Popliteal Artery Aneurysm

The diagnosis of aneurysm of the popliteal artery means focal dilatation of this vessel - an abnormal expansion of its wall (in the form of protrusion), leading to an increase in lumen relative to the normal diameter of not less than 150%.

This is a disease of the circulatory system, of which the arteries are part, and according to ICD-10 its code is I72.4 (Aneurysm and stratification of the arteries of the lower extremities).

Epidemiology

Aneurysm of the popliteal artery is considered a rare disease, and its frequency is estimated in the population at 0.1–1%. However, among the  aneurysms of the peripheral arteries,  it is the most common: it accounts for 70-85% of aneurysms of the lower extremities. [1]

As clinical statistics show, the prevalence of this pathology increases with age, reaching a maximum of cases after 60-70 years. The main patients (95-97%) are men (most likely due to their predisposition to atherosclerosis). [2]

The presence of aneurysm of the popliteal artery in 7-20% of cases (according to other sources, in 40-50%) is associated with aneurysm in other vessels. In particular, in individuals with  abdominal aortic aneurysm, the  incidence of popliteal artery aneurysms is 28% higher than in the general population.

In addition, in 42% of patients (according to other data, in 50–70%) contralateral (bilateral) popliteal aneurysms are noted. [3]

Causes of the popliteal artery aneurysms

The popliteal artery (Arteria poplitea) - a direct continuation of the superficial femoral artery (Arteria femoralis) - passes between the medial and lateral heads of the calf muscle (behind the popliteal muscle) and supplies blood to the tissues of the distal lower extremity. Passing through the popliteal fossa, smaller vessels branch from the artery to the area of the knee joint, forming anastomoses that supply the joint with blood. Further, beneath the knee joint, there is bifurcation of the popliteal artery with division into the anterior tibial artery (Arteria tibialis anterior) and the tibial-peroneal or tibial-fibular trunk (Truncus tibiofibularis).

To date, the exact causes of aneurysms, including popliteal artery aneurysms, are unknown. Researchers suggest that the cause may be genetic or acquired defects of the media (Tunica media) - the middle membrane of the arterial vessels, as well as inflammatory processes, in particular, inflammatory arteritis. Perhaps the tendency of this artery to focal dilatation is associated with the stresses of the walls of the vessel during flexion-extension of the knee joint.

But most experts believe that atherosclerosis is the cause of popliteal aneurysm in 90% of cases  . [4],  [5], [6]

Risk factors

Modifiable risk factors include: dyslipidemia (elevated cholesterol and triglycerides in the blood), which is associated with atherosclerosis, as well as arterial hypertension, connective tissue pathologies (such as Marfan syndrome and Ehler-Danlos syndrome), smoking, diabetes and injuries. [7]

Non-modifiable risk factors include old age, male gender, Caucasian race and family history of aneurysmal disease.

The presence of an aneurysm in the family history should be taken into account, which may be indirect evidence of a mutation in the elastin gene or related proteins necessary for the formation and maintenance of elastic fibers that affect the mechanical properties of arterial walls.

The formation of a false aneurysm [8]is  [9]caused by a repeated injury to the arterial wall with a spike of the osteochondroma during flexion and extension of the knee. This recurring trauma leads to chronic abrasion of the popliteal artery and the adventitious defect followed by pseudo-aneurysm. [10], [11]

Treatment of a false aneurysm of the popliteal joint involves surgical removal of exostosis [12]and restoration of the vascular axis. Some authors suggest prophylactic removal of exostoses located on the vascular axis to prevent the onset of such accidents, while others suggest that surgical removal is indicated in the event of a malignant change or when the vascular axis is impaired.[13]

Pathogenesis

The popliteal artery is an extraorgan muscle-type distribution artery; Normally, its diameter varies from 0.7 to 1.5 cm, but it is different throughout the length of the vessel. And the average diameter of the enlarged area in most cases reaches 3-4 cm, although more significant dilatations are not excluded - up to gigantic aneurysms.[14]

The true pathogenesis of the popliteal artery aneurysm is unknown and is associated with several factors.

