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Median sacral vein

The median sacral vein is a small, midline retroperitoneal vein that accompanies the median sacral artery along the anterior surface of the sacrum and coccyx. Despite its small size, it has important surgical and radiological significance due to its anatomical relations with the aortic bifurcation, iliac vessels, and presacral space. It serves as a venous channel connecting the pelvic venous system with the inferior vena cava.

Synonyms

  • Vena sacralis mediana

  • Midline sacral vein

  • Presacral midline vein

Origin, Course, and Drainage

  • Origin:

    • Formed by small venous tributaries from the anterior sacrum and coccyx

  • Course:

    • Ascends vertically along the anterior surface of the sacrum

    • Accompanies the median sacral artery in the retroperitoneum

    • Lies anterior to the L5–S1 vertebral junction and sacroiliac region

    • Passes posterior to the left common iliac vein near the aortic bifurcation

  • Drainage:

    • Empties into the left common iliac vein or at times directly into the junction of the common iliac veins (formation of the inferior vena cava)

    • Communicates with the lateral sacral veins and pelvic venous plexuses

Relations

  • Anteriorly: Parietal peritoneum of the presacral space

  • Posteriorly: Anterior surface of sacrum and coccyx

  • Laterally: Common iliac vessels and ureters

  • Superiorly: Aortic bifurcation and origin of common iliac veins

  • Inferiorly: Pelvic venous plexuses, sacrum, and coccygeal veins

Function

  • Drains venous blood from the anterior sacrum and coccyx

  • Provides communication between pelvic venous plexuses and the iliac venous system

  • Acts as a collateral venous pathway in cases of iliac or caval obstruction

Clinical Significance

  • Surgical relevance: May cause troublesome bleeding during presacral surgery (rectal, urological, or gynecological operations)

  • Tumor spread: Can be a pathway for metastasis or local invasion from pelvic malignancies

  • Trauma: May be injured in pelvic fractures causing presacral venous bleeding

  • Venous obstruction: Serves as a collateral in iliac vein thrombosis or IVC obstruction

MRI Appearance

T1-weighted images:

  • Vein appears as a tubular structure of low signal intensity

  • Surrounded by bright retroperitoneal fat, improving visibility

T2-weighted images:

  • Flowing blood may appear as signal void (black lumen)

  • Slow flow or thrombosis may appear as intermediate-to-bright signal intensity

STIR (Short Tau Inversion Recovery):

  • Vein lumen normally dark due to flow void

  • Thrombus or stasis may show bright signal

  • Fat around the vein suppressed (appears dark)

T1 Fat-Sat Post-Contrast:

  • Normal vein enhances with contrast, showing bright signal lumen

  • Thrombosed vein shows lack of enhancement with possible perivenous enhancement in inflammation

3D T2 SPACE / CISS:

  • Vein seen as a flow void tubular structure in midline presacral location

  • Excellent for mapping venous anatomy and its relationship to sacrum and iliac vessels

CT Appearance

Non-Contrast CT:

  • Appears as a small tubular soft tissue density anterior to sacrum

  • Surrounded by fat, making it distinguishable

  • Thrombosis: seen as hyperdense or isodense filling defect

Post-Contrast CT:

  • Normally enhances as a linear contrast-filled vessel draining to common iliac vein

  • Thrombosis: non-enhancing intraluminal filling defect

  • May show surrounding fat stranding if associated with inflammatory process or tumor infiltration

MRI image

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MRI image

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CT image

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