Download Craniovertebral Junction

Craniovertebral Junction
Ayberk Özkavaklı
What is craniovertebreal junction?
 The craniocervical (craniovertebral) junction
represents the complex transitional zone between
the cranium and the spine and comprises a
complex balance of different elements: it should be
considered anatomically and radiologically a
distinct entity from both the cranium and, in
particular, the cervical spine. It is composed of
osseous structures articulated with synovial joints,
intrinsic ligaments and membranes and muscles. As
well as housing the spinal cord and multiple cranial
nerves, it is also approximated by critical vasculature
supplying both the brain and the cervical spinal
cord parenchyma.
 The requirements placed on the craniocervical
junction are onerous—not only must it house, protect
and support structures critical for function, it must
also simultaneously provide significant mobility.
Atlas
 The atlas is the first cervical vertebra,
commonly called C1. It is an atypical
cervical vertebra with unique features. It
articulates with the dens of the axis and
the occiput, respectively allowing
rotation of the head, and flexion,
extension and lateral flexion of the
head. Unlike the rest of the cervical
vertebrae, with exception to the similarly
structured axis (C2), the anterior rami are
sent posteriorly instead of anteriorly.
Gross anatomy of Atlas
 The atlas is composed of an
anterior arch and a posterior
arch, paired lateral masses, and
paired transverse processes. It
has the dens of the axis sit where
a centrum (body) of a typical
vertebra would be. The
transverse ligament holds the
dens of the axis against the
anterior arch of the atlas and
divides its vertebral canal into
two parts. The anterior 1/3 is
occupied by the dens. The
posterior 2/3 contains the spinal
cord, which occupies 1/3 of the
total vertebral canal space.
 anterior arch
 anterior tubercle: sits on the anterior aspect of the
anterior arch and is the site of attachment of
the anterior longitudinal ligament
 posterior facet for the dens: sits on the posterior
aspect of the anterior arch
 upper border: attachment of the anterior atlantooccipital membrane and lateral parts of
the anterior longitudinal ligament
 lower border: attachment of the anterior atlantooccipital membrane and lateral parts of
the anterior longitudinal ligament
 posterior arch
 3/5th of circumference of the ring
 posterior tubercle: sits posteriorly to the posterior
arch, is a rudimentary spinous process and
attachment site for the ligamentum nuchae
 superior surface: contains paired grooves for the C1
nerve and vertebral artery, sits just posterior to the
lateral mass
 superior border: attachment for the posterior
atlanto-occipital membrane
 inferior border: attachment for the ligamentum
flava
 lateral masses
 paired, ovoid
 superior articular facet: kidney-shaped, concave and articulates with
the occipital bone
 inferior articular facet: circular, with a flat or slightly concave surface articulating
with the lateral atlanto-axial joint
 medial surface: marked by vascular foramina and a tubercle for the attachment
of the transverse ligament
 transverse processes
 longer than all of the transverse processes of the cervical vertebrae except C7
 typically covered by costal lamella
 transverse foramina: contains the vertebral arteries
 anterior tubercle: sometimes present on the anterior aspect of the transverse
process
Articulations
 atlanto-occipital joint: hyaline-covered synovial joint between the occipital condyle and
concave facet of the lateral mass of the atlas. Covered by a capsule and innervated by C1,
this joint allows for flexion, extension and lateral flexion.
 median atlanto-axial joint: hyaline-covered synovial joint between the dens of axis back of
the anterior arch of the atlas which allows for the rotation of the head. The dens is held in
place by the transverse ligament, with a bursa between the two.
 lateral atlanto-axial joint: hyaline-covered synovial joint between the inferior articular facet of
the atlas and the superior articular facet of the axis which allows for the rotation of the head.
A capsule innervated by the C2 nerve surrounds the joint.
Ligaments
 transverse ligament: strong band
that runs posterior to the dens of
the axis, holding it in place. Each
end is attached to tubercles on
the anterior arch of the atlas. The
former is attached to the basilar
part of the occipital bone, in close
relation with the membrana
tectoria; the latter is fixed to the
posterior surface of the body of
the axis; hence, the whole
ligament is named the cruciate
ligament of the atlas.
 atlanto-axial ligaments: attach
from the lower border of the
anterior arch of the atlas to front of
the body of the axis. Provides
tertiary support against ventral
translation of the dens
Musculotendinous

anterior atlanto-occipital membrane: attached to upper border of the anterior arch to the outer margins of foramen magnum

posterior atlanto-occipital membrane: attached to upper border of the posterior arch to the outer margins of foramen magnum. At each lateral margin,
there is a gap for the passage of the C1 nerve and vertebral artery, which sometimes ossifies and become foramen. Innervated by C1.

