Development of the back
760
5
noItceS
become apparent soon after birth, although some individuals show rami of each pair of spinal nerves. At later stages, satellite cells originat-
symptoms later in life, especially degrees of urinary dysfunction. Very ing from the dermomyotome enter the myotome. The mechanism of
rarely, tethering symptoms may be associated with abnormal develop- development of endo-, peri- and epimysium in relation to the epaxial
ment of the vertebral centra, e.g. when a midline cartilaginous or muscles has not been conclusively determined.
osseous spicule or a fibrous septum projects into the vertebral canal.
These obstacles may split the spinal cord or intraspinal nerve roots into
two columns, a condition termed diastematomyelia. Usually, patients HYPAXIAL MUSCLE: VENTROLATERAL
with this condition have a cutaneous abnormality, such as a dimple, TRUNK MUSCLES
pigmented naevus or patch of hair, along their back at the level of the
tethering. Two modes of production of hypaxial musculature are seen, according
to axial level (see Fig. 44.7). At cervical and trunk levels, myotubes are
Ultrasound antenatal imaging of the back produced by the ventrolateral edge of the dermomyotome in a manner
similar to the production of epaxial muscles. As development proceeds,
lateral growth of the dermomyotome means that the ventrolateral
Antenatal ultrasound assessment of the fetal spine at 18–20 weeks rou-
border extends ventrolaterally into the developing lateral and ventral
tinely assesses the three ossification centres of each vertebra (in the
body wall. This process has been shown to depend on the homeobox-
centrum and bilaterally at the lamina–pedicle junction), in the axial,
containing transcription factor Pitx2 (Eng et al 2012). The somite struc-
coronal and sagittal planes. In the coronal plane, the posterior ossifica-
tures that invade the somatopleure of the abdominal and thoracic walls
tion centres have a characteristic ‘railtrack’ appearance; the twelfth rib
thus consist of two layers, dermomyotome and myotome, that give rise


is adjacent to the twelfth thoracic vertebra; the first sacral vertebra is
to the muscle blastemata for the intercostal and oblique muscles, trans-
level with the top of the iliac wing. Longitudinal scans of the fetal spine
versus abdominis and rectus abdominis. At this time, the number of
can demonstrate scoliosis and hemivertebrae.
somatopleural fibroblasts situated within the muscle-forming zone
In spina bifida, the posterior ossification centres show abnormal
increases, and myotubes can be first seen. There is a subsequent ventral
widening in the axial plane, forming a U or V shape; they point out-
shift of the already separated muscle blastemata within the growing
wards from each other and are no longer parallel. Anomalies of the
abdominal wall as they attain their definitive positions. Muscle differ-
spine (spina bifida) are among the most common fetal malformations
entiation continues and muscular connective tissue, tendons and
noted on antenatal ultrasound examination. The Northern Congenital
aponeuroses develop.
Abnormality Survey reported a total prevalence at birth and termination
At occipital and limb levels, a ventrolateral dermomyotomal lip is
of 17.9/10,000 between 1984 and 1996 in the UK and Ireland, in com-
not formed in the same way; instead, cells undergo epithelial/
parison to the prevalence in Europe of 11.5 cases/10,000 over the same
mesenchymal transformation and migrate to their destination. Myo-
time period. For further details, consult Weston (2014).
blasts move from the occipital dermomyotomes into the developing
mandibular processes to form the intrinsic muscles of the tongue,
whereas those opposite the early limb buds migrate into the limbs as
DEVELOPMENT OF DERMOMYOTOMES
dorsal and ventral muscle masses that give rise to the shoulder, hip and
appendicular muscles. (For a review of dermomyotomal development,
The dermomyotome, which forms from the dorsal half of the early see Scaal and Christ (2004).)
somite, gives rise to all the skeletal muscle in the trunk and limbs and
to the intrinsic muscles of the tongue. Muscles in the head arise from


the unsegmented paraxial mesoderm rostral to the occipital somites. OTHER STRUCTURES DERIVED FROM THE SOMITES
The dorsomedial lip (border) of the dermomyotome is an infolding
of the epithelial plate of the somite and becomes a proliferative epithe- Dermal precursors arise from the central portion of the dermomyotome
lial site from which mediolateral growth of the dermomyotome itself and, possibly, also from the dorsomedial dermomyotome lip (see Fig.
occurs. Three structures are required for myogenesis: the neural tube, 44.7). The cells undergo an epithelial/mesenchyme transformation
the notochord/neural floor plate complex and the (early) dorsally from the dermomyotome and migrate to the dorsomedial subectoder-
placed ectoderm. There is a balance between levels of Shh from the mal space overlying the dorsal neural tube. Their transformation seems
notochord and Wnts from the dorsal neural tube and ectoderm, which to be controlled by factors from the neural tube. There is a sharp bound-
promotes myogenesis; high levels of either alone lead to sclerotomal or ary between dermis that is somite-derived and that which is derived
non-myogenic dermomyotomal development (Scaal and Christ 2004). from the somatopleuric mesenchyme of the lateral plate (and which
Myogenic determination factors, MyoD, myogenin, Myf 5 and herculin/ covers the limbs, part of the lateral and all of the ventral body wall).
MRF 4, can first be detected in the medial half of the somite as early as Somitic cells are now considered to give rise to smooth muscle cells
stage II, several hours prior to the onset of myotome formation. within and around the developing somites, and within the tunica media
The mode of formation of mononucleated, postmitotic, primitive of the descending aorta (Wiegreffe et al 2007). All compartments of the
myotubes from the dermomyotome has been elucidated in the chick epithelial somite, including the somitocoele cells, give rise to angio-


but not yet confirmed in mammals (Gros et al 2004) (Fig. 44.17). In blasts. The early ventral half of the somite gives rise to the endothelium
this model, all four borders of the dermomyotome give rise to myo- of ventrolateral blood vessels. Angioblastic cells arising from the dorso-
tomal cells, produced in two phases. First, cells are produced from the medial dermomyotome migrate mainly into the dorsal dermis, whereas
dorsomedial dermomyotomal lip by direct ingression and bidirectional those arising from the dorsolateral part move to the ventrolateral body
extension. Second, myotomal precursor cells are released by the caudal wall and limbs (Scaal and Christ 2004).
dermomyotomal border, followed, in turn, by the cranial dermomyo-
tomal border, and lastly, by the ventrolateral dermomyotomal lip.
Those myotomal cells arising from the dorsomedial dermomyotomal
border contribute cells exclusively to the epaxial domain, while those Bonus e-book images
from the ventrolateral border contribute cells exclusively to the hypaxial
domain. The cells arising from the cranial and caudal borders move
into both epaxial and hypaxial domains (Scaal and Christ 2004) (see
Fig. 44.15 Fetal myelomeningocele. Upper panel: three-dimensional
Fig. 44.7). Later in development, proliferative muscle progenitor cells
ultrasound maximum transparency mode shows the spinal defect
originating from the de-epithelializing dermomyotome contribute to
in the coronal (A and B) and oblique (C) views. Lower panel:
fetal muscle growth (Gros et al 2005). three-dimensional ultrasound surface rendering mode shows the
spinal defect in the sagittal (A and B) and coronal (C) views.
EPAXIAL MUSCLE: DORSAL TRUNK MUSCLES Fig. 44.16 Fetal magnetic resonance image shows a lumbar
myelomeningocele in the sagittal section.
Epaxial muscles arise from the dorsomedial lip of the dermomyotome.


Early myotome cells are postmitotic embryonic myoblasts; later in Fig. 44.17 The metameric structure of the myotomes of a 5-day-old
development, they fuse to form syncytia, which produce the intrinsic chick embryo, visualized by whole-mount immunohistochemistry
muscles of the back. They bridge the early segmental borders, joining with an antibody staining for myosin heavy chain.
vertebrae together. The epaxial muscles are innervated by the dorsal


Development of the back
760.e1
44
Retpahc
Fig. 44.17 The metameric structure of the myotomes (arrows)
of a 5-day-old chick embryo, visualized by whole-mount
immunohistochemistry with an antibody staining for myosin heavy chain.


761
44
Retpahc
key references
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sclerotome. Anat Embryol (Berl) 208:333–50. embryos.
An overview of the formation and different developmental fates of the
Scaal M, Christ B 2004 Formation and differentiation of the avian dermo-
sclerotome.
myotome. Anat Embryol 208:411–24.
Hita-Contreras F, Roda O, Martínez-Amat A et al 2014 Embryonic and early An overview of the development of the dorsal somite compartment to dermis
fetal period development and morphogenesis of human craniovertebral and muscle.
junction. Clin Anat 27:337–45.
Stern CD, Vasiliauskas D 2000 Segmentation: a view from the border. Curr
This paper presents first and early second trimester development of bones,
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joints and ligaments of the craniovertebral junction.
A presentation of three different models of somite formation in the context
Müller F, O’Rahilly 2003 Segmentation in staged human embryos: the occip- of molecular data.
itocervical region revisited. J Anat 203:297–315.


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Christ B, Huang R, Scaal M 2004 Formation and differentiation of the avian embryos.
sclerotome. Anat Embryol (Berl) 208:333–50. O’Rahilly R, Müller F, Meyer DB 1990 The human vertebral column at the
An overview of the formation and different developmental fates of the end of the embryonic period proper. 4. The sacrococcygeal region. J Anat
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Christ B, Huang R, Wilting J 2000 The development of the avian vertebral Ordahl CP 1993 Myogenic lineages within the developing somite. In:
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Crockard HA, Stevens JM 1995 Craniovertebral junction anomalies in inher- Liss, pp. 165–76.
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Eng D, Ma HY, Xu J et al 2012 Loss of abdominal muscle in Pitx2 mutants Pang D, Thompson DN 2014 Embryology, classification, and surgical man-
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Gasser RF 2006 Evidence that some events of mammalian embryogenesis Pourquié O 2011 Vertebrate segmentation. From cyclic gene networks to
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CHAPTER Spinal cord and spinal nerves:
45
gross anatomy
This chapter deals with the gross anatomy of the structures that lie The spinal cord varies in transverse width, gradually tapering cranio-
within the vertebral canal and their extensions through the interverte- caudally, except at the levels of the enlargements. It is not cylindrical,
bral foramina, the spinal nerve or radicular (‘root’) canals. The internal being wider transversely at all levels, especially in the cervical segments.
organization of the spinal cord is described in Chapter 20. The cervical enlargement, the source of the large spinal nerves that
The spinal cord and its blood vessels and nerve roots lie within a supply the upper limbs, extends from the third cervical to the second
meningeal sheath, the theca, which occupies the central zone of the thoracic segments. Its maximum circumference (approximately 38 mm)
vertebral canal and extends from the foramen magnum, where it is in is in the sixth cervical segment (a spinal cord segment provides the
continuity with the meningeal coverings of the brain, to the level of the attachment of the rootlets of a pair of spinal nerves). The lumbar
second sacral vertebra in the adult. Distal to this level, the dura extends enlargement, the source of the large spinal nerves that supply the lower
as a fine cord, the filum terminale externum, which fuses with the limbs, extends from the first lumbar to the third sacral segments; the
posterior periosteum of the first coccygeal segment. Tubular prolonga- equivalent vertebral levels are the ninth to twelfth thoracic vertebrae.
tions of the dural sheath extend around the spinal roots and nerves into Its greatest circumference (approximately 35 mm) is near the lower part
the lateral zones of the vertebral canal and out into the root canals, of the body of the twelfth thoracic vertebra, below which it rapidly
eventually fusing with the epineurium of the spinal nerves. Between the dwindles into the conus medullaris.
theca and the walls of the vertebral canal is the epidural (spinal extra- Fissures and sulci extend along most of the external surface. A ventral
dural) space, which is loosely filled with fat, connective tissue contain- (anterior) median fissure (sulcus) and a posterior median sulcus and


