Internal iliac artery

The internal iliac artery, also known as the hypogastric artery, is a major blood vessel in the pelvic region that supplies oxygenated blood to the pelvic organs, gluteal region, and parts of the reproductive organs. It originates from the common iliac artery and is one of its two main branches, the other being the external iliac artery. The internal iliac artery is vital for delivering blood to several pelvic structures, including the bladder, uterus, prostate, and parts of the thigh.

Location

The internal iliac artery is located in the pelvic cavity. It branches from the common iliac artery at the level of the sacroiliac joint, which is located near the lower lumbar vertebrae. After branching off, it descends into the pelvis along the medial side of the psoas major muscle, where it divides into two divisions: the anterior division, which supplies pelvic organs and the perineum, and the posterior division, which supplies the gluteal region and pelvic walls.

Structure and Anatomy

The internal iliac artery is a major vessel responsible for supplying blood to the pelvic organs, perineum, gluteal region, and parts of the reproductive and lower urinary systems. Below is a detailed description of its anatomy, including its origin, course, branches, and relationships with surrounding structures.

Origin

The internal iliac artery originates from the common iliac artery, which is formed by the bifurcation of the abdominal aorta at the level of the fourth lumbar vertebra (L4). The common iliac artery divides into the external iliac artery, which supplies the lower limb, and the internal iliac artery, which primarily supplies the pelvis. The internal iliac artery arises at the level of the sacroiliac joint and descends into the pelvic cavity.

Course

After originating from the common iliac artery, the internal iliac artery descends posteromedially into the pelvic cavity. It runs anterior to the sacroiliac joint and medial to the psoas major muscle, lying close to the pelvic wall. As it enters the pelvis, it follows the concave curve of the pelvic brim and then divides into two divisions: the anterior division and the posterior division. These divisions give rise to multiple branches that supply the pelvic organs, walls, and surrounding tissues.

Branches

The internal iliac artery divides into two main divisions—anterior and posterior—each giving rise to several branches that supply various pelvic structures.

Anterior Division

The anterior division primarily supplies the pelvic organs, the perineum, and parts of the thigh and gluteal region. Its branches include:

• Umbilical Artery:Gives rise to the superior vesical arteries that supply the upper part of the bladder. In adults, the distal portion of the umbilical artery becomes obliterated and forms the medial umbilical ligament.
• Obturator Artery:Travels through the obturator canal to supply the adductor muscles of the medial thigh and contributes to the vascular supply of the hip joint.
• Inferior Vesical Artery (Males):Supplies the lower part of the bladder, seminal vesicles, prostate, and adjacent structures.
• Vaginal Artery (Females):In females, the vaginal artery replaces the inferior vesical artery, supplying blood to the vagina and parts of the bladder.
• Uterine Artery (Females):A critical artery in females that supplies the uterus, fallopian tubes, and parts of the vagina.
• Middle Rectal Artery:Provides blood to the lower part of the rectum and forms anastomoses with other rectal arteries.
• Internal Pudendal Artery:Exits the pelvis through the greater sciatic foramen and re-enters via the lesser sciatic foramen, supplying the perineum, external genitalia, and the muscles of the pelvic floor.
• Inferior Gluteal Artery:Passes through the greater sciatic foramen below the piriformis muscle and supplies the gluteus maximus and parts of the posterior thigh muscles.

Posterior Division

The posterior division primarily supplies the pelvic walls, the sacrum, and the gluteal region. Its branches include:

• Iliolumbar Artery:Ascends posteriorly to supply the iliacus and psoas major muscles, as well as the lower lumbar vertebrae.
• Lateral Sacral Arteries:These arteries descend along the anterior surface of the sacrum, sending branches through the sacral foramina to supply the sacral vertebrae, spinal meninges, and sacral nerves.
• Superior Gluteal Artery:Exits the pelvis through the greater sciatic foramen above the piriformis muscle and supplies the gluteus medius, gluteus minimus, and tensor fasciae latae muscles.

Relations to Other Structures

The internal iliac artery and its branches are closely related to several key anatomical structures in the pelvis:

• Ureter: The ureter crosses over the internal iliac artery on its way to the bladder. This relationship is important during pelvic surgeries, where damage to the ureter must be avoided.
• Pelvic Organs: The branches of the internal iliac artery are closely related to the bladder, uterus, prostate, and rectum, supplying blood to these organs and surrounding tissues.
• Nerves: The internal iliac artery and its branches run in proximity to important pelvic nerves, including the sciatic nerve, lumbosacral trunk, and pudendal nerve. Care must be taken to avoid nerve injury during pelvic procedures.

Variations

The branching pattern of the internal iliac artery can vary significantly between individuals. Some common variations include:

• Aberrant Obturator Artery: The obturator artery may arise from the external iliac artery or the inferior epigastric artery rather than from the anterior division of the internal iliac artery. This is known as an aberrant obturator artery and occurs in about 20% of individuals.
• Variable Origin of Branches: The origin of other branches, such as the inferior gluteal artery, internal pudendal artery, or uterine artery, can also vary between individuals.

Function

The internal iliac artery plays a vital role in supplying blood to several key structures within the pelvic region, lower abdomen, and portions of the lower limb. Below is a detailed explanation of its specific functions.

Blood Supply to Pelvic Organs

The internal iliac artery is the primary blood source for many pelvic organs, ensuring that they receive oxygen and nutrients to maintain their physiological functions.

