Volume 5, Case 2
Tai-Chuen Lin, Medical Student
Loren G. Yamamoto, MD, MPH
Kapiolani Medical Center For Women And Children
University of Hawaiʻi John A. Burns School of Medicine
Introductory Notes
Most spinal cord injuries are attributed to trauma. Absence of radiographic findings does not exclude a spinal cord injury. A substantial portion of spinal cord injuries in children (25% to 50%) have no radiographic abnormalities--SCIWORA (spinal cord injury without radiographic abnormalities). Some patients with cervical spine injury may also have thoracolumbar lesions. In the younger child, injuries to the cervical spine often involve the upper three vertebrae.
Pediatric Considerations
Pediatric anatomy differs from the adult in several important ways, particularly in the ossification pattern of the cervicocranium (occiput-atlas-axis) and the normal laxity of the developing soft tissue structures of the cervicocranium. These differences can lead to false positive interpretation as fractures, subluxations, and/or tumors etc. (Refer to Case 5 of Volume 1, Cervical Spine Malalignment - True or Pseudo Subluxation?, and Case 1 of Volume 5, Fever With Neck Stiffness . . . Rule Out Meningitis).
Clinical Aspects
The assessment of cervical spine injuries must first be a clinical evaluation. Clinical and radiographic data should be interpreted together to yield the most accurate assessment.
Diagnostic strategies depend on whether the patient is conscious and can freely move his or her neck. Unconscious or poorly conscious patients should be examined radiographically while maintaining cervical spine immobilization since history and examination will be unreliable.
A conscious patient with a significant cervical spine injury will complain of pain. A significant cervical spine injury is not likely to be present in a patient without neck pain who is alert, not intoxicated, and lacks other painful injuries (that may distract neck pain). Normal cervical range of motion is consistent with the absence of a cervical spine injury and such patients generally do not need any radiographs.
Anatomy
In order to properly evaluate the radiographic images of the cervical spine, an understanding of the cervical spine anatomy is necessary to appreciate the structural organization that lends to spinal stability. The vertebrae are bony building blocks connected by ligamentous and muscular structures. This resulting stable skeleton provides the scaffold for the soft tissue structures that communicate between the head and the thorax, the spinal cord being one of the most delicate and important.
The cervical spine is made up of seven sequentially numbered cervical vertebrae, C1 through C7. Superiorly, C1 is connected to the occiput of the cranium. Inferiorly, C7 is connected to the first thoracic vertebrae, T1. The upper portion of the cervical spine, C1 and C2, together with the occiput is also referred to as the cervicocranium. All vertebrae share many common features. These will be reviewed along with features unique to the cervical vertebrae. C1 and C2 are atypical cervical vertebrae and will be treated separately.
Vertebral Body
The anterior and most easily identifiable structure of a vertebra is the vertebral body, also known as the centrum. The body is the largest and appropriately the main weight-bearing structure of a vertebra. The back of the body also forms the anterior border of the spinal canal.
View C4.
The three line diagrams on the left from top to bottom include an axial view, viewed from the top (Top), an anterior view (AP), and a lateral view (Lat). The three photographs of C4 on the right from top to bottom include a view from the top (Top), a view from the bottom (Bottom), and an oblique view from the bottom (Bottom oblique).
Identify the following structures on these diagrams and photos:
SP - spinous process
L - lamina (forms roof of the neural arch)
P - pedicle (forms supports of the neural arch)
SC - spinal canal
VB - vertebral body
SAF - superior articular facet
IAF - inferior articular facet
TF - transverse foramen
Gr - groove for spinal nerve (transverse process)
U - uncinate process
The neural arch is formed by the laminae, the base of the spinous process and the pedicles. The pedicles are very short in the cervical spine. The facet joints are formed by the inferior and superior facets such that the C4-C5 facet joint is formed by the inferior articular facet of C4 and the superior articular facet of C5.
On a lateral film, the body is a rhomboid with the posterior portion slightly taller than the anterior portion.
View lateral C-spine view.
