Variations in size and in symmetry of foramina of the human skull

The goal of this report is to define an average size and size range for many of the skull's foramina and to determine in which paired foramina asymmetry is commonly found so that researchers and clinicians examining foramina may have an anatomical reference. The incidence of foraminal variations is also discussed. Information on skull foraminal size and symmetry is increasingly important because of the advancements in radiologic techniques such as magnetic resonance imaging (MRI) and computed tomography (CT). These methods are making difficult diagnoses of pathologic conditions of skull foramina possible. The foramina of 100 randomly selected dry skulls were measured and the symmetry of paired foramina was noted. The average, largest, and smallest sizes for 29 different foramina and the length of one canal are listed. Information regarding the symmetry of 27 paired foramina and the length symmetry of the infraorbital canal was also gathered. Specific data collected for paired foramina include the percent of skulls in which (1) neither foramen of the pair was present, (2) both foramina of a pair were present, (3) both foramina of the pair are present and were both the same size within 0.5 mm, and (4) both foramina of a pair are present but there was greater than 0.5 mm difference in size between them.