General Anatomic Descriptions

The abdominal aorta divides into the common iliac arteries at approximately the level of L4. The middle sacral artery, usually a very small vessel, arises from the posterior surface of the aortic bifurcation and extends inferiorly along the anterior surface of the sacrum, in the midline, to the distal tip of the coccyx. The length of the common iliac artery is variable. Each common iliac artery divides into an external iliac artery and internal iliac artery (Fig. 73-1).

FIGURE 73-1 Schematic drawing of the pelvic arterial vessels.

(Adapted from Uflacker R. Atlas of Vascular Anatomy: An Angiographic Approach, 2nd ed. Philadelphia, Lippincott Williams & Wilkins, 2006.)

The external iliac artery has only two branches, the deep circumflex iliac and inferior epigastric arteries. Both arise approximately at the point where the inguinal ligament crosses anterior to the external iliac artery, and both serve as markers on arteriograms for the junction of the external iliac artery and common femoral artery. Some experts consider the inferior epigastric artery to arise from the proximal femoral artery. The deep circumflex iliac artery extends superolaterally from its origin on the lateral aspect of the external iliac artery, and supplies the pelvic side wall. It anastomoses with the iliolumbar and superior gluteal arteries, branches of the internal iliac artery, and with the ascending branch of the lateral circumflex femoral artery, a branch of the profunda femoral artery. The inferior epigastric artery arises from the medial aspect of the external iliac artery and dips inferiorly and medially before turning superiorly to course deep to the rectus abdominis muscle in the anterior abdominal wall (Fig. 73-2). Superiorly, it anastomoses with the superior epigastric artery, a branch of the internal thoracic artery.

FIGURE 73-2 A, Schematic drawing of the external iliac, common femoral, superficial femoral arteries, and branch vessels. B, Angiogram of the right external and common iliac arteries and branch vessels (contralateral oblique view).

(A, adapted from Uflacker R. Anatomy Atlas of Vascular Anatomy: An Angiographic Approach, 2nd ed. Philadelphia, Lippincott Williams & Wilkins, 2006.)

The internal iliac artery has anterior and posterior divisions. Branches of the anterior division primarily supply the pelvic viscera, whereas branches of the posterior division supply pelvic bones and muscles (Fig. 73-3A).

FIGURE 73-3 A, Angiogram of the right internal iliac artery, with anterior and posterior divisions. B, Angiogram of the posterior division of the left internal iliac artery.

Typically, the three branches of the posterior division are the iliolumbar artery, lateral sacral artery, and superior gluteal artery (see Fig. 73-3B). The iliolumbar artery extends laterally and superiorly to divide into two branches that supply the iliacus muscle and ilium (iliac branch) and the psoas major and quadratus lumborum muscles (lumbar branch). The lateral sacral artery extends medially and then superiorly to supply the spinal meninges and the roots of the sacral nerves. The superior gluteal artery, the largest branch of the internal iliac artery, extends laterally, passes above the piriformis muscle through the greater sciatic foramen as it leaves the pelvis posteriorly, and supplies the gluteal muscles, overlying soft tissues and skin. These posterior division branches may, on occasion, arise from the anterior division or from trunks formed by various combinations of internal iliac artery branches (see later).

The anterior division of the internal iliac artery divides into a number of named arteries. As with the posterior division branches, the anterior division vessels may occasionally arise from the posterior division or from trunks formed by various combinations of internal iliac artery branches.

The three principal branches of the anterior division are the obturator artery, inferior gluteal artery, and internal pudendal artery (Fig. 73-4A). The obturator artery courses along the pelvic brim, bifurcates above the obturator notch, and passes laterally through the obturator foramen to supply muscles of the thigh and ligament of the femoral head. It is usually the most lateral of the anterior division branches. A distal branch of the obturator artery anastomoses with the medial circumflex femoral artery, a branch of the profunda femoral artery. The inferior gluteal artery has a variable intrapelvic course, typically concave laterally. It courses inferiorly, anterior to the piriformis muscle and sacral plexus, extends laterally, and exits the bony pelvis via the greater sciatic notch. It supplies the muscles and skin of the buttock and posterior surface of the thigh. In rare cases, it gives rise to a persistent sciatic artery (see later). The internal pudendal artery courses inferiorly along the anterior surface of the piriformis muscle, lateral to the inferior gluteal artery, and enters the ischiorectal fossa through the lesser sciatic foramen. It has numerous small named branches. It supplies the perineum and external genitalia.

