Anatomic development of the vocal tract during the first two decades of life: Evidence on prepubertal sexual dimorphism from MRI and CT studies

The growth of the vocal tract (VT) is known to be nonuniform insofar as there are regional variations in anatomic maturation. This study presents quantitative anatomic data on the developing VT from 604 imaging studies (277 male; 327 female) between birth and 20 years. Data analyses include detailed assessment on the growth of the oral (anterior or horizontal) and pharyngeal (posterior or vertical) regions of the VT for both sexes. The oral region of the VT was segmented into lip-thickness, anterior-cavity-length, and orophayrngeal-width; and the pharyngeal region of the VT into posterior-cavity-length, and nasopharyngeal-length. Findings from all variables/segments indicate differences in growth trend, rate, and type (somatic versus neural) between males and females. However, it appears that prepubertal sex differences at specific age ranges are masked by overall growth rate differences between males and females. Comparing males versus females, using a limited age range of 60 months, unveiled prepubertal sexual dimorphism in the oral/horizontal region where differences appear more pronounced in the oropharyngeal-width segment. Such novel anatomic findings indicate one possible source for noted sex differences in formant frequencies before age 10, where there is no sexual dimorphism in VT length. [Work supported by grants NIH-NIDCD R03-DC4362, R01-DC006282, and NIH-NICHHDP30-HK03352.]