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Radiology > VASCULAR/INTERVENTIONAL
Lower-Extremity Atherosclerotic Arterial Disease
Article Last Updated: Feb 9, 2007
AUTHOR AND EDITOR INFORMATION
Section 1 of 11  
Author: Chadi Chahin, MD, Staff Physician, Department of Radiology, Aultman Health Foundation/Mercy Medical Center
Chadi Chahin is a member of the following medical societies: American College of Radiology
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
Editors: Anthony Watkinson, MD, Professor of Interventional Radiology, The Peninsula Medical School; Consultant and Senior Lecturer, Department of Radiology, The Royal Devon and Exeter Hospital, UK; Bernard D Coombs, MB, ChB, PhD, Consulting Staff, Department of Specialist Rehabilitation Services, Hutt Valley District Health Board, New Zealand; George Hartnell, MB, Professor of Radiology, Tufts University School of Medicine, Director of Cardiovascular and Interventional Radiology, Department of Radiology, Baystate Medical Center; Robert M Krasny, MD, Consulting Staff, Department of Radiology, The Angeles Clinic and Research Institute; Kyung J Cho, MD, FACR, William Martel Professor of Radiology, Fellowship Program Director, Department of Radiology, Division of Interventional Radiology, University of Michigan Medical School
Author and Editor Disclosure
Synonyms and related keywords:
arteriosclerosis obliterans, lower extremity peripheral vascular disease, lower extremity peripheral arterial disease, atherosclerosis, lower-extremity peripheral arterial disease, LEPAD
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.
Clinical Details
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.
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)
Findings
Conventional radiographs of the lower extremities are not useful in screening or confirming LEPAD. Conversely, lower-extremity arterial calcifications are common incidental findings. The presence and extent of arterial wall calcification is not correlated with the clinical symptoms.
Findings
Currently, contrast-enhanced arterial CT is evolving in the diagnosis and treatment of lower-extremity vascular disease. Disadvantages of conventional CT include the use of ionizing radiation and the requirement for contrast materials.
Findings
Recently, MRA has emerged as a safe and noninvasive alternative to conventional angiography in the diagnosis of lower-extremity vascular disease. Using MRA studies, a radiologist should be able to detect signs of narrowing (stenosis), dilatation (aneurysm) in the vessel, or a complete interruption of flow, and he or she should be able to compare the results in both legs.
Initial reports used 2-dimensional (2D) and 3-dimensional (3D) time-of-flight (TOF) MRA with limited success. These methods rely on the detection of flow-related phenomena to produce angiographic images. Images were degraded by patient motion (primarily due to long scanning times, which may been > 1 h). Other causes of poor image quality include turbulence, pulsating arteries, saturation, and poor signal-to-noise ratios (SNRs). However, the TOF is still considered a better technique than contrast-enhanced MRA for evaluating infrapopliteal vessels because MRA depends on blood flow in the immediate vicinity of the region imaged.
Contrast-enhanced 3D MRA has become the method of choice. The technique relies on the detection of contrast enhancement in the vascular lumen to produce findings that are comparable to those of conventional catheter angiography. The current technique uses the bolus-chasing method material in which vessels are imaged sequentially as contrast flows distally. Multiple overlapping fields of view are used, and images are obtained in the coronal or sagittal planes (usually in 3 coronal stations). This technique also uses subtraction to improve the resultant vascular images by suppressing the background and reducing the volume averaging.
Images demonstrate the contrast-enhanced anatomy of the arterial lumen. Stenosis is depicted as areas of narrowing, and occlusion is depicted as areas of absent signal intensity. Ulceration and aneurysm can also be defined.
Use of bolus-chasing MRA enables radiologists to establish protocols for different studies by adjusting the bolus dose and time, the infusion rate, the region of interest, the section thickness, and the position in the imaging plane by considering the purpose of the study, the patient's condition, and the equipment available.
Bolus-chasing MRA is rapidly evolving for many reasons such as the technology revolution that made equipment widely available, improvements in technical capabilities (eg, increased field strengths, dedicated coils, increased SNRs, decreased repetition times, improved bolus-detection techniques, MR SmartPrep technique). With these changes, along with the increased familiarity and confidence of referring physicians with this new modality, bolus-chasing MRA will replace conventional catheter angiography.
False Positives/Negatives
The value of the study can be increased by using newer magnetic resonance devices with higher resolution, by using gadolinium-based contrast agent, and by having the expertise to interpret the images. However, even when all available resources are used, false-positive and false-negative results may still be encountered, especially in patients who have undergone previous interventions. For example, indwelling stents can cause severe artifacts and may render findings inaccurate or nondiagnostic. To date, no established data are available; however, multiple studies reveal a sensitivity and specificity of more than 90% with the bolus-chase technique. The rate is slightly better in evaluating the iliac, femoral, and popliteal segments. Gadolinium-based contrast agents (gadopentetate dimeglumine [Magnevist], gadobenate dimeglumine [MultiHance], gadodiamide [Omniscan], gadoversetamide [OptiMARK], gadoteridol [ProHance]) have recently been linked to the development of nephrogenic systemic fibrosis (NSF) or nephrogenic fibrosing dermopathy (NFD). For more information, see the eMedicine topic Nephrogenic Fibrosing Dermopathy. The disease has occurred in patients with moderate to end-stage renal disease after being given a gadolinium-based contrast agent to enhance MRI or MRA scans.
