible limb loss. Furthermore, the outcome for those who develop acute clot formation or embolism isn’t generally good, with a 15% risk of amputation due to blocked vessels providing outflow. It is worth mentioning that an examination should be done on both sides of the back of the knee with the knee semi-bent. About 60% of patients with popliteal aneurysms have a pulse that can be felt at the knee joint level.

Testing for Popliteal Artery Aneurysm

If your doctor suspects that you have a popliteal artery aneurysm (a swelling in the artery behind your knee), they may use a type of ultrasound called a duplex ultrasonography to confirm this. This procedure allows them to see the blood vessel in detail, check if it’s functioning correctly, and measure its diameter. They can also check for a blood clot, which can form in the thick wall of the artery.

If the duplex ultrasonography isn’t suitable or doesn’t provide enough information, they might also consider other types of scans such as Computed Tomography (a type of detailed X-ray) or magnetic resonance angiography (a type of MRI scan that uses magnetic field and radio frequency waves to provide pictures of blood vessels inside the body). These scans can also measure the exact size of any swelling in the artery and help the doctor plan for any surgery that might be needed.

Sometimes, a conventional angiography might be used. This is a type of X-ray that uses a contrast material (dye) and a camera to take pictures of blood flow in an artery. This test is usually done in more serious cases, for instance, if the doctor is considering a non-surgical procedure to repair the aneurysm, or if there is a risk of sudden acute limb ischemia, a severe lack of blood flow to your limbs that requires immediate treatment.

Treatment Options for Popliteal Artery Aneurysm

If you have symptoms of popliteal artery aneurysms, which are enlarged blood vessels behind your knee, you’ll need to have them fixed. This is crucial to prevent blood clots or losing the limb. If the aneurysm is more than 2 cm across but doesn’t cause symptoms, doctors usually recommend surgery to prevent dangerous events like critical limb ischemia, which is severe lack of blood flow. Surgery is usually suggested if the aneurysm tilts more than 45 degrees, even if you don’t have symptoms, to avoid sudden blood flow blockage caused by bending of the blood vessel.

Popliteal artery aneurysms smaller than 2 cm that don’t cause any symptoms can be watched over with duplex surveillance, which is an imaging test that evaluates blood flow to your leg arteries. But larger aneurysms may need surgery.

The conventional way to fix a popliteal artery aneurysm is through an open surgery. In this process, the blood vessel above and below the bulging part is tied up and a graft is used to shunt blood flow around the trouble spot. This graft might be a vein taken from your body (saphenous vein) or a synthetic graft. Another method involves removing the aneurysm and using a graft to reconnect the healthy parts of the blood vessel above and below it. However, the first method is more common.

Another modern and popular method is called an endovascular approach. This allows the surgeon to fix the aneurysm by placing a metal mesh (stent) inside the blood vessel. This approach can offer shorter hospital stays and less time in surgery compared to open surgery. However, it does have higher chances of needing a repeat procedure, including clotting of the stent within 30 days after the surgery. But both methods are considered safe and have similar risks for death or limb loss.

If you have a blood clot in your popliteal artery aneurysm, the treatment strategy depends on your specific situation. If you are not experiencing symptoms or are unable to walk, or if despite clot-dissolving treatment (thrombolysis) you have poor blood flow, doctors might not recommend surgery. Surgical bypassing of the blood vessel is usually preferred if you have severe symptoms or your limb is at significant risk. If you’re experiencing a sudden, severe lack of blood flow to your limb, urgent bypass surgery may be needed. An intravenous medicine to prevent clotting (heparin) is also given continuously to stop clot extension. Some doctors believe that emergency removal of the clot (thrombectomy) followed by bypass surgery might be better if limb-threatening ischemia is suspected.

Regarding detection of multiple blood clots in your leg arteries, intravenous clot-dissolving treatment followed by opening the blood vessel with a graft might be your best option, especially for older, symptom-free patients with popliteal artery aneurysms. The occurrence of popliteal artery aneurysms in the general population is not very common. Therefore, screening of unselected patients is not cost-effective. But if you already have a popliteal artery aneurysm, there’s a good chance you might also have it on the other side or in the belly (abdominal aortic aneurysm). Depending on several factors- younger age, availability of suitable vein for grafting, potential complications with the blood flow to your leg, and lower surgery risk- open surgery might be the preferred option. Endovascular repair might be the better choice if you are older, don’t have a suitable graft, or are at a higher risk during surgery.

If your blood flow to your toes or foot (tibial or pedal runoff) is poor, open surgery using a graft is usually the better option for patients at moderate risk. However, for high-risk patients, especially those with high cardiovascular risk or severe venous stasis or lymphedema (swelling in legs), management becomes a challenge. If you are not expected to live long and have an asymptomatic popliteal artery aneurysm, watchful waiting is usually preferred. If treatment is needed in such cases, the less taxing endovascular repair, with potentially less postsurgical headaches, is preferred over open surgery, irrespective of graft availability or quality of blood flow to the feet.

For patients with conditions involving the weakening of connective tissues in the body, it is unclear whether open or endovascular repairs are a better option for repairing a popliteal aneurysm. Using endovascular approaches in such cases is generally not preferred due to the risk of damaging a weak artery and causing further enlargement of the blood vessel. Although some experts might still suggest caution, recent experiences have yielded hopeful results with the endovascular approach. As of now, the best graft for open reconstruction is not known, while synthetic grafts have shown inferior results in the long term with vein grafts possibly leading to aneurysms.

When trying to diagnose a particular medical condition, doctors need to consider other illnesses or medical conditions that may have similar symptoms. In medical terms, this is called a “differential diagnosis.” When doing a differential diagnosis, doctors may need to rule out:

Baker cyst: a fluid-filled cyst that causes a bulge and a feeling of tightness behind your knee.
Lymph node: These small, bean-shaped structures produce cells which fight infection and are a crucial part of our immune system.
Varicosity: This refers to varicose veins, which are swollen, twisted veins that you can see just under the surface of the skin.
Cystic adventitial disease: This is a rare vascular condition that primarily affects young men and can cause claudication or leg pain.