longus colli: deep grooves of the anterior surface of the body

levator scapulae: tip of the transverse processes

splenius cervicis: transverse processes

obliquus capitis superior: transverse processes

obliquus capitis inferior: transverse processes

rectus capitis posterior minor: tubercle on the posterior arch of the atlas
Axis
 The axis is the second cervical vertebra, commonly called C2. It is an
atypical cervical vertebra with unique features and important relations that
make it easily recognisable. Its most prominent feature is the odontoid
process, which is embryologically the body of the atlas (C1)1,2. It plays an
important role in rotation of the head with the majority of movement
occurring around the dens and at the atlanto-axial joint.
Gross anatomy of axis

The axis is formed by a body with the attached dens, two lateral
masses, a posterior neural arch (formed by the pedicle and a
thick lamina), and a large spinous process, which is commonly
bifid.
Anterior components of the axis are composed of:

dens: conical in shape

body

lateral mass

transverse process with foramina transversarium

superior articular facets

inferior articular facets
Posterior elements of the axis are composed of:

pedicle

lamina

spinous process

has several muscle attachments

semispinalis cervicis

rectus capitis posterior major

inferior oblique
Articulations
 superior articular facet with inferior articular facet of C1
 dens articulates with the posterior aspect of the anterior arch of C1
 inferior articular facet with superior articular facet of C3
 uncovertebral articulation with C3
Foramen Magnum

The foramen magnum is the largest foramen of the skull and is part of the occipital bone. It is oval in shape with a large anteroposterior diameter 2.
Gross Anatomy

The foramen magnum is found in the most inferior part of the posterior cranial fossa 3. It is traversed by vital structures including
the medulla oblongata. In the midline, the anterior margin is the basion and the posterior margin is the opisthion.
Relations

anteriorly: basilar part of occipital bone

anterolaterally: occipital condyles, hypoglossal canal, jugular foramen

posteriorly: squamous part of occipital bone with the internal occipital crest
Contents

medulla oblongata

meninges

spinal root of the accessory nerve

vertebral arteries

anterior and posterior spinal arteries

tectorial membrane and alar ligaments
Tectorial membrane and Alar ligament
The tectorial membrane of atlanto-axial
joint (occipitoaxial ligaments) is situated within the vertebral
canal.

It is a broad, strong band which covers the dens and its
ligaments, and appears to be a prolongation upward of
the posterior longitudinal ligament of the vertebral
column.

It is fixed, below, to the posterior surface of the body of
the axis, and, expanding as it ascends, is attached to the
basilar groove of the occipital bone, in front of
the foramen magnum, where it blends with the
cranial dura mater.