ing small arteries and lymphatics, and an important venous plexus. septum almost completely separate the cord into right and left halves;
Three-dimensional appreciation of the anatomy of the spinal theca and they are joined by a commissural band of nervous tissue that contains
its surroundings is essential for the efficient management of spinal pain a central canal (see Fig. 20.1).
and of spinal injuries, tumours and infections. Equally significant clini- The ventral median fissure extends along the whole ventral surface
cally is the anatomy of the often-precarious blood supply of the spinal with an average depth of 3 mm, although it is deeper at caudal levels.
cord and its associated structures. The increasing application and refine- It contains a reticulum of pia mater. Dorsal to it is the anterior white
ment of diagnostic imaging and endoscopic procedures lend a new commissure. Perforating branches of the spinal vessels pass from the
importance to topographical detail here. fissure to the commissure to supply the central spinal region. The pos-
terior median sulcus is shallower, and from it a posterior median
septum penetrates more than halfway into the cord, almost to the
central canal. The septum varies in anteroposterior extent from 4 to
SPINAL CORD
6 mm, and diminishes caudally as the canal becomes more dorsally
placed and the cord contracts. The patency of the central canal dimin-
The spinal cord occupies the superior two-thirds of the vertebral canal ishes with age: a postmortem study found the canal to be patent along
(Figs 45.1–45.2). It is continuous cranially with the medulla oblon- the length of the cord in infants under 1 year of age, but occluded in
gata, just below the level of the foramen magnum, at the upper border most segments with increasing age after the second decade (Yasui et al
of the atlas. It terminates caudally as the conus medullaris. During 1999).
development, the vertebral column elongates more rapidly than the Dorsal rootlets of spinal nerves enter the cord along a posterolateral
spinal cord, so that there is an increasing discrepancy between the sulcus that lies from 1.5 to 2.5 mm lateral to each side of the posterior


anatomical level of spinal cord segments and their corresponding ver- median sulcus. The white matter between the posteromedian and pos-
tebrae (p. 252). At stage 23, the vertebral column and spinal cord are terolateral sulci on each side is the dorsal (posterior) funiculus. In cervi-
the same length and the cord ends at the last coccygeal vertebra. In cal and upper thoracic segments, a longitudinal posterointermediate
later fetal life, the conus medullaris lies between the third lumbar and sulcus marks a septum dividing each posterior funiculus into two large
fifth sacral vertebrae. In premature and term neonates, it lies between tracts on either side, a medial fasciculus gracilis and a lateral fasciculus
the first and third lumbar vertebrae, and in children between the ages cuneatus. A ventrolateral (anterolateral) funiculus lies between the pos-
of 1 and 7 years, it lies between the twelfth thoracic and third lumbar terolateral sulcus and ventral median fissure, and is subdivided into
vertebrae (Barson 1970, Vettivel 1991, Malas et al 2001, Kesler et al ventral (anterior) and lateral funiculi by ventral spinal rootlets that pass
2007, Suresh et al 2013). In the adult, the spinal cord terminates on through its substance to issue from the surface of the cord. The ventral
average at the level of the middle third of the body of the first lumbar funiculus is medial to, and includes, the emerging ventral rootlets,
vertebra (Macdonald et al 1999) (see Fig. 43.79), which corresponds whilst the lateral funiculus lies between the roots and the posterolateral
approximately to the transpyloric plane. However, it may end as high sulcus. In upper cervical segments, nerve rootlets emerge through each
as the middle third of the body of the eleventh thoracic vertebra or lateral funiculus to form the accessory nerve, which ascends in the
as low as the middle third of the body of the third lumbar vertebra vertebral canal lateral to the spinal cord and enters the posterior cranial


(Macdonald et al 1999). Its position rises slightly in vertebral flexion, fossa via the foramen magnum (see Fig. 29.11).
and there is some correlation with the length of the trunk, especially in
females. (For dimensional data, consult Barson and Sands (1977).)
The filum terminale, a filament of connective tissue approximately DORSAL AND VENTRAL ROOTS
20 cm long, descends from the apex of the conus medullaris. Its upper
15 cm, the filum terminale internum, is continued within extensions The paired dorsal and ventral roots of the spinal nerves are continuous
of the dural and arachnoid meninges and reaches the caudal border of with the spinal cord (see Fig. 45.1F). They cross the subarachnoid space
the second sacral vertebra. Its final 5 cm, the filum terminale externum, and traverse the dura mater separately, uniting in or close to their
fuses with the investing dura mater, and then descends to the dorsum intervertebral foramina to form the (mixed) spinal nerves. Since the
of the first coccygeal vertebral segment. The filum is continuous above spinal cord is shorter than the vertebral column, the more caudal spinal
with the spinal pia mater. A few strands of nerve fibres, which probably roots descend for varying distances around and beyond the cord to
represent the roots of rudimentary second and third coccygeal spinal reach their corresponding foramina. In so doing, they form a divergent
nerves, adhere to its upper part. The central canal is continued into the sheaf of spinal nerve roots, the cauda equina, which is gathered round
filum for 5–6 mm. A capacious part of the subarachnoid space sur- the filum terminale in the spinal theca, mostly distal to the apex of
rounds the filum terminale internum, and is the site of election for the cord.
access to the cerebrospinal fluid (CSF) via a lumbar puncture (see Ventral spinal roots contain efferent somatic and, at some levels,
762 below). preganglionic sympathetic, axons that extend from neuronal cell bodies


763
54
RETPAHC
Spinal cord
A
E
Dura mater, lined by
arachnoid
B
Ligamentum denticulatum,
Dura mater lowest process
C1 Conus medullaris Nerve roots of first
lumbar spinal nerve
C
Dura mater Filum terminale
T1 internum
Fifth lumbar ventral root
Fifth lumbar dorsal root
D
Dura mater
Third sacral
spinal ganglion
Filum terminale externum
Posterior grey column
Dorsal nerve rootlets Spinal ganglion
L1
F Dorsal ramus
Ventral (anterior) median fissure
Ventral nerve rootlets Ventral ramus
S1
Anterior grey column Lateral grey column
Fig. 45.1 A, The brain and spinal cord with attached spinal nerve roots and dorsal root ganglia, photographed from the dorsal aspect. Note the fusiform
cervical and lumbar enlargements of the cord, and the changing obliquity of the spinal nerve roots as the cord is descended. The cauda equina is
undisturbed on the right but has been spread out on the left to show its individual components. B–D, The formation of a typical spinal nerve, ventral
aspect. B, Cervical level. C, Thoracic level. D, Lumbar level. E, The lower end of the spinal cord, filum terminale and cauda equina exposed from behind.
The dura mater and the arachnoid have been opened and spread out. F, A spinal cord segment showing the mode of formation of a typical spinal nerve
and the gross relationships of the grey and white matter. (A, Dissection by MCE Hutchinson, photograph by Kevin Fitzpatrick, London. B–D, With
permission from Waschke J, Paulsen F (eds), Sobotta Atlas of Human Anatomy, 15th ed, Elsevier, Urban & Fischer. Copyright 2013.)


SPinAl CoRd And SPinAl nERvES: gRoSS AnATomy
764
5
noiTCES
in the ventral horns and intermediolateral columns, respectively. There
are also afferent nerve fibres in these roots. The rootlets comprising each
ventral root emerge from the anterolateral sulcus in groups over an
elongated vertical elliptical area (see Fig. 45.1F). Dorsal spinal roots
bear ovoid swellings, the spinal ganglia, one on each root proximal to
its junction with a corresponding ventral root in an intervertebral
foramen. Each root fans out into 6–8 rootlets before entering the cord
in a vertical row in the posterolateral sulcus. Dorsal roots are usually
said to contain only afferent axons (both somatic and visceral), which
Cranial dura are the central processes of unipolar neurones in the spinal root ganglia,
but they may also contain a small number (3%) of efferent fibres and
autonomic vasodilator fibres.
Occipital bone
Each ganglionic neurone has a single short stem that divides into a
medial (central) branch that enters the spinal cord via a dorsal root,
Medulla oblongata and a lateral (peripheral) branch that passes peripherally to a sensory
end organ. The central branch is an axon while the peripheral one is
an elongated dendrite (but when traversing a peripheral nerve is, in
general structural terms, indistinguishable from an axon). The region
of spinal cord associated with the emergence of a pair of nerves is a
spinal segment but there is no actual surface indication of segmenta-
Cervical
tion. Moreover, the deep neural sources or destinations of radicular
enlargement
fibres may lie far beyond the confines of the ‘segment’ so defined.
MENINGES
T1
DURA MATER
In some areas within the skull, the dura mater can be distinguished
Subarachnoid space from the endosteum, but at the base of the skull around the foramen
magnum the two layers are fused and adherent to the bone. Distal to
the foramen magnum, within the vertebral column, the dura is distinct
from the tissues that line the vertebral canal, and separated from them
Epidural space Spinal cord


