Involuntary motion coordinated with voluntary movment
Congenital anomalies and Normal skeletal variants- Cervical spine
Congenital anomalies and
Normal skeletal variants-
Dr . M Sanal kumar
(Flat skull base, Martin’s anomaly)
•Flattening of the angle between the clivus and body of
•Platybasia may occur as an isolated congenital
• In conjunction with skeletal dysplasia -
achondroplasia, osteogenesis imperfecta..
•Majority are asymptomatic.
•Rarely, upward displacement secondary to
degenerative changes of the upper cervical joints
and ligaments may precipitate symptoms.
• Neurological complications of the brainstem-
infarction and syrinx formation;
•Cerebellar dysfunction from infarction and gliosis;
•The skull base angle (Martin’s basilar angle) can
be determined by measuring the angle subtended
between lines from the nasion to sella turcica to
the anterior foramen magnum.
•The normal range is 123–152°.
•Platybasia is designated when the angle is >
Martin’s basilar angle
The three points are the nasion (frontal–nasal
the center of the sella turcica (mid-point between
the clinoid processes),
and the basion (anterior margin of the foramen
Basilar Invagination/ Basilar Impressio
Basilar impression describes the condition of a relative
cephalad position of the upper cervical vertebra to the
base of the skull.
No gender predilection. Majority are asymptomatic .
Two types of basilar impression are described: primary
Primary Basilar Impression- congenital ,often
Secondary Basilar Impression- acquired condition
, resulting from disease softening of the occipital
bone in which the weight of the cranium deforms the
base.(Paget’s disease, osteomalacia, fibrous
and osteogenesis imperfecta.)
Rheumatoid arthritis - most common of the arthritides
to cause secondary basilar impression-bone and
transverse ligament destruction.
The onset of symptoms typically begins in the 3rd–
Chamberlain's line is a line drawn on lateral skull
radiograph between posterior end of hard palate to
the posterior lip of the foramen magnum.
If the tip of the dens is greater than 3mm above
Chamberlain's line then basilar invagination is
McGregor's line extends from the upper surface of
the posterior edge of the hard palate to the most
caudal point of the occipital curve.
If the tip of the odontoid process is more than 4.5mm
above McGregor's line then basilar invagination is
McRae's line is defined by the opening of the
If the tip of the dens migrates above this line then
impaction is present.
Boogard’s Line and Angle
Boogard’s line -A line is drawn connecting the
nasion to the opisthion.
Boogard’s angle -(a) A line is drawn between the
basion and opisthion (Macrae’s line) (b) A second line
is drawn from the dorsum sellae to basion along the
plane of clivus. (c) The angle between these two lines
In basilar impression—the basion will be above
Boogard’s line, and the angle will be > 135°.
Occipitalization of the Atlas
(Atlas assimilation, atlanto-occipital fusion, block atlas)
•Failure of segmentation and separation of the most
caudal occipital sclerotome during the first few weeks
of fetal life.
• It is the most cephalic block vertebra of the spine and
the most common anomaly of the craniovertebral
•M: F- 5:1 ; Population incidence - 0.75–3%.
•A short neck, low hair line, and restricted neck
motion is found in more than two thirds of cases.
•Nuchal and facet joint pain.
•Premature and severe degenerative joint disease
at C1–C2 and C2–C3 are common.
•Risk for significant neurological dysfunction
increases with age, usually beginning in the 3rd–
•A spectrum of non-segmentation ranging from
complete to incomplete forms.
•Complete fusion -fusion of the anterior and posterior
arches and bilateral atlanto-occipital joint fusion.
•In virtually all cases the anterior arch will be fused
to the anterior margin (basion) of the foramen
magnum, and the transverse process of the atlas will
be either absent or fused to the occiput.
•In 90% of cases, details of the fused atlas posterior
arch can be discerned at the occiput on a plain film.
•Up to 70% of occipitalizations will have an
accompanying block vertebra of C2–C3.
• Anomalies of the dens like agenesis, hypoplasia, os
odontoideum, ossiculum terminale, and abnormal tilt
are common- predispose the patient to instability.
•Basilar impression is a common tandem finding and
should be considered in the assessment
The occipital bone is formed from the union of four
to five somites, which normally fuse together to
encircle the foramen magnum.
The last occipital somite, or pro- atlas somite, may
fail to fully incorporate into the occiput, resulting in
occipital or pro-atlas vertebrae.
Manifestations of occipital vertebrae include the
third condyle, paramastoid process, epitransverse
process, and various occipital ossicles.
•Third condyle is the most common form of an occipital
• An anterior midline bony process located between the
two occipital condyles and continuous with the anterior
foramen magnum extends a variable distance caudally.
