Prenatal development of the human tympanic ring: a morphometric study with clinical correlations.

ABSTRACT

PURPOSE: To establish normal reference values for the human Tympanic Ring (TR) during prenatal development, and to describe and interpret its growth dynamics. METHODS: Fifty spontaneously aborted human fetuses aged 12-37 weeks with normal external characteristics were evaluated. The parameters measured in the TR were the cephalocaudal and dorsoventral axes, total area, thickness, height, and length and angle of the notch of Rivinus (NR). Data were subjected to statistical analysis. RESULTS: The following values were obtained at the end of fetal development cephalocaudal and dorsoventral axes, 10.03 and 8.3 mm, respectively; ratio between the two axes, 120%; total area, 65.63 mm2; height and thickness, 0.88 mm and 1.10 mm, respectively; and length and angle of the NR, 4.66 mm and 26.2 degrees, respectively. There were variations in the length of the dorsoventral axis throughout fetal development that affected all other parameters, except for the cephalocaudal axis. There were no sex-based differences in TR size. CONCLUSION: The prenatal development of the TR is dynamic as evidenced by the size variations noted throughout fetal development. Notwithstanding, this structure is a reliable and sensitive marker of developmental abnormalities of the external and middle ear.