As of late December 2006, the FDA had received reports of 90 such cases. Worldwide, over 200 cases have been reported, according to the FDA. NSF/NFD is a debilitating and sometimes fatal disease. Characteristics include red or dark patches on the skin; burning, itching, swelling, hardening, and tightening of the skin; yellow spots on the whites of the eyes; joint stiffness with trouble moving or straightening the arms, hands, legs, or feet; pain deep in the hip bones or ribs; and muscle weakness. For more information, see the FDA Public Health Advisory or Medscape.
Findings
Spectral Doppler US and color-flow vascular imaging supplement gray-scale US in identifying blood vessels, confirming the direction of blood flow, and detecting vascular stenosis or occlusion.
Gray-scale US illustrates the anatomy of the scanned region, usually in vertical or longitudinal planes. Blood flow and its speed and direction are detected by measuring the Doppler shift originating from a sample volume inside the artery.
Doppler shift is measured by processing the returning Doppler signals by using the fast–Fourier transform spectrum analyzer that sorts the data into individual components and displays them as a function of time on velocity scales (displayed in real time). Blood velocity and frequency shift are directly related mathematically. Therefore, faster movement of the red blood cells (RBCs) and the larger numbers of cells in the vessel moving toward the transducer result in the representation of greater velocity on the screen; this is depicted as brighter colors.
In addition, data are displayed as waveforms. Different blood vessels have unique flow characteristics that can be recognized by the Doppler spectral waveforms produced. Two major waveforms are identified, ie, high resistance and low resistance ones. The type of waveform is determined by the type of vessel and by vessel compliance. The waveform is also defined by its monophasic, biphasic, or triphasic pattern. Triphasic patterns are found most often in the lower extremities.
Using gray-scale technique, a significant atherosclerotic vascular lesion can be detected only by thickening of the vessel wall or segmental narrowing of the lumen (which usually represents plaque or mural thrombus). Aneurysms and intimal flaps may also be identified.
LEPAD often diagnosed by using US, which depicts a change in the flow pattern on Doppler spectrum imaging. Proximal to the lesion, the flow pattern is normal. At the stenosis, the peak systolic velocity increases in proportion to the degree of stenosis. The diastolic portion of the Doppler waveform depends on the artery distal to the lesion and the severity of the lesion. Diastolic flow may be significantly increased or absent. Systolic velocity distal to the lesion is equal or lower than the velocity proximal to the stenosis.
The peak systolic velocity is affected less by distal vasodilation than by diastolic velocity (which also affects the collateral vessels that develop because of the decreased blood supply). Therefore, the peak systolic velocity is the preferred Doppler velocity parameter to be measured by using the Doppler spectrum at the site of a suggested stenosis. Vascular stenosis may also be reflected as a change of the waveform from triphasic to biphasic or monophasic.
The absence of a flow signal may represent occlusion, vascular calcifications, or technical error. Thrombosis is usually seen as echogenic material in the artery. Large collateral branches are likely to indicate high-grade stenosis or more distal occlusion.
A thorough examination provides information about the entire common femoral, superficial femoral, and popliteal arteries. Examination of the deep femoral and tibial vessels is usually limited.
False Positives/Negatives
Multiple published studies evaluated the femoropopliteal segment. The reported sensitivity was more than 85%, and the specificity was more than 92% in detecting segmental arterial lesions.
Findings
Arteriography is the most accurate method with which to identify the diseased segment of the artery because it can reveal stenosis, dilatation, occlusion, plaque ulceration, or thrombotic material (which is usually manifested by filling defects).
Lower-extremity arterial disease occurs in 2 types, ie, acute ischemia and chronic ischemia.
Acute ischemia
Acute ischemia usually results from a thromboembolic event. Usually, the patient complains of an acute onset of symptoms, especially severe pain. Angiographic findings in this setting are cutoff or runoff with few or no collaterals, which may occur at any level, although these are more common at the level of tibial or foot arteries.
Chronic ischemia
Chronic ischemia occurs in as many as 80% of patients with lower-extremity arterial disease. The occlusive process demonstrates different patterns according to the level of the lesion and the pattern of the disease.
- At the level of the common femoral artery: When the disease occurs in this location, a collateral circulation is derived from the common iliac-iliolumbar artery, the internal iliac–superior gluteal artery, the internal iliac–inferior gluteal artery, or the external iliac–deep iliac circumflex artery. All of these branches reconstitute with the profunda femoris artery to supply blood to the lower extremity.
- At the level of the superficial femoral artery: Disease may occur at the level of proximal, middle, or distal third. In all cases, the collateral circulation from the profunda femoris artery to the popliteal artery carries blood to the lower limb.
