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Dorsal exiting nerve root

The dorsal exiting nerve root is the posterior sensory root of a spinal nerve as it emerges from the spinal cord and passes through the intervertebral foramen. Each dorsal root carries afferent fibers responsible for transmitting sensory information such as touch, pain, temperature, and proprioception from peripheral tissues to the central nervous system.

It contains the dorsal root ganglion (DRG), which houses the cell bodies of sensory neurons. After joining with the ventral (motor) root, it forms a mixed spinal nerve. Clinically, dorsal exiting roots are important in spinal pathology, radiculopathy, and targeted nerve root injections.

Synonyms

  • Posterior nerve root

  • Sensory spinal nerve root

  • Exiting root of spinal nerve

Origin, Course, and Structure

  • Origin: Arises from the posterolateral aspect of the spinal cord, specifically from the dorsal horn, via multiple rootlets

  • Course:

    • Rootlets merge to form the dorsal root

    • Enlarges at the dorsal root ganglion (DRG), located just proximal to the intervertebral foramen

    • Joins the ventral root to form the mixed spinal nerve

    • Exits the spinal canal through the intervertebral foramen, becoming part of the peripheral nerve system

  • Structure:

    • Contains only afferent (sensory) fibers before merging with the ventral root

    • DRG contains pseudounipolar sensory neuron cell bodies

Relations

  • Medially: Spinal cord and dorsal horn gray matter

  • Laterally: Mixed spinal nerve at intervertebral foramen

  • Superior/Inferior: Adjacent vertebral pedicles

  • Anterior: Intervertebral disc and vertebral body

  • Posterior: Ligamentum flavum and lamina

Function

  • Transmits sensory information from periphery to CNS, including:

    • Touch

    • Pain

    • Temperature

    • Vibration

    • Proprioception

  • Forms reflex arcs in coordination with ventral (motor) roots

  • Provides dermatomal distribution of sensation

Clinical Significance

  • Radiculopathy: Compression by herniated disc, spondylosis, or foraminal stenosis causes pain and sensory deficits

  • Target for procedures: Selective nerve root blocks, epidural steroid injections

  • Imaging relevance: Important to identify DRG and nerve root signal changes in trauma, infection, tumor, or demyelinating disease

  • Surgical relevance: Landmark in decompression and spinal surgeries

MRI Appearance

T1-weighted images:

  • Dorsal root and ganglion appear as low-to-intermediate signal intensity

  • Surrounded by bright epidural or foraminal fat, improving contrast

T2-weighted images:

  • Nerve root shows intermediate to mildly hyperintense signal compared to muscle

  • Pathology (edema, compression, inflammation) appears brighter

STIR (Short Tau Inversion Recovery):

  • Normal root: low signal

  • Pathological root (edema, neuritis): bright hyperintensity

T1 Fat-Sat Post-Contrast:

  • Normal root: minimal or no enhancement

  • Pathology: focal or diffuse enhancement in neuritis, tumor, or infection

3D T2 SPACE / CISS:

  • Root shows intermediate to mildly hyperintense signal compared to muscle

  • Surrounded by bright CSF in the spinal canal or foramen, giving high contrast

  • Excellent for detecting compression, root sleeve cysts, or small lesions

CT Appearance

Non-Contrast CT:

  • Root itself not directly visualized; appears as a linear soft tissue density in the foramen

  • Indirect signs: foraminal narrowing, bony compression, or disc herniation

Post-Contrast CT (CT Myelography):

  • Root is outlined by intrathecal contrast within CSF

  • Shows filling defects, compression, or displacement due to disc, tumor, or osteophyte

  • Useful alternative when MRI is contraindicated

MRI image

Dorsal exiting nerve root MRI axial anatomy image-img-00000-00000

MRI image

Dorsal exiting nerve root MRI sagittal anatomy image-img-00000-00000