Objective: To determine the computed tomography (CT) appearance of minimally displaced type II odontoid fractures and the optimal protocols to evaluate these fractures by CT.
Materials and methods: The CT scans of five patients with minimally displaced type II odontoid fractures and 71 patients without odontoid pathology were reviewed for signs of fracture. A phantom consisting of a cadaver specimen with a type II odontoid fracture was evaluated with several protocols on four CT scanners. The protocols differed in slice thickness and reconstruction algorithm. Helical scanning was also performed, and parasagittal and coronal reformations were created from each image set.
Main results: Multiple cortical disruptions longer than 1 mm were demonstrated on the scans of all five patients with type II odontoid fractures. Only three of the 71 patients without odontoid fractures had multiple cortical disruptions, and none were longer than 1 mm. In the phantom study, thinner sections demonstrated cortical disruptions better than thicker sections. Similarly, images reconstructed with a bone reconstruction algorithm demonstrated the cortical disruptions better than images reconstructed with a soft-tissue reconstruction algorithm. Helical scans (1 mm thick) adequately demonstrated the reduced Type II odontoid fracture. Parasagittal and coronal reformations failed to demonstrate a fracture line through the base of the odontoid process on all image sets.
Conclusions: Cortical disruptions greater than 1 mm and multiple cortical disruptions may be the only findings of odontoid fractures and should suggest the diagnosis. Evaluation of potential type II odontoid fractures is improved as CT section thickness is reduced (down to 1 mm) and is also improved by use of a bone reconstruction algorithm. The apparent absence of a fracture line through the base of the odontoid process on parasagittal or coronal reformations does not rule out the diagnosis.