Foramen arcuale: a rare morphological variation located in atlas vertebrae.

Objective: To investigate the incidence of foramen arcuale in dry atlas vertebrae which may cause clinical problems.

Materials And Methods: Eighty-one dry human cervical vertebrae were examined. The evaluated parameters of two atlas vertebrae including foramen arcuale were as follows: maximum antero-posterior, transverse diameters and areas of the right and left superior articular facets and transverse foramina; maximum antero-posterior diameters, heights, areas and central sagittal thickness of bony arch forming roof of foramen arcuale, respectively. All parameters were measured with caliper in milimeters.

Results: Thirteen of eighty-one cervical vertebrae specimens (13/81, 16.05%) were atlas and the two of thirteen atlas vertebrae (2/13, 15.38%) had macroscopically complete foramen arcuale. Each of the two atlas vertebrae was including one foramen arcuale (one on the left and one on the right side). There was a statistically significant difference (p = 0.04) between the mean antero-posterior diameter of superior articular facet located on each side of atlas vertebrae, whereas not (p = 0.51) between mean antero-posterior diameter of transverse foramina. There was not any significant difference between the mean transverse diameters and areas of superior articular facets and transverse foramina located on each side of atlas vertebrae, respectively. Each of the areas of transverse foramina located on the same sides with foramen arcuale in two atlas vertebrae was less than the mean areas of transverse foramina located ipsilateral side with each foramen arcuale in thirteen atlas vertebrae.

Conclusion: The present study provides additional information about the incidence and topography of the atlas vertebrae including foramen arcuale.