The Iliac Arteries Immediately Subdivide Into The

The iliac arteries, vital conduits of blood supply, play a pivotal role in nourishing the lower extremities and pelvic region. Immediately upon descending into the pelvis, each common iliac artery bifurcates, giving rise to two major branches: the internal iliac artery and the external iliac artery. This division marks a critical juncture in the arterial network, dictating the pathways through which blood reaches specific anatomical territories. Understanding the subsequent branching patterns and target areas of these arteries is fundamental to comprehending the vascular anatomy of the lower body.

Internal Iliac Artery: The Pelvic Provider

The internal iliac artery, also known as the hypogastric artery, courses medially into the pelvis and serves as the primary blood supplier to the pelvic organs, pelvic walls, perineum, and gluteal region. Its branching pattern is complex and variable, often differing slightly between individuals. However, the general arrangement and target areas remain consistent, making it possible to delineate key branches and their respective functions.

Major Branches of the Internal Iliac Artery

The internal iliac artery typically divides into an anterior and a posterior division, each giving rise to distinct branches:

• Anterior Division: This division primarily supplies the pelvic viscera, perineum, and medial thigh. Key branches include:

  • Umbilical Artery: In the fetus, this artery carries deoxygenated blood to the placenta. After birth, the distal portion obliterates to form the medial umbilical ligament, while the proximal portion remains patent as the superior vesical artery, supplying the bladder.
  • Superior Vesical Artery: As mentioned above, this artery arises from the patent portion of the umbilical artery and supplies the superior part of the bladder.
  • Inferior Vesical Artery: Present primarily in males, this artery supplies the bladder, seminal vesicles, and prostate. It may also give rise to the artery to the ductus deferens. In females, this artery is often replaced by the vaginal artery or arises as a branch of the vaginal artery.
  • Middle Rectal Artery: Supplies the rectum. It anastomoses with the superior rectal artery (a branch of the inferior mesenteric artery) and the inferior rectal artery (a branch of the internal pudendal artery), providing collateral circulation.
  • Obturator Artery: Passes through the obturator foramen to supply the medial thigh muscles. An important variation occurs when the aberrant obturator artery arises from the external iliac artery or inferior epigastric artery, which can be vulnerable during surgical procedures in the femoral triangle.
  • Internal Pudendal Artery: This is a major artery supplying the perineum and external genitalia. It exits the pelvis through the greater sciatic foramen, curves around the ischial spine, and re-enters the perineum through the lesser sciatic foramen. It gives rise to branches such as the inferior rectal artery, perineal artery, dorsal artery of the penis/clitoris, and deep artery of the penis/clitoris.
  • Inferior Gluteal Artery: Exits the pelvis through the greater sciatic foramen, inferior to the piriformis muscle. Supplies the gluteal region, hip joint, and posterior thigh.
  • Uterine Artery (Females only): A vital artery supplying the uterus, uterine tubes, and superior vagina. It crosses superior to the ureter ("water under the bridge") and gives rise to the vaginal artery.
  • Vaginal Artery (Females only): Supplies the vagina and adjacent bladder. It may arise directly from the internal iliac artery or as a branch of the uterine artery.

• Posterior Division: This division primarily supplies the posterior pelvic wall, lumbar region, and gluteal region. Key branches include:

  • Iliolumbar Artery: Ascends to supply the iliacus muscle, psoas major muscle, quadratus lumborum muscle, and lumbar vertebrae. It also gives off a spinal branch that enters the vertebral canal.
  • Lateral Sacral Arteries: Supply the sacrum, sacral nerve roots, and erector spinae muscles.
  • Superior Gluteal Artery: The largest branch of the internal iliac artery. It exits the pelvis through the greater sciatic foramen, superior to the piriformis muscle. It supplies the gluteus maximus, gluteus medius, and gluteus minimus muscles.

Clinical Significance of the Internal Iliac Artery

• Pelvic Fractures: Severe pelvic fractures can rupture branches of the internal iliac artery, leading to significant hemorrhage. Angiography and embolization may be required to control the bleeding.
• Postpartum Hemorrhage: In cases of severe postpartum hemorrhage unresponsive to other treatments, internal iliac artery ligation may be performed to reduce blood flow to the uterus.
• Pelvic Tumors: The internal iliac artery and its branches can be involved in the blood supply to pelvic tumors, necessitating careful consideration during surgical resection.
• Aneurysms: Aneurysms of the internal iliac artery are rare but can occur. They may present with pelvic pain or lower extremity ischemia.

External Iliac Artery: The Leg's Lifeline

The external iliac artery, larger than the internal iliac artery, continues along the pelvic brim, passing deep to the inguinal ligament to enter the thigh. Once it crosses under the inguinal ligament, it becomes the femoral artery, the primary artery of the lower limb. The external iliac artery supplies blood to the lower limb and abdominal wall.

