Two features of the atlas vertebra simulating fractures by tomography.

The bipartite superior joint surface and the pseudonotch of the atlas, although well described in anatomic and radiologic literature, may be mistaken for fractures by tomography. The first may appear as a trough on the superior articular surface of the lateral mass of the atlas. The second, the normal tubercle for insertion of the transverse ligament of the atlas, may look like a separate ossicle or a chip fracture.