by the epidural space (see below). The spinal dura mater forms a tube
Subarachnoid whose upper end is attached to the edge of the foramen magnum and
T7 space to the posterior surfaces of the second and third cervical vertebral
Epidural space bodies, and also by fibrous bands to the posterior longitudinal liga-
Dura-arachnoid ment, especially towards the caudal end of the vertebral canal. The dural
mater tube narrows at the lower border of the second sacral vertebra. It invests
the thin spinal filum terminale, descends to the back of the coccyx, and
blends with the periosteum.
Epidural space
The epidural space lies between the spinal dura mater and the tissues
T12 Nerve roots that line the vertebral canal (see Fig. 45.2). It is closed above by fusion
of the spinal dura with the edge of the foramen magnum, and below
by the posterior sacrococcygeal ligament that closes the sacral hiatus. It
contains loosely packed connective tissue, fat, a venous plexus, small
Lumbosacral arterial branches, lymphatics and fine fibrous bands that connect the
enlargement
theca with the lining tissue of the vertebral canal. These bands, the
L1
meningovertebral ligaments, are best developed anteriorly and later-
L2 Conus medullaris
ally. Similar bands tether the nerve root sheaths or ‘sleeves’ within
their canals. There is also a midline attachment from the posterior
spinal dura to the ligamentum nuchae at atlanto-occipital and atlanto-
axial levels (Dean and Mitchell 2002). The venous plexus consists of
Filum terminale internum longitudinally arranged chains of vessels, connected by circumdural
Filum terminale venous ‘rings’. The anteriorly placed vessels receive the basivertebral
internum Dura-arachnoid mater veins.
The shape of the space within each spinal segment is not uniform,
though the segmental pattern is metamerically repeated. It is difficult
to define the true shape of the ‘space’ because it changes with the intro-
duction of fluid or as a result of preservation techniques. In the lumbar
region, the dura mater is apposed to the walls of the vertebral canal


anteriorly and attached by connective tissue in a manner that permits
Termination of displacement of the dural sac during movement and venous engorge-
S3 S2 dural sac ment. Adipose tissue is present posteriorly in recesses between the liga-
mentum flavum and the dura. The connective tissue extends for a short
Filum terminale externum distance through the intervertebral foramina along the sheaths of the
Filum terminale
spinal nerves. Like the main thecal sac, the root sheaths are partially
externum
tethered to the walls of the foramina by fine meningovertebral
Sacral hiatus ligaments.
Co1
Epidural injections
Contrast media and other fluids injected into the epidural space at the
Fig. 45.2 The epidural and subarachnoid spaces. sacral level can spread up to the cranial base. Local anaesthetics
injected near the spinal nerves, just outside the intervertebral foramina,
may spread up or down the epidural space to affect the adjacent spinal
nerves or may pass to the opposite side. The paravertebral spaces of


Spinal cord and spinal nerves: gross anatomy
764.e1
54
RETPAHC
A variety of pathological processes can occur within the epidural
space, compressing the dura and resulting in pain and potential neuro-
logical disturbance. Among the more common pathological entities
seen are infection, haematoma and tumours (Figs 45.3–45.4).
Fig. 45.4 A sagittal thoracic MR image showing a large ventral spinal
epidural haematoma (arrow) resulting in severe neck and upper thoracic
pain and ataxia.
Fig. 45.3 A T1 post-contrast sagittal lumbar spinal magnetic resonance
(MR) image showing a spinal epidural abscess (arrow) adherent to the
lumbar dura and spinal nerves in a 28-year-old female with a history of
intravenous drug abuse.


765
54
RETPAHC
Cerebrospinal fluid (CSF)
each side communicate via the epidural space, particularly at lumbar border is continuous with the subpial connective tissue of the cord and
levels. its lateral border forms a series of triangular processes, the apices of
For a review of the morphology of the epidural space and a discus- which are fixed at intervals to the dura mater. The first crosses behind
sion of the nature of the lining layer of the vertebral canal, see Newell the vertebral artery where it is attached to the dura mater, and is sepa-
(1999). rated by the artery from the first cervical ventral root. Its site of attach-
ment to the dura mater is above the rim of the foramen magnum, just
Subdural space behind the hypoglossal nerve; the accessory nerve ascends on its pos-
terior aspect (see Fig. 29.11). The last of the dentate ligaments lies
between the exiting twelfth thoracic and first lumbar spinal nerves and
The subdural space is a potential space in the normal spine because the
is a narrow, oblique band that descends laterally from the conus med-
arachnoid and dura are closely apposed (Haines et al 1993). It does
ullaris. Changes in the form and position of the dentate ligaments
not connect with the subarachnoid space but continues for a short
during spinal movements have been demonstrated by cine-radiography.
distance along the cranial and spinal nerves. Accidental subdural cath-
Beyond the conus medullaris, the pia mater continues as a coating of
eterization may occur during epidural injections. Injection of fluid into
the filum terminale.
the subdural space may damage the cord either by direct toxic effects
or by compression of the vasculature.
INTERMEDIATE LAYER
ARACHNOID MATER
In addition to the well-defined coats of arachnoid and pia mater, the
The spinal arachnoid mater surrounds the spinal cord and is continu- cord is also surrounded by an extensive intermediate layer of leptome-
ous with the cranial arachnoid mater (Fig. 45.5). It is closely applied ninges. This layer is concentrated in the dorsal and ventral regions, and


to the deep aspect of the dura mater. At sites where vessels and nerves forms a highly perforated, almost lace-like structure that is focally com-
enter or leave the subarachnoid space, the arachnoid mater is reflected pacted to form the dorsal, dorsolateral and ventral ligaments of the
on to the surface of these structures and forms a thin coating of lep- spinal cord. Dorsally, the intermediate layer is adherent to the deep
tomeningeal cells over the surface of both vessels and nerves. Thus a aspect of the arachnoid mater and forms a discontinuous series of
subarachnoid angle is formed as nerves pass through the dura into the dorsal ligaments that attach the spinal cord to the arachnoid. The dor-
intervertebral foramina. At this point, the layers of leptomeninges solateral ligaments are more delicate and fenestrated, and they extend
(arachnoid and pia) fuse and become continuous with the perineu- from the dorsal roots to the parietal arachnoid. As the intermediate
rium. The epineurium is in continuity with the dura. Such an arrange- layer spreads laterally over the dorsal surface of the dorsal roots, it
ment seals the subarachnoid space so that particulate matter does not becomes increasingly perforated and eventually disappears. A similar
pass directly from the subarachnoid space into nerves. The existence of arrangement is seen over the ventral aspect of the spinal cord but the
a pathway of lymphatic drainage from the CSF is controversial. intermediate layer is less substantial.
The intermediate layer is structurally similar to the trabeculae that
cross the cranial subarachnoid space, i.e. it has a collagenous core
PIA MATER coated by leptomeningeal cells. The intermediate layers of leptomenin-
ges around the spinal cord may act as a baffle within the subarachnoid
The spinal pia mater (see Fig. 45.5) closely invests the surface of the space to dampen waves of CSF movement in the vertebral canal. Inflam-
spinal cord and passes into the ventral median fissure. The subpial col- mation within the spinal subarachnoid space may result in extensive
lagenous layer in the spinal subpial ‘space’ is thicker than it is in the fibrosis within the intermediate layer and the complications of chronic


cerebral region and is continuous with the collagenous core of the liga- arachnoiditis (Fig. 45.6).
mentum denticulatum (denticulate ligament).
The ligamentum denticulatum is a flat, fibrous sheet on either side
of the spinal cord between the ventral and dorsal spinal roots. Its medial COVERINGS AND RELATIONS OF THE
SPINAL ROOTS AND NERVES IN THE
RADICULAR CANAL
Dura mater Tubular prolongations of spinal dura mater, closely lined by arachnoid,
extend around the spinal roots and nerves as they pass through the
lateral zone of the vertebral canal and through the intervertebral
foramina (see Figs 45.5, 45.6A). These prolongations, the spinal nerve
sheaths or root sheaths, gradually lengthen as the spinal roots become
increasingly oblique. Each individual dorsal and ventral root runs in
the subarachnoid space with its own covering of pia mater. Each root
Dura mater cut and
reflected pierces the dura separately, taking a sleeve of arachnoid with it, before
joining within the dural prolongation just distal to the spinal ganglion.
The dural sheaths of the spinal nerves fuse with the epineurium, within
or slightly beyond the intervertebral foramina. The arachnoid prolonga-
tions within the sheaths do not extend as far distally as their dural
coverings, but the subarachnoid space and the CSF it contains extend
sufficiently distally to form a radiologically demonstrable root sleeve
Arachnoid mater for each nerve. Shortening or obstruction of this sleeve seen on mag-
(outer layer) netic resonance imaging (MRI) indicates compression of the spinal
nerve. At the cervical level, where the nerves are short and the vertebral
movement is greatest, the dural sheaths are tethered to the periosteum
Intermediate layer of of the adjacent transverse processes. In the lumbosacral region, there is
arachnoid less tethering of the dura to the periosteum, though there may be an
(removed below)
attachment posteriorly to the facet joint capsule.
Ligamentum
denticulatum CEREBROSPINAL FLUID (CSF)
Ventral nerve


The cerebrospinal fluid is described in detail in Chapter 18. Although
root
Pia mater covering
there is free communication between the spinal and cerebral subarach-
the cord
Dorsal root noid spaces, the mode of circulation of the spinal CSF and the contribu-
ganglion
tion that it makes to the overall circulation of CSF remain uncertain in
humans: CSF may be absorbed from the spinal subarachnoid space;
Fig. 45.5 Part of the spinal cord exposed from the anterior aspect to spinal arachnoid granulations and villi have been described (Kido et al
show the meningeal coverings. 1976).


SPinAl CoRd And SPinAl nERvES: gRoSS AnATomy
766
5
noiTCES
A Arachnoid mater Body wall
muscles
Dura mater
Spinal Sympathetic
nerve ganglion Prevertebral
flexor
Meningeal
Subarachnoid branch
space
Spinal
Pia mater
cord
Dorsal root
Dural sleeve
Ventral root
Dorsal root Spinal
ganglion nerve Ventral ramus
Dorsal ramus
Spinal extensors Articular branch
Fig. 45.7 The formation and branching pattern of a typical spinal nerve.
Ventral
ramus
Dorsal ramus
C2
C3
C4 Vertebrae
C7 C5
2B T1
1A
T2
2A T3
1B
3
T4
2
and T6 T5
3
T6
Type 1 Type 2 Type 3
T7
B C D
T8
Fig. 45.6 A, A lumbar spinal nerve and its roots and meningeal coverings. T12 T9
B–D, Extradural anomalies of the lumbar nerve roots. L1
T10
T11
SPINAL NERVES
Dorsal rami
L5 T12 L1 S1–3
In those body segments that largely retain a metameric (segmental)
L3 L2 Dorsal
structure, e.g. the thoracic region, spinal nerves show a common plan rami S4, 5
(Fig. 45.7). The dorsal, epaxial, ramus passes back lateral to the articu- and Co1
lar processes of the vertebrae and divides into medial and lateral Perforating
branches that penetrate the deeper muscles of the back; both branches cutaneous
innervate the adjacent muscles and supply a band of skin from the nerve
posterior median line to the lateral border of the scapula (Fig. 45.8). Gluteal
The ventral, hypaxial, ramus is connected to a corresponding sympa- rami of
thetic ganglion by white and grey rami communicantes. It innervates posterior
cutaneous
the prevertebral muscles and curves around in the body wall to supply
nerve


the lateral muscles of the trunk. Near the mid-axillary line, it gives off Limit of skin area supplied by nerves shown here
a lateral branch that pierces the muscles and divides into anterior and
Fig. 45.8 The cutaneous distribution of the dorsal rami of the spinal
posterior cutaneous branches. The main nerve advances in the body
nerves. The nerves are shown lying on the superficial muscles. The nerves
wall, where it supplies the ventral muscles and terminates in branches
are numbered on the right side; the spines of the seventh cervical, sixth
to the skin.
and twelfth thoracic, and first and fifth lumbar vertebrae are labelled on
Spinal nerves are united ventral and dorsal spinal roots, attached in
the left side.
series to the sides of the spinal cord. The term spinal nerve strictly
applies only to the short segment after union of the roots and before
branching occurs. This segment, the spinal nerve proper, lies in the as individual ‘root values’. The peripheral nerves emerge through the
intervertebral foramen; it is sometimes mistakenly called the ‘nerve intervertebral foramina. At thoracic, lumbar, sacral and coccygeal levels,
root’. There are 31 pairs of spinal nerves: 8 cervical, 12 thoracic, 5 the numbered nerve exits the vertebral canal by passing below the
lumbar, 5 sacral and 1 coccygeal. The abbreviations C, T, L, S and Co, pedicle of the corresponding vertebra, e.g. L4 nerve exits the interverte-
with appropriate numerals, are commonly applied to individual nerves bral foramen between L4 and L5. However, in the cervical region, nerves