•It occasionally forms an articulation with the apex of the
odontoid process or anterior arch of the atlas.
Large third condyles may be seen on true lateral
radiographs as oval or round bone densities equal in
size or smaller than the anterior arch of the atlas.
Paracondylar, Paramastoid and
•These are variations of congenital bone bars
that extend between the occiput and transverse
processes of the atlas.
• They may be unilateral or bilateral
•The paramastoid process is a bony
protuberance that originates from the jugular
process of the occiput and projects inferiorly
toward the atlas transverse process.
•A paracondylar process arises slightly more
•An epitransverse process is attached to the atlas
transverse process and directed superiorly toward the
•Symptoms due to the paracondylar process are
unusual but may be found in conjunction with muscle
contracture and pain.
•A paramastoid process occurs in at least 20% of
occipitalizations. Large processes may be palpable in
asthenic individuals and may inhibit atlanto-occipital
•Frequently overlooked on both AP and lateral
radiographs because of the superimposed
•A slightly rotated open-mouth view will shift the
molars on the side opposite the direction of head
rotation away from the area of interest.
•The process is typically cone-shaped, broader at
its occipital base, and narrower distally; it often
•An accessory joint may be present between the
Vertebralization of the Atlas
(Regressive occipital vertebra, double atlas)
•Vertebralization is an embryologic tendency for a
part of the pro-atlas to not incorporate into the
occiput; it is rare.
• This results in duplication of all or part of the atlas
vertebra at the C0–C1 interspace.
•A complete double atlas is very rare . There may
be an extra posterior arch, anterior arch,
transverse processes, or lateral masses.
•Combined fusion of the anterior atlas arch with the
basion (occipitalization) and the posterior arch with the
axis (vertebralization) has been recorded.
• The condition may precipitate atlantoaxial instability
with insufficiency of the transverse ligament.
•The odontoid process is often elongated and may be
malformed. Various degrees of bony fusion of the
upper joint surfaces with the occiput is seen.
Agenesis of the Atlas Posterior
Arch•Lack of ossification of the posterior arch of the
atlas may be complete and bilateral, may be purely
unilateral, or may manifest as small clefts (i.e.,
• Dense fibrous connective tissue remains at the
site devoid of ossification.
•Pain or neurological complications are rare.
•Atlantoaxial instability has been described.
• There is occasional association with C2–C4 block
vertebrae and Klippel-Feil syndrome.
• It needs to be differentiated from occipitalization,
osteolytic metastases, aneurysmal bone cyst, and
•The lateral view is the best projection for
identifying the various forms of aplasia.
Bilateral Posterior Arch Agenesis-The
characteristic triad of
findings is absence of the atlas posterior arch,
union of the posterior tubercle to the axis spinous
process (axis megaspinous sign), and
compensatory enlargement and sclerosis of the
•Unilateral Posterior Arch Agenesis (Hemi-Atlas)
-Uncommon. The condition is best determined on
the AP open mouth view and CT.
•Isolated Clefts of the Posterior Arch-Isolated
clefts of the posterior arch are most common in the
midline posteriorly, accounting for 97% of arch
clefts. These clefts range from 1 to 5 mm and are
best seen on oblique and slightly off-lateral
•Thin posterior arch- The width of the posterior
arch is thin and attenuated maximally at the
vertebral artery sulcus. An association with Turner’s
syndrome and gonadal dysgenesis has been
• Short posterior arch- The atlas posterior arch is
thick and bulky, and the diameter of the spinal canal
is diminished. A described tandem finding is a thick,
bulky dens that may contribute to symptomatic
•Hypoplasia of the Posterior Arch- Two forms of
hypoplasia of the posterior arch are described: thin
Accessory Atlantoaxial Joint
(Cervical Baastrup’s Disease)
•Enlargement of the posterior arch occasionally forms
an accessory joint space with the adjacent axis
•The radiologic hallmarks are enlargement of the
posterior tubercle, flat corticated opposing surfaces,
and a smooth joint space.
•Occasionally, signs of degeneration—including
osteophytes, sclerosis, and a narrowed joint space—
Posterior Spina Bifida Occulta of
the Atlas•Spina bifida occulta (SBO) is an embryologic failure
in midline ossification of the vertebral neural arch.
The gap is filled with fibrous tissue.
•Seen in 1–5% of the population, and this site is the
second most common region to be affected, after the
•Can occur simultaneously with occipitalization and
anterior arch spina bifida (bipartite atlas).
•Axial compression trauma may result in fracture
through the site of non-union.
