eMedicine Specialties > Radiology > Vascular/Interventional

Lower-Extremity Atherosclerotic Arterial Disease

Author: Chadi Chahin, MD, Staff Physician, Department of Radiology, Aultman Health Foundation/Mercy Medical Center
Coauthor(s): Barry Rose, MD, Associate Professor of Radiology, Northeastern Ohio Universities College of Medicine; Program Director, Department of Radiology, Aultman Hospital; Sam Stuhlmiller, MD, Consulting Staff, Department of Radiology, Aultman Hospital
Contributor Information and Disclosures

Updated: Feb 9, 2007

Introduction

Background

Atherosclerosis is the leading cause of occlusive arterial disease of the lower extremities. Atherosclerosis is also a leading cause of death and disability in the developed world. The term is derived from the Greek sclerosis, which refers to the thickening of the arterial intima and athere, the accumulation of lipid that characterizes the typical lesion. These lesions affect large and medium-sized arteries. Despite the familiarity of this disease, some of its fundamental characteristics remain poorly recognized and understood.

Pathophysiology

Lipid deposition is an early event in atherogenesis, as is widely known, and it occurs when influx and deposition of cholesterol into the arterial wall exceed efflux. Development of an atherosclerotic lesion can be divided into 3 stages in which the following form: (1) a fatty streak, (2) a fibrous plaque, and (3) a complicated lesion.

The fatty-streak stage involves the formation of lipid-filled smooth muscle cells in the tunica intima, and it is believed to be reversible. No obstruction is present in the affected vessel.

During the second stage of fibrous plaque formation, lipid-laden smooth muscle cells are surrounded by collagen, elastic fibers, and mucoprotein matrix. The lesion can protrude into the lumen of the artery and cause obstruction. This lesion occurs at the level of the tunica intima, and it may also involve the muscular tunica media. Frequently, the lesion is located at arterial bifurcations.

In the third stage, a complicated lesion ensues when fibrous plaques are altered over time by hemorrhage, calcification, and mural thrombus. The intimal surface may become ulcerated as the lipid-laden plaque enlarges and hardens, and this can lead to embolism. The complicated lesion is often a cause of vessel obstruction.

Frequency

United States

On the basis of ankle-brachial blood-pressure ratios, the prevalence of lower-extremity peripheral arterial disease (LEPAD) is approximately 3% in people younger than 60 years. The prevalence increases to 20% in people older than 70 years.

Mortality/Morbidity

• The mortality associated with this disease results from associated cardiovascular and cerebrovascular pathology. The mortality rate in patients with LEPAD is 6 times higher than that of age-matched control subjects, and it is almost exclusively the result of death due to myocardial infarction and stroke. The 10-year survival rate decreases from 80% to 55% in healthy individuals (average age, 66 y) compared with patients with symptoms of LEPAD.
• Morbidity in this disease is usually the limitation of physical activities because of pain (claudication), ulceration, or amputation. The most frequent complications include unhealed ulcer, gangrene, and eventual amputation.

Race

No racial predilection exists for the development of LEPAD.

Sex

Males and females have an equal risk of LEPAD; however, atherosclerosis of the lower extremities is seen most frequently in elderly men.

Age

The highest incidence occurs in those aged 50-70 years.

Anatomy

The external iliac artery continues under the inguinal ligament as the common femoral artery, which divides into the superficial femoral and deep femoral (profunda femoris) arteries. The only major branch of the superficial femoral is the supreme geniculate artery. The profunda femoris artery usually arises 3-4 cm below the inguinal ligament from the lateral border of the artery and gives rise to several major branches, ie, the lateral circumflex femoral, the medial circumflex femoral, and the perforating arteries. These branches anastomose with branches of the internal iliac artery to provide collateral circulation in the presence of external iliac occlusion.

The superficial femoral artery extends downward behind the knee where it becomes the popliteal artery after it exits the lower boundary of the adductor canal through the adductor hiatus. Below the knee, direct continuation of the popliteal artery is the tibioperoneal trunk starting at the level of an anterior branch, ie, the anterior tibial artery. The tibioperoneal trunk bifurcates to form the posterior tibial and the peroneal arteries. At the knee level, the popliteal artery gives rise to 2 groups of arteries, ie, the genicular arteries and the sural arteries. The former include 2 superior genicular arteries, the middle genicular artery, and 2 inferior genicular arteries that form the anastomotic network around the knee, and the latter include 2 or 3 arteries that supply blood to the gastrocnemius muscle.

