I n t e g r a t i ve I m a g i n g • R ev i ew
Carr et al.
Pseudotrauma of the Spine
FOCUS ON:
Downloaded from www.ajronline.org by 94.97.41.105 on 01/07/19 from IP address 94.97.41.105. Copyright ARRS. For personal use only; all rights reserved
Integrative Imaging
Review
CME
SAM
Robert B. Carr 1,2
Kathleen R. Tozer Fink1
Joel A. Gross1
Carr RB, Tozer Fink KR, Gross JA
Imaging of Trauma
Imaging of Trauma: Part 1,
Pseudotrauma of the Spine—
Osseous Variants That May
Simulate Injury
OBJECTIVE. Anatomic variants and incomplete ossification and fusion of the developing spine may result in an erroneous diagnosis of injury or disease. This article reviews some
of the more common imaging findings that may present as pseudotrauma. Normal development of the spine is reviewed, including synchondroses and ossification centers. Imaging of
common variants is presented, with a focus on CT.
CONCLUSION. Recognition of the normal developing spine and variants can prevent
an incorrect diagnosis of injury and inappropriate treatment.
I
njuries to the spinal column are
common in patients who sustain
blunt trauma, and up to 15% of
such patients will have a fracture
of the thoracolumbar spine [1]. Radiography
and CT are the mainstays for the initial evaluation of these patients. Anatomic variations
are common, and many variants may be mistaken for acute spinal injury. Knowledge of
the normal ossification patterns of the spine
and the appearance of these variants will
help prevent an incorrect diagnosis.
Keywords: pseudotrauma, spine development, spine
variants
DOI:10.2214/AJR.12.9083
Received April 14, 2012; accepted after revision
June 13, 2012.
1
Department of Radiology, University of Washington,
Harborview Medical Center, Seattle, WA.
2
Present address: Department of Radiology, Massachusetts General Hospital, 55 Fruit St, GRB273A, Boston,
MA 02114. Address correspondence to R. B. Carr
(rcarr2@u.washington.edu).
CME/SAM
This article is available for CME/SAM credit.
AJR 2012; 199:1200–1206
0361–803X/12/1996–1200
© American Roentgen Ray Society
1200
Normal Development
The atlas (C1) and axis (C2) show unique
patterns of vertebral ossification, different
from the similar pattern of development of
the remaining cervical, thoracic, and lumbar
vertebrae. The atlas develops from three primary ossification centers: one anterior arch
and two neural arches (Fig. 1). The neural
arches are usually ossified at birth, but the
anterior arch may not ossify until the child is
1 year old. The ossification centers are separated by two anterior synchondroses and a
single posterior synchondrosis. The posterior
synchondrosis typically fuses between 3 and
5 years of age, and the anterior synchondroses fuse between 5 and 8 years of age.
The axis develops from five primary ossification centers: two vertically oriented odontoid
centers, two neural arches, and one centrum
(Fig. 2). The two odontoid centers usually fuse
before birth. The neural arches fuse posteriorly by 3 years old, and they fuse to the odontoid and centrum at between 3 and 6 years of
age. The centrum and odontoid centers fuse between 3 and 6 years of age across the subdental
synchondrosis. A secondary ossification center
known as the os terminale forms at the cranial
tip of the odontoid by 3 years old and fuses with
the odontoid by 12 years old.
The C3 through L5 vertebrae are similar in
their patterns of development. These vertebrae
each have three primary ossification centers:
one centrum and two neural arches (Fig. 3), but
the shapes of the ossification centers vary between the cervical, thoracic, and lumbar spine.
Fusion of the primary ossification centers is
usually complete by 6 years old. It is important
to note that the vertebral body is not analogous
to the centrum; the vertebral body is comprised
of the centrum as well as the ventromedial portions of both neural arches. Several secondary
centers of ossification develop around 16 years
old and fuse by 25 years old. Typically, there
are five secondary ossification centers, located
at the tip of the spinous process, the tips of the
transverse processes, and the upper and lower
margins of the vertebral body (ring apophyses).