Myelomeningoceles of the craniocervical junction
have an associated atlas SBO in 70% of cases.
•On the lateral view there is absence of the
spinolaminar junction line and the posterior arch is
thin and attenuated, with club-shaped, tapered, or
•Differentiation from fracture is based on location and
the clubbed smoothly corticated opposing ends.
•The anterior tubercle is often sclerotic and enlarged
and is a useful sign for a congenital absence of
Ponticles of the Atlas
•Calcification or ossification along the margins of
normally occurring foramina in the atlanto-occipital
ligament is referred to as ponticles.
•There are two types of atlas ponticles: posterior
•A posterior ponticle of the atlas is ossification or
calcification of the oblique portion of the atlanto-
occipital membrane that bridges the posterior lateral
mass and the posterior arch.
•It forms the peripheral border of the arcuate foramen,
which transmits the vertebral artery and veins, the first
cervical nerve, and the perivascular sympathetic
•It is usually bilateral and asymmetrical and exhibits no
Three clinical associations have been made:
vertebrobasilar insufficiency, Barre-Lieou syndrome,
and chronic upper cervical syndrome.
•Vertebrobasilar Insufficiency- the adventitia of the
vertebral artery is contiguous with the periosteum of
the ponticle, and atlantoaxial movements may create
traction or compression of the artery.
Barre-Lieou Syndrome. Headaches; retrorbital pain;
facial vasomotor disturbance; and visual, phonation,
and swallowing difficulties.
Chronic Upper Cervical Syndrome- The symptom
A posterior ponticle is best seen on a lateral
radiograph of the cervical spine; it forms a partial or
complete foramen at the ventral and superior aspect
of the vertebral arch.
(Ponticulus lateralis, pons lateralis)
•A lateral ponticle is ossification in the oblique occipital
membrane as it passes laterally from the superolateral
aspect of the atlas lateral mass to the transverse
•The anomaly appears to have no clinical relevance
and is incidentally seen in 3% of cervical radiographs.
Radiologic Features-The lateral ponticle is seen only
on open mouth view and is manifest as a curvilinear
ossification between the transverse process and the
lateral mass of the atlas, often forming a distinct
Agenesis of the Atlas Anterior Arch
•Isolated congenital absence of the anterior arch of
the atlas is rare.
•Acquired destruction of the anterior arch may
occur secondary to inflammatory arthropathy,
especially rheumatoid arthritis, tumor, and infection.
•Lateral radiographs demonstrate absence of the D-
shaped, corticated anterior arch of the first cervical
Non-Union of the Atlas Anterior Arc
•Non-union of the atlas anterior arch may occur as an
isolated anomaly or in tandem with a cleft of the
posterior arch (bipartite atlas).
•The cleft through the anterior arch is vertically
orientated and usually in the midline. On AP open
mouth views the defect may be visible superimposed
over the dens and may resemble a bipartite dens
•The most common congenital anomalies of the axis
vertebra involve the odontoid process.
•Generally discovered when radiographs are taken of
the cervical spine for other clinical reasons, most
•The most common anomalies of C2 are ossiculum
terminale, os odontoideum, agenesis, and
•Other anomalies of the axis include block vertebra
Ossiculum terminale persistens (Of
Terminal ossicle, ununited summit epiphysis,Bergmann
ossicle.•The secondary apical ossification center at the tip of
the dens (summit epiphysis) normally appears at 2
years of age and unites to the dens by age 12–13
•Failure of union to the dens produces an isolated
ossicle at the tip.
•Rarely, it has been associated with brainstem
symptoms when the transverse ligament dislocates
into the cleft to allow atlantoaxial instability.
•There is an increased incidence of a terminal ossicle
in Down’s syndrome, which may also be a factor in
•On conventional radiographs the ossicle appears as a
3- to 5-mm, discrete, ovoid, or diamond-shaped ossicle
visible at the most cephalic portion (odontoid summit) of
•The tapered inferior margin may be mildly invaginated
into a V-shaped cleft in the subadjacent dens.
•This is a normal finding of the odontoid seen in 25% of
patients < 12 yrs of age; but it is usually not seen
afterthis age, at which time it constitutes non-union
•Os odontoideum is defined as non-union of the
dens with the axis body.
• A transverse, radiolucent cleft separates an
ossicle of variable size from the axis body.
• The transverse ligament is usually intact.
•Normal development of the dens includes a
synchondrosis separating the base of the dens
from the C2 vertebral body.
•It normally ossifies to connect the odontoid to the
•The majority of patients are asymptomatic.
•Postural changes of the cervical spine may be
•Palpable anterior gliding of the atlas may be detected
during cervical flexion.