FIGURE 73-4 A, Angiogram of the anterior division of the left internal iliac artery. B, Angiogram of the left uterine artery, with cervicovaginal branch.

The remaining branches of the anterior division are less prominent (see Fig. 73-1). The superior vesical artery has an inferomedial course until it reaches the lateral aspect of the bladder, at which point it courses along the superior surface of the bladder; its position varies depending on the degree of bladder distention. It supplies up to 80% of the bladder, as well as the distal ureters and, in males, the ductus deferens. The inferior vesical artery has an inferomedial course whose position is not dependent on the degree of bladder distention. It is a small vessel, difficult to appreciate angiographically, which supplies the inferolateral surface of the bladder, the trigone and, in males, the seminal vesicles and prostate. In females, the analogous vessel is sometimes termed the vaginal artery. It supplies the vagina, posteroinferior portions of the bladder, and pelvic part of the urethra. The vaginal artery may be a single vessel or two or three separate arteries. The inferior vesical artery often forms a common trunk with the middle rectal artery. The middle rectal artery may arise from the anterior division, but is frequently a branch of another artery in the internal iliac artery distribution. This small vessel is the most posterior of the anterior division vessels, and descends inferomedially to the ipsilateral side of the middle portion of the rectum. It anastomoses with the superior and inferior rectal arteries to supply the rectum and sometimes inferior vesical–vaginal artery territory. The uterine artery has a characteristic U-shaped course; it descends, turns medially to course along the broad ligament, and then ascends in the parametrium along the lateral border of the uterus. The cervicovaginal artery, which supplies the cervix and vagina, arises near the junction of the medial and ascending portions. The ascending portion is typically convoluted and gives off numerous convoluted branches that extend medially (see Fig. 73-4B). In postpartum women, the uterine artery may extend superiorly, without demonstrating the U-shaped course typical of the nongravid uterus.

Other arteries arise outside the pelvis but terminate within it. These are the superior rectal artery, which is the continuation of the inferior mesenteric artery in the pelvis, and the gonadal arteries—internal spermatic (testicular) arteries in the male and ovarian arteries in the female. The gonadal arteries arise from the abdominal aorta at the L2 or L3 level and accompany the gonadal veins into the pelvis.

Detailed Description of Specific Areas

Normal Variants

The common iliac arteries are absent in fewer than 1% of individuals. In this case, the aorta divides into four branches, the internal and external iliac arteries bilaterally.

Variations of the internal iliac artery and its branches are common. Typically, the internal iliac artery divides into two branches, as noted earlier. However, this arrangement is seen in approximately 60% of cases, and the remaining 40% demonstrate one (10%), three (20%), or four or more (10%) principal trunks. The sequence of branch origins and trunk formation is extremely variable. The obturator artery may arise from the external iliac artery or the inferior epigastric artery. A persistent sciatic artery, which arises from the inferior gluteal artery, is a rare but clinically important variant (Fig. 73-5). Because it is often symptomatic, it is discussed separately later.

FIGURE 73-5 Schematic drawing of persistent sciatic artery.

Differential Considerations

Arterial bypass grafts for infrarenal aortic or iliac artery disease originate from the axillary artery or the infrarenal aorta and insert in the external iliac, common femoral, or profunda femoral arteries, depending on the site(s) of disease (Fig. 73-6). Common femoral artery to common femoral artery grafting can be performed for unilateral common iliac or external iliac artery disease (Fig. 73-7). Lower extremity atherosclerosis requiring surgical bypass can be treated with a graft originating at the common femoral artery and terminating at the popliteal artery (ideally, superior to the knee joint), posterior tibial artery, or anterior tibial artery, as required (Fig. 73-8).

FIGURE 73-6 CTA scan showing axillary-femoral (Ax-fem) bypass graft.

FIGURE 73-7 CTA scan showing femoral-femoral (Fem-fem) bypass graft.

FIGURE 73-8 CTA scan showing femoral-popliteal (Fem-pop) bypass graft.