The lateral view of a very young child is shown on the left compared to the lateral view of a teenager on the right. Alignment is assessed by the integrity of lines drawn along: 1) the anterior borders of the vertebral bodies, 2) the posterior borders of the vertebral bodies and 3) the anterior borders of the vertebral arch's apex (spinolaminal line). The facet joints should be clearly visible.
View identifying landmarks.
The contour lines of alignment are shown. Identify the following areas on the radiographs:
F - facet joint
SP - spinous process
L - lamina
Od - odontoid
On an AP view, the lateral superior edges of the body form bilateral ridges, called the uncinate processes (U).
View AP C-spine view.
A posterior view of the cervical spine is shown on the left. An anterior view is shown in the center.
Axial compression can result in compression fractures which can lead to decreased vertebral body height or a burst fracture that fragments the vertebral body. A strong lateral force can cause a shearing action and create fractures of an uncinate process. Hyperflexion and hyperextension may also result in teardrop fractures of the anterior superior or inferior corner of the body.
Between the vertebral bodies are the intervertebral disks. These function as shock absorbers. As in the lumbar region, rupture of the annulus can lead to encroachment into the spinal canal. The vertebral body also serves as the attachment site of the anterior and posterior longitudinal ligaments. Tears in these ligamentous structures can result from displacement or extensive fractures of the vertebral body. Without these ligamentous connections, the vertebral column is unstable.
Neural Arch
Posterior to the vertebral body is the neural arch (vertebral arch covering the spinal canal). The neural arch refers to all the structures dorsal to the body. The arch serves to protect the spinal cord, provide attachment sites for ligaments and muscles, and forms synovial joints that facilitate movement of the vertebral column. The major structures that make up the arch include: 1) the pedicles, 2) the laminae, 3) the spinous process, 4) the articular processes and facets, and 5) the transverse processes.
View C4.
Pedicles
The pedicles ("little feet") form the supports of the neural arch as it is attached to the vertebral body. In the cervical spine, the pedicles are short. They project posteriorly (dorsally) from the body and form the lateral borders of the spinal canal. Superior and slightly larger inferior vertebral notches above and below the pedicles form intervertebral foramina in the articulated vertebral column. Through these foramina pass the cervical spinal nerves.
View lateral.
On a lateral film, the pedicles appear as small connections between the body and the articular processes (see below). On the AP view, the pedicles appear as small doughnut densities on the lateral upper portion of the vertebral body, just below the uncinate processes. Fractures in this region can disrupt the spinal nerves or the spinal cord itself.
View AP.
Laminae
The laminae (meaning "layers") form a roof over the neural arch, supported by the pedicles. In addition to the obvious protective function, the laminae also serve as the site of attachment for the ligamentum flavum. Because the laminae are thinner in the C-spine compared to other vertebrae, their relative radiolucency appears as an apparent gap between the posterior cortex of the articular facets and the anterior cortex of the spinous process (posterior aspect of the neural arch) on the lateral view. In general, the laminae (L) are not easily appreciable on an AP view.
View lateral.
Spinous Process
The spinous process projects dorsoinferiorly from the point of union of the laminae. Unique to the typical cervical vertebrae, the spinous processes of C3 through C6 are typically bifid at the tips. The spine of C7 is an easily visible surface landmark called the vertebra prominens. The spinous processes are the site of attachment for a number of ligamentous and tendinous structures. The major ligaments associated with the spine include the interspinous and supraspinous ligaments as well as the ligamentum nuchae. A number of intrinsic muscles of the spine as well as large back muscles such as the trapezius, the levator scapularis, and the rhomboids are attached to the cervical spinous processes. Excessive load on these muscles may result in avulsion of the spinous processes of C6 and C7, commonly known as the clay shoveller's fracture. This fracture is more commonly found in adults.
View lateral.
On a lateral view, the spinous processes appear as triangular extensions. The anterior border with the laminae (spinolaminal line) is an easily visible feature marking the posterior border of the vertebral canal (spinal canal). On an AP view, the spinous processes appear as a midline density superimposed on the vertebral body. The bifid nature of some of the cervical spines can be easily appreciated in this view.
View AP.
