Internal Iliac Artery: Anatomy, Branches, and Procedures

The internal iliac artery is the main blood supply to the pelvis, feeding the bladder, rectum, reproductive organs, pelvic floor muscles, and gluteal muscles of the buttock. It branches off the common iliac artery on each side of the body, roughly at the level of the sacroiliac joint, and then divides further into an intricate tree of smaller vessels. Surgeons, radiologists, and obstetricians deal with this artery more often than most people realize, because it sits at the center of procedures ranging from emergency hemorrhage control to kidney transplantation to cancer treatment.

Where the Artery Sits and How It Divides

The aorta, your body’s largest artery, splits into left and right common iliac arteries near the navel. Each common iliac then forks again: the external iliac continues down the leg to become the femoral artery, while the internal iliac dives into the pelvis. Once inside the pelvis, the internal iliac typically splits into two trunks called the anterior and posterior divisions. The posterior division is the smaller of the two and mainly supplies the pelvic wall and gluteal region. The anterior division is larger and more clinically significant, sending branches to the bladder, uterus or prostate, rectum, and perineum.

In a cadaveric study of 106 pelvic halves, the posterior division’s arteries arose from a common trunk about 62% of the time; in the remaining cases, individual branches came off the main internal iliac artery independently, with the iliolumbar artery being the first branch in roughly 28% of specimens.¹ The anterior division carries the uterine artery, the obturator artery, the internal pudendal artery, the inferior gluteal artery, and several others. These names matter less to a general reader than the key point: each branch goes to a specific organ or muscle group, so knowing exactly where it originates determines what tissue is at risk during surgery or embolization.

Branching Variations Are the Rule, Not the Exception

Textbook diagrams show a single neat branching pattern, but real anatomy is messier. A South Indian cadaveric study found branching variations in 61% of hemipelvises examined, with the anterior division showing more variability (48% of cases) than the posterior division (20%).² In 3% of those specimens, the internal iliac artery did not divide into two divisions at all. The obturator artery varied in a quarter of cases, and the iliolumbar artery in nearly a third.

Population-level differences make this even more complex. A CT-based study of a western Mexican population classified arteries using the standard Adachi system and found that the most common pattern (Type I) appeared in about 71% of patients, but the second most frequent variant was Type V at roughly 13%, a pattern that is rare in most other populations studied.³ This kind of ethnic and geographic variation means that a surgeon trained on anatomy atlases drawn from European cadavers can encounter surprise configurations in patients from different backgrounds.

For interventional radiologists threading a catheter through these vessels, an unexpected branch origin can turn a routine procedure into a difficult one. The obturator artery, for instance, sometimes arises from the external iliac or even from the inferior epigastric artery rather than from the internal iliac. A surgeon who does not recognize the variant can injure the artery during hernia repair or pelvic surgery. CT angiography and MR angiography have become standard pre-procedural mapping tools for exactly this reason, allowing clinicians to visualize how a particular patient’s internal iliac artery branches before they operate.⁴ Three-dimensional MR angiography can also map pelvic arteries in women before uterine artery embolization for fibroids, providing a detailed roadmap of branch origins.⁵

Tying Off the Artery to Stop Obstetric Bleeding

One of the oldest and most dramatic uses of the internal iliac artery in medicine is surgical ligation, physically tying it shut to stop life-threatening bleeding during or after childbirth. When a woman hemorrhages massively after delivery and simpler measures fail, clamping the internal iliac artery on one or both sides reduces the pulse pressure downstream, converting arterial-type bleeding into slower, venous-type flow that can clot on its own. The surgical approach involves opening the retroperitoneal space, dissecting alongside the rectum, identifying the artery, and placing a suture or clip around it distal to where the posterior division branches off.⁶

Success rates are high. One study reported that bilateral internal iliac artery ligation controlled hemorrhage in about 97% of cases, often allowing women to avoid hysterectomy entirely.⁷ A larger series of 90 women found the procedure successful in about 83%, with the remaining 17% still requiring hysterectomy.⁸ These numbers reflect a procedure that works well as a second-line option before resorting to removing the uterus, which permanently ends fertility.

The reason ligation does not kill pelvic tissue is the internal iliac artery’s rich network of collateral connections. Blood finds alternative routes, primarily through the ovarian arteries from the aorta and through anastomoses between branches of the external and internal iliac systems. This collateral supply is robust enough that women can menstruate normally and become pregnant again after bilateral ligation, though the evidence on subsequent fertility is mixed and based on small cohorts.

