The odontoid process: various configuration types in MR examinations.

PURPOSE: Several developmental anomalies have been described with respect to the odontoid process. The purpose of the study was to describe the MR appearance of the odontoid process and to calculate the prevalence of its morphological variants.

METHODS AND MATERIALS: We retrospectively reviewed 133 patients (85 males and 48 females, age range of 19-81 years, mean 39.5), examined within a 7-year period. Patients were divided into two age groups: ≤30 and >30-year-old. The morphology of the odontoid process was classified into type I: pyramidal tip and type II: ovoid or convex tip. The incidence of os odontoideum and os terminale and the presence of longitudinal cleft were also recorded. Fischer's exact test was used for statistical analysis (p < 0.05).

RESULTS: Type I was identified in 54 cases (40.6 %) and type II in 79 cases (59.4 %). Os odontoideum was recorded in one case (0.7 %), os terminale in 24 cases (18 %) and the presence of a longitudinal cleft (partial or complete) in 86 cases (64.7 %). Type I showed a higher prevalence in the ≤30 age group (p < 0.05). No differences were shown between sexes.

CONCLUSION: The configuration types of odontoid process are reported herein. The clinical relevance of this morphological variation needs to be elucidated with further studies.