OBJECTIVE: In humans, the inner ear reaches its final configuration and adult size during fetal life. According to the literature, this occurs between 18 and 25 weeks of amenorrhea (WA). The ossification of the otic capsule is believed to arrest any further configuration change. There have, however, been some observations of slight changes in the orientation of the semicircular canals (SCCs) occurring later in fetal life. The present study aim was to examine changes of angulations between bony SCCs during fetal life.
PATIENTS: Fifty-four human fetuses aged 22 to 40 WA.
INTERVENTION: Computed tomography scanner.
MAIN OUTCOME MEASURE: SCC angulation (in degrees) studied with Amira software.
RESULTS: We found mean angles between the lateral SCC and anterior SCC, the lateral SCC and posterior SCC, and the anterior SCC and posterior SCC of 88.67, 92.60, and 90.19 degrees, respectively. Inter-SCC angles did not change significantly between the different age groups (22 WA, 24 WA, 26 WA, 29-31 WA, 34-36 WA, 38-40 WA). There was no difference of angulation between males and females and no intraobserver or interobserver variability.
CONCLUSION: The absence of correlation of SCC angles with age in our sample of fetuses indicates that the three-dimensional configuration of the SCC has already reached its adult form at 22 WA. As often described in the literature, these angles are close to orthogonality, probably reflecting an optimal vestibular function configuration.