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Intervertebral foramen

The intervertebral foramen (neural foramen) is the bilateral opening formed between adjacent vertebrae through which the spinal nerve roots, dorsal root ganglion, and segmental vessels exit the spinal canal. These foramina are present at every vertebral level except C1–C2 and serve as critical conduits allowing neural and vascular communication between the spinal canal and the peripheral body.

The shape and orientation of the foramen vary by region: cervical foramina are oval and angled anterolaterally, thoracic foramina are smaller and more vertically oriented, and lumbar foramina are larger and dorsolaterally directed. The intervertebral foramen is formed by bony, articular, and discal components, making it a key structural and functional element of the vertebral column.

Synonyms

  • Neural foramen

  • Spinal nerve exit foramen

  • Intervertebral canal opening

Location and Structure

  • Present: At each segment of the spine between adjacent vertebrae (except C1–C2).

  • Shape: Oval or slit-like opening depending on spinal region and posture.

  • Orientation:

    • Cervical spine: Angled 45° anterolaterally

    • Thoracic spine: More vertical, narrower

    • Lumbar spine: Large, dorsolateral orientation

  • Dimensions: Vary with flexion–extension, disc height, and facet alignment.

Boundaries

  • Superior: Inferior vertebral notch of the pedicle above

  • Inferior: Superior vertebral notch of the pedicle below

  • Anterior: Intervertebral disc and posterolateral vertebral body

  • Posterior: Facet (zygapophyseal) joint, ligamentum flavum, and articular processes

  • Medial: Lateral recess and dural sleeve region

Contents

  • Spinal nerve root

  • Dorsal root ganglion (within or just beyond the foramen, depending on region)

  • Radicular artery and small veins

  • Perineural fat

  • Recurrent meningeal branches

  • Segmental lymphatics

Relations

  • Anteriorly: Vertebral body, uncovertebral joint (cervical), intervertebral disc

  • Posteriorly: Facet joint, superior and inferior articular processes

  • Superiorly/Inferiorly: Adjacent pedicles forming the foraminal roof and floor

  • Laterally: Paraspinal soft tissues and muscles

  • Medially: Spinal canal and lateral recess

Function

  • Provides passage for spinal nerve roots and dorsal root ganglia to exit the spinal canal

  • Allows segmental neurovascular structures to communicate between the spine and periphery

  • Protects neural tissues via cushioning foraminal fat and rigid bony walls

  • Adapts to posture-related changes in vertebral alignment and disc height

MRI Appearance

T1-weighted images

  • Bone cortex: Low signal

  • Bone marrow: Bright (fatty)

  • Neural foraminal fat: Bright, outlining the exiting spinal nerve

  • Spinal nerve root: Intermediate signal

  • Dorsal root ganglion: Slightly brighter than nerve due to higher cellularity

T2-weighted images

  • Bone cortex: Low signal

  • Marrow: Bright but slightly less intense than on T1

  • Neural foraminal fat: Intermediate-to-bright

  • Spinal nerve root / ganglion: Intermediate

  • Ligamentum flavum: Low signal

STIR

  • Bone marrow: Dark to intermediate (fat suppressed)

  • Perineural fat: Suppressed and dark

  • Spinal nerve: Intermediate

  • Ligamentous structures: Low signal

T1 Fat-Saturated Post-Contrast

  • Foraminal fat: Suppressed (dark)

  • Spinal nerve root / ganglion: Mild uniform enhancement

  • Surrounding neurovascular tissues: Thin vascular enhancement along radicular vessels

  • Bone marrow: Mild homogeneous enhancement

CT Appearance

Non-Contrast CT

  • Bone cortex: High density and sharply defined

  • Foraminal shape: Clearly depicted based on pedicles, facet joints, and disc margins

  • Marrow: Lower attenuation compared to cortical bone

  • Facet joints: Outlined as cortical surfaces forming the posterior border

  • Disc margin: Soft tissue density anterior boundary

MRI image

Intervertebral foramen mri axial image

MRI image

Intervertebral foramen MRI sagittal image

CT image

Intervertebral foramen ct sag image-img-00000-00000