Its anterior surface is in relation with the transverse
ligament of the atlas, and its posterior surface with the
dura mater.
The alar ligaments join the lateral margins of the sloping
upper margin of the dens of C2 to the lateral margins of
the foramen magnum (adjacent to the occipital condyles)
and lie on either side of the apical ligament. They are paired
ligaments that are very strong and limit rotation of the head.
Vertebral Artery
 origin: branch of the 1st part of the subclavian
artery
 course: ascends posterior to the internal
carotid artery in the transverse foramina of
the cervical vertebrae
 branches
 numerous small branches
 radicular/spinal branches
 posterior inferior cerebellar artery (PICA)
 termination: combines with the contralateral
vertebral artery to form the basilar artery
 key relationships: posterior to the internal
carotid artery; ascends anterior to the roots of
the hypoglossal nerve (CN XII)
Segments
 The vertebral artery is typically
divided into 4 segments:
 V1 (preforaminal): origin to
transverse foramen of C6
 V2 (foraminal): from the
transverse foramen of C6 to
the transverse foramen of C2
 V3 (atlantic or
extradural): from C2 to the
dura
 V4 (intradural): from the dura
to their confluence to form
the basilar artery
Chiari Malformations
Background
 Chiari malformations, types I-IV, refer to a spectrum of congenital hindbrain abnormalities
affecting the structural relationships between the cerebellum, brainstem, the upper
cervical cord, and the bony cranial base.
Epidemiology
 Although Chiari malformation is still listed as a rare disease by the Office of Rare Diseases of
the National Institutes of Health, this categorization is based on outdated data from before
the MRI era. With routine use of MR imaging, Chiari malformation is discovered with
increasing frequency. For Chiari I, prevalence rates of 0.1-0.5% with a slight female
predominance are suggested by recent studies. [5]Chiari II is found in all children with
myelomeningocele, although less than one-third develop symptoms referable to this
malformation.
Etiology
 Based on analysis of familial aggregation, a genetic basis for Chiari I has been
suggested. Recent studies suggest linkage to chromosomes 9 and 15. It is hypothesized
that Chiari type I originates as a disorder of para-axial mesoderm, which subsequently
results in formation of a small posterior fossa. The development of the cerebellum within this
small compartment results in overcrowding of the posterior fossa, herniation of the
cerebellar tonsils, and impaction of the foramen magnum. This theory is consistent with the
observed association of Chiari I and other hereditary mesodermal connective tissue
disorders, such as Ehlers-Danlos syndrome.
 Theories regarding embryogenesis of Chiari II malformation must take into account its
invariable association with myelomeningocele. An attractive theory is the "CSF loss" theory.
It is hypothesized that escape of fluid through the open placode in myelomeningocele
results in an inadequate stimulus for mesenchymal condensation at the skull base. The
disordered and inadequate growth of the posterior fossa results in upward herniation of
vermis, downward herniation of brainstem, and distortion of tectum (tectal beaking).
Furthermore, collapse of the developing ventricular system because of fluid loss results in
associated abnormalities such as agenesis of corpus callosum and enlargement of massa
intermedia
Pathophysiology
 Symptoms of Chiari I develop as a result of 3 pathophysiological consequences of the
disordered anatomy: (1) compression of medulla and upper spinal cord, (2) compression
of cerebellum, and (3) disruption of CSF flow through foramen magnum. Compression of
cord and medulla may result in myelopathy and lower cranial nerve and nuclear
dysfunction. Compression of cerebellum may result in ataxia, dysmetria, nystagmus, and
dysequilibrium. Disruption of CSF flow through foramen magnum probably accounts for the
most common symptom, pain.
 Accordingly, headache and neck pain in Chiari I are often exacerbated by cough and
Valsalva maneuver. Hydrocephalus occurs less frequently. Furthermore, the disordered
flow of CSF through foramen magnum may result in formation of syringomyelia and central
cord symptoms such as hand weakness and dissociated sensory loss. These symptoms are
usually asymmetrical, as a syrinx has a tendency to develop in the side of the spinal cord
that is more significantly affected by tonsillar ectopia
Medical Therapy
 Patients with Chiari I malformations who have minimal or equivocal
symptoms without syringomyelia can be treated conservatively. Mild neck
pain and headaches can be treated with analgesics, muscle relaxants,
and occasional use of a soft collar. Frankly symptomatic patients should be
offered surgical treatment.
Surgical Therapy
 The goals of surgical treatment are decompression of cervicomedullary
junction and restoration of normal CSF flow in the region of foramen
magnum. Considerable controversy has existed throughout the years
about the surgical steps that are required to achieve these goals.
Characteristic
Chiari I
Chiari II
Usual age of diagnosis
Adults and older children
Infants and young children
Clinical findings
•Headache and neck pain (worsened by cough or
Valsalva maneuver)
•Myelopathy
•Cerebellar symptoms
•Lower brainstem symptoms (eg, dysarthria,
dysphagia, downbeat nystagmus)
•Central cord symptoms (eg, hand weakness,
dissociated sensory loss, cape anesthesia)
•In infants, signs of brainstem dysfunction
predominate: swallowing/feeding difficulties,
stridor, apnea, weak cry, nystagmus
•Weakness of extremities
Primary anatomical abnormalities
•Herniation of cerebellar tonsils through foramen
magnum, producing compression of
cervicomedullary junction
•Herniation of lower brainstem through foramen
magnum
•Cephalad course of cranial nerves
•Kinking of cervicomedullary junction
•"Beaking" of tectum
•Upward herniation of vermis through incisura
•Nearly vertical tentorium
Myelomeningocele
No
Always
Hydrocephalus
Less than 10% of cases
Very common
Syringomyelia
30-70%
Common
Associated abnormalities
•Craniocervical hypermobility syndromes
•Klippel-Feil anomaly
•Hereditary connective tissue disorders and
neurofibromatosis type II
•Callosum corpus pellucidum septum of agenesis
•Hypoplasia or
•Enlargement of massa intermedia
•Heterotopias and gyral abnormalities
Shared associated abnormalities
•Basilar invagination
•Occipitalization of atlas
•Bifida of C1 posterior arch
•Foramen magnum variant anatomy
•Basilar invagination
•Occipitalization of atlas
•Bifida of C1 posterior arch
•Foramen magnum variant anatomy
Sagittal and coronal MRI images of Chiari type I malformation. Note descent of cerebellar tonsils (T) below the level of
foramen magnum (white line) down to the level of C1 posterior arch (asterisk).
Axial MRI image at the level of foramen magnum in Chiari type I malformation. Note crowding of foramen magnum
by the ectopic cerebellar tonsils (T) and the medulla (M). Also note the absence of cerebrospinal fluid.
T2 hyperintense region on MRI (arrow) depicting edema in central cord region
of a patient with Chiari I malformation. Left untreated, this patient is likely to
develop cavitation of the edematous central cord, resulting in syringomyelia.
Intraoperative photograph of
Chiari type 1 malformation
showing descent of cerebellar
tonsils well below the level of
foramen magnum
Intraoperative photograph of
duraplasty with pericranial graft. The
duraplasty provides additional room
for cerebellar tonsils at the
craniocervical junction, while
achieving closure of dura and
prevention of cerebrospinal fluid leak.
Syrinx
Terminology
 The use of the term has grown out of the difficultly in distinguishing between
the two conditions using current imaging modalities. It may also be known
as hydrosyringomyelia or syringohydromyelia. Diagnosis is made by MRI
and electromyography.
 In hydromyelia, there is dilatation of the central canal of the spinal cord. In
syringomyelia and syringobulbia, there is dissection through the ependymal
lining of the central canal and a CSF collection within the cord itself.
 Clinically, there is no difference between the two and severity of symptoms
is related to the location and size of the syrinx.
Clinical presentation
 Symptoms, which may not occur immediately, include flaccid weakness of
the hands and arms as well as "cape-like" distribution of pain and
temperature sensory loss with preservation of position, vibration and touch
(dissociated sensory loss).
Pathology
 They may be congenital (90%) or acquired.
Congenital causes include:
 myelomeningocoele
 Chiari I malformation
 Chiari II malformation
 Dandy-Walker malformation
 Klippel-Feil syndrome
Acquired (secondary) causes include:
 post-traumatic: occurs in ~5% of patients with spinal cord injury usually from a whiplash
type injury; symptoms may start many months or years after injury
 cervical canal stenosis
 post-inflammatory
 secondary to a spinal cord tumour
 secondary to a haemorrhage
 due to vascular insufficiency
Chiari I malformation with syrinx
This is a sagittal T2-weighted MR image of the cervical
spine and shows abnormal position of the cerebellar
tonsils (yellow arrow) below the foramen magnum
(dashed line), indicating a Chiari I malformation. In this
case, the malformation is associated with a huge syrinx
(red arrows) that extends throughout the spinal cord. In
some cases of Chiari I malformation, the patient will be
asymptomatic however many cases are associated
with a syrinx and/or hydrocephalus and may therefore
present with symptoms such as upper or lower limb
weakness or headaches.
Syrinx. This fluid-filled cavity (arrows) in the
cervical spinal cord is a syrinx, which can be
caused by dilatation of the central canal
(hydromyelia) or a build-up of fluid within
the substance of the cord (syringomyelia).
Distinguishing between the two on MRI can
be very difficult, and doesn’t really matter
as their clinical behaviour is identical. These
may be congenital or acquired; acquired
causes include trauma and spinal cord
tumours.
References

