Elongated styloid process: when is it really elongated?

The styloid process (SP) is often denoted as elongated when it is longer than 30 mm or 33 mm. These dimensions, based on early reports, do not respect the natural variation of the SP. The aim of this study is to investigate the natural variation of the length of the SP. Knowing this variation is a prerequisite for consistent terminology in anatomy and anthropology; it is essential for the classification of the SP as elongated on panoramic radiographs (PRs).

1000 consecutive PRs of a normal population were retrieved from inactive files at the Dental School of the Hannover Medical University. Measurements of the length of the SPs were made directly on the radiographs from the caudal margin of the tympanic plate to the tip of the SP.

On 521 of the 1000 PRs the length of the SP could be measured at least on one side. As there was no significant difference between distributions on the left and right side, both sides were combined to give a total of 837 measurements. The median was 28.0 mm, the interquartile range was from 23.0 mm to 36.0 mm. The distribution depends significantly on age and gender. The 90th percentile varies between 42 mm for women under 35 years and 49 mm for men aged over 35 years.

The medians in our sample correspond to the thresholds for elongated SP quoted in the literature. Our results show that these thresholds are too low, since they are exceeded in 50% of normal patients. We propose that the SP should be considered to be elongated only if its length exceeds 45 mm, which corresponds to the average of the 90th percentiles for different sex and age groups.