External iliac artery

The external iliac artery is a major blood vessel that supplies blood to the lower limbs. It is a continuation of the common iliac artery and is one of the two main terminal branches of the common iliac artery, with the other being the internal iliac artery.

Location

The external iliac artery originates from the common iliac artery at the level of the L5 vertebra, just anterior to the sacroiliac joint. It travels along the pelvic brim, following the medial border of the psoas major muscle. The artery runs deep in the pelvic region, passing underneath the inguinal ligament and becoming the femoral artery as it enters the thigh. Along its course, it gives off branches like the inferior epigastric artery and deep circumflex iliac artery, which supply the lower abdominal wall and pelvis.

Anatomy

Origin

The external iliac artery is one of the two terminal branches of the common iliac artery, with the other being the internal iliac artery. The common iliac artery divides at the level of the L5 vertebra, just anterior to the sacroiliac joint. The external iliac artery arises from this bifurcation and continues its course down toward the lower limb. The artery primarily serves the lower extremity, pelvis, and parts of the lower abdominal wall.

Course

After originating from the common iliac artery, the external iliac artery runs along the pelvic brim (the curved ridge at the upper boundary of the pelvic inlet), following the medial border of the psoas major muscle. It courses inferiorly and anteriorly, running within the pelvis but staying relatively close to the pelvic brim, beneath the parietal peritoneum.

As the artery travels downward, it approaches the inguinal ligament, which marks the transition from the pelvis to the thigh. Just before passing under the inguinal ligament, the external iliac artery gives off important branches, including the inferior epigastric artery and the deep circumflex iliac artery. After passing underneath the inguinal ligament, the external iliac artery transitions into the femoral artery, which is the primary blood supply to the lower limb.

Branches

The external iliac artery gives rise to two important branches before it continues as the femoral artery:

• Inferior Epigastric Artery: This artery arises just above the inguinal ligament and ascends obliquely along the posterior surface of the rectus abdominis muscle within the rectus sheath. It supplies blood to the lower anterior abdominal wall, including the rectus abdominis muscle. The inferior epigastric artery also anastomoses with the superior epigastric artery, forming a critical collateral circulation pathway.
• Deep Circumflex Iliac Artery: This artery branches laterally from the external iliac artery, running along the iliac crest and supplying the muscles and skin of the lower anterior abdominal wall and iliac fossa. It also anastomoses with the iliolumbar and lumbar arteries, contributing to the vascular network of the abdominal wall and pelvis.

Termination

The external iliac artery terminates as it passes under the inguinal ligament, at which point it continues as the femoral artery. The femoral artery is the primary blood vessel that supplies oxygenated blood to the lower limb. The transition from external iliac artery to femoral artery occurs in the femoral triangle, an anatomical region of the upper thigh.

Anatomical Relations

• Psoas Major Muscle: The external iliac artery runs along the medial border of the psoas major muscle, which helps guide the artery as it descends toward the inguinal region. The artery’s close association with this muscle is clinically relevant during surgeries or interventions involving the pelvic or abdominal regions.
• Iliac Vein: The external iliac vein runs parallel to the artery, typically positioned medial to it. The artery and vein travel together along the pelvic brim, maintaining a close relationship before they pass under the inguinal ligament.
• Inguinal Ligament: The external iliac artery passes deep to the inguinal ligament, a fibrous structure that stretches from the anterior superior iliac spine to the pubic tubercle. The inguinal ligament acts as a boundary between the pelvis and the thigh, marking the point at which the artery transitions into the femoral artery.
• Inferior Epigastric Artery: As the external iliac artery approaches the inguinal ligament, it gives rise to the inferior epigastric artery, which ascends toward the lower anterior abdominal wall. The inferior epigastric artery plays a key role in supplying blood to the rectus abdominis muscle and other abdominal structures.
• Parietal Peritoneum: The external iliac artery lies deep to the parietal peritoneum, the membrane that lines the abdominal and pelvic cavities. The artery’s positioning under this membrane helps protect it during its course within the pelvic region.

Branches and Collateral Circulation

The branches of the external iliac artery, particularly the inferior epigastric and deep circumflex iliac arteries, are important contributors to the collateral circulation of the lower abdomen and pelvis. These vessels form anastomoses with neighboring arteries, ensuring continuous blood flow to vital structures even in cases of arterial obstruction or injury.

• Inferior Epigastric Artery: Forms an anastomosis with the superior epigastric artery, which descends from the internal thoracic artery. This anastomotic connection provides an important pathway for blood flow to the abdominal wall, particularly in cases where the blood supply from the lower limb is compromised.
• Deep Circumflex Iliac Artery: This artery anastomoses with the iliolumbar and lumbar arteries, which originate from the abdominal aorta. These anastomoses provide a secondary blood supply to the lower abdominal wall and iliac fossa.

Anatomical Variations

The external iliac artery can present with some anatomical variations, particularly in its branching patterns. For example, the origin of the inferior epigastric artery can vary slightly, sometimes arising higher or lower along the course of the external iliac artery. In rare cases, the deep circumflex iliac artery may also arise from a slightly different location, such as the femoral artery, instead of the external iliac artery. These variations are important to recognize, especially during surgeries or interventional procedures involving the abdominal or pelvic regions.