Luijkx, T. (n.d.). Atlas (C1) | Radiology Reference Article. Retrieved March 30, 2017, from
https://radiopaedia.org/articles/atlas-c1

Neck - Atlas of Anatomy. (n.d.). Retrieved March 30, 2017, from
http://doctorlib.info/medical/anatomy/39.htm

Maingard, J. (n.d.). Axis (C2) | Radiology Reference Article. Retrieved March 30, 2017, from
https://radiopaedia.org/articles/axis-c2

Maingard, J. (n.d.). Foramen magnum | Radiology Reference Article. Retrieved March 30, 2017, from
https://radiopaedia.org/articles/foramen-magnum

Wong, A. (n.d.). Alar ligament | Radiology Reference Article. Retrieved March 30, 2017, from
https://radiopaedia.org/articles/alar-ligament

Tectorial membrane of atlanto-axial joint. (2017, March 28). Retrieved March 30, 2017, from
https://en.wikipedia.org/wiki/Tectorial_membrane_of_atlanto-axial_joint

Gaillard, F. (n.d.). Vertebral artery | Radiology Reference Article. Retrieved March 30, 2017, from
https://radiopaedia.org/articles/vertebral-artery

Chiari Malformation. (2017, January 06). Retrieved March 30, 2017, from
http://emedicine.medscape.com/article/1483583-overview

Jones, J. (n.d.). Syrinx | Radiology Reference Article. Retrieved March 30, 2017, from
https://radiopaedia.org/articles/syrinx-1

Chiari I malformation with syrinx. (n.d.). Retrieved March 30, 2017, from
http://www.svuhradiology.ie/case-study/chiari-i-malformation-with-syrinx/
TEŞEKKÜRLER
AYBERK ÖZKAVAKLI