3D T2 MR Imaging-Based Measurements of the Posterior Cervical Thecal Sac in Flexion and Extension for Cervical Puncture.

The posterior C1-C2 thecal sac is larger with neck extension than flexion, independent of prone or supine positioning. Given that this space is the target for cervical puncture, findings suggest that extension is the ideal position for performing the procedure, and the decision for prone-versus-supine positioning can be made on the basis of operator comfort and patient preference/ability.