Postnatal Development of the Vestibular Aqueduct Trajectory on CT: Establishing Age-Specific Norms to Distinguish Normal from Arrested (Hypoplastic) Development

Background and purpose: Although the otic capsule is fully formed at birth, the vestibular aqueduct (VA) continues to mature postnatally. Failure of this maturation-VA hypoplasia-identifies a subgroup of Menière's disease (MD) patients and can be detected on CT by measuring the VA's angular trajectory (ATVA). However, the age at which ATVA stabilizes and hypoplasia can be reliably diagnosed remains unclear. We therefore defined the normal timeline of ATVA development to establish age-specific CT norms for distinguishing physiologic VA development from fetal/hypoplastic arrest. Results: Inter-reader agreement was excellent (ICC = 0.92 ATVA; 0.88, RL thickness). Mean ATVA declined from 135° (±7.5°) in infants to 98° (±6.0°) in adolescents. By 80% prediction interval, the ATVA upper limit fell below 140° by ∼1.8 years, 130° by ∼3.1 years, and 120° by ∼10.4 years. The 95% interval excluded ATVA ≥140° by ∼3.0 years and ≥130° by ∼10.3 years, but not >120° before age 16 years. No ears above age 8 years fell in the fetal category (≥140°), and none above age 12 years in the intermediate category (121°-139°). First-derivative analysis showed ATVA change plateaued at ∼5.0 years. RL thickness ≥1.2 mm universally corresponded to mature ATVA (≤120°). Conclusions: ATVA transitions from fetal (≥140°) to mature (≤120°) trajectory over the first decade, stabilizing by ∼5 years. ATVA >120° before ∼10 years reflects normal development; after ∼12 years, it indicates adult-persistent hypoplasia. RL thickness ≥1.2 mm serves as a practical surrogate for mature VA orientation. These benchmarks empower radiologists to differentiate normal maturation from MD-associated VA hypoplasia, enabling early risk stratification and management. Abbreviations: VA = vestibular aqueduct; ATVA = angular trajectory of the vestibular aqueduct; RL = retrolabyrinthine bone; MD = Menière's disease; ED = endolymphatic duct; ES = endolymphatic sac.