“…Torticollis is the presenting syndrome, and the dislocation can be missed [2,15,25]. CT increases the likelihood of making the diagnosis [2,19,30] and, when images in rotation are obtained, is useful for evaluating reducibility of the lesion [2,14,26]. Fielding and Hawkins [12] distinguish four stages based on the extent of the shift of C1 on C2: type 1 is characterized by bilateral rotatory dislocation around the dens with a normal atlas-dens interval; type 2 by unilateral rotatory dislocation around one of the lateral masses with a 3-to 5-mm atlas-dens interval, indicating the presence of transverse ligament disruption; type 3 by a greater than 5-mm atlas-dens interval, indicating disruption of both the transverse ligament and the alar ligaments; and type 4 by posterior displacement of C1 due to failure of the dens.…”