Atlas Assimilation Patterns in Different Types of Adult Craniocervical Junction Malformations

Study Design: This is a cross-sectional analysis of resonance magnetic images of 111 patients with craniocervical malformations and those of normal subjects.

Objective: To test the hypothesis that atlas assimilation is associated with basilar invagination (BI) and atlas’s anterior arch assimilation is associated with craniocervical instability and type I BI.

Summary of Background Data: Atlas assimilation is the most common malformation in the craniocervical junction. This condition has been associated with craniocervical instability and BI in isolated cases.

Methods: We evaluated midline Magnetic Resonance Images (MRIs) (and/or CT scans) from patients with craniocervical junction malformation and normal subjects. The patients were separated into 3 groups: Chiari type I malformation, BI type I, and type II. The atlas assimilations were classified according to their embryological origins as follows: posterior, anterior, and both arches assimilation.

Results: We studied the craniometric values of 111 subjects, 78 with craniocervical junction malformation and 33 without malformations. Of the 78 malformations, 51 patients had Chiari type I and 27 had BI, of whom 10 presented with type I and 17 with type II BI. In the Chiari group, 41 showed no assimilation of the atlas. In the type I BI group, all patients presented with anterior arch assimilation, either in isolation or associated with assimilation of the posterior arch. 63% of the patients with type II BI presented with posterior arch assimilation, either in isolation or associated with anterior arch assimilation. In the control group, no patients had atlas assimilation.

 

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No conflict of interest has been declared by the author(s).