The anterior tibial recurrent artery is a significant branch of the proximal anterior tibial artery and provides a link with the genicular network. The anterior tibial artery extends downward supplying the anterior compartment of the leg and extends into the dorsum of the foot as the dorsalis pedis artery. The posterior tibial artery gives rise to the fibular artery, which is a small branch that anastomoses with the genicular network of the knee. The third main branch off the lower leg is the peroneal artery, which gives rise to perforating branches above the ankle that communicate with the distal anterior tibial and posterior tibial arteries.

At the level of the posterior foot, the posterior tibial artery branches to the medial plantar artery and the lateral plantar artery. The dorsalis pedis branches to the lateral tarsal artery, medial tarsal artery, arcade artery, and planter arch. All of these branches combine to carry the blood supply to the foot.

Although the most common site is the distal superficial femoral artery (at the level of the adductor canal), more than 1 location usually is involved at the same time. The popliteal artery alone is less likely to be involved. The anterior tibial artery is involved primarily in patients with diabetes.

Presentation

The most common presenting symptom in patients with peripheral vascular disease is intermittent claudication. The patient complains of pain, cramping, or muscle fatigue, which occurs during exercise and is relieved by rest. The site of claudication is distal to the location of the narrowed (stenotic) segment. With progression of the disease, resting pain develops. At this stage, patients complain of pain or numbness of the foot, which frequently occurs at night while the foot is nondependent. Symptoms improve when the foot is placed in a dependent position. With more severe disease, resting pain may be present continuously.

Signs of peripheral vascular disease encountered on physical examination include the following: decreased or absent distal pulses; bruit over a tightly narrowed artery; hair loss; thickened nails; shiny skin; a skeletonized appearance; pallor on elevation; rubor on dependency; and, in advanced disease, ulcers and gangrene.

Finally, the progression of the disease is closely associated with cigarette smoking and diabetes mellitus. Smoking cessation improves the patient's symptoms, especially the pain. Also, along with diabetic control, smoking cessation slows the progression of the disease.

Preferred Examination

The first step in assessing a patient is to record pulse-volume (plethysmography) and blood pressure measurements in the upper and lower extremities to compare the pressures. An ankle-brachial index (ABI) is determined. This is usually measured by dividing the highest systolic measurement in the lower extremity by the measurement in the upper extremity on the same side. An ABI of less than 0.95 is a strongly predictive sign of lower-extremity perfusion compromise. This noninvasive test provides information regarding the intravascular blood flow at different sites of the leg (upper thigh, lower thigh, above the ankle) as a waveform. Triphasic readings are normal and change to biphasic or monophasic in the diseased state.

Doppler ultrasonography (US) has become the second line in the evaluation of lower extremity arterial disease. Doppler US findings provide good information about the anatomy and physiology of the vessels.

Conventional arteriography is the most accurate test used to define the anatomy at this time, but it is indicated only when surgical intervention is considered. Conventional arteriography is not a screening study.

Computed tomography angiography (CTA) and magnetic resonance angiography (MRA) are noninvasive means of imaging that offer valuable information. They may replace conventional arteriography in the future. However, at this time, the applications for CTA and MRA remain limited.

Limitations of Techniques

Doppler US is a valuable diagnostic test; it is inexpensive and widely available, but does not offer detailed description of the length, severity, or type of the diseased portion of the vessel, all of which help in planning surgical or endoluminal intervention. Although vascular mapping can be performed to evaluate the iliac vessels and the femoropopliteal arterial segments, it is time and labor consuming (with examinations sometimes requiring as long as 2 h). It is also operator dependent.

Arteriography remains the most accurate and informative test. Arteriography is the criterion standard, but it is considered an invasive diagnostic method. This examination is associated with complications such as hematoma at the puncture site, those due to radiation exposure, intimal flap dissection, or arterial wall rupture, and nephrotoxicity due to the intravenous contrast material (which poses greater risk because of the common association of LEPAD with renal arterial disease and renal disease). Therefore, arteriography is preserved for preoperative evaluation only.

MRA is a rapidly developing and a promising study that may replace diagnostic angiography in the future. MRA is noninvasive, it does not require the use of ionizing radiation, and the contrast agent used is relatively non-nephrotoxic. This modality is associated with limitations such as its cost, its availability, the limited depiction of small vessels, its contraindications, and the possible overestimation of the degree of stenosis.

Differential Diagnoses

Other Problems to Be Considered

Acute thrombosis
Embolus
Thromboembolic occlusion
Neuromuscular disorder
Venous insufficiency
Arthritis, hip or knee
Lumbar lordosis
Chronic compartment compression syndrome
Popliteal artery entrapment syndrome
Popliteal cystic degeneration (adventitial)
Exposure to radiation
Fibromuscular dysplasia
Ergot poisoning
Buerger syndrome
Congenital arterial defect
Terminal aortic occlusion (Leriche disease)

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