Chapter 8
Spinal Nerve Roots
Abdullah Al-Salti R2
24 February 2010
Outline:
1.
2.
3.
4.
The anatomy of the
spinal nerve roots .
Their relation to the
vertebral structures.
Regions of
innervations .
Common clinical
disorders.
Anatomy Of The Spinal Nerve Roots
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31 pairs spinal nerves:
There are 8 cervical (C1-C8),12
thoracic (T1-T12),5 lumber (L1L5),5 sacral(S1-S5)and
1coccygeal(Co1)spinal segments.

Formation: each spinal nerve is
formed by union of anterior and
posterior roots at intervertebral
foramen
– The anterior root－contains motor
fibers for skeletal muscles. Those from
T1 to L2 contain sympathetic fibers;
S2 to S4 also contain parasympathetic
fibers.
– The posterior root－contains sensory
fibers whose cell bodies are in the
spinal ganglion.
General Description
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In adults , the spinal cord normally
ends with the conus medullaris at
the level of the L1 or L2 vertebral
bones.
The roots of the cauda equina are
organized such that the most
centrally located roots are from the
most caudal segments of the spinal
cord.
Sensory and motor nerve roots arise
from each segment of the spinal
cord except for the C1 and Co1
segments,which have no sensory
roots.
The cervical enlargements (C5T1)gives rise to the nerve roots for
the arms ,and the lumbosacral
enlargments (L1-S3)gives rise to
the nerves roots for the legs.
Vertebral Structures.
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Each vertebral bone has a
sturdy cylindrical vertebral
body located anteriorly.
Posteriorly,the neural
elements are surrounded by
an arch of bone formed by
the (pedicles,transverse
processes,laminae,and
spinous processes).
The superior and inferior
articular processes or facet
joints form additional points
of mechanical contact
between adjacent vertebrae.
Intervertebral disc (nucleus
pulposus surrounded by
annulus fibrosis).
General Description
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The spinal cord runs through the spinal
canal (vertebral foramen) and is
surrounded by pia,arachnoid ,dura
mater .
Unlike in the cranium , there is a
layer of epidural fat between the
dura and the periosteum in the
spinal canal,which is a useful
landmark on MRI scans.
There is a valveless meshwork of
epidural veins called Batsons plexus
that is thought to play a role in the
spread of metastatic cancers and
infections in the epidural space.
Ligamentum flavum is particularly
prominent in cervical and lumber
regions and can sometimes
become hypertrophied and
contribute to spinal cord or nerve
root compression.
The nerve roots exit the spinal canal
via the neural (intervertebral)
foramina.
General Description
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Disc herniation are most
common at the cervical and
lumbosacral levels.
For both cervical and
lumbosacral disc herniations,
the nerve root involved
usually corresponds to the
lower of the adjacent two
vertebrae. Example C5-C6
and L5-S1.
Cervical discs are usually
constrained by the posterior
longitudinal ligament to
herniate laterally toward the
nerve root, rather than
centrally toward the spinal
cord.
General Description