Pelvic Trauma and Catheter-Based Embolization

High-energy pelvic fractures, the kind you see in car crashes and falls from height, can shear through branches of the internal iliac artery and cause massive retroperitoneal bleeding. Because the bleeding is deep in the pelvis and not easily accessible through open surgery, transcatheter embolization has become a first-line treatment at many trauma centers.⁹ A radiologist threads a catheter from the groin up into the internal iliac system, identifies the bleeding vessel on fluoroscopy, and plugs it with coils, gel foam, or other materials.

The internal iliac artery and its branches are the most commonly embolized vessels in pelvic fracture bleeding, followed by the superior gluteal and obturator arteries. Technical success rates range from 74% to 100% depending on the study and severity of injury.¹⁰ The same embolization principles apply to postpartum hemorrhage when surgical ligation is not feasible or when the team prefers a less invasive approach. A follow-up study of women who underwent pelvic artery embolization for postpartum hemorrhage found that about 73% had regular menstruation afterward, and among those who attempted another pregnancy, roughly a third eventually delivered a live baby, though miscarriage rates were high in this small cohort.¹¹

Aneurysms of the Internal Iliac Artery

An aneurysm, a balloon-like weakening and expansion of an artery wall, can form in the internal iliac artery just as it can in the aorta. Isolated internal iliac artery aneurysms are uncommon but dangerous because they sit deep in the pelvis where they can grow large before causing symptoms. One multi-center study found that about half of patients were asymptomatic at diagnosis, while roughly 38% presented with abdominal pain, including a subset with rupture. Among those who ruptured, 30-day mortality was 17%.¹²

Endovascular repair, using stent grafts and coils placed through catheters, has become the preferred treatment because open surgical access to the deep pelvis is technically demanding and carries higher morbidity. A pooled review of 55 patients treated endovascularly for internal iliac artery aneurysms reported technical success in 71% of cases, with satisfactory mid-term results and about 18% treated on an urgent or emergency basis for rupture.¹³ More recent techniques using iliac branch devices, which maintain flow through the internal iliac artery while excluding the aneurysm, have improved outcomes and reduced the ischemic side effects associated with simply blocking the artery off.

What Happens When the Internal Iliac Artery Is Blocked

During endovascular aortic aneurysm repair, surgeons sometimes need to cover or embolize one or both internal iliac arteries to get a proper seal for the stent graft. This is where the consequences of losing internal iliac flow become clinically apparent. The most common complaint is buttock claudication, a cramping pain in the buttock muscles during walking caused by insufficient blood flow to the gluteal muscles. In one prospective study, 12 of 13 patients who had internal iliac embolization experienced claudication on a six-minute walk test, and the problem was significantly worse and more persistent when both sides were embolized compared to just one.¹⁴

A matched case-control study found that short-term buttock claudication occurred in about 71% of patients whose internal iliac artery was occluded during aneurysm repair, compared to 35% in controls whose artery was preserved. Even at long-term follow-up, 57% of the occluded group still had symptoms versus 26% in controls.¹⁵ Erectile dysfunction was very common in both groups in this study, likely reflecting the older age and vascular disease burden of these patients rather than the artery occlusion alone.

Preserving flow through at least one internal iliac artery has become a priority in modern aortoiliac surgery. A comparison of patients whose internal iliac flow was interrupted versus preserved found buttock claudication in about 18% of limbs with interrupted flow and in none of the limbs with preserved flow.¹⁶ Iliac branch devices that maintain perfusion through the internal iliac artery have made this preservation feasible, though they add complexity and cost to the procedure.

How Collateral Circulation Compensates

The pelvis has one of the most extensive collateral networks in the body. When the internal iliac artery is slowly occluded by atherosclerosis or deliberately blocked during surgery, blood reroutes through a web of alternative pathways. These can be classified broadly as connections between the visceral and systemic circulation, between different systemic arteries, and between different visceral arteries.¹⁷

One particularly important rescue pathway runs from the deep femoral artery in the thigh, through the medial femoral circumflex artery, and connects to the obturator artery, which feeds back into the internal iliac territory and the gluteal arteries. Research has identified this pathway as a major collateral route for preserving pelvic circulation after one-sided internal iliac artery interruption.¹⁸ This is why preserving the deep femoral artery during leg surgery matters, and it partly explains why some patients tolerate internal iliac occlusion with minimal symptoms while others develop debilitating claudication: the robustness of these collateral paths varies from person to person.

The Internal Iliac Artery in Kidney Transplantation

When a donor kidney is placed in the pelvis during transplantation, the surgeon needs an artery to connect it to. The most common approach uses the external iliac artery, but the internal iliac artery is an alternative, particularly when the external iliac is heavily calcified or has been used for a prior transplant. The technique involves performing an end-to-side or end-to-end connection between the renal artery and the internal iliac artery.¹⁹

A comparative study of kidney transplants anastomosed to the internal versus external iliac artery found no significant differences in urinary output recovery, creatinine clearance, surgical complications, hospital stay, or graft survival over three years of follow-up. Erectile dysfunction rates were also similar between the two groups, driven mainly by pre-existing medical conditions and patient age rather than the choice of artery.²⁰ This equivalence gives surgeons flexibility, though the internal iliac option does sacrifice future pelvic blood supply on that side.

