Dorsal Traversing Nerve Root: Anatomy, Course, Relations, Function, Clinical Significance, MRI & CT Imaging

Topic

Dorsal traversing nerve root

The dorsal traversing nerve root is part of the spinal nerve root complex. It carries sensory (afferent) fibers from the dorsal root ganglion into the spinal cord. At each vertebral level, dorsal roots emerge from the posterolateral spinal cord, pass through the subarachnoid space, and converge at the intervertebral foramen with the ventral root to form a mixed spinal nerve.

The term “traversing root” is often used in spine imaging and surgery to describe the nerve root that runs downward and exits at the next lower vertebral foramen (e.g., the L4 traversing root exits through the L4–L5 foramen). This makes the traversing root highly relevant in disc herniation, foraminal stenosis, and surgical planning.

Synonyms

Posterior traversing nerve root
Dorsal root of spinal nerve
Sensory root of spinal nerve

Origin, Course, and Components

Origin: Arises from the dorsolateral aspect of the spinal cord via multiple rootlets
Course:
- Rootlets converge to form the dorsal root
- Courses within the thecal sac in the subarachnoid space
- Joins the ventral root at the intervertebral foramen to form a mixed spinal nerve
- Traverses downward inside the spinal canal before exiting at the level below (traversing pattern)
Components:
- Sensory (afferent) fibers transmitting touch, pain, temperature, and proprioception
- Cell bodies located in the dorsal root ganglion (DRG)

Relations

Anteriorly: Intervertebral disc and vertebral body
Posteriorly: Ligamentum flavum and lamina
Superiorly/Inferiorly: Adjacent nerve roots within the thecal sac
Laterally: Exits via the intervertebral foramen, related to pedicles and facet joints

Function

Conducts sensory information from peripheral receptors to the spinal cord
Involved in reflex arcs and sensory pathways
Clinical correlate: irritation produces radicular pain and sensory deficits in corresponding dermatomes

Clinical Significance

Disc herniation: Traversing nerve roots are commonly compressed by posterolateral herniations
Stenosis: Foraminal and lateral recess stenosis frequently impinge on the traversing root
Radiculopathy: Produces characteristic dermatomal pain, paresthesia, or sensory loss
Surgical relevance: Identification of traversing vs. exiting roots is crucial in discectomy and spinal decompression
Imaging relevance: Differentiation of traversing from exiting root is critical in MRI interpretation of lumbar pathology

MRI Appearance

T1-weighted images:

Traversing root appears as a thin linear structure with low-to-intermediate signal intensity
Surrounded by bright epidural or foraminal fat, which provides contrast

T2-weighted images:

Traversing nerve root shows intermediate to mildly hyperintense signal compared to muscle
CSF around it is bright, delineating the root clearly

STIR (Short Tau Inversion Recovery):

Normal root is low signal
Pathological root (edema, neuritis) appears bright hyperintense

T1 Fat-Sat Post-Contrast:

Normal root shows minimal or no enhancement
Pathological root may show linear, nodular, or diffuse enhancement (inflammation, tumor, infection)

3D T2 SPACE / CISS:

Traversing root shows intermediate to mildly hyperintense signal compared to muscle
Surrounded by very bright CSF, giving excellent contrast
Provides fine resolution of rootlets, root course, and nerve compression by disc or stenosis

CT Appearance

Non-Contrast CT:

Root itself is not directly visible
Can be inferred within the neural foramen surrounded by fat
Compression or displacement can be inferred by bony narrowing or disc herniation

Post-Contrast CT (CT Myelography):

Nerve roots outlined by contrast in the subarachnoid space
Traversing root appears as a filling defect within contrast-opacified CSF if compressed
Useful in patients unable to undergo MRI

MRI image

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