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External iliac vein

The external iliac vein is the major venous continuation of the femoral vein, beginning at the level of the inguinal ligament. It ascends superiorly along the pelvic brim, medial to the external iliac artery, and joins with the internal iliac vein to form the common iliac vein.

The EIV receives tributaries from the inferior epigastric vein, deep circumflex iliac vein, and in some cases, accessory pelvic veins. It forms an important component of the iliocaval venous system, serving as the principal channel for venous return from the lower limb to the inferior vena cava (IVC).

Anatomically, it runs in close relation to pelvic structures, making it vulnerable during pelvic surgery, hernia repair, and lymph node dissection. Clinically, it is a critical site for iliac vein thrombosis, May–Thurner syndrome (compression by right common iliac artery), and venous stenting procedures.

Synonyms

  • Vena iliaca externa

  • Pelvic continuation of femoral vein

Function

  • Drains venous blood from the lower limb and lower anterior abdominal wall

  • Acts as a major tributary to the common iliac vein and IVC

  • Provides collateral pathways via anastomoses with internal iliac and pelvic veins

  • Plays a central role in deep vein thrombosis (DVT) propagation and venous stenting

MRI Appearance

T1-weighted images:

  • EIV appears as a linear hypointense lumen medial to the external iliac artery

  • Surrounded by intermediate-to-bright signal pelvic fat

T2-weighted images:

  • Normal vein: signal void due to fast blood flow

  • Thrombosed vein: intraluminal hyperintense signal replacing signal void

STIR:

  • Suppresses fat, outlining the vein more clearly

  • Thrombosis: bright hyperintense lumen and perivenous edema

T1 Fat-Suppressed Post-Gadolinium:

  • Normal EIV enhances brightly and homogeneously

  • Thrombosis: seen as a non-enhancing intraluminal filling defect

  • Useful for detecting tumor thrombus, extrinsic compression, and venous collaterals

MRV (Magnetic Resonance Venography):

  • Normal signal: bright hyperintense venous lumen after gadolinium

  • Thrombosis: hypointense or non-enhancing filling defect

  • Provides excellent delineation of EIV course, patency, collaterals, and compression (e.g., May–Thurner syndrome)

  • Useful in pre-stent evaluation and DVT mapping

CT Appearance

Non-contrast CT:

  • Vein seen as a tubular soft-tissue density medial to external iliac artery

  • Acute thrombosis: hyperdense lumen compared to muscle

CT Post-Contrast:

  • Normal vein enhances with contrast

  • Thrombosis: intraluminal filling defect

  • Can show compression from pelvic masses, arterial pulsation, or lymphadenopathy

CTV (CT Venography):

  • Normal signal: vein lumen opacifies as bright hyperdense structure

  • Thrombosis: seen as intraluminal non-opacified filling defect with collateral venous development

  • 3D reconstructions display EIV’s full course and relation to common iliac bifurcation, pelvic organs, and lymphatics

  • Gold standard for detecting iliac DVT, extrinsic compression, and venous stent planning

CT image

external iliac vein CT axial image

MRI image

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

CT image

External iliac vein ct coronal anatomy image-img-00000-00000