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Posterior external vertebral venous plexus

The posterior external vertebral venous plexus is part of the vertebral venous system, located on the posterior surface of the vertebral arches. It consists of interconnected venous channels that run along the spinous processes and laminae, communicating with the internal vertebral venous plexus through transverse veins and with the superficial veins of the back. This plexus is valveless, allowing bidirectional blood flow and providing an important collateral pathway between the caval and azygos venous systems. It plays a critical role in venous drainage of the spine, posterior musculature, and paravertebral tissues.

Synonyms

  • Posterior vertebral venous plexus

  • Dorsal external vertebral venous plexus

  • Paraspinal venous network

Function

  • Provides venous drainage of the posterior vertebral arches and paraspinal muscles

  • Communicates with the internal vertebral venous plexus, azygos system, and superficial veins of the back

  • Serves as a collateral pathway for venous return when caval or azygos flow is obstructed

  • Contributes to the spread of infection or metastases due to its valveless nature

  • Helps maintain spinal venous circulation under changes in posture and pressure

MRI Appearance

T1-weighted images (non-contrast):

  • Appears as flow voids (signal loss) along the posterior vertebral elements due to venous flow

  • When thrombosed or engorged, may appear as intermediate to high signal intensity structures in the paraspinal region

T2-weighted images:

  • Normal venous channels show flow voids, while slow flow or dilated veins may appear as hyperintense tubular or serpiginous structures

  • Adjacent soft tissue edema may also appear hyperintense if pathology is present

MRA / MR Venography (post-contrast):

  • Venous channels show uniform enhancement with gadolinium

  • Useful for detecting venous engorgement, thrombosis, or collateral venous flow patterns

  • MR venography can map the entire vertebral venous plexus network

T1 Post-Contrast:

  • Plexus veins demonstrate homogeneous enhancement

  • Enhancing paraspinal serpiginous vessels confirm venous nature

  • Helps differentiate vascular channels from cystic or solid soft tissue masses

CT Appearance

Non-contrast CT:

  • Small venous channels are usually not visible unless dilated or thrombosed

  • Paraspinal venous engorgement may appear as soft tissue density tubular structures adjacent to laminae and spinous processes

CT Angiography / Venography (contrast-enhanced):

  • Plexus veins opacify with contrast, appearing as enhancing venous channels along posterior vertebrae

  • CTA/CTV is useful for evaluating venous malformations, thrombosis, or collateral venous pathways

  • Provides high-resolution detail of bony landmarks and venous relationships

MRI images

Posterior external vertebral venous plexus mri axial image -img-00000-00000