Direct measurement of ear canal volume in a pediatric population: can we explain its individual variation in terms of age and body weight?

OBJECTIVE

The aim of this work was to measure the external auditory canal (EAC) volume in children directly and to analyze its variation according to age and body weight.

METHODS

This was a prospective study at a university-based, secondary referral hospital. Volumes of the bony and cartilaginous EACs were measured using a 1 ml tuberculin syringe filled with 95% ethyl alcohol before inserting ventilation tube(s). Three hundred thirty-eight ears from 194 children (107 boys and 87 girls) were enrolled in this study (mean age=58.8 ± 25.2 months). They were between the 10th and 90th percentiles for age and gender based on the 2007 growth chart for Korean children.

RESULTS

EAC volume tended to increase with age. The volumes of cartilaginous and total EACs were significantly larger in boys than in girls. The volume of the bony EAC was significantly larger in right than in left ears. Under the assumption that EAC volume is a linear function of age as well as body weight, these factors explained less than one-third of overall variation. Preferably, the growth of EAC seemed to be not linear with aging in pediatric population.

CONCLUSIONS

Our cubic model seemed to be more fit to the growth of EAC than simple linear model did and age and body weight alone were not clinically useful predictors of ear canal volume needed for the fitting of hearing aids in pediatric population. Because this variation can result in a large variation of real ear to coupler difference (RECD), this study supports that individual measurement of the RECD is crucial for fitting appropriate hearing aids in children.