Spinal nerves
767
54
RETPAHC
C1–7 pass above their corresponding vertebrae. C1 leaves the vertebral SPINAL NERVES PROPER
canal between the occipital bone and atlas, and hence is often termed
the suboccipital nerve. The last pair of cervical nerves does not have a Immediately distal to the spinal ganglia, ventral and dorsal roots unite
correspondingly numbered vertebra and C8 passes between the seventh to form spinal nerves. These very soon divide into dorsal and ventral
cervical and first thoracic vertebrae. Each nerve is continuous with the rami, both of which receive fibres from both roots (see Fig. 45.6A). At
spinal cord by ventral and dorsal roots; each dorsal root bears a spinal, all levels above the sacral, this division occurs within the intervertebral
sensory ganglion (dorsal root ganglion). foramen. Division of the sacral spinal nerves occurs within the sacral
vertebral canal, and the dorsal and ventral rami exit separately through
posterior and anterior sacral foramina at each level. Spinal nerves tri-
SPINAL ROOTS AND GANGLIA
furcate at some cervical and thoracic levels, in which case the third
branch is called a ramus intermedius. At or distal to its origin, each
Ventral (anterior) roots
ventral ramus gives off recurrent meningeal (sinuvertebral) branches
and receives a grey ramus communicans from the corresponding sym-
Ventral roots contain axons of neurones in the ventral (anterior) and pathetic ganglion. The thoracic and first and second lumbar ventral
lateral spinal grey columns. Each emerges as a series of rootlets in two rami each contribute a white ramus communicans to the corresponding
or three irregular rows in an area approximately 3 mm in horizontal sympathetic ganglia. The second, third and fourth sacral nerves also
width. supply visceral branches, unconnected with sympathetic ganglia, which
carry a parasympathetic outflow direct to the pelvic plexuses.
Dorsal (posterior) roots Cervical spinal nerves enlarge from the first to the sixth nerve. The
seventh and eighth cervical and the first thoracic nerve are similar in


Dorsal roots contain centripetal processes of neurones sited in the size to the sixth cervical nerve. The remaining thoracic nerves are rela-
spinal ganglia. Each consists of medial and lateral fascicles that both tively small. Lumbar nerves are large, increasing in size from the first to
diverge into rootlets that enter the spinal cord along the posterolateral the fifth. The first sacral is the largest spinal nerve; thereafter the sacral
sulcus. The rootlets of adjacent dorsal roots are often connected by nerves decrease in size. The coccygeal nerves are the smallest spinal
oblique filaments, especially in the lower cervical and lumbosacral nerves. The size of the spinal nerve and its associated structures within
regions. the intervertebral foramen is not in direct relation to the size of the
Little is known of the detail of the regions of entry and emergence foramen. At lumbar levels, though L5 is the largest nerve, its foramen
of afferent and efferent rootlets in humans, but these zones of transition is smaller than those of L1–4, which renders this nerve particularly
between the central and peripheral nervous systems have been exten- liable to compression.
sively described in rodents (Fraher 2000). In the radicular (‘root’) canal and intervertebral foramen, the spinal
nerve is related to the spinal artery of that level and its radicular branch,
Appearance and orientation of roots and to a small plexus of veins. At the outer end of the foramen, the
at each spinal level nerve may lie above or below transforaminal ligaments.
Meningeal nerves
The size and direction of spinal nerve roots vary. The upper four cervical
roots are small, while the lower four are large. Cervical dorsal roots have
a thickness ratio to the ventral roots of 3 : 1, which is greater than in Recurrent meningeal (or sinuvertebral) nerves (Fig. 45.9) occur at all
other regions. The first dorsal root is an exception, being smaller than vertebral levels. They are mixed sensory and sympathetic nerves, repre-
the ventral, and it is occasionally absent. The conventional view is that sented by numerous fine filaments amongst which one, or two to four,


the first and second cervical spinal roots are short, running almost larger trunks may be evident. At cervical levels, the autonomic roots
horizontally to their exits from the vertebral canal, and that from the arise from the grey rami that form the vertebral nerve. At thoracic and
third to the eighth cervical levels the roots slope obliquely down. Obliq- lumbar levels, each nerve is formed by a somatic root from the ventral
uity and length increase successively, although the distance between ramus and by an autonomic root from the grey ramus communicans
spinal attachment and vertebral exit never exceeds the height of one of that segment. Each nerve pursues a recurrent course through the
vertebra. An alternative view states that upper cervical roots descend,
the fifth is horizontal, the sixth to eighth ascend, the first two thoracic
roots are horizontal, the next three ascend, the sixth is horizontal and
the rest descend (Kubik and Müntener 1969). This view is based on the
observation that the cervicothoracic part of the spinal cord grows more
in length than other parts.
Thoracic roots, except the first, are small, and the dorsal root only Pedicle (cut surface)
slightly exceeds the ventral in thickness. They increase successively in
Sinuvertebral nerve
length. In the lower thoracic region, the roots descend in contact with
Intervertebral disc
the spinal cord for at least two vertebrae before emerging from the
vertebral canal.
Lower lumbar and upper sacral roots are the largest, and their root-
Posterior longitudinal ligament
lets are the most numerous. Coccygeal roots are the smallest. Kubik and
Müntener (1969) confirm that lumbar, sacral and coccygeal roots
descend with increasing obliquity to their exits. The spinal cord ends
near the lower border of the first lumbar vertebra, and so the lengths
of successive roots rapidly increase; the consequent collection of roots
is the cauda equina (see Fig. 45.1A). The largest roots, and hence the
largest spinal nerves, are continuous with the spinal cervical and lumbar
enlargements and innervate the upper and lower limbs.
Spinal ganglia (dorsal root ganglia)
Spinal ganglia are large groups of neurones on the dorsal spinal roots.


Each is oval and reddish; its size is related to that of its root. A ganglion
is bifid medially where the two fascicles of the dorsal root emerge to
enter the cord. Ganglia are usually sited in the intervertebral foramina,
immediately lateral to the perforation of the dura mater by the roots
(see Fig. 45.1B). However, the first cervical ganglion lies on the vertebral
arch of the atlas, the second lies behind the lateral atlanto-axial joint, Fig. 45.9 The course and skeletal distribution of the lumbar sinuvertebral
the sacral lie inside the vertebral canal, and the coccygeal ganglion nerves. Each nerve supplies the intervertebral disc at its level of entry
usually lies within the dura mater. The first cervical ganglia may be into the vertebral canal, the disc above, and the intervening posterior
absent. Small aberrant ganglia sometimes occur on the upper cervical longitudinal ligament. In about one-third of cases, the nerve at a particular
dorsal roots between the spinal ganglia and the cord. level may be represented by more than one filament.


SPinAl CoRd And SPinAl nERvES: gRoSS AnATomy
768
5
noiTCES
intervertebral foramen, passing ventral to the spinal nerve, to enter the Cervical dorsal spinal rami
vertebral canal, where it divides into ascending, descending and trans-
verse branches. These branches communicate with corresponding
Each cervical spinal dorsal ramus, except the first, divides into medial
branches from the segments above and below, and from the opposite
and lateral branches that all innervate muscles. In general, only medial
side, forming arcades along the floor of the vertebral canal. Meningeal
branches of the second to fourth, and usually the fifth, supply the skin.
branches of the arcades form a plexus on the ventral surface of the dural
Except for the first and second, each dorsal ramus passes posteriorly
sac and nerve root sleeves that attenuates laterally; the posterior para-
around an articular pillar as far as the root of the transverse process
median dura is devoid of nerve endings. Skeletal branches are distrib-
medial to a posterior intertransverse muscle, which it supplies.
uted to the posterior longitudinal ligament, the periosteum of the
vertebral bodies, and to the posterior and posterolateral aspects of the First cervical dorsal ramus
intervertebral discs (Garcia-Cosamalon et al 2010). Vascular branches
(suboccipital nerve)
accompany the veins and arteries of the vertebral canal and those of the
The first cervical dorsal ramus, the suboccipital nerve, is larger than the
vertebral bodies. The upper three cervical meningeal nerves ascend
ventral (see Fig. 43.76). It emerges superior to the posterior arch of the
through the foramen magnum into the posterior cranial fossa, where
atlas and inferior to the vertebral artery, and enters the suboccipital
they innervate the dura mater that covers the clivus. En route, they
triangle to supply rectus capitis posterior major and minor, obliquus
innervate the median atlanto-axial joint and its ligaments.
capitis superior and inferior, and semispinalis capitis. A filament from
the branch to inferior oblique joins the second dorsal ramus. The sub-
Functional components of spinal nerves


