Presentation
Driver of vehicle involved in high speed MVA (car vs tree).
Patient Data
Widening of the lateral atlanto-axial joints bilaterally, (right greater than left) with increased median atlantoaxial joint distance, and widening of the right atlanto-occipital joint. Blood is present deep to the PLL at the level of the dens and is associated with soft tissue thickening in this region suggestive of ligamentous disruption. Stranding also seen within the C1/2 interspinous space also indicative of ligamentous sprain /disruption.
Unstable atlanto axial joint, with extensive ligamentous injury resulting in pathological widening of the median and lateral atlantoaxial joints, with disruption of the both the anterior and posterior longitudinal ligaments at this level. This is associated with pre-dentate space widening, with partial disruption of the anterior atlantoaxial membrane, disruption of the transverse ligament, corrugated in appearance and avulsed on the left side, and with disruption of the longitudinal band of the cruciform ligament as well. Increased STIR signal within the region of the ligamentum nuchae/interspinous ligament at C1/2 and C2/3 levels. There is an associated hemorrhagic contusion and edema of the spinal cord and medulla evidenced by elevated T2 signal extending from the inferior half of the medulla to mid-C3 level.
Case Discussion
This case illustrates a craniocervical junction distraction injury.
Craniocervical biomechanical continuity depends on the integrity of the skull base, atlas, and axis and their attaching ligaments. The articulations of the craniocervical junction are defined by the middle atlantoaxial joint, which consists of two synovial compartments that surround the dens and allow rotation of C1 and C2 with respect to each other, and the paired lateral atlantoaxial and atlanto-occipital articulations. These joints are supported by several ligaments, the most crucial of which are the tectorial membrane, the alar ligaments, and the transverse fibers of the cruciate ligament (transverse ligament) in maintaining craniocervical integrity.
The most prevalent cause of craniocervical junction injuries is high speed motor vehicle collisions. The injury mechanism is commonly severe hyperflexion accompanied by axial compression. In some cases, it is the result of hyperextension with axial compression and rotation. There is resulting dislocation of the craniocervical junction and atlanto-axial distraction. These are considered grossly unstable injuries since the rotational and shearing forces at the craniocervical junction disrupt the ligamentous continuity of the tectorial membrane, the alar ligaments, and the transverse ligament. Thus, there is loss of atlanto-axial continuity, and resultant separation.
Conventional radiographic and CT findings in craniocervical distraction injuries include:
- Prevertebral soft-tissue swelling
- Basion-dens interval > 12 mm
- Basion–posterior axial line interval > 12 mm anteriorly or >4 mm posteriorly
- Abnormal power’s ratio (used to diagnose occipitocervical dislocation)
- Power’s ratio is the (distance from the basion to the posterior arch of C1) divided by the (distance from the anterior arch of C1 to the opisthion). A ratio of 1 is considered normal. Normal. If > 1.0, this is suggestive of anterior dislocation. A ratio < 1.0 is suspicious for:
- posterior atlanto-occipital dislocation
- odontoid fractures
- ring of atlas fractures
- Widening or incongruity of the articulation between the occipital condyles and the lateral masses of C1
- C1-C2 dislocation or subluxation and resultant widening of the C1-C2 facets
- Fractures of the bony structures of the craniocervical junction
MR imaging findings in craniocervical distraction injuries, usually best viewed sagittal or coronal MR imaging with T2-weighted or STIR sequences, include:
- Prevertebral soft-tissue swelling
- Interspinous, or nuchal ligament edema
- Fluid within the articular capsules
- Facet widening
- Epidural hematoma with/without resultant spinal cord injury
Craniocervical junction distraction injuries are often accompanied by significant neurologic and vascular compromise. Many patients sustaining these injuries die as a direct result or present with profound sensory and motor sequelae and/or deficits including ventilator-dependent quadriplegia. Early diagnosis, cervical spine stabilization and cardiorespiratory support are imperative for patient survival and/or recovery.
Case courtesy of Associate Professor Pramit Phal
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