Imaging description

C2, also known as axis, is one of the most complex and unusual vertebral bodies. It is crucial for weight-bearing as well as nodding and lateral movement of the head. Developmentally it has four ossification centers at birth, one each for a neural arch, one for the body, and one for the odontoid process. A secondary ossification center appears at the apex of the odontoid process (os terminale) between 3 and 6 years of age, and fuses to the odontoid process by the age of 12 years [1].

Classic imaging with radiography in case of a traumatic injury to C2 can exhibit linear lucency through the odontoid process or vertebral body. An open-mouth frontal-view radiograph can also show transverse or oblique fracture lines. However, it is increasingly being replaced by CT scan for possible traumatic injury to the cervical spine in the developed world [2]. CT is highly sensitive to detect lucent fracture lines and displacement of the fracture fragments, and for evaluation of the tip of the odontoid process or involvement of pedicles and foramen transversarium. In acute cases, soft tissue swelling anterior to C2 is visualized. Sagittal and coronal reconstructions increase the sensitivity of the CT scan, as sometimes axial imaging may be confusing. A 3mm slice thickness is optimal, with no increasing advantage of having thinner sections [3]. Sagittal T1- and T2-weighted MRI exhibits high T2 signal bone marrow edema as well as soft tissue injury in the prevertebral compartment. The extent of possible cord compression is also well evaluated with MRI.