Lateral cervical radiographs showing the case. The C2/C3 spinolaminar line was marked, and the ventral aspect of the posterior arch of C1 lies ventral to this line. The C2/C3 spinolaminar line was drawn, starting from C3 and extending cranially through C2 to the lamina of C1. When the ventral lamina of C1 lay ventral to this line, the spinolaminar test is defined as positive, which indicated the possibility of the existence of a relatively narrow canal of C1.