Articular Processes and Articular Facets
The articular processes are cylindrical structures at the junction of the pedicles and the laminae. Like the pedicles, articular processes also delimit the lateral margins of the spinal canal. The articular facets, the oblique elliptical ends of the cylinders, are higher anteriorly and lower posteriorly.
View articular facets of C4.
Capsular articular ligaments join adjacent inferior and superior articular facets of successive vertebrae to form synovial joints. Strong rotary forces can stretch or tear these ligaments resulting in unilateral or bilateral dislocated facets.
View lateral.
On a lateral view, the articular processes are rhomboidal in shape and superimposed upon one another. Unlike the vertebral body which slopes downward anteriorly, the articular processes slope sharply downward posteriorly. They appear superimposed on the spinal canal.
View oblique view.
The skeletal model on the left shows variability in the intervertebral disk spacing due to poor positioning of the model bones during photography. This oblique view shows the intervertebral foramina formed by the inferior notch of the pedicle of the vertebrae above and the superior notch of the pedicle of the vertebrae below.
Transverse Processes
The transverse processes project outward anteroinferiorly from the pedicles like half-cylindrical scoops.
View C4.
Along the grooved portion of the transverse process pass the ventral rami of the cervical nerves. The dorsal rami pass more posteriorly. In the middle of the transverse process is a foramen for the vertebral artery as it courses upward toward the foramen magnum. Lesions in this region can damage the nerves of cervical and brachial plexi as well as compromise the arterial supply of the posterior brain.
The Cervicocranium
The articulations between the occiput, the atlas (C1), and the axis (C2) are highly specialized to allow the extensive range of motion of the head upon the neck. As such, C1 and C2 differ sufficiently from the typical vertebrae that they deserve special mention.
View odontoid view.
The atlas (C1) articulates superiorly with the occipital bone. The occipital bone forms the base of the cranium, and articulation with the cervical spine is via the pair of large convex occipital condyles situated on either side of the anterior half of the foramen magnum. The brain stem becomes the spinal cord as it leaves the cranium through the foramen magnum. Anterior to the foramen magnum is an upward incline to the dorsum sellae called the clivus. The posterior aspect of the foramen magnum is in-line with the posterior arch of C1 and C2 (the spinolaminar line).
Lacking a body, the atlas is essentially a ring with prominent articular processes that are appropriately called lateral masses. The lateral masses divide the ring into a smaller anterior and a larger posterior arch.
View C1-C2 cross section CT scan.
On the inner aspects of the lateral masses are tubercles for the transverse ligament that run between these tubercles. The concave superior facets articulate with the convex condyles of the occipital bone, while the larger inferior facets (of C1) articulate with C2.
Because the atlas lacks a body, the lateral masses are the major weight bearing structures, and a compression force (axial load) can result in a bursting fracture of the ring of C1. The upper CT image shows such fracture of the C1 ring.
View odontoid view.
On an open-mouth odontoid view, the lateral masses are easily visible as trapezoidal wedges. The anterior and posterior arches are superimposed over the odontoid process.
Radiographically, the surfaces of the anterior atlantoaxial gap are parallel to each other and the distance is less than 5 mm in a child. Widening of this space can be a result of a transverse ligament tear, allowing unstable motion between the two bones.
View lateral.
On a lateral view, the atlas is a simple ring structure seen edge on. The lateral masses are superimposed on the odontoid process of C2 and are difficult to identify. The inner aspect of the anterior arch can be easily appreciated, as can the inner aspect of the posterior arch. Note that the anterior arch articulates with the anterior aspect of the odontoid, while the posterior arch forms the very first posterior border of the vertebral canal.
The most prominent feature of C2 (axis) is the odontoid process, also called the dens. Both names refer to its resemblance to a tooth. The odontoid process projects superiorly from the body of the axis. Articular processes centered around the odontoid have smooth superior facets that facilitate rotational articulation within the atlas. The inferior facets are more posterior and in-line with the articular processes of the rest of the cervical vertebrae area. On a lateral view, the axis appears much like a typical cervical vertebra, however, it is easily identified by the odontoid process projecting vertically from the body and the large and wide spinous process.
View odontoid view.