occipital nerve occasionally has a cutaneous branch that accompanies
the occipital artery to the scalp, and connects with the greater and lesser
A typical spinal nerve contains somatic efferent fibres and somatic and
occipital nerves. It may also communicate with the accessory nerve.
visceral afferent fibres. Some, but not all, spinal nerves also contain
preganglionic autonomic fibres. Second cervical dorsal ramus
Somatic components The second cervical dorsal ramus is slightly larger than the ventral and
all the other cervical dorsal rami (see Figs 43.76, 30.22). It runs between
Somatic efferent fibres innervate skeletal muscles and are axons of α, β
the lamina of the axis and inferior oblique, below which it divides into
and γ neurones in the spinal ventral grey column. Somatic afferent
a large medial and smaller lateral branch. The dorsal ramus or its
fibres convey impulses into the central nervous system from receptors
medial branch receives communicating branches from the first cervical
in the skin, subcutaneous tissue, muscles, tendons, fasciae and joints;
dorsal ramus that pass both through and around inferior oblique. A
they are peripheral processes of unipolar neurones in the spinal ganglia.
descending communicating branch crosses the C2–3 facet joint to reach
Visceral components the third cervical dorsal ramus.
Preganglionic visceral efferent sympathetic fibres are axons of neu-
greater occipital nerve
rones in the spinal intermediolateral grey column throughout the
thoracic and upper two or three lumbar segments; they join the The medial branch, termed the greater occipital nerve, passes trans-
sympathetic trunk via corresponding white rami communicantes and versely across inferior oblique deep to semispinalis capitis, which it
synapse with postganglionic neurones that are distributed to smooth innervates. Near the origin of inferior oblique, it turns rostrally along
muscle, myocardium or exocrine glands. The preganglionic visceral rectus capitis posterior major, where it receives a communicating branch
efferent parasympathetic fibres are axons of neurones in the spinal from the third occipital nerve before turning dorsally to pierce semispi-


lateral grey column of the second to fourth sacral segments; they leave nalis capitis. It emerges on to the scalp by passing above an aponeurotic
the ventral rami of corresponding sacral nerves and synapse in pelvic sling between trapezius and sternocleidomastoid near their occipital
ganglia. The postganglionic axons are distributed mainly to smooth attachments. It ascends with the occipital artery and divides into
muscle or glands in the walls of the pelvic viscera. Visceral afferent branches that connect with the third occipital and lesser occipital
fibres have cell bodies in the spinal ganglia. Their peripheral processes nerves, and which supply the back of the auricle and the skin of the
pass through white rami communicantes and, without synapsing, scalp as far forwards as the coronal suture. The lateral branch of the
through one or more sympathetic ganglia to end in the walls of the second cervical dorsal ramus supplies longissimus capitis, semispinalis
viscera. Some visceral afferent fibres may enter the spinal cord in the capitis and splenius capitis, and sends a communicating branch to the
ventral roots. lateral branch of the third cervical dorsal ramus.
Central processes of ganglionic unipolar neurones enter the spinal
cord by dorsal roots and synapse on somatic or sympathetic efferent Greater occipital neuralgia
neurones, usually through interneurones, completing reflex paths. Greater occipital neuralgia is a syndrome of pain and paraesthesiae felt
Alternatively, they may synapse with other neurones in the spinal or in the distribution of the greater occipital nerve. This is usually caused
brainstem grey matter that give origin to a variety of ascending tracts. by damage or irritation to the greater occipital nerve but more rarely
can result from a similar process in the lesser occipital nerve or both
greater and lesser occipital nerves. A similar syndrome may be caused
VARIATIONS OF SPINAL ROOTS AND NERVES by upper facet joint arthritis involving the second cervical root (Vanel-
deren et al 2010).
The courses of spinal roots and nerves in relation to the thecal sac and
vertebral and radicular canals may be aberrant. An individual interver- Third cervical dorsal ramus


tebral foramen may contain a duplicated sheath, nerve and roots, which The third cervical dorsal ramus is intermediate in size between the
will then be absent at an adjacent level. Abnormal communications second and fourth. It courses back round the articular pillar of the third
between roots may occur within the vertebral canal. These anomalies cervical vertebra, medial to the posterior intertransverse muscle, and
have been described and classified for the lumbosacral spine by Neidre divides into medial and lateral branches. The lateral branch passes
and Macnab (1983) (see Fig. 45.6). dorsally across the surface of semispinalis capitis to supply it and the
overlying longissimus capitis and splenius capitis. It receives a com-
municating branch from the lateral branch of the second cervical dorsal
RAMI OF THE SPINAL NERVES ramus, and sends a similar branch to the lateral branch of the fourth
cervical dorsal ramus. The deep medial branch curves dorsally and
Ventral (anterior) primary rami supply the limbs and the anterolateral medially around the waist of the articular pillar before ending in mul-
aspects of the trunk, and in general are larger than the dorsal rami. tifidus. It sends an articular branch to the C3–4 facet joint, and may
Thoracic ventral rami run independently and retain a largely segmental also send a branch into semispinalis capitis. The superficial medial
distribution. Cervical, lumbar and sacral ventral rami connect near their branch, the third occipital nerve, curves around the lateral and dorsal
origins to form plexuses. Dorsal rami do not join these plexuses. The surfaces of the C2–3 facet joint, which it supplies. It continues trans-
ventral rami are described in the appropriate regional sections. versely, deep to semispinalis, which it supplies, and sends a communi-
Dorsal (posterior) primary rami of spinal nerves are usually smaller cating branch to the greater occipital nerve. Just above the second
than the ventral rami and are directed posteriorly. Retaining a segmental cervical spinal process, the third occipital nerve turns dorsally to pierce


distribution, all, except for the first cervical, fourth and fifth sacral and semispinalis capitis, splenius capitis and trapezius, and becomes cuta-
the coccygeal, divide into medial and lateral branches that supply the neous over a small area immediately below the superior nuchal line.
muscles and skin of the posterior regions of the neck and trunk (see Communicating branches join the cutaneous branches of the greater
Fig. 45.8). and lesser occipital nerves.


Spinal nerves
769
54
RETPAHC
Dorsal rami of the lower five cervical nerves
The dorsal rami of the lower five cervical nerves curve back round the
vertebral articular pillars and divide into lateral and medial branches.
The lateral branches supply longissimus cervicis, splenius cervicis and
iliocostalis cervicis. The medial branches curve around the lateral and
dorsal surfaces of the articular pillar of their segment, deep to semispi-
nalis capitis. They send articular branches to the facet joints above and
below their course before entering and supplying multifidus. Terminal
branches reach interspinalis at each segment. Cutaneous branches arise
First lumbar nerve,
consistently from the fourth, and commonly from the fifth, sixth and
dorsal ramus
eighth, but not usually from the seventh medial branches. These
First lumbar nerve,
branches pass across multifidus or through semispinalis cervicis and
ventral ramus
turn dorsally around the medial border of semispinalis capitis, to pierce
splenius cervicis and trapezius and reach the skin. Articular branch
Thoracic dorsal spinal rami
Second lumbar nerve,
At each segmental level, the thoracic dorsal rami pass dorsally through dorsal ramus
an aperture bounded by the transverse processes superiorly and inferi-
orly, the facet joint medially, and the superior costotransverse ligament Medial branch
laterally. Thereafter, each dorsal ramus follows a prolonged course later- Intermediate branch
ally, between the anterior lamella of the superior costotransverse liga-
Interspinous branch
ment anteriorly, and the costolamellar ligament and the posterior
Articular branch
lamella of the superior costotransverse ligament posteriorly. In this
narrow space, the dorsal ramus divides into lateral and medial branches. Lateral branch
The lateral branches continue laterally as far as the costotransverse joint,
Intermediate branch plexus
above which they turn dorsally and inferiorly to supply the levatores
costarum, and enter the longissimus thoracis and iliocostalis muscles.
Lateral branches from the upper six thoracic dorsal rami remain intra-
muscular. Those from the lower six levels emerge from iliocostalis lum-
borum to pierce serratus posterior inferior and latissimus dorsi in line


with the costal angles. They descend across as many as four ribs before Fourth lumbar nerve,
becoming superficial. The twelfth thoracic lateral branch sends a fila- ventral ramus
ment medially along the iliac crest and then passes down to the anterior
gluteal skin. Some upper thoracic lateral branches may become
cutaneous.
Transverse process
Each medial branch hooks dorsally around the lateral margin of the
posterior lamella of the superior costotransverse ligament, lying a vari- Zygapophysial (facet) joint
able distance above the tip of the transverse process. At the first to
fourth, and at the ninth and tenth thoracic levels, the medial branches Fifth lumbar nerve,
dorsal ramus
cross the superior tip of the transverse process to turn inferiorly and
medially across the posterior surface of the transverse process, lying
between the attachment sites of multifidus medially and semispinalis
laterally. Each nerve continues this oblique course to supply multifidus
and semispinalis. At the fifth to eighth thoracic levels, the medial Fig. 45.10 A left posterolateral view of the lumbar spine showing the
branches assume a course parallel to that of other levels, but do not branches of the lumbar dorsal rami.
reach the transverse process, instead passing superior and dorsal to the
plane of the transverse processes. At the eleventh and twelfth levels, in
keeping with the relatively short transverse processes at these levels, the
superior articular process. Opposite the base of the lumbosacral joint,
medial branches run close to the superior articular processes. Each
it sends a branch into the lowest fibres of longissimus thoracis, and a
medial branch supplies articular branches to the facet joints above and
communicating branch to the first sacral dorsal ramus, before terminat-
below its course. Medial branches of the upper six thoracic dorsal rami
ing as a medial branch that hooks around the lumbosacral joint to end
furnish cutaneous branches that pierce trapezius and the rhomboids to
in multifidus.
reach the skin near the spinous processes. Cutaneous branches may
occasionally arise from the medial branches of the lower six thoracic
Sacral dorsal spinal rami
dorsal rami.


Lumbar dorsal spinal rami Sacral dorsal rami are small, diminishing in size inferiorly; other than
the fifth, all emerge through the dorsal sacral foramina. The upper three
are covered at their exit by multifidus, and divide into medial and lateral
After leaving its spinal nerve, each of the first to fourth lumbar dorsal
branches. Medial branches are small and end in multifidus. Lateral
rami passes through an aperture in the dorsal leaf of the intertrans-
branches join together and with branches of the last lumbar and fourth
verse ligament just above a transverse process (Fig. 45.10). Each dorsal
sacral dorsal rami to form loops dorsal to the sacrum. Branches from
ramus supplies the overlying medial intertransverse muscle before
these loops run dorsal to the sacrotuberous ligament and form a second
dividing into lateral and medial branches. The lateral branches supply
series of loops under gluteus maximus. From these, two or three gluteal
the longissimus and iliocostalis components of the lumbar erector
branches pierce gluteus maximus (along a line from the posterior supe-
spinae. The upper three lumbar lateral branches emerge from the
rior iliac spine to the coccygeal apex) to supply the posterior gluteal
lateral border of iliocostalis lumborum and pierce the aponeurosis of
skin.
latissimus dorsi to become cutaneous. They cross the iliac crest to
The dorsal rami of the fourth and fifth sacral nerves are small and
reach the gluteal skin; some reach as far as the level of the greater tro-
lie caudal to multifidus. They unite with each other and with the coc-
chanter. Medial branches cross the junction of the superior articular
cygeal dorsal ramus to form loops dorsal to the sacrum; filaments from
process and transverse process, and hook medially between the mam-
these supply the skin over the coccyx.
millary and accessory processes, deep to the mammillo-accessory liga-
ment. Medial to the ligament, each medial branch sends articular
Coccygeal dorsal spinal ramus
branches to the facet joints above and below its course, before entering
multifidus, which it supplies. Terminal branches reach interspinalis at


each segment. The coccygeal dorsal spinal ramus does not divide into medial and
The fifth dorsal ramus has a longer course than other dorsal rami. It lateral branches. It communicates with the fourth and fifth sacral dorsal
arches over the ala of the sacrum, lying against the root of the first sacral rami to supply the skin over the coccyx.


