Asymmetry of the sphenoid bone and its suitability as a reference for analyzing craniofacial asymmetry.

The purposes of this study were to evaluate the asymmetry of the sphenoid bone and to determine its suitability as a reference for analyzing asymmetry of the skull. Thirty-seven dry skulls from India were divided into group A (n = 18), with a right-left length discrepancy of less than 2 mm for both the external acoustic meatus-frontozygomatic suture and external acoustic meatus-subspinale, and group B (n = 19), with a right-left length discrepancy of more than 2 mm for either of these 2 parameters. The skulls were then examined with regard to the percentage of asymmetry of the sphenoid bone, the angles between the cranial base and the facial axis, and the distance between reference surfaces of the sphenoid bone and facial landmarks by 3-dimensional measurement system. The following results were obtained: 1. Asymmetry of the sphenoid bone, while slight, was found in both groups. There were no significant differences between the 2 groups. 2. The cranial base and the facial axis did not form a right angle in group A, and there were no significant differences between the 2 groups. 3. The distances between reference surfaces of the sphenoid bone and the lower landmarks of the facial bone were greater than those of the upper landmarks. 4. The external acoustic meatus was the most suitable reference for analysis of craniofacial asymmetry.