•Compression syndromes of the upper cervical cord
and brainstem are encountered.
•Os odontoideum is better tolerated than other causes
of atlantoaxial instability because mobility of the dens
prevents cord compression between the dens and the
atlas posterior arch (guillotine mechanism).
•The ossicle is readily overlooked or obscured unless
carefully looked for.
•The open mouth view is particularly important for
depicting the upper cervical Complex.
•On this view the ossicle is round to oval in shape and
is usually about one half the size of the normal
• There is typically a distinct circumferential cortex.
• The separating cleft lies above the level of the
superior articular facets of the axis, and a residual
•The ossicle may be aligned with the stump
(orthoptic) or subluxed laterally (dystopic).
•On the lateral film - altered appearance of the
anterior arch of the atlas may be the only marker
which includes enlargement, sclerosis, and an
angular posterior surface where it invaginates into
•Hypertrophy of the atlas anterior arch is often
present as an indication of chronic biomechanical
stress and is useful in ruling out an acute dens
•The transverse ligament is usually intact, and the
Hypoplastic and agenetic Odontoid
process•A failure of the dens to form and ossify is an
•Total absence of the dens is referred to as agenesis,
whereas partial formation is hypoplasia.
•Hypoplasia of the dens is present when it measures
< 12 mm in vertical height.
•The majority of cases are discovered incidentally on
•Torticollis, suboccipital pain, and neuralgia; upper
cervical crepitus; and vertebrobasilar symptoms may
• Occasionally with atlantoaxial instability,
neurological symptoms from dysfunction of the
cerebellum, brainstem, and cervical cord may occur.
•With absence of the odontoid, atlantoaxial instability
of up to 10 mm may remain asymptomatic because
the cord is not readily compressed.
•In true agenesis there is no evidence of a dens on
•On the lateral film no dens will be visible and there
are no dental landmarks to assess the atlantodental
• The anterior arch of the atlas may take a number of
altered forms, including enlargement, sclerosis, and a
rounded posterior surface.
•The posterior arch of the atlas may be hypoplastic, is
occasionally sclerotic, and may exhibit a claw-like
spur from the posterior tubercle curving superiorly.
(Congenital synostosis, blocked vertebrae,
congenital vertebral fusion, failure of vertebral
segmentation, intercorporeal fusion)
•Embryological failure of normal spinal segmentation
resulting in fusion of one or more contiguous
vertebral segments is described as congenital block
•This most likely is the result of locally decreased
blood supply during the 3rd– 8th week of fetal
development.• Incidence range from 0.4% to 0.7% , with no sex
•The cervical spine is most commonly involved,
followed by the lumbar and thoracic areas.
•The most common individual motion segments
involved are reported as C5–C6, C2–C3, T12–L1,
•Most vertebral fusions are rarely symptomatic and
are usually found incidentally on radiographs.
•Physical examination is typically unremarkable.
Head tilt, neck deformity, or loss of intersegmental
mobility may be identified, particularly when multiple
motion segments are involved.
•Neurological changes may be identified from nerve
•Radiographs in the frontal, lateral, and oblique
planes should be supplemented with flexion–
•The lateral view shows the characteristic triad of
vertebral body hypoplasia, small disc, and variable
posterior arch fusion.
•The involved vertebral bodies are maximally
hypoplastic in their sagittal dimension near the
intervening vestigial disc space, such that the
•The overall vertical dimension of a congenital block
vertebra is roughly equal to the height of two normal
vertebrae plus an intervertebral disc (law of blocks).
•The involved disc space is thin and variably ossified.
The nucleus pulposus is often visible as a dense
•There is variable fusion of the posterior arches in up
to 50% of cases at the level of body union, reflected
as a single large spinous, laminae, or articular pillar.
•Immediately adjacent to the fusion site the first
mobile vertebral body is often flattened and widened.
Immediately adjoining intervertebral disc spaces may
develop premature degenerative joint disease as
early as the 2nd or 3rd decade of life.
Klippel-Feil syndrome (KFS) is currently a loosely
applied eponym used to describe congenital
segmentation defects of the cervical spine.
The term Klippel-Feil syndrome should be reserved
for congenital fusions involving more than one
motion segment (i.e., more than two cervical
Klippel and Feil’s original classification
KFS I- extensive cervical segmental fusion
•The classic Klippel-Feil triad of short webbed neck,
low posterior hairline, and reduced cervical motion is
present in approximately 50% percent of cases.
•There may be the illusion of no neck, with the head
seeming to be continuous with the shoulders.