Branches of the External Iliac Artery

The external iliac artery gives rise to two main branches before becoming the femoral artery:

• Inferior Epigastric Artery: Arises just proximal to the inguinal ligament and ascends along the anterior abdominal wall, deep to the rectus abdominis muscle. It supplies the lower abdominal wall muscles and skin. It anastomoses with the superior epigastric artery (a branch of the internal thoracic artery), providing collateral circulation.
• Deep Circumflex Iliac Artery: Arises laterally from the external iliac artery, near the inguinal ligament. It runs along the iliac crest, supplying the iliacus muscle, abdominal wall muscles, and skin.

Clinical Significance of the External Iliac Artery

• Peripheral Artery Disease (PAD): The external iliac artery is a common site for atherosclerosis, leading to narrowing or blockage of the artery. This can cause claudication (leg pain with exercise), critical limb ischemia, and even amputation.
• Aortoiliac Occlusive Disease: The external iliac artery can be affected by aortoiliac occlusive disease, a condition in which plaque buildup narrows or blocks the aorta and iliac arteries. This can cause buttock and thigh claudication, erectile dysfunction (Leriche syndrome), and lower extremity ischemia.
• Femoral Artery Access: The external iliac artery serves as a common access point for endovascular procedures, such as angioplasty and stenting, to treat PAD and other vascular conditions.
• Lymph Node Dissection: During lymph node dissection for pelvic or lower extremity cancers, the external iliac artery must be carefully preserved to maintain blood flow to the leg.

Anastomoses: Ensuring Collateral Circulation

Anastomoses, connections between different arteries, play a crucial role in providing collateral circulation. If one artery becomes blocked or narrowed, blood can still reach the tissues it supplies via these alternative routes. Several important anastomoses involve branches of the internal and external iliac arteries:

• Pelvic Anastomoses: The superior rectal artery (from the inferior mesenteric artery) anastomoses with the middle rectal artery (from the internal iliac artery) and the inferior rectal artery (from the internal pudendal artery), providing collateral circulation to the rectum.
• Abdominal Wall Anastomoses: The superior epigastric artery (from the internal thoracic artery) anastomoses with the inferior epigastric artery (from the external iliac artery), providing collateral circulation to the anterior abdominal wall. The deep circumflex iliac artery (from the external iliac artery) also contributes to this network.
• Gluteal Anastomoses: The superior gluteal artery (from the internal iliac artery) anastomoses with the inferior gluteal artery (from the internal iliac artery) and branches of the femoral artery, providing collateral circulation to the gluteal region and hip joint.
• Obturator Anastomoses: The obturator artery (from the internal iliac artery) may anastomose with the femoral circumflex arteries (from the femoral artery) in the medial thigh.

Developmental Considerations

The development of the iliac arteries is complex and involves significant remodeling of the embryonic vasculature. The common iliac arteries arise from the umbilical arteries, which initially carry blood to the placenta. After birth, the distal portions of the umbilical arteries obliterate to form the medial umbilical ligaments, while the proximal portions persist as the superior vesical arteries. The internal and external iliac arteries differentiate from the common iliac arteries, with the internal iliac artery retaining a greater resemblance to the embryonic umbilical artery. Variations in the branching patterns of the internal iliac artery are common and reflect the plasticity of the developing vascular system.

Detailed Anatomical Relationships

Understanding the anatomical relationships of the iliac arteries to surrounding structures is crucial for surgeons and interventional radiologists. Here's a more detailed look:

• Common Iliac Artery: The common iliac arteries are retroperitoneal structures, meaning they lie behind the peritoneum. They run along the medial border of the psoas major muscle. The left common iliac artery is crossed anteriorly by the sigmoid colon and mesentery. The ureters also cross anterior to the common iliac arteries.
• Internal Iliac Artery: The internal iliac artery courses medially into the pelvis, passing anterior to the sacroiliac joint. It lies posterior to the ureter and lateral to the rectum. The internal iliac vein lies posterior and medial to the artery. The lumbosacral trunk (a major nerve branch of the lumbar plexus) lies posterior to the internal iliac artery.
• External Iliac Artery: The external iliac artery runs along the pelvic brim, following the medial border of the psoas major muscle. It is covered by the peritoneum. The genitofemoral nerve runs along the surface of the psoas major muscle, lateral to the external iliac artery. The external iliac vein lies medial to the artery. The deep inguinal lymph nodes are located around the external iliac artery.

Imaging Modalities

Various imaging modalities are used to visualize the iliac arteries and diagnose vascular disease. These include:

• Duplex Ultrasound: A non-invasive technique that uses sound waves to image the arteries and measure blood flow velocity. It can detect stenosis (narrowing) or occlusion (blockage) of the iliac arteries.
• Computed Tomography Angiography (CTA): A CT scan with intravenous contrast that provides detailed images of the iliac arteries. It can detect aneurysms, dissections, and atherosclerotic disease.
• Magnetic Resonance Angiography (MRA): An MRI scan with intravenous contrast that provides images of the iliac arteries. It is useful for patients with contraindications to CT contrast.
• Conventional Angiography: An invasive procedure in which a catheter is inserted into the femoral artery or brachial artery and advanced to the iliac arteries. Contrast is injected, and X-ray images are taken. It is considered the "gold standard" for imaging the iliac arteries but is used less frequently due to the availability of less invasive techniques.