Surface Anatomy and Palpation

Although the external iliac artery runs deep within the pelvis, its continuation, the femoral artery, is more superficial and can be palpated in the femoral triangle just below the inguinal ligament. The location of the external iliac artery makes it challenging to palpate directly, but its course can be approximated by tracing the path of the femoral artery upward toward the pelvis.

Function

Primary Blood Supply to the Lower Limb

The external iliac artery is the primary artery that supplies oxygenated blood to the lower limbs. After passing under the inguinal ligament, it becomes the femoral artery, which provides blood to the muscles, bones, and skin of the lower extremities. This transition allows the external iliac artery to serve as the main conduit for delivering blood from the aorta to the lower limb, supporting essential functions like walking, running, and standing.

Contribution to the Blood Supply of the Lower Abdominal Wall

The external iliac artery provides blood to the lower anterior abdominal wall through its two main branches, the inferior epigastric artery and the deep circumflex iliac artery. These arteries ensure that the muscles, fascia, and skin of the lower abdomen receive adequate blood supply.

• Inferior Epigastric Artery: This artery ascends toward the lower abdomen and supplies the rectus abdominis muscle, one of the key muscles involved in trunk flexion and stabilization. By providing oxygenated blood to this muscle, the external iliac artery helps maintain its function during activities that require bending, lifting, or maintaining posture. The inferior epigastric artery also supports the overlying skin and subcutaneous tissues.
• Deep Circumflex Iliac Artery: This artery travels along the iliac crest and supplies the muscles and skin of the lower abdominal wall and lateral pelvic region. The deep circumflex iliac artery helps maintain the health and function of these muscles, which are involved in stabilizing the core and assisting with lateral movements of the trunk.

Support for the Rectus Sheath and Collateral Circulation

The inferior epigastric artery, a branch of the external iliac artery, enters the rectus sheath and anastomoses with the superior epigastric artery (a branch of the internal thoracic artery). This anastomosis provides an essential source of collateral circulation for the anterior abdominal wall. Collateral circulation ensures that blood flow is maintained even if one part of the arterial system is obstructed or damaged. This redundancy in the blood supply is crucial for maintaining the viability of the abdominal wall muscles and skin, especially in cases of trauma, surgery, or vascular diseases.

Role in Supporting Inguinal Structures

The external iliac artery provides blood to the structures of the inguinal region, such as the inguinal canal and its contents. The inguinal canal is a passageway through which the spermatic cord (in males) or round ligament of the uterus (in females) passes. The cremasteric artery, a branch of the inferior epigastric artery, supplies the cremaster muscle in males, which is responsible for raising and lowering the testes to regulate their temperature. This function is important for maintaining an optimal temperature for spermatogenesis (the production of sperm).

In females, the cremasteric artery supplies the round ligament of the uterus, which helps support the uterus and stabilize it during pregnancy. By providing blood to these structures, the external iliac artery indirectly supports reproductive health and the stability of the reproductive organs.

Support for Pelvic Structures and Iliac Region

The deep circumflex iliac artery, another branch of the external iliac artery, contributes to the blood supply of the iliac crest and surrounding tissues, including muscles and skin of the lateral pelvic region. The deep circumflex iliac artery forms anastomoses with the iliolumbar artery and the lumbar arteries, providing an alternative route for blood flow in the event of an obstruction or injury to one of the main arteries. This anastomotic network is crucial for maintaining the blood supply to the pelvic region, supporting the integrity of the abdominal wall and pelvis.

Nutrient Supply and Oxygenation of Tissues

Like all arteries, the external iliac artery is responsible for delivering oxygenated blood and nutrients to the tissues it supplies. The muscles, fascia, skin, and bones of the lower abdominal wall and pelvis rely on the external iliac artery and its branches to receive the oxygen and nutrients necessary for cellular function and metabolism. By ensuring proper oxygenation, the external iliac artery helps maintain the health of these tissues and supports their ability to recover from injuries, stress, or physical activity.

Removal of Metabolic Waste Products

The external iliac artery’s blood flow helps in the removal of metabolic waste products from the tissues, such as carbon dioxide and lactic acid, which are byproducts of muscle activity and cellular metabolism. Efficient removal of these waste products is essential for preventing fatigue, maintaining tissue health, and promoting muscle recovery after exertion. The artery’s role in maintaining healthy blood flow to the lower abdominal wall, pelvis, and lower limbs supports tissue function and repair.

Role in Supporting Hernia Repairs and Abdominal Surgery

The external iliac artery is closely associated with the inguinal region, where it plays an important role in surgeries such as inguinal hernia repair. Since the inferior epigastric artery forms the lateral boundary of Hesselbach’s triangle (a common site for direct inguinal hernias), knowledge of the external iliac artery’s course and branches is crucial during surgical procedures in this area. The artery ensures that the lower abdominal wall and inguinal region remain well-supplied with blood, promoting tissue healing after surgery.

Contribution to the Femoral Artery and Lower Limb Circulation

The primary role of the external iliac artery is to continue as the femoral artery, the main blood vessel that supplies the lower limb. Once the external iliac artery passes under the inguinal ligament, it becomes the femoral artery, which provides oxygenated blood to the muscles, skin, and bones of the thigh, leg, and foot. This transition is critical for ensuring that the lower limbs receive a sufficient blood supply for activities such as walking, running, and maintaining balance. The external iliac artery acts as the main conduit for delivering blood to the femoral artery, which is essential for overall limb function.