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Spinal cord ischaemia
VASCULAR SUPPLY OF SPINAL CORD,
ROOTS AND NERVES
The spinal cord can rely for neither its transverse nor its longitudinal
blood supply entirely on the longitudinal arteries. The anterior longi-
ARTERIES
tudinal artery and the intramedullary arteries are functional end-arteries,
although overlap of territories of supply has been described (Backes and
The spinal cord and its roots and nerves are supplied with blood by Nijenhuis 2008). Damage to the anterior longitudinal artery can result
both longitudinal and segmental vessels (Fig. 45.11). Three major lon- in loss of function of the anterior two-thirds of the cord (Fig. 45.13).
gitudinal vessels, a single anterior and two posterior spinal arteries The longitudinal arteries cannot supply the whole length of the cord,
(each of which is sometimes doubled to pass on either side of the dorsal and the input of the segmental medullary feeder vessels is essential.
rootlets) originate intracranially from the vertebral artery and terminate This is especially true of the artery of Adamkiewicz, which may effec-
in a plexus around the conus medullaris. The anterior spinal artery tively carry the major supply for the lower cord; damage to this indi-
forms from the fused anterior spinal branches of the vertebral artery, vidual artery compromises perfusion of the distal cord and may be
and descends in the ventral median fissure of the cord. Each posterior responsible for paraplegia following aortic bypass procedures. For many
spinal artery originates either directly from the ipsilateral vertebral years, it was assumed that the anterior spinal artery system provided the
artery or from its posterior inferior cerebellar branch, and descends in dominant supply to the cord, but clinical evidence implies that the
a posterolateral sulcus of the cord. The segmental arteries are derived posterior spinal arteries may be as important as the anterior system in
in craniocaudal sequence from spinal branches of the vertebral, deep protecting the cord. The mid-thoracic cord, distant from the main ante-
cervical, intercostal and lumbar arteries. These vessels enter the vertebral rior medullary feeders, is particularly liable to become ischaemic after


canal through the intervertebral foramina and anastomose with periods of hypotension; T4–9 has been described as the critical vascular
branches of the longitudinal vessels to form a pial plexus on the surface zone of the spinal cord, where interference with the circulation is most
of the cord. The segmental spinal arteries send anterior and posterior likely to result in paraplegia.
radicular branches to the spinal cord along the ventral and dorsal roots.
Most anterior radicular arteries are small and end in the ventral nerve
roots or in the pial plexus of the cord. The small posterior radicular VEINS
arteries also supply the dorsal root ganglia; branches enter at both
ganglionic poles to be distributed around ganglion cells and nerve Intramedullary veins within the substance of the spinal cord drain into
fibres. (See also Crock (1996).) a circumferential plexus of surface veins, the coronal plexus (venous
plexus of the pia mater). Six tortuous longitudinal channels are usually
Segmental radiculomedullary identified within this plexus: anterior and posterior spinal veins (ante-
feeder arteries rior and posterior median veins) and four others that run on either side
of the ventral and dorsal nerve roots (Fig. 45.14). Only the anterior
spinal vein, which drains the central grey matter, is consistently com-
Some radicular arteries, mainly situated in the lower cervical, lower
plete. It receives sulcal veins and small pial veins from the coronal
thoracic and upper lumbar regions, are large enough to reach the
plexus and is largest in calibre in the lumbosacral region. The posterior
ventral median fissure, where they divide into slender ascending and
spinal vein is frequently variable, appearing plexiform in some seg-
large descending branches. These are the anterior radiculomedullary
ments and as a single channel in others. These vessels connect freely
feeder arteries (Dommisse 1975). They anastomose with the anterior
and drain superiorly into the cerebellar veins and cranial sinuses, and
spinal arteries to form a single or partly double longitudinal vessel of
segmentally into medullary veins mainly. The segmental veins drain
uneven calibre along the ventral median fissure. The largest anterior
into the intervertebral veins and thence into the external vertebral


medullary feeder, the great anterior radiculomedullary artery of Adam-
venous plexuses (see Fig. 43.21), the caval and azygos systems.
kiewicz, varies in level, arising from a spinal branch of either one of the
lower posterior intercostal arteries (T9–11), or of the subcostal artery
Segmental veins
(T12), or less frequently of the upper lumbar arteries (L1 and L2). It
most often arises on the left side (Carmichael and Gloviczki 1999).
Reaching the spinal cord, it sends a branch to the anterior spinal artery Anterior and posterior radiculomedullary veins run along some of the
below and another to anastomose with the ramus of the posterior ventral and dorsal roots. Like the medullary feeder arteries, they are
spinal artery, which lies anterior to the dorsal roots. It may be the main largest in the cervical and lumbar regions of the cord, but do not neces-
supply to the lower two-thirds of the cord. Central branches of the sarily occur in the same segments as the medullary feeders. They drain
anterior spinal artery enter the ventral median fissure, and then turn the cord but not the roots themselves. Very small anterior and posterior
right or left to supply the ventral grey column, the base of the dorsal radicular veins occur in most spinal segments, accompanying and
grey column, including the dorsal nucleus, and the adjacent white draining the ventral and dorsal roots and some of the cord at the points
matter (Fig. 45.12). of entry and exit of the rootlets; they usually drain into the interverte-
Each posterior spinal artery contributes to a pair of longitudinal bral veins.
anastomotic channels, anterior and posterior to the dorsal spinal
roots. These are reinforced by posterior medullary feeders from the
THE EFFECTS OF INJURY
posterior radicular arteries. The latter are variable in number and size,
but smaller, more numerous and more evenly distributed than the
anterior medullary feeders. The anterior channel is joined by a ramus SPINAL CORD INJURY AND VERTEBRAL
from the descending branch of the great anterior segmental medullary COLUMN INJURY
artery of Adamkiewicz. In all longitudinal spinal arteries the width of


the lumen is uneven and complete interruptions may occur. At the Various clinical definitions have been described in the International
conus medullaris they communicate by anastomotic loops. Anastomo- Standards Booklet for Neurological and Functional Classification of Spinal
ses other than those between the pial or peripheral spinal arterial Cord Injury, which was a landmark publication in standardizing the
branches may be important, e.g. a posterior spinal series of anastomoses language of the neurological examination as it relates to spinal cord
between rami of the dorsal divisions of segmental arteries near the injury (Ditunno et al 1994). ‘Tetraplegia’ refers to impairment or loss
spinous processes. of neural function secondary to a cervical injury. ‘Paraplegia’ refers to
loss of function in the thoracic, lumbar or sacral segments of the cord.
Intramedullary arteries
‘Dermatome’ refers to the area of skin innervated by cutaneous axons
in the distribution of a single spinal nerve. ‘Myotome’ refers to the
The central branches of the anterior spinal artery supply about two- muscle fibres innervated by the motor axons of a single spinal nerve.
thirds of the cross-sectional area of the cord. The rest of the dorsal grey ‘Neurological level’ is the first level where motor and sensory function
and white columns and peripheral parts of the lateral and ventral white is normal on both sides of the body. ‘Sensory level’ refers to the most
columns are supplied by numerous small radial vessels that branch caudal level with normal sensation on both sides of the body. ‘Motor
from posterior spinal arteries and the pial plexus. In a microangio- level’ refers to the most caudal segment with antigravity strength, pro-
graphic study of the human cervical spinal cord, up to six anterior, and viding that the next most rostral level is stronger. ‘Complete injury’
eight posterior, radicular spinal arteries were described, and up to eight occurs when there is an absence of motor and sensory function below
central branches arose from each centimetre of the anterior spinal artery the motor and sensory levels and absence of function in the lowest
(Turnbull et al 1966). sacral segment. ‘Incomplete injury’ refers to partial preservation of


Spinal cord and spinal nerves: gross anatomy
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Sulcal (central) branch to Fig. 45.12 Arterial disposition within the spinal cord.
Right posterior spinal artery
right side of spinal cord (Reprinted from Netter Anatomy Illustration
Collection, © Elsevier Inc. All Rights Reserved.)
Peripheral branches
Posterior from pial plexus
radicular artery
Sulcal (central) branch to
Anterior segmental
left side of spinal cord
medullary artery
Left posterior spinal artery
Pial arterial plexus Zone supplied by
penetrating branches
Anterior and posterior from pial plexus
radicular arteries
Zone supplied by
central branches
Zone supplied by both
central branches
Anterior spinal artery and branches
from pial plexus
Anterior segmental
medullary artery
Pial arterial plexus
Fig. 45.13 A, A sagittal thoracic MR image showing
spinal cord ischaemic changes (arrow) secondary to
thrombotic occlusion of the artery of Adamkiewicz in
a patient with a hypercoagulable disorder. B, The
changes were noted to be in the distribution of the
anterior spinal artery, as seen on this axial image.
B
A


The effects of injury
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Anterior view Posterior view
Posterior cerebral artery
Superior cerebellar artery
Basilar artery
Anterior inferior cerebellar artery
Posterior inferior cerebellar artery
Posterior inferior cerebellar artery
Posterior spinal arteries
Anterior spinal artery
Vertebral artery Vertebral artery
Anterior segmental
medullary arteries
Posterior segmental
medullary arteries
Ascending cervical
artery Ascending cervical
artery
Deep cervical artery Deep cervical artery
Subclavian artery Subclavian artery
Posterior segmental
Anterior segmental medullary arteries
medullary artery
Posterior intercostal artery
Pial arterial plexus Thoracic Posterior intercostal arteries
vertebrae
Major anterior
segmental medullary
artery (artery of
Adamkiewicz)
Posterior intercostal artery
Anterior segmental
medullary artery Posterior segmental
medullary arteries
Anastomotic loops to
Anastomotic loops to
posterior spinal arteries
anterior spinal arteries
Lumbar artery
Lumbar arteries
Lumbar
vertebrae
Cauda equina arteries
Lateral sacral artery
Lateral sacral artery
Sacrum
Fig. 45.11 Arteries of the spinal cord. (Reprinted from Netter Anatomy Illustration Collection, © Elsevier Inc. All Rights Reserved.)
earbetrev
lacivreC
sensory and/or motor function below the neurological levels, as well as sustained to 24 hours after injury, followed by a phase of reflex return
evidence of ‘sacral sparing’ (evidence of preserved function of the lowest (Ditunno et al 2004).
sacral segment) (Ditunno et al 2004). ‘Spinal shock’ refers to the In the assessment of a patient with spinal injury and neurological
absence of reflexes and motor/sensory function below the level of injury damage, it is important to remember that the level of cord and root
and occurs typically from the time at which spinal cord injury is injury will not coincide with that of the skeletal damage to the vertebral