More and more studies confirm the relationship between the pathogenesis of aneurysms and changes in the structure of the vascular wall and its biomechanical properties. The latter directly depend on the components of the extracellular matrix of the artery wall, in particular, elastin and collagen fibers, which (together with smooth muscle tissue) form the middle membrane of the artery (middle layer of its wall) - media (Tunica media).

The dominant protein of the extracellular matrix of media is mature elastin - a hydrophobic connective tissue protein structurally organized in the form of plates, which also have smooth muscle cells (located in concentric rings) and collagen fibers. Thanks to elastin, the walls of blood vessels can be reversibly stretched, and the strength of the vascular wall is provided by collagen fibers.

The process of forming the walls of blood vessels, including elastogenesis - the transformation of the soluble monomeric protein tropoelastin (produced by fibro and chondroblasts, smooth muscle cells and endothelium), occurs during embryonic development, and their structure is constant throughout life.

But at the same time, with age or due to pathological effects, the structure of elastic fibers can change (due to destruction and fragmentation). In addition, inflammatory processes induce the synthesis of tropoelastin, which in adults is not able to transform into elastin. All this affects the biomechanics of arteries in the direction of reducing the elasticity and elasticity of their walls.

As for arterial hypertension and atherosclerosis, increased pressure causes stretching of the walls of the artery passing through the popliteal fossa. And the deposition of cholesterol on the intima of the vascular wall creates zones of narrowing of the artery, leading to local turbulence in blood flow, which increases pressure on the nearest section of the vessel and leads to a decrease in its wall thickness and a change in the structure of the medial layer.

Symptoms of the popliteal artery aneurysms

The first signs of a popliteal aneurysm, which at the initial stage is almost asymptomatic in almost half of the patients, are manifested by the presence of a palpable pulsating mass in the popliteal fossa.

Clinical manifestations of aneurysms include: ruptures (5.3%); deep vein thrombosis (5.3%); sciatic nerve compression (1.3%); leg ischemia (68.4%) and asymptomatic pulsating formations 15 (19.7%). [15]

According to a 2003 study, small popliteal artery aneurysms were associated with a higher incidence of thrombosis, clinical symptoms, and distal occlusion. [16]

As the pathological process progresses, paresthesia in the leg and pain under the knee are noted, which are the result of compression of the peroneal and tibial nerve. Also, pain can occur in the skin of the medial side of the lower leg, ankle or foot.

Due to compression of the popliteal vein, soft tissues of the lower leg swell. And with a progressive narrowing of the lumen of Arteria poplitea, associated with the formation of a blood clot, a symptom such as intermittent claudication appears.

In cases of acute thrombosis of the aneurysm, the pain intensifies and becomes sharper, the skin on the leg turns pale (due to ischemia), the fingers on the foot become colder and become cyanotic (their cyanosis develops).

Forms

Arterial aneurysm under the knee can affect one limb or both, and will be diagnosed, respectively, as one or two-sided.

In form distinguish between such types of aneurysms of the popliteal artery, such as spindle-shaped and saccular (in the form of a sac). Most popliteal artery aneurysms are spindle-shaped, and bilateral account for up to a third of cases.

Complications and consequences

Aneurysms of the popliteal artery cause thrombosis (blood clot formation) and embolization (moving clot fragments into smaller vessels) - with a high risk of limb loss. And these are their main consequences and complications.

According to some reports, aneurysmal sac thrombosis occurs in 25-50% of cases, which causes ischemia of limb tissues with a frequency of limb loss from 20% to 60% and mortality up to 12%. [17]A distal embolism leading to vascular occlusion is detected in 6-25% of patients with popliteal artery aneurysm.[18]

In every fourth case of thromboembolism, there is a need for amputation of the affected limb.

A rupture of the popliteal artery aneurysm is observed on average in 3-5% of cases. Popliteal aneurysms usually tear into the popliteal space, limited by muscles and tendons. The main symptoms are pain and swelling.[19]

Diagnostics of the popliteal artery aneurysms

Imaging is critical in diagnosing the popliteal artery aneurysm.

Instrumental diagnostics uses:

• standard angiography with contrast;
• two-dimensional ultrasonography or  duplex scanning of the arteries of the lower extremities ;

Ultrasound methods are very effective in screening painful formations of the popliteal space. These methods easily differentiate popliteal cysts from thrombophlebitis and, in addition, allow for a consistent assessment without discomfort for the patient. [20]

• CT or MR angiography.