Variants of the Atlas (C1)
There are several ossification and fusion
variants of the atlas. The anterior arch usually
develops from a single ossification center, but
uncommonly there may be up to four small
ossification centers that form the anterior arch
[2]. When multiple, these centers are usually
symmetric (Fig. 4). Nonfusion of the atlas ossification centers is a normal finding in young
children. However, in some cases fusion never occurs, resulting in a cleft that persists into
AJR:199, December 2012
Downloaded from www.ajronline.org by 94.97.41.105 on 01/07/19 from IP address 94.97.41.105. Copyright ARRS. For personal use only; all rights reserved
Pseudotrauma of the Spine
adulthood. A cleft shows smooth corticated
margins, which helps distinguish it from a
fracture. Atlantal clefts most commonly occur
at the posterior synchondrosis but may occur
anywhere within the C1 ring (Fig. 5).
In approximately 0.1% of the population,
the anterior ossification center fails to form.
This may result in overgrowth of the neural
arches as they attempt to fuse anteriorly, resulting in an anterior midline cleft [3]. There is
often associated hypertrophic change (Fig. 6).
Alternatively, an anterior midline cleft could
form from incomplete fusion of a bipartite or
multipartite anterior ossification center.
A normal groove is present along the posterolateral aspect of the atlas on each side,
which transmits the vertebral artery and suboccipital (C1) nerve. These structures are covered
by the posterior atlantooccipital membrane.
This membrane may become ossified, resulting
in formation of a ponticulus posticus, meaning
“little posterior bridge” in Latin. If ossification
results in a complete osseous ring surrounding
the vertebral artery, it forms the arcuate foramen (Fig. 7). This variant has been described
in association with neurologic symptoms, such
as headache and neck pain. It has also been described as a complicating feature in surgical
lateral mass fixation [4]. Occasionally, the atlantooccipital membrane may be partially ossified, resulting in an apparent bone fragment
posterior to the superior articular process. This
should not be confused with a fracture of the
atlas or occipital condyle (Fig. 8).
in the expected anatomic position posterior to
the anterior arch of C1. A dystopic os odontoideum is located anywhere else, often near the
foramen magnum and sometimes fused with
the basion [6, 7]. The cause of os odontoideum
has long been debated, with theories suggesting both congenital and acquired causes. Current evidence suggests that an os odontoideum
may result from trauma during childhood [6].
A feature that helps distinguish an os odontoideum from a type 2 odontoid fracture is the
distance between the intact odontoid process
and ossific fragment. A fracture will usually
have a narrow zone of separation between the
fracture fragments, and the overall size and
shape of the odontoid process will be maintained. An os odontoideum usually results in
a larger gap between the os and the odontoid
process, and it usually does not exhibit the expected contour of the upper odontoid process
[8]. Hypertrophy of the anterior arch of C1 is a
common associated finding (Fig. 11).
Anterior pseudosubluxation of C2 on C3 is
usually seen in children less than 8 years old.
It is caused by ligamentous laxity and a more
horizontal orientation of the facet joints in
children compared with adults. Displacement
is usually most pronounced on flexion radiographs, and it may resolve during extension.
A line may be drawn along the posterior cortical margin of the spinal canal at C1 and C3
(sometimes referred to as the “spinolaminar
line”). This line should pass within 2 mm of
the equivalent location at C2 (Fig. 12).
Variants of the Axis (C2)
The centrum and odontoid ossification
centers fuse across the subdental synchondrosis. A remnant of this synchondrosis often persists into adulthood. It appears as a
sclerotic line surrounded by lucency and
should not be mistaken for trauma (Fig. 9).
There are three entities that may result in an
ossific density adjacent to the cranial aspect of
the odontoid process: persistent os terminale,
os odontoideum, and odontoid fracture. The
os terminale is a normal secondary ossification center that usually fuses to the odontoid
process by 12 years old [5]. However, an unfused os terminale may persist into adulthood.
It presents as a well-corticated ossicle that
abuts the odontoid tip. It lies superior to the atlantodental articulation and transverse atlantal
ligament (Fig. 10).
An os odontoideum is larger than a persistent
os terminale. It is a smooth well-corticated ossicle located superior to a small odontoid process. An orthotopic os odontoideum is located
Variants of the C3 Through
L5 Vertebrae
Anterior wedging of the cervical vertebral
bodies is a normal finding in young children.
This is often most pronounced at the C3 level
(Fig. 12). There may be a difference in height of
up to 3 mm between the anterior and middle aspects of the vertebral bodies, which should not
be mistaken for a compression fracture [9]. This
wedging will resolve as the child matures.