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Anterior spinal vein Fig. 45.14 The venous drainage of the spinal
cord. (With permission from Miyasaka K, Asano
Radial perforating vein T, Ushikoshi S et al 2000 Vascular anatomy of
the spinal cord and classification of spinal
arteriovenous malformations. Interv Neuroradiol.
Spinal ganglion Posterior spinal vein 6 Suppl 1:195–8.)
Transmedullary anastomosis
Pial venous network
Sulcal vein
Spinal nerve
Dura mater
Arachnoid mater
Pial venous network
Pial vein
Radiculomedullary vein
Radicular vein
column. In estimating the vertebral levels of cord segments in the adult, segments, and cutaneous sensibility is lost in the perineum, buttocks,
a useful approximation is that, in the cervical region, the tip of a verte- the back of the thighs and the legs, and soles of the feet. The roots of
bral spinous process corresponds to the succeeding cord segment (i.e. lumbar nerves descending to join the cauda equina may be damaged
the sixth cervical spine is opposite the seventh spinal segment); at upper at this level, causing complete paralysis of both lower limbs. Lesions
thoracic levels, the tip of a vertebral spine corresponds to the cord two below the first lumbar vertebra may divide or damage the cauda equina,
segments lower (i.e. the fourth spine is level with the sixth segment), but severe nerve damage is uncommon and is usually confined to the
and in the lower thoracic region, there is a difference of three segments spinal roots at the level of the trauma. Neurological symptoms may also
(i.e. the tenth thoracic spine is level with the first lumbar segment). The occur as a result of interference with the spinal blood supply, particu-
eleventh thoracic spine overlies the third lumbar segment and the larly in the lower thoracic and upper lumbar segments.
twelfth is opposite the first sacral segment. In making this estimate by
palpation of the vertebral spines, it is important to remember the rela-
tionship of the individual spines to their vertebral bodies. Clinical Spinal cord injury without radiological


localization may be off by several levels because other factors may come abnormality: ‘SCIWORA’
into play, such as vascular insufficiency or venous obstruction, resulting
in the lesion being localized as significantly lower than it actually is
The spinal cord may be damaged without radiological evidence of
(Rousseff and Tzvetanov 2006, Sonstein et al 1996).
skeletal injury to the vertebral column. This most commonly occurs
Complete division above the fourth cervical segment causes respira-
with motor vehicle accidents but also has been reported with sports
tory failure because of the loss of activity in the phrenic and intercostal
injuries and falls. MRI may or may not show evidence of cord injury
nerves. Lesions between C5 and T1 paralyse all four limbs (quadriple-
after SCIWORA occurs; the majority of patients sustaining these injuries
gia), the effects in the upper limbs varying with the site of injury: at the
have an abnormal MRI scan.
fifth cervical segment, paralysis is complete; and at the sixth, each arm
is positioned in abduction and lateral rotation, with the elbow flexed
and the forearm supinated, due to unopposed activity in deltoid, Spinal cord syndromes
supraspinatus, rhomboid and the brachial flexors (all supplied by the
fifth cervical spinal nerves). Upper limb paralysis is less marked in lower
cervical lesions. Lesions of the first thoracic segment paralyse small Available with the Gray’s Anatomy e-book
muscles in the hand and damage the sympathetic outflow to the head
and neck, resulting in contraction of the pupil, recession of the eyeball,
LESIONS OF THE SPINAL ROOTS,
narrowing of the palpebral fissure and loss of sweating in the face and
neck (Horner’s syndrome). However, sensation is retained in areas NERVES AND GANGLIA
innervated by segments above the lesion; thus cutaneous sensation is
retained in the neck and chest down to the second intercostal space Spinal roots, nerves and ganglia may be damaged in the vertebral and
because this area is innervated by the supraclavicular nerves (C3 and root canals and at the intervertebral foramina. Neurofibromas and


C4). At thoracic levels, division of the cord paralyses the trunk below schwannomas may occur on the roots and nerves in the root canals. As
the segmental level of the lesion, and both lower limbs (paraplegia). they enlarge, these tumours become dumbbell-shaped, with both an
The first sacral neural segment is approximately level with the thoraco- intraspinal and an extraspinal component in continuity; the clinical
lumbar vertebral junction; injury, which commonly occurs here, paraly- picture may thus include paradoxical features as the asymmetrical
ses the urinary bladder, the rectum and muscles supplied by the sacral space-occupying lesion grows. Root compression usually presents


Spinal cord and spinal nerves: gross anatomy
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Typical neural abnormalities include cord oedema, haemorrhage,
contusion or transection. Typical extraneural abnormalities include
intervertebral disc protrusion or herniation, ligamentum flavum
bulging, cervical spondylitis, prevertebral soft tissue oedema, ligamen-
tous abnormalities and/or ossification of the posterior longitudinal
ligament. Originally, this was considered a paediatric diagnosis but it
has now been shown to be equally common in adults. Spinal stenosis
and pre-existing cord compression have been postulated as a risk factor
for SCIWORA but clinical series have not supported this (Boese and
Lechler 2013, Boese et al 2013).
For cervical spinal injury, several cord syndromes have been described,
relating the clinical picture to the anatomy of the neurological lesion
within the cord. The most common of these is central cord syndrome,
which usually results from hyperextension injury to an osteoarthritic
neck, when the major injury is to the central grey matter. This typically
gives an incomplete cord injury pattern with greater motor loss in the
upper extremities than in the lower limbs. There is also variable sensory
loss and neurogenic bladder dysfunction (Pouw et al 2010). In anterior
cord syndrome, which may occur in flexion–compression injuries of the
neck, the damage occurs in the area of supply of the anterior spinal
artery, sparing the posterior columns; the motor loss is usually propor-
tionately greater in the lower than in the upper limbs, while sensory
loss is less of a problem. A third syndrome that may be seen with pen-
etrating trauma is Brown–Séquard syndrome. This is an injury directed
to one side of the spinal cord, where there is ipsilateral loss of motor
function and pinprick sensation and contralateral loss of pain and
temperature sensation (Lee et al 1990). The anatomical basis for these
symptoms is injury to the ipsilateral posterior columns and corticospi-
nal tract, and injury to the lateral spinothalamic tract, which conveys
contralateral pain and temperature sensation (see p. 306).


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Key references
acutely with pain, which may be severe. The pain, paraesthesias and features (Fig. 45.15). There are lower motor neurone signs in the legs
numbness occur in a dermatomal distribution; dermatomal overlap with fasciculation and muscle atrophy. Sensory loss usually involves the
may make it difficult to demonstrate sensory loss on the trunk. Severe perineal or ‘saddle area’, as well as other lumbar and sacral dermatomes.
traction injuries of the upper limbs may cause avulsion of spinal roots There may be congenital abnormalities, e.g. spina bifida (p. 759),
from the cord in the cervical region. lipomata or diastematomyelia, and the conus may extend below the
lower border of L1, often with a tethered filum terminale (Fig. 45.16).
The anatomical basis for pain of spinal origin Extramedullary lesions include prolapsed intervertebral discs. A midline
(central) disc protrusion in the lumbar region may present with involve-
ment of the sacral segments only.
In the diagnosis and description of pain of spinal origin, it is particu-
Two distinct clinical syndromes, conus medullaris syndrome and
larly important to distinguish between radicular pain and somatic
cauda equina syndrome, have been described, the latter being much
referred pain.
more common. Cauda equina syndrome typically presents in men who
Radicular pain is caused by disorders that affect a spinal nerve or its
have a lumbar disc herniation in the setting of lumbar spinal stenosis,
dorsal root ganglion. This type of pain characteristically radiates, along
with symptoms of asymmetric saddle anaesthesia and asymmetric lower
a narrow band, into the area of the limb (or trunk wall) that the spinal
extremity weakness, and delayed presentation of atonic bladder and
nerve supplies, and is typically (although not always) lancinating in
flaccid anal sphincter. Conus medullaris syndrome typically presents
quality, not unlike an electric shock.
with symmetric saddle anaesthesia, symmetric motor deficit and earlier
Referred pain is pain felt in the distribution of a nerve that is not
atonic bladder and sphincter dysfunction. The usual causes are intra-


the nerve that innervates the source of pain, although typically these
dural tumours or vascular lesions (Radcliff et al 2011).
nerves are derived from the same spinal cord segment. Referred pain is
Tethered cord syndrome may be associated with occult or non-occult
felt deeply across a broad area, and is usually aching in quality; although
spinal dysraphism. In its classic form, it refers to an unusually low
it may radiate into a limb (or around the trunk wall), it is typically
conus medullaris (although in some 14–18% of cases the position of
constant in location. Patients may find it hard to define the outer
the conus is anatomically normal). There is some debate as to what
boundaries of this pain but they can clearly identify the centre of its
constitutes an abnormally low conus, whether below the L1–2 disc
distribution. Referred pain can be subdivided into somatic referred pain
space or below the lower border of the body of the L2 vertebra. Most
and visceral referred pain, according to its origin. As its name implies,
commonly, tethered cord syndrome is associated with a short filum
visceral referred pain is caused by disorders in viscera; in some cases,
terminale more than 2 mm wide, but it also may be related to an intra-
the referral can be quite remote from the viscus, e.g. cardiac pain that
dural lipoma. Traction on the caudal cord and loss of filum terminale
radiates into the neck. Somatic referred pain is caused by disorders of
elasticity are thought to predispose to decreased blood flow in the cord,
muscular and skeletal structures. Examples include lumbar spinal pain
referred to the gluteal region, thigh or leg; cervical spinal pain referred leading to symptoms (Filippidis et al 2010). The clinical presentation
to the upper limb girdle; and cervical or thoracic spinal pain referred varies according to age. In children, the most common presentation
to the chest wall, where it may mimic cardiac pain. Often the source of includes foot deformities, neurological deficits, spinal deformity and
somatic referred pain cannot be determined by clinical examination, various cutaneous findings such as a lumbar capillary angioma. In


and invasive tests are required to pinpoint its location. adults, the syndrome more commonly presents with perianal pain and
leg weakness (see Fig 45.16) (Pang and Wilberger 1982).
LESIONS OF THE CONUS AND CAUDA EQUINA
CLINICAL PROCEDURES
Lesions of the conus and cauda equina, e.g. tumours, cause bilateral
deficit, often with pain in the back extending into the sacral segments
Available with the Gray’s Anatomy e-book
and to the legs. Loss of bladder and erectile function can be early
Bonus e-book images
Fig. 45.3 A T1 post-contrast sagittal lumbar hypercoagulable disorder. B, The changes puncture needle through skin, subcutaneous
spinal magnetic resonance (MR) image were noted to be in the distribution of the tissue, supraspinous ligament, interspinous
showing a spinal epidural abscess adherent anterior spinal artery, as seen on this axial ligament between the spinous processes,
to the lumbar dura and spinal nerves in a image. ligamentum flavum, dura mater, into the
28-year-old female with a history of subarachnoid space and between the nerve
intravenous drug abuse. Fig. 45.15 A sagittal MR image showing a roots of the cauda equina. B, A horizontal
spinal ependymoma, a tumour arising from section of lumbar vertebra illustrating the
Fig. 45.4 A sagittal thoracic MR image the filum terminale, which can be seen just course of a lumbar puncture needle through
showing a large ventral spinal epidural below the conus medullaris. skin, subcutaneous tissue, between the
haematoma resulting in severe neck and spinous processes and laminae, ligamentum
upper thoracic pain and ataxia. Fig. 45.16 A sagittal MR image showing a flavum, epidural space, dura mater, into the
tethered filum terminale resulting in low-lying subarachnoid space and between the nerve
Fig. 45.12 Arterial disposition within the conus. roots of the cauda equina.
spinal cord.
Fig. 45.17 The lumbar interlaminar window Fig. 45.19 Palpation of the sacral cornua for