In the pelvis, a persistent sciatic artery can be clinically important. The sciatic artery normally involutes by the 22-mm embryo stage, with remnants persisting as the proximal portion of the inferior gluteal artery, popliteal artery, and peroneal artery.¹ Rarely, the sciatic artery persists, either because of failure of development of the superficial femoral artery or failure of regression of the sciatic artery.² A persistent sciatic artery is the continuation of the internal iliac artery (see Fig. 73-5), arising from the anterior division distal to the origin of the internal pudendal artery. It follows the course of the inferior gluteal artery through the greater sciatic foramen, where it may accompany the posterior cutaneous nerve or sciatic nerve. It continues inferiorly along the posterior aspect of the adductor magnus and then passes through the popliteal fossa to form the popliteal artery and supply the leg and foot.¹ The reported incidence, based on angiographic series, is 0.01% to 0.05%.² Bilateral persistent sciatic arteries are estimated to occur in about 10% of these individuals.²

Approximately 60% of individuals with a persistent sciatic artery are symptomatic. The most common symptom is lower extremity ischemia.³ Approximately 40% of patients with a persistent sciatic artery develop an aneurysm of the vessel at the level of the greater trochanter, believed to be caused by repetitive microtrauma from the sacrospinal ligament and piriformis muscle during hip flexion and extension.⁴ These patients may present with thrombosis, distal embolization, or a buttock mass. Symptomatic patients have a risk of limb loss as high as 25%.

On imaging studies in these individuals, the internal iliac artery is larger than the external iliac artery. The persistent sciatic artery is ectatic and courses laterally at the level of the femoral head before turning inferiorly. On oblique views, it can be appreciated as a posterior structure. The external iliac artery and common femoral artery are in their normal locations, but may be small. The superficial femoral artery tapers in the thigh, may bifurcate on the region of the adductor canal, and then disappears. Persistent sciatic arteries are readily appreciated on CT angiography (CTA), which also permits the determination of aneurysm size, despite the possible presence of luminal thrombus.³

General Anatomic Descriptions

The femoral artery (usually referred to in clinical practice as the common femoral artery) is the continuation of the external iliac artery distal to the inguinal ligament. It is the usual percutaneous access site for catheter angiography. The femoral artery is variable in length. It divides into the profunda femoral artery posterolaterally and the superficial femoral artery anteromedially (Fig. 73-9) and may also give rise to the superficial circumflex iliac artery, external pudendal arteries, and muscular branches, although this is variable.

FIGURE 73-9 Angiogram of the bilateral superficial femoral and profunda femoral arteries.

The profunda femoral artery (deep femoral artery) is the largest branch of the femoral artery and supplies the thigh muscles anteriorly and posteriorly. It normally gives rise to the medial and lateral circumflex femoral arteries and then continues inferiorly as it gives off several perforating branches (see Fig. 73-9).

The superficial femoral artery extends inferiorly to the inferior end of the adductor canal (Hunter’s canal), where it continues as the popliteal artery (Fig. 73-10A). The adductor canal is a fascia-lined compartment bounded by the vastus medialis muscle anteriorly and laterally and the adductor magnus and adductor longus muscles posteriorly, which winds medially and posteriorly around the femur. The junction of the superficial femoral artery and popliteal artery is thus in the distal thigh, and not at the level of the knee joint, as is occasionally—and incorrectly—stated in clinical practice. The superficial femoral artery serves as conduit to the leg and foot. It gives rise to multiple small muscular branches and, just superior to its entrance into the adductor canal, it gives rise to the descending (supreme) genicular artery.

FIGURE 73-10 A, Angiogram of the left popliteal artery to trifurcation. B, Schematic drawing of the popliteal artery and branch arteries around the knee.

(B, adapted from Uflacker R. Atlas of Vascular Anatomy: An Angiographic Approach, 2nd ed. Philadelphia, Lippincott Williams & Wilkins, 2006.)

