Residency · Residency · Interventional Radiology

Peripheral Arterial Disease: Anatomy and Classification

Lower Extremity Arterial Anatomy

Aortoiliac Segment

The abdominal aorta bifurcates into the common iliac arteries at the level of the L4 vertebral body. Each common iliac artery (CIA) divides into the external iliac artery (EIA) and the internal iliac artery (also called the hypogastric artery). The EIA becomes the common femoral artery (CFA) as it passes below the inguinal ligament. A key collateral pathway exists through communications between the internal iliac artery branches and profunda femoris branches, forming the cruciate anastomosis.

Femoropopliteal Segment

The CFA bifurcates into the superficial femoral artery (SFA) and the profunda femoris artery (PFA). The SFA traverses the adductor canal (Hunter canal) and becomes the popliteal artery at the adductor hiatus. The PFA is a critical collateral vessel, often called the "lifeline of the leg," because it supplies the thigh musculature and provides collateral flow around SFA occlusions. The popliteal artery courses through the popliteal fossa behind the knee.

Infrapopliteal (Tibial) Segment

The popliteal artery trifurcates into three vessels. The anterior tibial artery (ATA) passes through the interosseous membrane to reach the anterior compartment and becomes the dorsalis pedis artery at the ankle. The tibioperoneal trunk is a short segment that divides into the posterior tibial artery (PTA), which runs behind the medial malleolus to supply the plantar arteries, and the peroneal artery, which runs along the fibula and serves as an important collateral vessel. At least one tibial vessel must be patent to the foot for adequate perfusion, a concept central to the angiosome framework.

Pedal Vasculature

The dorsalis pedis artery, a continuation of the ATA, runs on the dorsum of the foot. The plantar arteries arise from the PTA and divide into medial and lateral plantar branches that form the plantar arch. The pedal arch connects the dorsalis pedis and plantar arteries. The angiosome concept divides the foot into territories supplied by specific source arteries. Direct revascularization to the affected angiosome may improve wound healing, though evidence for this approach remains mixed.

Rutherford Classification of Chronic Limb Ischemia

Categories

The Rutherford classification stratifies chronic limb ischemia into seven categories. Grade 0, Category 0 describes asymptomatic disease. Grade I encompasses claudication, subdivided into Category 1 (mild), Category 2 (moderate), and Category 3 (severe). Grade II, Category 4 describes ischemic rest pain. Grade III covers tissue loss: Category 5 includes minor tissue loss such as a non-healing ulcer or focal gangrene with diffuse pedal ischemia, while Category 6 describes major tissue loss extending above the transmetatarsal level where a functional foot is no longer salvageable.

Fontaine Classification (European alternative)

The Fontaine classification provides an alternative staging system. Stage I is asymptomatic. Stage IIa describes mild claudication with a walking distance greater than 200 meters, while Stage IIb covers moderate to severe claudication at less than 200 meters. Stage III is rest pain, and Stage IV denotes tissue loss including ulceration or gangrene.

Critical Limb Ischemia (CLI) / Chronic Limb-Threatening Ischemia (CLTI)

Rutherford categories 4 through 6 and Fontaine stages III through IV define critical limb ischemia, now more commonly termed chronic limb-threatening ischemia (CLTI). It is defined by the presence of rest pain or tissue loss persisting for more than 2 weeks with hemodynamic evidence of arterial insufficiency. Without revascularization, CLTI carries a high risk of limb loss, with major amputation rates of 25 to 40 percent at one year. The annual mortality rate of 20 to 25 percent reflects significant cardiovascular comorbidity in this population.

Hemodynamic Assessment

Ankle-Brachial Index (ABI)

The ABI is measured by dividing the systolic blood pressure at the ankle (using the dorsalis pedis and posterior tibial arteries) by the higher of the two brachial pressures. Normal values range from 1.0 to 1.4. Borderline values of 0.91 to 0.99 warrant further evaluation. Mild PAD corresponds to an ABI of 0.71 to 0.90 and is typically associated with claudication. Moderate PAD falls between 0.41 and 0.70, while severe PAD or CLI presents with values below 0.40. An ABI greater than 1.4 indicates non-compressible vessels, which is common in diabetic and ESRD patients. In these cases, the toe-brachial index (TBI) should be used instead, with normal values above 0.7 and values below 0.3 indicating severe ischemia. Digital arteries are less susceptible to medial calcification.

Segmental Pressures

Segmental pressures are obtained using pressure cuffs at multiple levels: high thigh, above knee, below knee, and ankle. A pressure drop of more than 20 mmHg between adjacent segments suggests hemodynamically significant disease at that level and is useful for localizing the site of obstruction.

Pulse Volume Recording (PVR)

Pulse volume recording provides a plethysmographic assessment of arterial perfusion at multiple levels. Waveform analysis distinguishes normal patterns (a sharp systolic peak with a dicrotic notch) from dampened patterns (blunted, monophasic waveforms). Importantly, PVR is not affected by vessel calcification, making it valuable in patients with non-compressible arteries.

Imaging for Procedural Planning

CT Angiography (CTA)

CTA is the gold standard for pre-procedural planning in most centers. It provides excellent spatial resolution for anatomic detail, calcification assessment, and runoff vessel evaluation. Its limitations include contrast nephrotoxicity, calcium blooming artifact, and limited temporal resolution. Dual-energy CT can reduce calcium blooming.

