Postnatal Development of the Vestibular Aqueduct Trajectory on CT: Establishing Age-Specific Norms to Distinguish...

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 patients with Menière disease and can be detected on CT by measuring the angular trajectory of the VA (ATVA). However, the age at which the 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.

We retrospectively reviewed temporal bone and head CTs in 159 children (318 ears) 0-16 years of age without an otologic abnormality. Two head and neck radiologists measured the ATVA and retrolabyrinthine bone (RL) thickness-previously established surrogates of VA hypoplasia-on axial reformatted images. Interreader reliability was assessed by the intraclass correlation coefficient. We modeled the ATVA versus age by using generalized additive mixed models. First-derivative analysis of the age spline identified when ATVA change plateaued. Eighty percent and 95% prediction intervals determined the ages at which the ATVA reliably fell below clinical thresholds (140°, 130°, 120°).

Interreader agreement was excellent (intraclass correlation coefficient = 0.92 ATVA; 0.88, RL thickness). The mean ATVA declined from 135° (SD, 7.5°) in infants to 98° (SD, 6.0°) in adolescents. At the 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 16 years of age. No ears older than 8 years of age fell in the fetal category (≥140°), and none older than 12 years of age fell in the intermediate category (121°-139°). First-derivative analysis showed that ATVA change plateaued at ∼5.0 years. RL thickness of ≥1.2 mm universally corresponded to a mature ATVA (≤120°).

ATVA transitions from a fetal (≥140°) to mature (≤120°) trajectory across 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 of ≥1.2 mm serves as a practical surrogate for mature VA orientation. These benchmarks empower radiologists to differentiate normal maturation from Menière disease associated VA hypoplasia, enabling early risk-stratification and management.