The popliteal artery extends from the inferior aspect of the adductor canal to a point inferior to the knee, where it divides into the tibial and peroneal arteries. Along its course, posterior to the femur and the tibia, it gives off a small medial genicular artery, multiple sural arteries, medial and lateral superior genicular arteries, and medial and lateral inferior genicular arteries (see Fig. 73-10B). The last four genicular arteries wrap around the femur and tibia to form an anastomotic network around the patella. They supply the articular capsule and ligaments of the knee joint. The sural arteries extend inferiorly to supply the calf muscles.

In the leg, the popliteal artery gives off the anterior tibial artery at the level of the inferior edge of the popliteus muscle. The popliteal artery continues as the tibioperoneal trunk, which then divides into the posterior tibial artery and peroneal artery (see Fig. 73-10).

The anterior tibial artery, a major source of supply to the foot, passes anteriorly between the two heads of the tibialis posterior muscle and through the interosseous membrane to the anterior leg. It extends inferiorly, medial to the fibula and continues on to the dorsum of the foot. After it crosses the inferior extensor retinaculum, it becomes the dorsalis pedis artery (Fig. 73-11).

FIGURE 73-11 Angiogram of the right runoff arteries—anterior tibial, peroneal, and posterior tibial arteries.

The posterior tibial artery, also a major source of supply to the foot, extends inferiorly in the posterior leg to reach the ankle behind the medial malleolus and continues on to the foot. In a frontal view, the posterior tibial artery is the most medial of the three major calf vessels (see Fig. 73-11).

The peroneal artery arises from the tibioperoneal trunk and extends inferiorly to a point about 5 cm superior to the lateral malleolus, where it divides into a perforating branch. This anastomoses with a branch of the anterior tibial artery and a communicating branch that anastomoses with a branch of the posterior tibial artery. On both frontal and lateral views, the peroneal artery is projected between the anterior tibial and posterior tibial arteries.

In the foot (Fig. 73-12), the posterior tibial artery divides into a relatively small medial plantar artery, which runs along the first ray, and a larger lateral plantar artery. These vessels run in the plantar aspect of the foot. The lateral plantar artery runs laterally and distally to the base of the fifth metatarsal and then swings medially to form one side of the plantar arch, which supplies plantar metatarsal and common digital arteries to the forefoot.

FIGURE 73-12 Angiogram of the lateral left foot.

The dorsalis pedis artery runs in the dorsum of the foot to the level of the metatarsal heads, where it swings laterally as the arcuate artery and gives off a variable number of metatarsal arteries and dorsal digital arteries to supply the forefoot. The arcuate artery anastomoses via a deep plantar branch with the lateral plantar artery to complete the plantar arch. Near its origin, the dorsalis pedis artery gives off a lateral tarsal branch, which may anastomose distally with the arcuate artery.

Detailed Description of Specific Areas

Normal Variants

The classic description of profunda femoral artery anatomy is accurate in only about 60% of limbs. In the remainder, one or more of the profunda femoral artery branches arises from the femoral artery. This is important information for the vascular surgeon planning an arterial bypass with an anastomosis to the femoral artery or profunda femoral artery. In fewer than 1% of patients, the origin of the profunda femoral artery is superior to the inguinal ligament. The profunda femoral artery lies lateral or posterolateral to the superficial femoral artery in only 50% of limbs. It is posterior to the superficial femoral artery in 40% of limbs, and medial to the superficial femoral artery in 10% of limbs. This information is valuable to the vascular surgeon and awareness of these variants is essential for the interpreting physician who is performing vascular ultrasound examinations.

The division of the popliteal artery into anterior tibial, posterior tibial, and peroneal arteries (the so-called trifurcation) follows the classic description in approximately 90% of limbs. In approximately 4% of limbs, there is a true trifurcation, with no tibioperoneal trunk. In approximately 1% of limbs, the posterior tibial artery is the continuation of the popliteal artery and the other branch of the popliteal artery is a combined trunk that divides into the anterior tibial and peroneal arteries. In approximately 3% of limbs, the anterior tibial artery arises from the popliteal artery superior to the popliteus muscle (high origin).

In 6% and 5% of limbs, the anterior tibial and posterior tibial arteries, respectively, may be hypoplastic or congenitally absent. In these limbs, the perforating and communicating branch, respectively, of the peroneal artery is enlarged and continues to the foot as the dorsalis pedis or posterior tibial artery. The peroneal artery is congenitally absent in fewer than 0.1% of limbs.

