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Common iliac vein

The common iliac vein (CIV) is a major pelvic venous trunk formed by the union of the external iliac vein and internal iliac vein at the level of the sacroiliac joint. The left and right CIVs join at the level of L5 vertebra to form the inferior vena cava (IVC).

The CIVs serve as the principal drainage pathways of the pelvis and lower limbs. The right CIV is shorter and more vertical, while the left CIV is longer and oblique, crossing beneath the right common iliac artery — a relationship that predisposes to May–Thurner syndrome (compression of the left CIV by the overlying artery).

The CIV receives tributaries including the iliolumbar veins, lateral sacral veins, and middle sacral vein, along with occasional communication with pelvic venous plexuses.

Clinically, the CIV is crucial in pelvic venous drainage, venous thrombosis, interventional radiology procedures, and surgical approaches to the retroperitoneum.

Synonyms

  • CIV

  • Vena iliaca communis

  • Iliac venous trunk

Function

  • Drains blood from the pelvis, lower limb, and abdominal wall via external and internal iliac systems

  • Contributes to the formation of the inferior vena cava

  • Plays a role in collateral circulation during obstruction or thrombosis

  • Important pathway in venous stenting and endovascular interventions

MRI Appearance

T1-weighted images:

  • CIV: linear hypointense lumen surrounded by bright perivascular fat

  • Thrombus: intermediate-to-hyperintense signal depending on age of clot

T2-weighted images:

  • Flowing blood: signal void

  • Acute thrombosis: hyperintense intraluminal signal

  • Chronic thrombosis: mixed signal intensity with wall thickening

STIR:

  • Suppresses fat to enhance vein conspicuity

  • Thrombosis or perivenous inflammation: bright hyperintense changes

T1 Fat-Suppressed Post-Gadolinium:

  • Normal CIV enhances brightly and homogeneously

  • Thrombosis: non-enhancing filling defect

  • Wall enhancement in phlebitis or tumor invasion

MRV (Magnetic Resonance Venography):

  • Flowing blood: bright hyperintense signal on contrast-enhanced MRV

  • Thrombosis: hypointense filling defect

  • Excellent for detecting May–Thurner syndrome, thrombosis, and pelvic collateral circulation

CT Appearance

Non-contrast CT:

  • CIV: tubular soft-tissue density anterior to sacroiliac joint and lumbar vertebrae

  • Thrombus: hyperdense intraluminal clot in acute stage

CT Post-Contrast:

  • CIV opacifies with contrast, showing its full caliber

  • Detects extrinsic compression, stenosis, and intraluminal pathology

CTV (CT Venography):

  • Normal: CIV lumen appears bright hyperdense with contrast

  • Thrombosis: intraluminal filling defect with or without vein expansion

  • Demonstrates May–Thurner compression, tumor encasement, and collateral venous pathways

  • 3D reconstructions map venous anatomy for surgical and endovascular planning

Clinical Significance

  • Deep vein thrombosis (DVT): CIV thrombosis is a common source of iliofemoral DVT and pulmonary embolism.

  • May–Thurner syndrome: Compression of left CIV by right iliac artery, leading to chronic venous obstruction.

  • Pelvic surgery: CIV injury during retroperitoneal or spinal surgery may cause massive hemorrhage.

  • Interventions: CIV is a key site for venous stenting, catheter placement, and thrombectomy procedures.

  • Oncology: Pelvic tumors (sarcoma, lymphoma, carcinoma) can invade or compress the CIV.

MRI image

Common iliac vein MRI axial anatomy image-img-00000-00000

MRI image

Common iliac vein MRI axial anatomy image-img-00000-00000_00001

CT image

Common iliac vein CT axial image