Postnatal changes in the styloid process, vagina processus styloidei, and stylomastoid foramen in relation to the function of muscles originating from the styloid process

Abstract

We investigated age-related changes in the styloid process in 88 skulls, aged from 5 months to 85 years of age. The osseous styloid process was not well developed in children. Its length increased significantly with age (from 2.3 mm in 11-20 age group to 16.3 mm in 61-85 group). In adolescent specimens (11-20 years of age), the median distance from the styloid process to the stylomastoid foramen was 0.7-0.8 mm, whereas in adult and old age specimens the two structures were completely adjacent or very close, usually less than 0.2 mm. The process was missing in 5% of the adult specimens. There was a statistically significant positive association between the length of the styloid process with age (r = 0.3210, 95% CI 0.0817-0.5254; P = 0.0097), whereas the distance from the styloid process to the stylomastoid foramen significantly decreased with age (r = -0.4518, 95% CI -0.6167 to -0.2490; P = 0.0001). Changes in the length and shape of the styloid process reflected altered function of the three muscles originating from the styloid process-m. stylopharyngeus, m. stylohyoideus and m. styloglossus. They have a common function of lifting the aerodigestive elements upward and backward, after the descent of the aerodigestive tract and final morphological differentiation of the vocal system during puberty. Relationship between altered muscle function and the morphology of the styloid process are important for understanding the clinical syndromes related to the styloid process, such as Eagle's syndrome.