Fig. 45.13 A, A sagittal thoracic MR image in extension and flexion. caudal epidural injection.
showing spinal cord ischaemic changes
secondary to thrombotic occlusion of the Fig. 45.18 A, A sagittal section of lumbar Fig. 45.20 Position of the needle in caudal
artery of Adamkiewicz in a patient with a vertebrae illustrating the course of a lumbar epidural injection.
KEY REFERENCES
Crock H 1996 An Atlas of Vascular Anatomy of the Skeleton and Spinal Newell RL 1999 The spinal epidural space. Clin Anat (New York, NY) 12:
Cord. London: Martin Dunitz. 375–9.
Ditunno JF Jr, Young W, Donovan WH et al 1994 The international stand- Pang D, Wilberger JE Jr 1982 Tethered cord syndrome in adults. J Neurosurg
ards booklet for neurological and functional classification of spinal cord 57:32–47.
injury. American Spinal Injury Association. Paraplegia 32:70–80. A review of a series of adult patients with tethered cord syndrome which
A landmark publication standardizing the language of the neurologic exam compares their clinical presentation to children with similar pathology.
as it relates to spinal cord injury. Radcliff KE, Kepler CK, Delasotta LA et al 2011 Current management review
Dommisse G 1975 The Arteries and Veins of the Human Spinal Cord From of thoracolumbar cord syndromes. Spine J 11:884–92.
Birth. Edinburgh: Churchill Livingstone. An in-depth review on the clinical aspects of cauda equina syndrome and
conus medularis syndrome.


Spinal cord and spinal nerves: gross anatomy
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ACCESS TO CEREBROSPINAL FLUID
The safest approach to the cerebrospinal fluid (CSF) is to enter the
lumbar cistern of the subarachnoid space in the midline, well below
the level at which the spinal cord normally terminates (see above). The
fine needle employed is unlikely to damage the mobile nerve roots of
the cauda equina. This procedure is called lumbar puncture. It is also
possible to access the CSF by midline puncture of the cerebellomedul-
lary cistern (cisterna magna) (Ch. 18): this is cisternal puncture.
Lumbar puncture: adult
Lumbar puncture in the adult may be performed with the patient either
sitting or lying on their side (lateral decubitus) on a firm, flat surface.
In each position, the lumbar spine must be flexed as far as possible, in
order to separate the vertebral spines maximally and expose the liga-
mentum flavum in the interlaminar window (Fig. 45.17). A line is then
taken between the highest points of the iliac crests: this line almost
always intersects the vertebral column at the L4 vertebral body or L4/
L5 intervertebral disc level (see Fig. 78.16). With the spines now identi-
fied, the skin is anaesthetized and a needle is inserted between the
spines of L3 and L4 (or L4 and L5). Exact identification of the level by
palpation is difficult (Broadbent et al 2000). The soft tissues that the
needle will traverse should also be anaesthetized; care should be taken
that the injection of an excessive amount of local anaesthetic does not
compromise appreciation of the structures being traversed. These will
be, in order: subcutaneous tissue, supraspinous ligament, interspinous
ligament, ligamentum flavum, epidural space containing the internal
vertebral venous plexus, dura, arachnoid, and finally, the subarachnoid
space (Fig. 45.18). The lumbar puncture needle may then be inserted
in the midline or just to one side, and angled in the horizontal and


sagittal planes sufficiently to pierce the ligamentum flavum in or very
near the midline. There is then a slight loss of resistance as the needle
enters the epidural space; careful advancement will next pierce the dura
and arachnoid to release CSF. For further details about the clinical
Fig. 45.15 A sagittal MR image showing a spinal ependymoma (arrow), a anatomy of lumbar puncture, see Boon et al (2004).
tumour arising from the filum terminale, which can be seen just below the
conus medullaris. The patient presented with pain in the back radiating to
the legs. At surgery to resect the ependymoma, it was found to be
adherent to the filum terminale.
Extension
Fig. 45.16 A sagittal MR image showing a tethered filum terminale
resulting in low-lying conus. The patient presented with back pain and
perineal disturbances consistent with ‘tethered cord syndrome’. The end
of the conus medullaris was noted to be at the L5 level.
Flexion
Fig. 45.17 The lumbar interlaminar window in extension and flexion.


SPinAl CoRd And SPinAl nERvES: gRoSS AnATomy
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A B
Interspinous Nerve roots of Lumbar vertebral
ligament cauda equina body
Skin Subarachnoid
space
Subcutaneous
tissue Epidural space
Spinous process
Supraspinous ligament Dura mater
Lumbar puncture
Ligamentum
needle
flavum
Subarachnoid Spinous
space laminae
Interspinous
Ligamentum ligament
flavum
Spinous
Dura mater process
Lumbar vertebral
bodies
Skin Subcutaneous tissue Lumbar puncture needle
Intervertebral disc
Fig. 45.18 A, A sagittal section of a lumbar vertebrae illustrating the course of a lumbar puncture needle through skin, subcutaneous tissue,
supraspinous ligament, interspinous ligament between the spinous processes, ligamentum flavum, dura mater, into the subarachnoid space and between
the nerve roots of the cauda equina. B, A horizontal section of a lumbar vertebra illustrating the course of a lumbar puncture needle through (in order)
skin, subcutaneous tissue, between the spinous processes and laminae, ligamentum flavum, epidural space, dura mater, into the subarachnoid space
and between the nerve roots of the cauda equina. (With permission from Boon JM, Abrahams PH, Meiring JH et al 2004 Lumbar puncture: anatomical
review of a clinical skill. Clin Anat. 17:544–53.)
Lumbar puncture: neonate and infant Further details of this difficult specialist technique are beyond the scope
of this book.
In premature and term neonates, the spinal cord usually terminates
between the first and third lumbar vertebrae. In children between the
ACCESS TO THE EPIDURAL SPACE
ages of 1 and 7 years, the conus medullaris lies between the twelfth
thoracic and third lumbar vertebrae (Barson and Sands 1977, Barson
The epidural space lies between the spinal dura and the wall of the
1970, Vettivel 1991, Malas et al 2001, Kesler et al 2007, Suresh et al


vertebral canal. It contains epidural fat and a venous plexus. Access to
2013). The supracristal plane intersects the vertebral column slightly
this space, usually in the lumbar region, is required for the administra-
higher (L3–4). These differences must be borne in mind when identify-
tion of anaesthetic and analgesic drugs, and for endoscopy. The caudal
ing the landmarks before undertaking lumbar puncture in the neonate
route is used mainly for analgesic injections.
and infant. A lumbar puncture is performed by placing the baby in a
position, either lying or sitting, that gives maximum convex curvature
Thoracic and cervical epidurals
to the lumbar spine. A needle with trocar is inserted into the back
between the spines of the third and fourth lumbar vertebrae and into
the subarachnoid space below the level of the conus medullaris. The It is possible to access the epidural space at thoracic and cervical levels,
space between L3 and L4 is approximately level with the iliac crests and but the specialist techniques required are beyond the scope of this
it is usual to insert the needle and trocar into the intervertebral space book.
immediately above or below the iliac crests. The distance from the skin
to the subarachnoid space is approximately 1.4 cm in neonates; it Lumbar epidural
increases progressively with age.
For access to the lumbar epidural space, the approach is as for lumbar
Cisternal puncture
puncture. The intention in epidural injection is to avoid dural puncture,
so the epidural space should be entered in the midline posteriorly,
In cisternal puncture, the cisterna magna (see Fig. 18.15) is entered by where the depth of the space is greatest. The skin–epidural distance has
midline puncture through the posterior atlanto-occipital membrane. been assessed in children at the L3–4 interspace; 1 mm/kg of body


Spinal cord and spinal nerves: gross anatomy
773.e3
54
RETPAHC
weight is considered to be a useful guideline for children between the
ages of 6 months and 10 years (Bösenberg and Gouws 1995). Tech-
niques for entering the epidural space rely on the appreciation of loss
of resistance to injection of saline (air is used by some) as the space is
entered. This loss of resistance results from the fact that when the needle
tip is in the ligamentum flavum, saline cannot be injected into the
dense ligament, but once the epidural space is entered, injection
becomes easier into the loose tissues of the space. As there is very little
distance between the ligamentum flavum and the underlying dura, care
must be taken not to continue advancing the needle once loss of resist-
ance has occurred.
Caudal epidural
The route of access to the caudal epidural space is via the sacral hiatus.
The space is therefore entered below the level of termination of the Fig. 45.19 Palpation of the sacral cornua for caudal epidural injection.
dural sac (the subarachnoid space and its contained CSF), which usually
extends only to the level of the second sacral segment. Occasionally,
the dural sac ends as high as the fifth lumbar vertebra, and very rarely
it may extend to the third part of the sacrum, in which case it is occa-
Termination of dural sac
sionally possible to enter the subarachnoid space inadvertently during
the course of a sacral nerve block. Epidural space
With the patient in the lateral position or lying prone over a pelvic
pillow, the sacral hiatus is identified by palpation of the sacral cornua Filum terminale externum
(Fig. 45.19). These are felt at the upper end of the natal cleft approxi-
mately 5 cm above the tip of the coccyx. Alternatively, the sacral hiatus Sacral hiatus
may be approximated by constructing an equilateral triangle based on
a line joining the posterior superior iliac spines; the inferior apex of
this triangle overlies the hiatus (see Fig. 78.16). After local anaesthetic
infiltration, a needle is introduced at 45° to the skin, in order to pen-
Second sacral segment