FIG 3. 30-year-old man with neck pain and occasional upper limb paresthesias.

A and B, Flexion (A) and extension (B) plain radiographs of the cervical spine show partial aplasia of the posterior arch of the atlas with an isolated posterior arch remnant. The isolated posterior fragment moves anteriorly into the spinal canal during extension (B).

C and D, Midsagittal T1-weighted (C) and T2-weighted (D) MR images reveal no compression or signal alteration of the spinal cord. Significant canal stenosis from C3 to C7 is present along with a superimposed disk bulge/protrusion at C5–C6.