Occasionally, there will be a single linear
osseous defect through the margins of a transverse foramen. This is not well described in
the literature but likely represents a small developmental cleft (Fig. 13). A ringlike structure, such as a transverse foramen, usually
fractures at two or more locations. Such fractures are often displaced. An isolated defect
within the bony wall of the transverse foramen is unlikely to represent a fracture.
Secondary ossification centers are a normal finding between the ages of 16 and 25
years. Occasionally, these centers may re-
AJR:199, December 2012
main unfused later into adulthood (Fig. 14).
The margins will always be smooth and corticated as opposed to acute fractures, which
are not corticated and often are irregular [10].
Herniation of disk material between the
ring apophysis and vertebral body may result
in a limbus vertebra. A small triangular bone
fragment with smooth corticated margins representing the ring apophysis will remain separated from the adjacent vertebral body. This
most commonly occurs in the lumbar spine
and most commonly affects the anterior-superior aspect of the vertebral body (Fig. 15).
A Schmorl node results from herniation of
disk material through the vertebral body endplate. This can occur anteriorly, posteriorly, or
centrally [11]. Occasionally, a Schmorl node
might be initially confused with an acute fracture, particularly if there is associated physiologic wedging of the vertebral body. The characteristic appearance of a Schmorl node as a
well-circumscribed rounded lucency in the
vertebral body with associated endplate defect
and a thin sclerotic rim should help differentiate the two entities.
Clefts may occur at several locations within the vertebrae (Fig. 16). The most common
location is a cleft through the spinous process (spina bifida occulta), resulting from
failed osseous fusion of the posterior synchondrosis. A cleft may also occur within the
pars interarticularis (spondylolysis), pedicle
(retrosomatic cleft), or lamina (retroisthmic
cleft). The most common of these is spondylolysis, which most commonly occurs at L5,
followed by L4, and less commonly at other levels. Spondylolysis is likely multifactorial in cause, due to repetitive stress in people
with a congenital predisposition [12].
Retrosomatic and retroisthmic clefts are
far less common than spondylolysis. The
cause of these clefts is unclear, but they are
likely associated with repetitive stress. These
clefts may result in symptoms of chronic instability but should be differentiated from
acute fractures. The characteristic location,
sclerotic margins, and associated degenerative changes are features that help differentiate them from acute fractures [13, 14].
Miscellaneous Conditions
Motion artifact may appear to represent an
acute injury, such as a fracture or facet subluxation, especially on reformatted images (Fig.
17). Abnormal displacement of structures,
such as tubes and soft tissues, may confirm
motion artifact, and multiplanar reformations
are often helpful in the evaluation.
1201
Carr et al.
Downloaded from www.ajronline.org by 94.97.41.105 on 01/07/19 from IP address 94.97.41.105. Copyright ARRS. For personal use only; all rights reserved
References
1. Berry GE, Adams S, Harris MB, et al. Are plain
radiographs of the spine necessary during evaluation after blunt trauma? Accuracy of screening
torso computed tomography in thoracic/lumbar
spine fracture diagnosis. J Trauma 2005;
59:1410–1413; discussion, 1413
2. Junewick JJ, Chin MS, Meesa IR, Ghori S, Boynton SJ, Luttenton CR. Ossification patterns of the
atlas vertebra. AJR 2011; 197:1229–1234
3. Choi JW, Jeong JH, Moon SM, Hwang HS. Congenital cleft of anterior arch and partial aplasia of
the posterior arch of the C1. J Korean Neurosurg
Soc 2011; 49:178–181
4. Huang MJ, Glaser JA. Complete arcuate foramen
precluding C1 lateral mass screw fixation in a patient with rheumatoid arthritis: case report. Iowa
Orthop J 2003; 23:96–99
5. Khanna G, El-Khoury GY. Imaging of cervical
spine injuries of childhood. Skeletal Radiol 2007;
36:477–494
6. Arvin B, Fournier-Gosselin MP, Fehlings MG. Os
odontoideum: etiology and surgical management.
Neurosurgery 2010; 66(3 suppl):22–31
7. Vargas TM, Rybicki FJ, Ledbetter SM, MacKenzie JD. Atlantoaxial instability associated with an
orthotopic os odontoideum: a multimodality imaging assessment. Emerg Radiol 2005; 11:223–225
8. Klimo P Jr, Coon V, Brockmeyer D. Incidental os
odontoideum: current management strategies.
