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Exiting nerve root of spinal nerve

The exiting nerve root refers to the ventral and dorsal root fibers that join to form a spinal nerve as it leaves the spinal canal through the intervertebral foramen. Each spinal segment gives rise to a pair of spinal nerves (31 pairs in total: 8 cervical, 12 thoracic, 5 lumbar, 5 sacral, and 1 coccygeal). The exiting root carries both motor and sensory fibers and is a common site of compression in spinal degenerative disease, disc herniation, trauma, or tumors.

Synonyms

  • Spinal nerve exiting root

  • Intervertebral foramen nerve root

  • Peripheral spinal root

Origin, Course, and Exit

  • Origin: Arises from union of dorsal (sensory) and ventral (motor) roots at the spinal cord

  • Course:

    • Travels laterally within the dural sleeve

    • Passes through the lateral recess and intervertebral foramen

    • Surrounded by fat and bordered by pedicles, vertebral body, and facet joint

  • Exit: Leaves the vertebral canal via the intervertebral foramen to join the peripheral nerve plexuses

Relations

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

  • Posteriorly: Lamina and ligamentum flavum

  • Superiorly/Inferiorly: Pedicles of vertebra above and below

  • Laterally: Paravertebral muscles and sympathetic chain

Function

  • Transmits motor fibers to skeletal muscles

  • Transmits sensory fibers from skin, joints, and muscles to CNS

  • Carries autonomic fibers to peripheral targets

  • Serves as a pathway for reflex arcs and voluntary movement

Clinical Significance

  • Common site of compression from disc herniation, spondylosis, ligament hypertrophy, or foraminal stenosis

  • Responsible for classic radicular pain syndromes (sciatica, cervical radiculopathy)

  • Target for nerve root blocks, steroid injections, and surgical decompression

  • Important in tumor evaluation (schwannomas, neurofibromas)

MRI Appearance

T1-weighted images:

  • Exiting nerve roots appear as linear low-to-intermediate signal structures

  • Surrounded by bright fat in the intervertebral foramen

T2-weighted images:

  • Nerve roots show intermediate to mildly hyperintense signal compared to muscle

  • Pathological nerve root compression, edema, or neuritis: brighter signal intensity

STIR (Short Tau Inversion Recovery):

  • Normal nerve root: low signal

  • Inflamed or compressed nerve root: bright hyperintensity

  • Surrounding fat suppressed to highlight pathology

T1 Fat-Sat Post-Contrast:

  • Normal nerve root enhances minimally or not at all

  • Pathologic root (neuritis, tumor, infection) shows focal or diffuse enhancement

3D T2 SPACE / CISS:

  • Nerve roots appear as intermediate to mildly hyperintense signal compared to muscle

  • Surrounded by very bright CSF, providing excellent contrast

  • Ideal for detecting root compression, tethering, or small intradural lesions

CT Appearance

Non-Contrast CT:

  • Nerve roots not directly seen but inferred within foramina

  • Foramen appears widened or narrowed in pathology

  • Herniated disc or osteophytes impinging on the root can be identified

Post-Contrast CT (CT Myelography):

  • Nerve roots outlined by contrast-filled CSF

  • Compression or displacement is visible as root sleeve cut-off, irregularity, or filling defect

  • Helpful in patients with MRI contraindications

MRI image

Exiting nerve root of spinal nerve coronal mri image

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Exiting nerve root of spinal nerve mri axial anatomy image-img-00000-00000

MRI image

Exiting nerve root of spinal nerve mri sagittal anatomy image-img-00000-00000

MRI image

Exiting nerve root of spinal nerve

CT image

Exiting nerve root of spinal nerve ct coronal anatomy image-img-00000-00000