On an open-mouth odontoid view, the axis is shaped like a fat bowling pin with wings. The odontoid and the body form the bowling pin, and the articular processes are the wings.
The articulation of the odontoid and the atlantal anterior arch is unique. Anteriorly, it is between the two bones; posteriorly, the dens articulates with the transverse ligament that is attached to the inner aspects of the atlantal lateral masses. The spinal cord travels in the space posterior to the transverse ligament.
View C1-C2 cross section CT scan.
The upper image is a CT scan axial image through the ring of C1. The odontoid process is visible anteriorly in the ring. The transverse ligament is not easily visible on this CT cut; however, it is posterior to the odontoid. The spinal cord is visible in the posterior portion of the ring of C1 (the spinal canal). Note the fracture in the anterior aspect of C1. The gap in the posterior portion of C1 is a growth plate. Compare this CT image with the bony model of C1 and C2.
View open mouth odontoid view.
Developmentally, the bodies of the axis and the dens arise from separate ossification centers. The odontoid (dens) itself has three ossification centers. There are two columnar centers, forming the body of the odontoid that typically fuse before birth, and a third center at the tip of the odontoid. During infancy, before the tip of the odontoid has ossified, the superior end of the odontoid may have a cleft in it radiographically. The odontoid of children may have a separate ossification center at the tip of the odontoid--the os terminale. A finding of a fragment at the superior-most tip of the odontoid may be due to a fracture or it may a normal ossification pattern.
The most common normal radiographic pattern mistaken for an odontoid fracture is the subdental synchondrosis. This is a linear lucency at the base of the dens. The dens usually fuses with the body of C2 somewhere between ages 3 and 6 years. However, a thin, sclerotic "scar" of the synchondrosis may be appreciable on the lateral view for many years thereafter.
Normal laxity of the soft tissues of the cervicocranium in the developing pediatric patient can make radiologic interpretations more difficult. Laxity of the prevertebral tissues can resemble abscesses, hematomas, or tumors, particularly if the film is taken in exhalation or in flexion. Laxity of the transverse atlantal ligaments -- spanning from the dens to the inner aspect of the lateral masses of the atlas -- allow greater range of motion between these two bones. This, in addition to the cartilaginous (non-ossified) nature of the outer layers of the odontoid, accounts for an increased anterior atlanto-odontoid (atlantodental) interval of 3-5 mm in infants. In addition, the margins of the anterior atlanto-odontoid interval can lose their parallelism during neck flexion. These pediatric norms can resemble atlantoaxial subluxation. Furthermore, laxity of the ligamentous structures around C3 can also resemble subluxation at the C2-C3 or C3-C4 junctions.
Radiographic Views
The three most common views employed in the emergency department are: 1) the lateral view, 2) the AP view, and 3) the AP open mouth odontoid. The lateral view can be taken as a cross-table lateral while the patient is still on a spine board in the emergency department. The anteroposterior views often require transporting the patient to the imaging department. Below is an introduction to reading these three common views.
Lateral neck
The lateral cervical spine radiograph is the most useful view. As many as 80-90% of cervical spine injuries can be detected on the lateral view alone. The quality of the film image obtained should be assessed. All cervical vertebrae, C1-C7, and the top part of T1 should ideally be visible. It is important to be able to count all 7 cervical and one thoracic vertebrae since the most common lesions occur at the upper and lower ends of the cervical spine. The most commonly missed lesions occur at the C7-T1 junction simply because it is not shown on the film.
To assess C-spine alignment, four imaginary lines can be drawn on the lateral film; which aid evaluation of vertebral alignment: 1) anterior longitudinal line, 2) posterior longitudinal line, 3) posterior facet margins (not shown on diagram), and 4) spinolaminar line.
View lateral.
The anterior and posterior longitudinal lines simply correspond to the locations of the anterior and posterior longitudinal ligaments. The spinolaminar line demarcates the posterior limits of the spinal canal. These lordotic contours should be smooth and without step-offs.