Surgical and Interventional Procedures

Various surgical and interventional procedures are performed on the iliac arteries to treat vascular disease. These include:

• Angioplasty and Stenting: A minimally invasive procedure in which a balloon catheter is inserted into the iliac artery and inflated to widen the narrowed segment. A stent (a small metal mesh tube) is then placed to keep the artery open.
• Bypass Grafting: A surgical procedure in which a graft (a synthetic tube or a vein from the patient's own body) is used to bypass a blocked or narrowed segment of the iliac artery. The graft is sewn to the artery above and below the blockage.
• Endarterectomy: A surgical procedure in which the plaque buildup is removed from the inner lining of the iliac artery.
• Thromboembolectomy: A surgical procedure to remove a thrombus (blood clot) or embolus (a traveling blood clot) from the iliac artery.
• Internal Iliac Artery Ligation: A surgical procedure in which the internal iliac artery is tied off to control bleeding in the pelvis, such as in cases of severe postpartum hemorrhage or pelvic trauma.

The Iliac Arteries: A Summary of Key Functions

• Blood Supply: The primary function of the iliac arteries is to provide blood supply to the lower extremities, pelvic organs, pelvic walls, perineum, and gluteal region.
• Collateral Circulation: The iliac arteries participate in important anastomoses that provide collateral circulation in case of arterial blockage.
• Surgical Access: The external iliac artery serves as a common access point for endovascular procedures.
• Landmark: The iliac arteries serve as important landmarks for surgeons and interventional radiologists.

Emerging Research and Future Directions

Research continues to refine our understanding of the iliac arteries and their role in health and disease. Areas of focus include:

• Advanced Imaging Techniques: Development of new imaging techniques, such as 4D flow MRI, to better visualize blood flow patterns in the iliac arteries and identify areas of turbulence that may be prone to atherosclerosis.
• Personalized Treatment Strategies: Tailoring treatment strategies for PAD based on individual patient characteristics, such as the location and severity of the arterial disease, the presence of comorbidities, and the patient's overall health status.
• Drug-Eluting Stents: Development of new drug-eluting stents that release medications to prevent restenosis (re-narrowing) of the artery after angioplasty.
• Gene Therapy and Stem Cell Therapy: Investigating the potential of gene therapy and stem cell therapy to promote angiogenesis (new blood vessel growth) and improve blood flow in patients with severe PAD.
• Computational Modeling: Using computational modeling to simulate blood flow in the iliac arteries and predict the outcome of different treatment strategies.

Frequently Asked Questions (FAQ)

• What happens if the iliac artery is blocked? A blockage in the iliac artery can lead to decreased blood flow to the lower extremity, causing claudication (leg pain with exercise), critical limb ischemia (severe pain at rest, non-healing wounds), and even amputation.
• How is iliac artery disease diagnosed? Iliac artery disease is typically diagnosed using a combination of physical examination, ankle-brachial index (ABI) measurement, duplex ultrasound, CTA, or MRA.
• What are the risk factors for iliac artery disease? Risk factors for iliac artery disease include smoking, diabetes, high blood pressure, high cholesterol, obesity, and a family history of vascular disease.
• Can iliac artery disease be prevented? Yes, adopting a healthy lifestyle, including quitting smoking, controlling blood sugar and blood pressure, lowering cholesterol, maintaining a healthy weight, and exercising regularly, can help prevent iliac artery disease.
• What is the difference between the internal and external iliac arteries? The internal iliac artery supplies the pelvic organs, pelvic walls, perineum, and gluteal region, while the external iliac artery supplies the lower limb and abdominal wall.
• Where does the external iliac artery become the femoral artery? The external iliac artery becomes the femoral artery as it passes under the inguinal ligament.
• What are the branches of the internal iliac artery? The branches of the internal iliac artery include the umbilical artery, superior vesical artery, inferior vesical artery, middle rectal artery, obturator artery, internal pudendal artery, inferior gluteal artery, uterine artery (in females), vaginal artery (in females), iliolumbar artery, lateral sacral arteries, and superior gluteal artery.
• What are the branches of the external iliac artery? The branches of the external iliac artery are the inferior epigastric artery and the deep circumflex iliac artery.

Conclusion

The division of the iliac arteries into the internal and external iliac arteries marks a critical point in the vascular anatomy of the lower body. The internal iliac artery serves as the primary blood supply to the pelvis and related structures, while the external iliac artery becomes the femoral artery, the major vessel of the lower limb. A thorough understanding of the branching patterns, anatomical relationships, and clinical significance of these arteries is essential for healthcare professionals involved in the diagnosis and treatment of vascular disease. The existence of anastomoses provides crucial collateral circulation, ensuring that tissues remain perfused even in the event of arterial obstruction. Continued research promises to further refine our understanding of these vital vessels and improve outcomes for patients with iliac artery disease.