Peripheral arterial blood flow is examined using ultrasound dopplerography of the vessels of the lower extremities.

Differential diagnosis

Differential diagnosis takes into account the possibility of the presence of patients with similar symptoms:

• cystic adventitious disease - the brush of the outer membrane of the wall of the popliteal artery (or Baker's cyst);
• inflammation of the popliteal lymph node;
• varicose veins of the popliteal vein;
• adventitia cyst (outer membrane of the wall) of the popliteal artery,
• syndrome of infringement of the dystopic popliteal artery ("trap" syndrome).

Treatment of the popliteal artery aneurysms

Asymptomatic aneurysms (up to 2 cm in size) are monitored under the supervision of duplex ultrasound, and conservative treatment of those diseases that are involved in the development of aneurysm is performed.

More details:

• Atherosclerosis Treatment
• High Cholesterol Treatment
• Limb angiopathy

Recently, if the operation does not put the patient at high risk, even vascular surgeons recommend eliminating even asymptomatic aneurysms due to frequent complications that occur even with small aneurysms.

Many doctors use a diameter of 2 cm with or without signs of thrombosis as an indication for preventive surgery, as evidenced by the 2005 recommendations of the American College of Cardiology / American Cardiology Association for Peripheral Artery Disease. [21] With asymptomatic aneurysms exceeding 4-5 cm, surgical intervention is required, since they can cause acute ischemia of the extremities, secondary due to vessel bending.

If symptoms are present, surgical treatment is required: either by open surgery, or by endovascular stent transplantation.

• Open surgical approach

With an open operation, ligation (ligation) of the popliteal artery above the knee and below the aneurysm is performed - with the exclusion of this section from the bloodstream, and then its reconstruction (revascularization) by installing an autologous transplant from the saphenous vein of the patient or an artificial vessel prosthesis. [22]

Surgical bypass surgery is considered the gold standard for the treatment of popliteal artery aneurysm (PAA), especially in young patients. [23]Large saphenous vein (GSV) is the ideal material, and prosthetic grafts are a reliable alternative to GSV for surgical bypass surgery.

• Endovascular approach

Recently, endovascular methods have gained popularity in the reconstruction of the popliteal artery as an alternative to an open surgical approach. This is achieved by excision of the aneurysmal sac with stent graft implantation. Recent studies show that popliteal artery stenting is a safe alternative treatment for popliteal aneurysm, especially in high-risk patients. The benefits of endovascular technique include a shorter hospital stay and shorter surgery time compared to open surgery. Disadvantages include higher 30-day graft thrombosis rates (9% in the endovascular treatment group versus 2% in the open surgical treatment group) and higher 30-day re-intervention rates (9% in the endovascular treatment group versus 4% in the open surgical treatment group) ) [24]

Acute thrombosis is treated with heparin (administered intravenously and by continuous infusion). And with threatening ischemia, they resort to thrombectomy, followed by shunting of the popliteal artery.

According to the 2007 Swedish National Survey, the incidence of limb loss within 1 year of surgery was about 8.8%; 12.0% for symptomatic and 1.8% for asymptomatic aneurysms (P <0.001). Risk factors for amputation were: the presence of symptoms, previous thrombosis or embolism, emergency treatment, an age older than 70 years, graft prosthetics and the absence of preoperative thrombolysis in acute ischemia. Amputation rate decreased over time (P = 0.003). The primary passability after 1 year, 5 years and 10 years was 84%, 60% and 51%, respectively. Overall survival was 91.4% for 1 year and 70.0% for 5 years. [25]

Prevention

Specific measures to prevent the development of aneurysms have not been developed, but it is important for vascular health: quit smoking, lose weight, control high blood pressure, cholesterol and blood sugar, as well as eat right and move more.

Early diagnosis of the popliteal artery aneurysm and surgical treatment before embolism, thrombosis and rupture are necessary to prevent formidable complications. [26]

Forecast

Timely identification of the popliteal artery aneurysm and its treatment provide a favorable prognosis. The absence of treatment increases the risk of complications by 30-50% for 3-5 years.

The most unfavorable outcome is amputation of the limb - with aneurysm rupture.