- At the level of the profunda femoris artery: The profunda femoris artery is almost always spared in atherosclerotic occlusive disease. If it is affected, it has a great significance in the planning of future interventions.
- At the level of the popliteal artery: Depending on the level of obstruction, the geniculate arteries form collaterals to supply blood to the anterior and posterior tibial distal to the level of obstruction.
- At the level of the anterior or posterior tibial arteries: In this location, the peroneal artery often is patent and supplies blood through the perforating branches to the foot.
- Combined pattern: This finding is most common in patients with severe ischemia. It usually involves the femoropopliteal portion, along with the anterior and/or posterior tibial arteries.
- At the level of the foot vessels: The arterial network of the foot (the foot or plantar arch) forms a continuous circuit that supplies blood to all segments, even in the presence of arterial occlusion.
The past decade has brought expanded use of endovascular therapies in the treatment of patients with lower-extremity occlusive vascular disease, with surgical revascularization procedures playing an ever-diminishing role. Several factors have contributed to this trend: patient risk factors for surgery, hospitalization time, recurrence rates, and comparison of minimally invasive approaches to highly invasive surgery. Interventional methods are divided into balloon angioplasty with intravascular stenting and those without stenting.
In the early days, the principle mode of action with balloon angioplasty was believed to be compression of the plaque. Currently, balloon angioplasty is known to be effective by creating a controlled plaque fracture with associated stretching of the media and adventitia of the artery, thereby enlarging the lumen. The increased use of balloon angioplasty has been accompanied by an increase in the awareness of recurrent postangioplasty stenosis, which created the need for early or late stenting. Recurrent stenosis is usually caused by recoil of the arterial wall and plaque or by the progression of atherosclerosis in the area.
The two most common types of stents include the following:
- Type 1 - Self-expandable stents (eg, Wallstent)
- Type 2 - Balloon expandable stents (eg, Palmaz stent) deployed by an angioplasty balloon
All of the published data show that best results are obtained when the disease in common iliac artery, although the outcome is also good when the disease is located in the superficial femoral or popliteal artery.
The field of endovascular surgery is growing rapidly, as are improvement in available instruments and expertise. Currently, atherosclerotic iliac artery stenosis responds well to simple balloon angioplasty, and it has the best results of all of the peripheral vessels. Although many complications and technical failures are still encountered, the excellent results of endoluminal treatment in patients with iliac artery occlusive disease and the relatively low risk for complications (compared with surgical revascularization) ensure an enduring role for this modality. The application of this study in other portions of the vascular tree is still being investigated, but results are promising.
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Pulse-volume recording study shows disease on the right side. Compare the waveforms and the ankle-brachial index numbers on both sides. |
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Gray-scale sonogram demonstrates the popliteal artery, which is located between the calipers. It measures 0.62 cm in diameter. Findings are normal in this study. |
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Color Doppler sonogram of the popliteal artery (same patient as in Image 2). The red color represents arterial blood flow, its direction, and its velocity inside the artery. These data were obtained by measuring the Doppler shifts originating from the sampled volume inside the artery). Findings are normal in this study. |
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Popliteal artery. Video illustrating the Images 1-3 was recorded during real-time color Doppler ultrasonography. |
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Digital subtraction angiogram (DSA) illustrates a high-grade short-segment stenosis of the lumen of the right superficial femoral artery (a). |
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Conventional catheter angiogram. The inflated angioplasty balloon technique was performed to treat the stenosis in the lumen of the right superficial femoral artery (same patient as in Image 5). |
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Cut-film angiogram illustrates complete embolic occlusion after angioplasty (a). The occlusion is seen distally at the level of the popliteal artery. The patient was treated with percutaneous catheter suction embolectomy. (Thrombolytic agents such as reteplase or alteplase may also be used.) |
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Magnetic resonance angiogram (MRA) obtained by using the bolus-chase technique shows the normal anatomy of the lower extremity arterial vasculature, including the aorta (a), the common iliac artery (b), the external iliac artery (c), the internal iliac artery (d), and the common femoral artery (e). |
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Magnetic resonance angiogram (MRA) obtained by using the bolus-chase technique shows the normal anatomy of the lower-extremity arterial vasculature, including the deep femoral artery (a) and the superficial femoral artery (b). |
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Magnetic resonance angiogram (MRA) obtained by using the bolus-chase technique shows the normal anatomy of the lower-extremity arterial vasculature, including the popliteal artery (a), the anterior tibial artery (b), the tibioperoneal trunk (c), the peroneal artery (d), and the posterior tibial artery (e). |
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This magnetic resonance angiogram (MRA) of the lower extremities was obtained by using the bolus-chase technique. A short-segment high-grade stenosis is present in the middle of the left superficial femoral artery. Note the collateral arterial supply. |
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This magnetic resonance angiogram (MRA) of the lower extremities was obtained by using the bolus-chase technique. Atherosclerotic disease involves the bilateral superficial femoral arteries. Note the multiple lesions, which are primarily in the middle portions, and the large collateral arterial supply. |
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Lower-Extremity Atherosclerotic Arterial Disease excerpt Article Last Updated: Feb 9, 2007
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