Neurosurg Focus 2011; 31:E10
9. Lustrin ES, Karakas SP, Ortiz AO, et al. Pediatric
cervical spine: normal anatomy, variants, and
trauma. RadioGraphics 2003; 23:539–560
10. Mellado JM, Larrosa R, Martin J, Yanguas N, Solanas S, Cozcolluela MR. MDCT of variations
and anomalies of the neural arch and its processes. Part 1. Pedicles, pars interarticularis, laminae,
and spinous process. AJR 2011; 197:189; [web]
W104–W113
11. Swischuk LE, John SD, Allbery S. Disk degenerative disease in childhood: Scheuermann’s disease,
Schmorl’s nodes, and the limbus vertebra—MRI
findings in 12 patients. Pediatr Radiol 1998;
28:334–338
12. Leone A, Cianfoni A, Cerase A, Magarelli N,
Bonomo L. Lumbar spondylolysis: a review. Skeletal Radiol 2011; 40:683–700
13. Wick LF, Kaim A, Bongartz G. Retroisthmic
cleft: a stress fracture of the lamina. Skeletal Radiol 2000; 29:162–164
14. Sakai T, Sairyo K, Takao S, Kosaka H, Yasui N.
Adolescents with symptomatic laminolysis: report of
two cases. J Orthop Traumatol 2010; 11:189–193
Fig. 1—Normal ossification of atlas.
A, 12-month-old girl with normal ossification
pattern. Axial CT image shows single anterior arch
(arrowhead) and paired neural arches (arrows).
B, Axial CT image in 14-year-old girl shows expected
appearance of atlas.
A
B
A
B
Fig. 2—Normal ossification of axis.
A, 6-month-old girl with normal ossification pattern. Coronal CT image shows odontoid (arrowhead), paired
neural arches (arrows), and centrum (asterisk).
B, Coronal CT image in 21-year-old woman shows expected appearance of axis.
1202
Fig. 3—5-month-old boy with normal ossification
pattern of C3 vertebra. Axial CT image shows
centrum (asterisk) and paired neurocentral
synchondroses (arrows).
AJR:199, December 2012
Downloaded from www.ajronline.org by 94.97.41.105 on 01/07/19 from IP address 94.97.41.105. Copyright ARRS. For personal use only; all rights reserved
Pseudotrauma of the Spine
Fig. 4—5-month-old boy with bipartite anterior arch.
Axial CT image shows anterior midline synchondrosis
(white arrow) separating two components of anterior
arch. Right anterior synchondrosis (arrowhead)
and posterior synchondrosis (black arrow) are
incompletely fused. Left anterior synchondrosis has
fused.
A
B
Fig. 5—Comparison of clefts and fractures.
A, 24-year-old woman with neck trauma. Axial CT image shows nonfusion of right neurocentral synchondrosis
(arrow) and posterior synchondrosis (arrowhead).
B, 10-year-old boy with acute fractures of atlas. Axial CT image shows irregular margins and displacement of
fracture near site of neurocentral synchondrosis (arrow) and second fracture more posteriorly (arrowhead).
Fig. 6—33-year-old man with congenital
nondevelopment of anterior arch. Axial CT image
shows focal hypertrophy and attempted anterior
fusion of neural arches (black arrow). There is
nonfusion posteriorly (white arrow).

Fig. 7—39-year-old woman with arcuate foramen.
Sagittal CT image shows typical appearance of
foramen (arrow), which transmits vertebral artery
and suboccipital nerve.

A
B
Fig. 8—58-year-old man with cervical trauma.
A and B, Axial (A) and sagittal (B) CT images show partial ossification of posterior atlantooccipital membrane
(arrow), which may simulate small fracture fragment.
AJR:199, December 2012
1203
Downloaded from www.ajronline.org by 94.97.41.105 on 01/07/19 from IP address 94.97.41.105. Copyright ARRS. For personal use only; all rights reserved
Carr et al.
Fig. 9—25-year-old woman with normal appearance
of subdental synchondrosis scar. Sagittal CT image
shows linear density (white arrow) surrounded by
lucency (black arrows).
A
B
Fig. 10—Appearances of os terminale.
A, 5-year-old girl with normal os terminale. Coronal CT image shows normal location of this secondary
ossification center superior to odontoid (arrow).