MR Angiography (MRA)

MRA can be performed with contrast enhancement (gadolinium) or with non-contrast techniques such as time-of-flight or quiescent-interval slice-selective (QISS) imaging. It avoids ionizing radiation, iodinated contrast, and calcium artifact. However, it tends to overestimate stenosis severity, is susceptible to metallic artifact from stents, is contraindicated with some implants, and has longer acquisition times. Non-contrast MRA is increasingly used in patients with renal insufficiency.

Duplex Ultrasound

Duplex ultrasound is the first-line screening test for PAD. A peak systolic velocity (PSV) ratio greater than 2.0 at a stenosis suggests more than 50 percent stenosis, while a ratio greater than 4.0 suggests more than 75 percent. It is operator dependent and limited in obese patients and heavily calcified vessels but is excellent for post-intervention surveillance.

Catheter Angiography (DSA)

Catheter angiography remains the reference standard for arterial imaging. It allows real-time assessment and simultaneous intervention but is invasive, requires arterial access, and involves contrast and radiation exposure.

TASC II Classification

Aortoiliac Disease

TASC A describes unilateral or bilateral single short (less than 3 cm) stenoses of the CIA or EIA. TASC B includes short (less than 3 cm) stenosis of the infrarenal aorta, unilateral CIA occlusion, and single or multiple stenoses 3 to 10 cm in the EIA. TASC C encompasses bilateral CIA occlusions, bilateral EIA stenoses 3 to 10 cm, unilateral EIA stenosis extending into the CFA, and unilateral EIA occlusion. TASC D covers infrarenal aortoiliac occlusion, diffuse disease involving the aorta and both iliac arteries, and extensive bilateral CIA/EIA disease. TASC A and B lesions are typically treated with endovascular approaches first, while TASC C and D have traditionally been surgical, though endovascular techniques are increasingly applied to these complex lesions.

Femoropopliteal Disease

TASC A includes a single stenosis under 10 cm or a single occlusion under 5 cm. TASC B encompasses multiple lesions, a single stenosis or occlusion under 15 cm, or a heavily calcified occlusion under 5 cm. TASC C describes multiple stenoses or occlusions totaling more than 15 cm or recurrent lesions after prior intervention. TASC D covers chronic total occlusion of the CFA or SFA greater than 20 cm involving the popliteal artery, as well as chronic popliteal and trifurcation occlusions.

<image>Anatomical illustration of the lower extremity arterial system from the aortic bifurcation to the pedal vessels, shown in anterior view. The illustration labels the common iliac artery, external iliac artery, internal iliac artery, common femoral artery, profunda femoris artery, superficial femoral artery (with the adductor canal segment highlighted), popliteal artery, anterior tibial artery, tibioperoneal trunk, posterior tibial artery, peroneal artery, dorsalis pedis artery, and the plantar arch. The angiosome territories of the foot are color-coded to show the vascular supply zones.</image>

<image>Diagram illustrating the ankle-brachial index measurement technique. A patient supine with blood pressure cuffs on both arms and both ankles. Doppler probes are shown at the brachial, dorsalis pedis, and posterior tibial arteries. A calculation box shows the formula: ABI = highest ankle systolic pressure / highest brachial systolic pressure, with a scale showing normal (1.0-1.4), mild PAD (0.71-0.90), moderate (0.41-0.70), severe (<0.40), and non-compressible (>1.4).</image>

<image>Comparison illustration of arterial waveforms in PAD. Three panels showing Doppler waveforms: (1) Normal triphasic waveform with sharp systolic peak, dicrotic notch, and brief reversed flow; (2) Moderate PAD biphasic waveform with reduced systolic peak and absent reversed flow; (3) Severe PAD/CLI monophasic waveform that is dampened and broadened. Each panel includes a corresponding pulse volume recording (PVR) tracing beneath it.</image>

Clinical Pearls

The profunda femoris artery is the key collateral in SFA disease and must always be preserved and protected during intervention. The ABI is the single most important screening test for PAD, though a normal resting ABI does not exclude disease -- exercise ABI may unmask early disease. In diabetic patients with non-compressible arteries (ABI greater than 1.4), toe pressures or TBI are more reliable.

CLTI (formerly CLI) is a limb-threatening emergency with a high associated mortality rate, and expedited revascularization is essential. The angiosome concept suggests that direct revascularization to the wound territory may improve healing, but evidence is mixed, and inline flow to the foot via any tibial vessel is the minimum goal. CTA is the primary planning modality for most IR interventions, though operators must be aware of the limitations of calcium blooming in heavily calcified legs. The TASC classification guides the initial approach (endovascular versus surgical), but endovascular-first strategies are increasingly applied to complex lesions.

References

• Inter-Society Consensus for the Management of PAD (TASC II), J Vasc Surg 2007
• Defined by the Global Vascular Guidelines on the Management of CLTI (GVG), J Vasc Surg 2019
• Defined by the AHA/ACC Guideline on the Management of PAD, Circulation 2016
• Defined by Defined by the Rutherford Vascular Surgery textbook, 9th edition
• Defined by Defined by Defined by the SVS reporting standards for lower extremity PAD

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