Collateral Pathways

Numerous collateral pathways exist through the pelvic vasculature to mitigate the effects of occlusions or severe stenoses of the infrarenal abdominal aorta, common iliac artery, internal iliac artery, external iliac artery, and common femoral artery. These may be broadly grouped into anterior, central, and posterior pathways.

The anterior pathway extends across the anterior chest wall and anterior abdominal wall via the internal thoracic artery and intercostal arteries, through the superior and inferior epigastric arteries, to the distal external iliac artery (Fig. 73-13). The posterior pathway extends from the posterior chest wall and posterior abdominal wall to the internal iliac artery via intercostal and lumbar arteries, and then through the iliolumbar and superior gluteal arteries. Both anterior and posterior collateral pathways provide alternate routes for ipsilateral arterial flow from the aorta to the pelvis.

FIGURE 73-13 Schematic drawing of the thoracoabdominal arterial anastomosis through the superior epigastric and inferior epigastric arteries; three-dimensional reconstruction, lateral view.

There are several central collateral pathways. There is a pathway from the abdominal aorta to the internal iliac artery via the inferior mesenteric artery, through anastomoses between the superior rectal artery and the middle and inferior rectal arteries. There are also multiple ipsilateral-contralateral pathways across the midline in the pelvis via the lateral sacral arteries posteriorly and most of the visceral branches anteriorly.

Finally, there are collateral pathways from the pelvis to the lower extremity—from the internal iliac artery to the ipsilateral femoral artery via the internal pudendal artery through anastomoses with the external pudendal arteries, from the external iliac artery to the ipsilateral profunda femoral artery via the deep circumflex iliac artery through anastomoses with the lateral circumflex femoral artery, and from the internal iliac artery to the ipsilateral profunda femoral artery via the obturator artery and the gluteal arteries through anastomoses with the circumflex femoral arteries and perforating branches.

Collateral formation in the thigh is common in patients with calf claudication, because the superficial femoral artery is a common site of atherosclerosis, especially as it exits the adductor canal. Collateral pathways are from the profunda femoral artery branches to the superficial femoral artery and from the superficial femoral artery proximal to the lesion to the superficial femoral artery distal to the lesion via muscular branches (Fig. 73-14).

FIGURE 73-14 A, Angiogram of the proximal left superficial femoral artery, with a distal occluded segment and reconstitution downstream via collaterals. B, Angiogram of the distal left superficial femoral artery via muscular collaterals from the profunda femoral artery.

There are numerous collateral pathways in the region of the knee. The genicular arteries form a rich anastomotic network, which comes into play when there is stenosis or occlusion of the popliteal artery. Collateral flow via the distal branches of the peroneal artery can supply the foot in patients with occlusion of the anterior tibial or posterior tibial artery (Fig. 73-15).

FIGURE 73-15 Schematic drawing of the occluded left popliteal artery, with reconstitution of the anterior tibial artery and tibioperoneal trunk via collaterals.

The plantar arch of the foot is complete in 99% of limbs. The blood supply to each of the metatarsals and toes is extremely variable with respect to the predominant supply from the dorsal or plantar arteries.

Pertinent Imaging Considerations

The arteries of the thigh and knee usually can be evaluated adequately in a frontal view. Imaging of the popliteal artery in the popliteal fossa sometimes requires a lateral view. A frontal view of the leg often demonstrates the distal anterior tibial artery and peroneal artery superimposed. When imaged with CTA or MRA, these vessels should also be evaluated in a lateral view, as should the vessels of the foot. Specific provocative maneuvers have been described to elicit vascular compression in patients with popliteal entrapment.¹⁰

KEY POINTS

Knowledge of the expected and possible variant arterial anatomy of the pelvis and lower extremities is essential for successful CTA and MRA scan prescription and interpretation.

Consideration of the clinical indication for a pelvic and/or lower extremity CTA and MRA will assist in the proper selection of imaging parameters (e.g., anatomic coverage, spatial resolution).

Evaluation of pelvic and lower extremity by CTA and MRA is optimized by oblique viewing of data using image postprocessing (e.g., maximum intensity projection, multiplanar reconstruction, and volume rendering).