A gross anatomical study of the styloid process of the temporal bone in Japanese cadavers

The incidence of an elongated styloid process (SP) and average length and diameter of SP have not been reported using Japanese cadavers. Data on the female-to-male ratio of an elongated SP vary. We calculated the average length and diameter of SP in Japanese cadavers and compared SP lengths between sexes.

Twenty-seven sides (right and left of bodies) in males and 51 sides in females were analysed. Measurements were obtained from the inferior external acoustic meatus to the distal tip of the SP. SP diameters at the proximal base, midpoint, and distal tip were measured. SP > 30 mm was considered elongated. We used Welch's t-test for the statistical analysis. Fisher's exact two-tailed test was also performed to analyse the female-to-male elongation ratio. A p-value < 0.05 was considered statistically significant.

Styloid process elongation prevalence was 29.5% in our sample. The average full length was 27.04 ± 7.88 mm overall; the average diameters were 5.41 ± 1.77 mm at the proximal base and 2.21 ± 1.22 mm at the distal tip. The average SP measurement was 26.81 ± 5.92 mm in males and 27.16 ± 8.79 mm in females (p = 0.74). The female-to-male ratio of SP elongation was 1:2 (p = 0.041). Females had longer full lengths of non-elongated SPs than males (p = 0.004). Males had wider diameters at the proximal base of elongated SPs than females (p = 0.017).

The average length of SP was 27.04 mm in the Japanese population and about 30% of the Japanese presented SP ≥ 30 mm. Male had significantly higher rate than female among the SP ≥ 30 mm, and female had significantly longer SPs than male among the SP < 30 mm. Anatomically, the SP gets narrow as distally goes. Our anatomical findings would be beneficial to creating treatment plans, diagnosis, and surgery.