B, 38-year-old woman with nonfusion of os terminale. Sagittal CT image shows persistent os terminale that
never fused to odontoid (arrow).
Fig. 11—Comparison of os odontoideum and chronic
type 2 odontoid fracture.
A, 26-year-old woman with os odontoideum.
Sagittal CT image shows os odontoideum (arrow),
hyperplastic anterior arch of C1 (arrowhead), and
small odontoid (asterisk). Notice gap between
odontoid and os odontoideum.
B, 86-year-old man with chronic type 2 odontoid
fracture. Sagittal CT image shows that fracture
fragment retains expected shape of odontoid
(asterisk) and there is small gap (arrow) separating
fragment from normal-appearing odontoid base.
A
B
A
B
C
Fig. 12—Pseudosubluxation of C2 on C3.
A, 12-month-old boy with acute trauma. Lateral radiograph shows anterior location of C2 relative to C3 but normal posterior spinolaminar line (black line), which helps
confirm that this is normal finding. Note normal anterior wedging of C3 vertebral body (arrow).
B and C, 7-year-old boy involved in motor-vehicle collision. Sagittal CT image (B) shows pseudosubluxation of C2 on C3 (arrow). Sagittal MR image (C) shows no evidence
of ligamentous injury (arrow).
1204
AJR:199, December 2012
Pseudotrauma of the Spine
Downloaded from www.ajronline.org by 94.97.41.105 on 01/07/19 from IP address 94.97.41.105. Copyright ARRS. For personal use only; all rights reserved
Fig. 13—68-year-old man with acute trauma. Axial
CT image shows small cleft in anterior aspect of right
transverse foramen of C5 (arrow). No other areas
of lucency were identified to suggest presence of
fracture.
A
B
C
Fig. 14—Comparison of fractures and secondary ossification centers.
A, 22-year-old woman involved in motor-vehicle collision. Sagittal CT image shows acute fracture through L4 spinous process (black arrow). Note irregular nonsclerotic
margins. Secondary ossification center is present at tip of L3 spinous process (white arrow). Note smooth sclerotic margins.
B, 19-year-old woman involved in motor-vehicle collision. Axial CT image shows acute fracture of right transverse process of C7 (arrow).
C, 17-year-old man involved in motor-vehicle collision. Axial CT image shows secondary ossification center at tip of right transverse process of T7 (arrow). Note smooth
corticated margins and compare with B.
Fig. 15—21-year-old man involved in fall. Sagittal CT
image shows limbus vertebra at anterior-superior
aspect of L3 vertebral body (arrow). Note sclerotic
margins and that triangular fragment does not match
with adjacent vertebral body, distinguishing this from
acute fracture.
AJR:199, December 2012
1205
Fig. 16—Locations and appearances of clefts. Note
irregular sclerotic margins of clefts in B, C, and D.
A, 42-year-old man with normal anatomy. Axial
CT image shows location of retrosomatic cleft (1),
spondylolysis (2), retroisthmic cleft (3), and spina
bifida occulta (4).
B, 33-year-old man with lumbar pain. Axial CT image
shows retrosomatic cleft involving pedicle (arrow).
C, 29-year-old man with lumbar pain. Axial CT shows
spondylolysis bilaterally (arrows).
D, 38-year-old woman with lumbar pain. Axial CT
shows left-sided retroisthmic cleft (arrow).
Downloaded from www.ajronline.org by 94.97.41.105 on 01/07/19 from IP address 94.97.41.105. Copyright ARRS. For personal use only; all rights reserved
Carr et al.
A
B
C
D
A
B
Fig. 17—52-year-old man involved in motor-vehicle
collision.
A and B, Sagittal CT images show apparent fracture
through inferior facet of C5 and anterior subluxation
of C5 on C6 (arrow). However, note similar offset
involving anterior soft tissues and endotracheal
tube (arrowhead, B). These findings were caused by
motion artifact.
F O R YO U R I N F O R M AT I O N
This article is available for CME/SAM credit. Log onto www.arrs.org, click on AJR (in the blue Publications box), click on
the article name, add the article to the cart, and proceed through the checkout process.
The reader’s attention is directed to part 2 accompanying this article, titled “Imaging of Trauma: Part 2, Abdominal Trauma
and Pregnancy—A Radiologist’s Guide to Doing What Is Best for the Mother and Baby,” which begins on page 1207.
1206
AJR:199, December 2012