• Bladder: The branches of the internal iliac artery, particularly the superior vesical and inferior vesical arteries in males (or vaginal artery in females), supply the urinary bladder. These arteries ensure proper perfusion to the bladder wall, enabling the bladder to store and expel urine effectively.
• Uterus and Vagina (Females): In females, the uterine artery supplies the uterus, including its body, cervix, and parts of the fallopian tubes. The vaginal artery provides blood to the vagina. These arteries are essential during pregnancy, menstruation, and reproductive processes, maintaining the health of the reproductive organs.
• Prostate and Seminal Vesicles (Males): In males, the inferior vesical artery supplies the prostate gland and seminal vesicles, essential for male reproductive health, particularly in producing seminal fluid.
• Rectum: The middle rectal artery, a branch of the internal iliac artery, provides blood to the lower portion of the rectum, supporting bowel function and aiding in the health of the gastrointestinal tract.

Blood Supply to the Gluteal Region

The internal iliac artery is critical for supplying blood to the gluteal muscles and surrounding structures in the buttock and hip areas.

• Superior Gluteal Artery: This artery, which arises from the posterior division of the internal iliac artery, supplies the gluteus medius, gluteus minimus, and tensor fasciae latae muscles. These muscles are crucial for hip stabilization, abduction, and movement of the lower limb.
• Inferior Gluteal Artery: This artery supplies the gluteus maximus, the largest muscle of the buttocks, which plays an essential role in hip extension, especially during walking, running, or climbing. It also supplies the hamstrings in the posterior thigh.

By supplying the muscles of the gluteal region, the internal iliac artery plays a significant role in maintaining proper lower limb movement, posture, and pelvic stability.

Blood Supply to the Hip Joint and Thigh

The internal iliac artery contributes to the vascularization of the hip joint and parts of the medial thigh, which are essential for hip movement and stability.

• Obturator Artery: The obturator artery, a branch of the anterior division of the internal iliac artery, passes through the obturator canal to supply the medial compartment of the thigh, which includes the adductor muscles responsible for moving the thigh inward. This artery also contributes to the blood supply of the hip joint, particularly through its acetabular branch, which nourishes the head of the femur.
• Anastomosis with Femoral Arteries: The internal iliac artery, through its branches, forms anastomoses (connections) with other arteries like the medial and lateral circumflex femoral arteries, which supply the hip joint and upper thigh. These anastomoses ensure continuous blood flow to the hip and thigh regions, even if one artery becomes obstructed.

Blood Supply to the Perineum and External Genitalia

The internal iliac artery plays an essential role in supplying the perineum and external genitalia, particularly through the internal pudendal artery, which branches off from the anterior division.

• Perineum: The internal pudendal artery provides blood to the perineal muscles, external anal sphincter, and pelvic floor muscles, which are critical for controlling urination, defecation, and supporting the pelvic organs.
• External Genitalia: In both males and females, the internal pudendal artery supplies blood to the external genitalia. In males, it supplies the penis (via branches such as the dorsal artery of the penis) and the scrotum. In females, it supplies the clitoris, labia, and other structures of the vulva.

The blood supply provided by the internal iliac artery to these areas is crucial for normal sexual function and urinary control.

Blood Supply to the Pelvic Walls and Lumbar Region

The internal iliac artery, particularly through its posterior division, is responsible for vascularizing the pelvic walls, muscles, and parts of the lumbar region.

• Iliolumbar Artery: The iliolumbar artery ascends from the posterior division of the internal iliac artery to supply the iliacus and psoas major muscles, which are critical for hip flexion. It also provides blood to the lumbar vertebrae, supporting the lower spine’s structural integrity.
• Lateral Sacral Arteries: The lateral sacral arteries descend to supply the sacrum and coccyx and send branches through the sacral foramina to provide blood to the sacral nerves and spinal meninges. This vascular supply is essential for supporting the lower spinal column and sacral region.

Contribution to Pelvic Vascular Network and Anastomoses

The internal iliac artery forms an integral part of the pelvic vascular network, contributing to a series of anastomoses with other arteries. This network ensures adequate blood flow to the pelvic region, even if one artery is blocked or damaged.

• Anastomoses with External Iliac and Femoral Arteries: The internal iliac artery branches, such as the obturator artery, form anastomoses with branches from the external iliac and femoral arteries, providing alternate routes of blood flow to the hip and thigh.
• Anastomoses with Rectal and Vesical Arteries: The internal iliac artery’s branches, such as the middle rectal and vesical arteries, form anastomoses with other arteries supplying the rectum and bladder, ensuring consistent blood flow to these critical pelvic organs.

Support for Pregnancy and Childbirth (Females)

In females, the internal iliac artery’s branches, particularly the uterine artery, play a critical role in supporting pregnancy and childbirth by supplying blood to the uterus. During pregnancy, the uterine artery expands to accommodate the increased blood flow necessary for fetal development and the growing placenta. This function is essential for sustaining a healthy pregnancy and supporting the uterus during labor and delivery.

Clinical Significance

The internal iliac artery is crucial in both surgical and clinical settings due to its role in supplying blood to vital pelvic organs, the gluteal region, the perineum, and parts of the lower limb. Its branches supply the bladder, uterus, prostate, rectum, gluteal muscles, and external genitalia, making it essential in surgeries involving these areas.

In procedures like hysterectomy, prostatectomy, or pelvic tumor resection, careful management of the internal iliac artery is required to prevent excessive bleeding. Damage to this artery or its branches can lead to significant complications, including hemorrhage, ischemia, or organ dysfunction.

In trauma cases, such as pelvic fractures, the internal iliac artery can be damaged, resulting in life-threatening hemorrhage due to its extensive vascularization of the pelvis. Embolization techniques may be used to control bleeding in cases of trauma or during the management of arteriovenous malformations (AVMs) or pelvic aneurysms. Additionally, its role in the blood supply to the uterus makes it significant in obstetrics, particularly in conditions like postpartum hemorrhage where the artery may need to be ligated or embolized to control bleeding.