MRI assessment of normal ligamentous structures in the craniovertebral junction.

We have established an imaging protocol in order to characterise the normal ligamentous structures in the craniovertebral junction. Thirty volunteers without a history of car accident or head or neck trauma underwent MR imaging with 2-mm-thick proton-density-weighted sections in three orthogonal planes. The alar ligaments were clearly seen in every case and had three different configurations in cross-section: round, ovoid or wing-like. A broadening from lateral to medial in the coronal plane was observed in all cases. The transverse ligament was clearly demonstrated in 26 out of 30 cases. The ligament was flattened where it arched across the dens. Towards the insertions the ligament twisted into an oblique-horizontal orientation. The lower tectorial membrane had a median portion merging with the dura, and a lateral portion separated from it. Between the dens and clivus this membrane either merged totally with dura or was partly separated from it by a thin layer of fat. The posterior atlanto-occipital membrane was clearly demonstrated. It either merged with the dura or was partly or totally separated from it by a fat layer. The anterior atlanto-occipital membrane was inconsistently seen and could not be evaluated. Our refined MR protocol improves the visualisation of the craniovertebral ligamentous structures, and may in the future give new insight into post-traumatic neck disorders up to now poorly understood.