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Neuroradiology Case of the Week

Case 405

May 2009

Virendra Kumar, MD, Judy Liu CC3, David Tuttle MD,
and P-L Westesson, MD, PhD, DDS

Clinical Presentation: A 14-year-old male presented with neck and back pain after he fell on his head while performing front handsprings.

Imaging Findings:

• Hyperflexion of the cervical spine with reversal of the cervical lordosis, centered at C4-5 level, with minimal anterolisthesis of C4 over C5.
• Decreased disc space anteriorly at C4-5 level, with posterior subligamentous herniation, along with tiny calcific focus in the posterior margin of the disc.
• Increase interspinous space between the C4 & C5 spinous processes with hyperintensity on the T2W images,involving soft tissue.
• No fracture.
• Focal cord hyperintensity at C4-5 level on T2W images suggestive of contusion.
• Grade 1 anterolisthesis of C4 on C5 with traumatic disc herniation with resulting severe narrowing of the spinal canal and spinal cord contusion.
• Injury to the anterior and posterior longitudinal ligaments.
• Soft tissue edema in the posterior soft tissues of the neck is consistent with injury to the interspinous and supraspinous ligaments at the C3-C5 level.
  

Diagnosis: Distracted flexion injury C4-C5 with traumatic herniated disk and left C5 radiculopathy with focal cord contusion

Discussion: Accidents, especially those with an abrupt change in speed, are one cause of cervical disc herniation. The weight of the head, when whipped rapidly or violently, exerts tremendous force on the neck muscles and structures. This force can weaken the wall (annulus fibrosus) of the disc, causing the disc material to bulge outward. Disc degeneration related to repetitive minor trauma can also lead to disc herniation.
     Because the discs between the cervical vertebrae are much smaller and generally bear a lesser load than discs in the lumbar region, herniations occur less often than in other areas of the spine. Posture or position problems, when chronic, may also weaken the muscles and structures of the spinal column.
     MRI is the best modality to look for spinal injury involving the ligaments and soft tissue without evidence of any fracture. MRI shows focal kyphosis with abnormal separation of facets/spinous processes in sagittal plane, with increased signal in interspinous ligament and canal compromise (all of these findings seen in this case).
     If conservative treatment fails to relieve the pain after 2 or 3 months, surgery may be necessary to relieve the pressure on the cervical nerves. After using an MRI or CT scan to determine the exact presence of the herniation, the herniated disc may be surgically removed either from the front (anterior) or the back (posterior) of the neck. Surgery may also be urgently recommended for progressive weakness, numbness or severe neck and arm pain depending upon the degree of cord compromise.
     Two to six percent of blunt trauma injuries are associated with cervical injuries. Most subaxial (C3-C7) injuries in adolescents occur between C5-C7 near the fulcrum at C5-C6, principally in pediatric patients over 8 years, when the vertebrae begin to ossify, the facets align vertically, and the cervical musculature develops. Fifty percent of spinal cord injuries occur in adolescents over 16 years of age, while only 3.9% occur in children under 16. Motor vehicle accidents comprise the greatest percentage of spinal cord injuries for both pediatric and adult populations; followed by sporting events and violence.
     The biomechanics of the developing pediatric spine differ from that of the adult spine, resulting in different injury patterns. The immature spine has greater ligamentous laxity, shallow facet joints, underdeveloped spinal processes, and physiologic wedging of the vertebral bodies. The hypermobility, larger head-to-body ratio and immature cervical musculature make younger children vulnerable to high torque forces and injury.
     The fulcrum of the cervical axis in children younger than 8 years old is located at C1-C3 and the area of maximal mobility progressively descends as the vertebrae ossify, and settles at C5-C6 at around 12 years of age through adulthood. Therefore, spinal injuries younger children typically are upper cervical as opposed to lower cervical injuries C3-C7, in patients 10 years and older.
     A normal variant in pediatric patients up to 14 years of age is pseudosubluxation, which is usually incidentally found at C2-C3, but can occur in C4-C5 as well. At least 3 mm subluxation at those levels occur in 40% of children under 8 years of age. Pseudosubluxation can be confused with a hangman's fracture.
     Primary spinal injury occurs when the force of impact exceeds the flexibility of the vertebral column. The pattern of injury results from the vector of the applied force as well as the position of the head and neck during impact. Typically, injuries consist of a combination of mechanisms. Mechanisms of injury include axial loading, hyperextension, dislocation, and flexion.
     Axial loading occurs when strain energy exceeds the absorptive capacity of the spinal column. The vertebral compression often affects C5-C6, occurring when the the head is lowered during direct blows to the top of the head. Burst fractures may also occur when the nucleus pulposis is forced into the vertebral body.
     Hyperextension injuries include avulsion fractures of the atlas, traumatic spondylolisthesis, laminar and pillar fractures. These commonly occur in motor vehicle accidents as "whiplash."  Hyperextension applies tensile forces on the anterior longitudinal ligament, causing injury to the ligament as well as the disc annulus. In severe extension, retrolisthesis can occur.
     Dislocation requires a significant rotational force, and can lead to compromise in the in spinal vasculature. Fracture-dislocation injuries usually occur in the cervical spine or at the thoracolumbar junction.
     Flexion forces can cause distraction of the posterior ligaments and lead to their rupture, usually in cervical spine. This can lead to anterolisthesis, wedge compression fractures, or facet dislocations. A fracture may enter the neural arches and exits the vertebral body anteriorly, causing a flexion distraction injury. Rapid hyperflexion of the neck applies great force to the posterior ligamentous structures, and cause variable sprain of the nuchal ligaments. The vertebra is then free to rotate in flexion over the next caudal segment. If the anterior structures such as the posterior longitudinal ligament or disc annulus are injured, anterior translation can occur.
     The combination of such forces may lead to disc herniations. Disc herniation is the displacement of the intervertebral disk, and may be specified by the degree and type. Protrusion is a bulge less than or equal to 25% of disk circumference, and is the displacement of the nucleus pulposus and inner annular material trough the annulus but not through the outer-most annular fibers. Disc extrusion extends through all the annular layers but retains a small isthmus to the primary disk. A sequestered disk or free disk fragment is completely detached from the primary disk.
     Radiculopathy often occurs during disc herniations and unilateral facet injuries, and present as weakness, numbness, and decreased deep tendon reflexes in a dermatomal distribution. If several roots are involved, avulsion injuries of the brachial plexus should be suspected.
     During the patient’s fall, a combination of principally axial loading and flexion forces likely caused damage to the anterior and posterior ligaments resulting in herniation of the disc and anterolisthesis of C4 on C5. He subsequently was surgically treated with an anterior cervical diskectomy with spinal cord decompression, C4-C5, anterior spinal fusion of C4-C5, harvest of left tricortical iliac crest strut graft, application of anterior plate C4-C5, posterior spinal fusion of C4-C5, and insertion of nonsegmental instrumentation at C4-C5.

References:

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