The neck is normally positioned with lordosis (extension). In adults, a straight C-spine (lack of lordosis) indicates the presence of muscle spasm and a possible occult fracture. In children, the absence of lordosis is commonly seen. When positioned on a spine board, the large occiput of most children positions their neck in a straight (without lordosis) or in a flexed alignment. This is common and does not necessarily indicate the presence of a significant injury. However, it does make interpretation of the radiographs more difficult since such poor positioning may cause artifact radiographic abnormalities.
Proper positioning of the atlantoaxial bones with the occiput can be assessed by noting the alignment of two imaginary lines. First, extension of a line down the slope of the clivus should point to the superior end of the dens (the os terminale). The posterior margin of the foramen magnum should be in line with the spinolaminar line. Such an alignment places the foramen magnum in-line with the spinal canal, this corresponds to the junction of the brain stem and the spinal cord.
Dislocation of articular facets or a fractured vertebrae may result in a discontinuity of the contours of these lines with implications of instability and decreased patency of the spinal canal lumen resulting in impingement of the spinal cord.
Widening of the retropharyngeal space is a sign of injury to either soft tissue or the adjacent vertebrae. The retropharyngeal space (essentially, the pre-vertebral soft tissue space) should be roughly half the width of a vertebral body. Fractures of the C-spine can result in hemorrhaging into the retropharyngeal space, resulting in widening of this soft tissue space on the lateral neck view.
The spacing of the facet joints, intervertebral spaces, and interspinous gaps can provide hints to the integrity of the mechanical stability of the connections between vertebrae. The width of these spaces should be fairly constant between sequential vertebrae. The articular surfaces should be parallel to each other. In addition, the spinous processes are generally equidistant from each other but converge toward a point at the base of the posterior neck. Pathologically, increased spacing often results from tearing of the supporting ligaments. Increased interspinous distances, "fanning," is often associated with a posterior longitudinal ligament tear. Decreased spacing could lead to invagination of connective tissue into the spinal canal.
The major features of all vertebra should be examined. The height of each vertebral body should be fairly constant from C3 through T1. A slight decrease in height of a vertebral body may be a compression fracture. A difference of greater than 25% can occur only if the posterior intervertebral ligaments are torn.
The pedicles, facets, and laminae of each vertebra should be superimposed upon each other in a properly taken radiograph. Doubling of facets and articular columns should be examined for evidence of unilateral or bilateral dislocated facets.
The cortical surfaces of each vertebra should be scrutinized for steps, breaks, or abnormal angulations. Blurred edges may result from fractures or dislocations. Often the tendons and ligaments are stronger than the bones themselves, and tear-drop shaped pieces of bone could be avulsed by a strong force acting on the anterior longitudinal ligament. In the clay shoveller's fracture (spinous process fracture), a downward force on the supraspinous ligament shears most of the C6 or C7 spinous process off its base.
AP View
The AP view is helpful in evaluating the vertical alignment of the spinous processes and the visualization of the vertebral body from the AP perspective. This view is also important in evaluating lateral displacement of fractures or entire vertebrae.
View AP.
Typically, in this view, the mandible and occiput are superimposed over C1 and C2, and sometimes the upper portions of C3 may be obscured. An adequate film should clearly show the vertebral column from C3 to T1.
Spinous processes should be aligned in the midline and be generally equidistant from one another. Misalignment of the spinous processes may suggest a dislocation or a fracture of an articular surface. Increased spacing between spinous processes or an apparent missing spinous process in this view may suggest a fractured spinous process, as in the clay shoveller's fracture (spinous process fracture). A widened gap may also be due to a tear of the posterior longitudinal ligament, resulting in "fanning" as seen on a lateral radiograph.
The trachea is easily visualized in this view. Disruption of tracheal radiolucency may also indicate nearby lesions.
The intervertebral spaces should be evaluated for uniformity from one vertebral pair to another. The spaces should be of similar distances apart and the articular surfaces should be fairly parallel to each other. Dislocations and ligamentous tears may produce widened or narrowed joint spaces in an AP view.
Lastly, the vertebrae should be evaluated for fractures. The cortical surfaces should be continuous and well defined. Each vertebral body should be rectangular and of similar size. The uncinate processes (U), bilateral raised lips on the superior surface of the vertebral bodies, are most easily evaluated for fractures from this AP view.
