common iliac artery

**Anatomy** - Origin: Abdominal aorta bifurcates at ~L4 into right and left common iliac arteries (the median sacral artery arises from the aortic bifurcation posteriorly). - Course: Run inferolaterally along the medial border of the psoas major, ~4-5 cm long, and end anterior to the sacroiliac joint (~L5-S1) by dividing into the external and internal iliac arteries. - Branches: Mainly terminal (external and internal iliac). There are no major named branches, though small twigs go to the ureter, peritoneum, psoas, and nearby nerves and lymph nodes. - Relations: The ureter crosses anterior to the common iliac bifurcation (or the start of the external iliac) at the pelvic brim, which matters in surgery ("water under the bridge"). The common iliac veins lie posterior and slightly medial to the arteries. The left common iliac vein passes posterior to the right common iliac artery. The IVC forms at L5 from the union of the common iliac veins, so the right common iliac artery lies anterior to the confluence. - Side differences: The right common iliac artery is longer and crosses anterior to the IVC origin and left common iliac vein.

**Distribution** - External iliac → becomes the femoral artery after passing under the inguinal ligament (gives off the inferior epigastric and deep circumflex iliac arteries) → lower limb. - Internal iliac → pelvic viscera, gluteal region, perineum (e.g., uterine, vaginal, internal pudendal, superior/inferior gluteal, obturator, middle rectal, and umbilical (superior vesical) arteries).

**Clinical significance (high-yield)** - **Aortoiliac occlusive disease (Leriche syndrome):** Atherosclerosis at the aortic bifurcation/common iliacs. Classic triad: buttock/thigh claudication, absent or diminished femoral pulses, and erectile dysfunction (impaired internal iliac flow). Treatment: risk factor modification, exercise, antiplatelets/statins, revascularization (angioplasty/stenting, aortobifemoral bypass). - **Common iliac artery aneurysm:** Most often accompany abdominal aortic aneurysm. They can rupture or compress the ureter, veins, or nerves (hydronephrosis, DVT, leg pain). - **May-Thurner syndrome (iliac vein compression):** The right common iliac artery compresses the left common iliac vein against the vertebral body. This causes left leg DVT or swelling, mainly in young women. Treatment: anticoagulation plus venous stenting. - **Aortic dissection or AAA extension:** It can involve the iliacs and cause acute limb ischemia. - **Ureteral injury:** The ureter crosses over the bifurcation of the common iliac. It is at risk in pelvic surgery (hysterectomy, oophorectomy), and it's a common board question about the "water under the bridge" relationship with the uterine artery. - **Collateral circulation:** With aortoiliac occlusion, flow reroutes via inferior mesenteric → superior rectal → internal iliac; lumbar/intercostal → inferior epigastric; and internal thoracic → superior epigastric → inferior epigastric → external iliac. - **Imaging/landmarks:** The aortic bifurcation at L4 (the level of the iliac crests) is a landmark for lumbar puncture (L3-L4/L4-L5 at the intercristal line, below the spinal cord's end at L1-L2).

**Embryology/other:** The iliac arteries arise from the paired dorsal aortae. The umbilical arteries arise from the internal iliacs and become the medial umbilical ligaments after birth.