Providing Insight for Pediatric Ear Surgery: Analysis of Middle Ear Development via HRCT.

Objectives: Providing insight for pediatric ear surgery via investigations on the development patterns of ossicles, mastoid, and external auditory canal (EAC).

Methods: This retrospective study analyzed high-resolution computed tomography (HRCT) scans of 191 healthy temporal bones ranging from infants to adults. Subjects were grouped by 1-year intervals for developmental regression models and 3-year intervals for stage comparisons using t-tests or Mann-Whitney U tests.

Results: The size of auditory ossicles and tympanic cavity (TC) remained stable during development, while the minimum diameter of the tympanic sinus (TS) entrance was reduced. Regarding mastoid pneumatization, the air cells can be observed at birth, became pronounced at 2 years old, and were fully developed around the age of 5, with subsequent growth primarily involving radial expansion. Furthermore, the EAC demonstrated significant growth with age: the width of EAC increased linearly ( $\hat{y}$  = 0.12x + 4.01, R² = 0.85), while the length of EAC followed a polynomial growth pattern ( $\hat{y}$  = -0.03x² + 1.15x + 6.25, R² = 0.96).

Conclusions: Ossicles and TC remain stable during development. Furthermore, mastoid air cells may have developed in the early stages of life, while their diameter increases synchronously with EAC. All in all, ossicular chain reconstruction surgery and endoscopic ear surgery can be performed in babies.

Level of evidence: NA Laryngoscope, 2024.