Open-Mouth Odontoid View
The AP open-mouth odontoid radiograph is used to evaluate the cervicocranium from another perspective. It is most valuable in assessing the relationship between the lateral masses of the atlas and the axis. The junction between C1 and C2 should be clearly visible. Visibility of the entire odontoid process is of secondary importance.
View odontoid view.
From this perspective, left and right symmetry is most helpful in evaluation. The two atlantal lateral masses should be equidistant from the dens, and the articular surfaces of the atlantoaxial lateral masses should be in perfect alignment. The inferior facets of the atlantal (C1) lateral masses should be parallel to and aligned with the upper facets of the axial (C2) lateral masses (white arrows point to the lateral margin of the facet joint). Lateral displacement of one or both of the atlantal lateral masses (black arrow) is suggestive of a Jefferson fracture in which the ring of C1 is fractured, bursting it open displacing the lateral masses outward.
The lateral masses should also be scrutinized for unequal size. In rotary subluxation, the atlas is turned such that one lateral mass is farther than the other from the radiographic film and may appear larger. However, rotary subluxation is best confirmed on a CT scan.
Laxity of ligamentous attachments surrounding the odontoid and incomplete ossification of the odontoid may allow up to two-thirds of the anterior atlantal arch to be above the tip of the odontoid process.
Fractures of the odontoid are common and can be seen on lateral and open-mouth odontoid views. These fractures are classified according to the location of the fracture. Type I is an oblique fracture through the upper portion of the odontoid. It should be noted that sometimes the upper incisors can obscure portions of the upper odontoid and simulate a Type I fracture.
Type II fractures occur at the base of the odontoid where it joins the body of C2. This is the most common odontoid fracture. Unfortunately, this is also the location of the subdental synchondrosis.
NOTE: While it is not unusual for the odontoid to be tilted posteriorly, it should NOT be tilted anteriorly. This is more indicative of an odontoid fracture. Widening of the subdental synchondrosis coupled with anterior tilting of the odontoid are highly indicative of an odontoid fracture.
A Type III odontoid fracture extends into the vertebral body of C2.
The odontoid image shows three open mouth odontoid radiographs on the right. The upper radiograph shows the odontoid well. However, the lateral margins of the lateral masses of C1 and C2 are obscured by the patient's lower teeth, making it impossible to assess the lateral alignment of the C1-C2 facet joints.
The middle image shows a bursting ring fracture of C1 with outward displacement of the C1 lateral masses (black arrow). The lower image shows normal alignment of the C1-C2 facet joints. The white arrow points to the lateral margin of the facet joint.
Other Special Views
In addition to the standard three views (lateral, AP, odontoid), other radiographic views can aid in obtaining a better perspective on a suspected lesion.
Swimmer's View: Recall that an adequate lateral film should reveal all seven cervical vertebrae and upper T1. Typically, downward traction on the arms will produce the adequate visualization in most cases. Should the C7/T1 junction still be obscured, a swimmer's view can be obtained by elevating the arm closest to the film. This posture yields a slightly oblique view of the vertebral column, but moves the shoulder joint above the C7/T1 junction. C7/T1 can easily be seen in this view; however, it is often overlapping with dense soft tissue and the bones of the shoulder.
View swimmer's view.
In this swimmer's view, note that the lower cervical spine can be seen, but in this case, it is still not optimal since C7 is still not visualized.
Oblique Projections: The oblique views provide good visualization of the posterior structures of the vertebral column, such as the intervertebral foramina and articulation of the facets. They are particularly helpful in evaluating suspected unilateral facet dislocations since only one half of the facets and intervertebral foramina are viewed at a time. The foramina are also best visualized on these views.
View oblique views.
Lateral Flexion and Extension Views: The flexion and extension views are obtained on a conscious patient who can actively bend their neck. Care must be taken in obtaining these views as there is risk of further displacement. In appropriate circumstances, these views may be particularly helpful in excluding ligamentous injury and potential instability. Some physicians have found the flexion view invaluable in detecting occult posterior ligamentous injuries resulting from hyperflexion.
References