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Thoracic ,lumber and sacral
nerve roots exit below the
correspondingly numbered
vertebral bone.Cervical nerve
roots,on the other hand, exit
above the correspondingly
numbered vertebral bone,
except for C8 exit between C7
and T1.
The lumosacral nerve roots exit
some distance above the
intervertebral discs.As they are
about to exit, the nerve roots
move into the lateral recess of
the spinal canal and at this point
that they are closest to the disc.
General Description
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Posterolateral disc
herniations in the
lumbosacral spine ,usually
impinge on nerve roots on
the lower vertebral bone.
Far lateral disc herniation
result in impingement of
the next higher nerve root.
Central disc herniation ,at
the level of cauda equina
can impinge on nerve roots
lower than the level of
herniation.
Dermatomes and myotomes.
Dermatomes:
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The sensory region of the skin
innervated by a nerve root.
Most of the head is supplied by
C2 , via the greater and lesser
occipital nerves.
Common land marks ,T4, T10
,T12.
There is a skip between C4 and
T2, with C5 through T1
represented on the upper
extremities.
There is considerable overlap
between adjacent dermatomes.
Myotome:
The muscles innervated by a single
nerve root.
Three Important Nerve Roots in the Arm
Three Important Nerve Roots in the Leg
Radiculopathy
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Pain and paresthesias (burning, tingling pain that radiates or shoots
down the nerve root ),radiating in the distribution of a nerve root,
often associated with sensory loss and paraspinal muscle spasm
– Sensory loss (often vague or ill defined)
– Weakness (often subjective, not present, or mild)
– Reflex loss (may be present or absent)
– Chronic radiculopathy can result in atrophy and fasciculations.
– T1 ---- Horner's syndrome .
Herniated disk is by far the most common cause.
Inflammation is important as a pain mechanism:
– Phospholipase A and E, NO, TNF, other pro-inflammatory
mediators are released by a herniated disk
– The dura surrounding the ventral and dorsal nerve root is bathed in
this exudate
– Inflammation or prior injury to nerve root is necessary to cause
compression to generate continued pain
Diagnostic Test
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Valsalva
– Cough, laughter, voluntary
contraction of abdominal wall
muscles, when straining, make
radicular pain worse
Stretching the involved nerve root —
L5S1—sitting worsens, C5C6—abduct
arm over head relieves.
Straight leg raising test.—L5S1
worsens.(10-60).
Crossed straight-leg raising test.
specificity over 90% for lumbosacral
nerve root compression.
Percussion of the spine.
May indicate metastatic disease
,epidural abscess,osteomyelitis,or
other disorders of the vertebral bones,
although this sign is often absent in
these conditions.
Imaging: Modalities
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X-rays: most useful in trauma to exclude fracture, not sensitive for
nerve root or spinal cord pathology.
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CT: most useful study for bony anatomy.
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MRI: most useful study for imaging disk, nerve root and spinal cord
pathology.
– Contrast is used if patient has had prior spine surgery in the affected area b/c
can light up scar tissue, or if tumor, infection, or other inflammatory etiology is
suspected.
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CT myelogram, CT/w dye injected into spine: in patients who cannot
obtain MRI, often the best study for imaging the nerve roots of a selected
area.
Other diagnostic modalites:
EMG and NCS
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In patients with acute radiculopathy, EMG studies will not
be of value until at least 3 weeks .
EMG studies can help the decision making process by
identifying the distribution and extent of spinal nerve root
damage, the degree of acute axon loss, and the likelihood
Treatment of Radiculopathy:
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Natural history of lumbosacral and cervical
radiculopathy:
– Up to 75% spontaneously improve
– Length of time required for improvement may
be several weeks or up to years!
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If there is a progressive neurologic deficit
or intractable pain, surgical referral is
appropriate ,otherwise, most patients can
avoid surgery
Empiric Treatment of
Radiculopathy:
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Medications:
– Pain control with NSAIDS and narcotic medications as
necessary
– Short course of corticosteroids in selected patients;
justification is to decrease inflammation around the
nerve root.
Gentle physical therapy (mobilization and stretching)
Bed rest
heating pads, ultrasound, gentle massage
Traction for the cervical spine
Epidural steroid injections for the LS spine
– Risks are higher in cervical spine
Transforaminal steroid injections for the LS spine
Cauda equina and conus
medullaris Syndromes:

Large midline disk herniation can cause
symptoms in both legs in the distribution of
multiple nerve roots, bilateral symptoms
with large full bladder
– Cauda equina syndrome:
 multiple
nerve roots bilaterally are
affected below the end of the spinal
cord at L1-2
– Conus medullaris syndrome:
 the
end of the spinal cord from about
T11-L1
Cauda equina and conus
medullaris Syndromes:
 Both
are potentially surgical emergencies
depending on the cause
 Warning signs that one of these may be present
are:
– Rapidly progressive bilateral lower extremity
weakness
– Saddle anesthesia
– Loss of ability to urinate voluntarily with a large
bladder and overflow incontinence
– Loss of rectal tone
Cauda Equina and conus
medullaris
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Differentiating the two is difficult, and they may
coexist:
– Cauda equina: More pain, asymmetric at onset, bladder
dysfunction not initially as severe. more of lower motor
neuron signs
– Conus medullaris: Often little pain, symmetric at onset,
severe bladder dysfunction. more of upper motor neuron
signs
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Key points:
– Emergent imaging with MRI is essential
– Make sure to image high enough to see the full conus! To at
least T10
References :
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Main reference :
Neuroanatomy through clinical cases.
HAL BLUMENFELD, M.D., PhD.
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Other references:
Cervical and low back pain and radiculopathy.
Jenice Robinson, MD Assistant Professor of Neurology Penn State College of Medicine NBS725
January 12, 2009.
DISEASES OF THE NERVE ROOTS
Kerry Levin
2008, American Academy of Neurology
SPINAL CORD ANATOMY, LOCALIZATION, AND OVERVIEW OF SPINAL CORD
SYNDROMES
Gregory Gruener, Jose´ Biller
2008, American Academy of Neurology
Human Anatomy, First Edition
McKinley & O'Loughlin
Lumbar Disc Herniation and Radiculopathy
KS Hospital Spine Center
Spinal Nerve Roots
Abdullah Al-Salti R2
24 February 2010