• The most consistent finding is limitation of neck
•The inability of the infant to rotate the head without
•Multiple block vertebrae produce vertebrae that are
hypoplastic with anterior concavity (wasp-waist
•The intervertebral disc spaces are small and may
have calcification of the nucleus pulposus.
Hemivertebrae may be visible on the frontal study.
•Careful attention must be given to assessing the
integrity of the dens and stability of the upper
•Flexion– extension studies should be obtained to
•KFS patients at highest risk for neurological
complications are those with atlantoaxial anomalies,
more than one block vertebra, and degenerative
changes at the adjacent mobile levels.
•The vertebral artery is prone to anomalous
development, and vertebrobasilar ischemia and
infarction have been recorded.
•Identification of spinal cord, nerve, and vertebral
artery abnormalities may require MRI and MRA
•At the 3rd fetal week the scapula develops in
the neck, at the C4–C5 level.
• Under ordinary conditions the scapula
migrates to its normal position by the 15th
day of gestation.
•Failure of migration results in sprengel’s
Sprengel’s deformity shows elevation of the scapula
and limited humeral abduction.
Torticollis, with or without muscle spasm, may be
•The scapula is hypoplastic, shortened vertically
•Scapula is rotated so that the glenoid process is
•The inferior angle rests above the normal T7 level.
Omovertebral Bone- Present in 30–40% of
Sprengel’s deformity cases. It is not always bone; it
may also be composed of cartilage or fibrous
The Rigault’s radiographic classification
Grade I - superomedial angle lower than T2 but
above T4 transverse process.
Grade II - superomedial angle located between
C5 and T2 transverse process.
Grade III - superomedial angle above C5
• Two thirds of patients presenting with sprengel’s
shoulder demonstrate associated scoliosis,
hemivertebrae, block vertebrae, spina bifida occulta,
or cervical ribs.
• It also occurs in 20–25% of Klippel-Feil syndrome
Cervical rib(Dorsalization of the cervical spine)
•A costal bony process that originates from
the cervical vertebra and forms true
articulations with the transverse process and
vertebral body constitutes a cervical rib.
•At least 95% of cervical ribs occur at C7,
but they have been recorded as high as C4.
•They vary greatly in size, shape, and
anatomic course and exhibit variation in their
•M: F- 2:1; Incidence- 0.5% of population, 66% are
•Most cervical ribs are asymptomatic and are
•Symptoms, when present are commonly related to
compression of neural or vascular structures in the
thoracic outlet (thoracic outlet syndrome).
•An osseous rib-like structure closely adjoining but not
fused to the distal end of the C7 transverse process is
typically seen projecting anteriorly and inferiorly over a
course of variable distance.
•Articulation with the C7 vertebral body is seen in the
• To avoid mistaking a cervical rib for an atypical
first thoracic rib- remember that C7 transverse
•Cervical ribs are one of many causes for
neurovascular compression syndromes of the
upper limb. The incidence of symptomatic cervical
ribs is probably < 5%.
•If these ribs cause symptoms, it is usually after
middle age, when the shoulders begin to droop.
The dominant arm is involved more commonly.
•The brachial plexus may be divided by a cervical
•Pathologic abnormalities associated with cervical
ribs include poststenotic subclavian artery aneurysm
and kinking or thrombosis of subclavian artery or
•Swelling of the upper limb may indicate obstruction
of the subclavian vein, either from mechanical
deformity or venous thrombosis.
•Arterial compression may result in a Raynaud-like
Elongation of the C7 Transverse
( False cervical rib, droopy transverse process
syndrome, apophysomegaly,and mega-apophysis.
•Elongation of the C7 transverse process is a
• The transverse processes curve and taper
distally, lack costotransverse and costovertebral
joints and are usually < 2 cm, and do not fuse with
the first rib.
Elongation of the C5 and C6 Transverse P
•Anterior tubercle of the transverse process is the
costal element homologue.
•It may be elongated, especially at C5 and C6, and is
occasionally encountered on cervical spine
•Rarely associated with brachial plexus pain
•Hypoplasia of the involved vertebral segments and
intervening intervertebral disc (IVD) space may also
•Complete or incomplete bony union may occur.
• Flexion– extension radiographs show reduced
mobility at C5–C6 and increased mobility at C4–C5.
•Mimics of the condition include osteophytes,
fracture, and expansile neoplasm.
Droopy Shoulder Syndrome
•Women are more commonly affected
• Radiographically, the thoracic spine may be
visualized down to the T2 vertebra on a routine
lateral cervical projection
•A long gracile neck with low-set shoulders may
be associated with thoracic outlet syndrome and
fatigue syndromes of the shoulder girdle.
• Exacerbation of the symptoms may occur if
loads are carried on the shoulders.