Internal Iliac Artery

The internal iliac artery is the principal artery of the pelvis, supplying most of the blood to the pelvic viscera and some to the musculoskeletal part of the pelvis; however, it also supplies branches to the gluteal region, medial thigh regions, and the perineum.

Each internal iliac artery, approximately 4 cm long, begins as the common iliac artery and bifurcates into the internal and external iliac arteries at the level of the IV disc between the L₅ and S₁ vertebrae. The ureter crosses the common iliac artery or its terminal branches at or immediately distal to the bifurcation. The internal iliac artery is separated from the sacro-iliac joint by the internal iliac vein and the lumbosacral trunk. It descends posteromedially into the lesser pelvis, medial to the external iliac vein and obturator nerve, and lateral to the peritoneum.

Anterior Division of Internal Iliac Artery

Although variations are common, the internal iliac artery usually ends at the superior edge of the greater sciatic foramen by dividing into anterior and posterior divisions (trunks). The branches of the anterior division of the internal iliac artery are mainly visceral (i.e., they supply the bladder, rectum, and reproductive organs), but they also include parietal branches that pass to the thigh and buttocks. The arrangement of the visceral branches is variable.

Umbilical Artery

Before birth, the umbilical arteries are the main continuation of the internal iliac arteries, passing along the lateral pelvic wall and then ascending the anterior abdominal wall to and through the umbilical ring into the umbilical cord.

Prenatally, the umbilical arteries conduct oxygen- and nutrient-deficient blood to the placenta for replenishment. When the umbilical cord is cut, the distal parts of these vessels no longer function and become occluded distal to branches that pass to the bladder. The occluded parts form fibrous cords called the medial umbilical ligaments. The ligaments raise folds of peritoneum (medial umbilical folds) on the deep surface of the anterior abdominal wall.

Postnatally, the patent parts of the umbilical arteries run antero-inferiorly between the urinary bladder and the lateral wall of the pelvis.

Obturator Artery

The origin of the obturator artery is variable; usually it arises close to the origin of the umbilical artery, where it is crossed by the ureter. It runs antero-inferiorly on the obturator fascia on the lateral wall of the pelvis, and passes between the obturator nerve and vein.

Within the pelvis, the obturator artery gives off muscular branches, a nutrient artery to the ilium, and a pubic branch. The pubic branch arises just before the obturator artery leaves the pelvis. It ascends on the pelvic surface of the pubis to anastomose with its fellow of the opposite side, and the pubic branch of the inferior epigastric artery, a branch of the external iliac artery.

In a common variation (20%), an aberrant or accessory obturator artery arises from the inferior epigastric artery and descends into the pelvis along the usual route of the pubic branch. Surgeons performing hernia repairs must keep this common variation in mind.

Inferior Vesical Artery

The inferior vesical artery occurs only in males, being replaced by the vaginal artery in females.

Uterine Artery

The uterine artery is an additional branch of the internal iliac artery in females, usually arising separately and directly from the internal iliac artery. It may arise from the umbilical artery. Developmentally, it is the homolog of the artery to the ductus deferens in the male. It descends on the lateral wall of the pelvis, anterior to the internal iliac artery, and passes medially to reach the junction of the uterus and vagina, where the cervix (neck) of the uterus protrudes into the superior vagina. As it passes medially, the uterine artery passes directly superior to the ureter. The relationship of ureter to artery is often remembered by the phrase "water (urine) passes under the bridge (uterine artery)." On reaching the side of the cervix, the uterine artery divides into a smaller descending vaginal branch, which supplies the cervix and vagina, and a larger ascending branch, which runs along the lateral margin of the uterus, supplying it. The ascending branch bifurcates into ovarian and tubal branches, which continue to supply the medial ends of the ovary and uterine tube, and anastomose with the ovarian and tubal branches of the ovarian artery.

Vaginal Artery

The vaginal artery is the homolog to the inferior vesical artery in males. It often arises from the initial part of the uterine artery instead of arising directly from the anterior division. The vaginal artery supplies numerous branches to the anterior and posterior surfaces of the vagina.

Middle Rectal Artery

The middle rectal artery may arise independently from the internal iliac artery, or it may arise in common with the inferior vesical artery or the internal pudendal artery.

Internal Pudendal Artery

The internal pudendal artery, larger in males than in females, passes inferolaterally, anterior to the piriformis muscle and sacral plexus. It leaves the pelvis between the piriformis and coccygeus muscles by passing through the inferior part of the greater sciatic foramen. The internal pudendal artery then passes around the posterior aspect of the ischial spine or the sacrospinous ligament and enters the ischio-anal fossa through the lesser sciatic foramen.

The internal pudendal artery, along with the internal pudendal veins and branches of the pudendal nerve, passes through the pudendal canal in the lateral wall of the ischio-anal fossa. As it exits the pudendal canal, medial to the ischial tuberosity, the internal pudendal artery divides into its terminal branches, the perineal artery and dorsal arteries of the penis or clitoris.

Inferior Gluteal Artery

The inferior gluteal artery is the larger terminal branch of the anterior division of the internal iliac artery, but may arise from the posterior division. It passes posteriorly between the sacral nerves (usually S₂ and S₃), and leaves the pelvis through the inferior part of the greater sciatic foramen, inferior to the piriformis muscle. It supplies the muscles and skin of the buttock, and the posterior surface of the thigh.

Posterior Division of Internal Iliac Artery

When the internal iliac artery divides into anterior and posterior divisions, the posterior division typically gives rise to the following three parietal arteries:

• Iliolumbar artery: This artery runs superolaterally in a recurrent fashion (turning sharply backward relative to its source) to the iliac fossa. Within the fossa, the artery divides into an iliac branch, which supplies the iliacus muscle and ilium, and a lumbar branch, which supplies the psoas major and quadratus lumborum muscles.

• Lateral sacral arteries: Superior and inferior lateral sacral arteries may arise as independent branches or via a common trunk. The lateral sacral arteries pass medially and descend anterior to the sacral anterior rami, giving off spinal branches, which pass through the anterior sacral foramina, and supply the spinal meninges enclosing the roots of the sacral nerves. Some branches of these arteries pass from the sacral canal through the posterior sacral foramina and supply the erector spinae muscles of the back and the skin overlying the sacrum.

• Superior gluteal artery: The largest branch of the posterior division, the superior gluteal artery supplies the gluteal muscles in the buttocks.