Cancer Treatment Through Internal Iliac Branches

Because the internal iliac artery feeds the bladder, prostate, uterus, and rectum, it serves as a delivery route for targeted chemotherapy in pelvic cancers. Infusing chemotherapy directly into the internal iliac artery delivers a high concentration of drug to the tumor bed while limiting systemic exposure. Early work on bilateral internal iliac artery chemotherapy infusion for advanced bladder cancer showed that about 60% of patients had a significant tumor response, with hematuria controlled in most cases and pain relieved in the majority.²¹ More recently, double balloon-occluded arterial infusion chemotherapy has been explored as a way to treat invasive bladder cancer while avoiding radical cystectomy (complete bladder removal).²²

Internal iliac branches also feed pelvic tumors more broadly. Identifying which specific branch supplies a tumor is critical for planning embolization, a technique used to shrink tumors before surgery or to cut off their blood supply as a palliative measure. CT angiography has proven valuable for mapping these feeding vessels in patients with pelvic tumors.²³

Erectile Function and the Pudendal Artery

The internal pudendal artery, one of the terminal branches of the anterior division of the internal iliac artery, is the main arterial supply to the penis. Atherosclerotic narrowing of this vessel can contribute to erectile dysfunction, and the association between coronary artery disease and ED is partly explained by shared vascular risk factors affecting arteries throughout the body. Interestingly, though, one study of men with suspected coronary artery disease found no significant correlation between the degree of internal pudendal artery narrowing and ED severity, suggesting that endothelial cell dysfunction rather than simple mechanical obstruction is the primary driver of erectile problems in these patients.²⁴

That said, when a focal blockage is clearly present and drugs like sildenafil don’t help enough, stenting or angioplasty of the internal pudendal artery has been attempted. A feasibility study using drug-eluting stents in the pudendal arteries of men with refractory ED found the procedure was safe and associated with meaningful improvements in both subjective and objective measures of erectile function.²⁵ This area remains experimental, with case reports exploring combinations of balloon angioplasty and regenerative cell therapy for the most difficult cases.²⁶

Prostate Artery Embolization

An increasingly popular minimally invasive treatment for benign prostatic hyperplasia (an enlarged prostate causing urinary symptoms) involves threading a catheter into the prostatic arteries, which branch from the internal iliac system, and injecting tiny particles to reduce blood flow to the gland. The prostate then shrinks over weeks to months, relieving symptoms without traditional surgery. A cadaveric study of prostatic arterial anatomy confirmed that the distribution pattern of prostatic arteries was consistent across specimens, but the exact origin of the main feeding vessel varied from patient to patient, arising from different branches of the internal iliac artery.²⁷ This variability is why pre-procedural imaging is so important: a radiologist who cannot find the prostatic artery at its expected origin needs to hunt through alternative branches, and the tiny caliber of these vessels makes the procedure technically demanding.

Persistent Sciatic Artery and Other Congenital Anomalies

During embryonic development, the internal iliac artery gives rise to branches that normally regress as the external iliac and femoral arteries take over blood supply to the leg. Occasionally, a fetal vessel called the sciatic artery persists into adulthood, remaining as an anomalous continuation of the internal iliac artery that runs through the buttock alongside the sciatic nerve and serves as the dominant blood supply to the lower leg. This persistent sciatic artery is rare, but it carries a high risk of aneurysm formation, with degeneration occurring in up to 60% of cases, potentially leading to clot formation, distal embolization, and sudden leg ischemia.²⁸ Sciatic artery aneurysms can also rupture or compress the sciatic nerve itself, causing pain and neurological symptoms in the leg.²⁹

Congenital pelvic arteriovenous malformations represent another category of anomaly involving internal iliac branches. These are abnormal tangles of arteries and veins present from birth that can grow over time and cause pain, bleeding, or heart failure if they shunt enough blood. Management guidelines developed from long-term follow-up recommend leaving asymptomatic, stable lesions alone with periodic imaging. Symptomatic or enlarging ones are best treated with embolization first, and surgical excision should only be attempted if the malformation is well localized and does not involve the bladder or bowel.³⁰ The rich arterial supply from multiple internal iliac branches makes complete surgical removal of diffuse pelvic AVMs extremely risky, and repeated embolization sessions are often the most practical strategy for symptom control.