A novel method to measure the external auditory canal: Normative data and practical implications

Purpose To accurately measure external auditory canal (EAC) dimensions by high resolution computed tomography (CT), and compare results with a traditional method of EAC measurement. Methods Using an advanced multidimensional open source digital imaging and communications in medicine (DICOM) analysis program (OsiriX, Pixmeo, Geneva, Switzerland) 91 adult EACs were analyzed on a previously obtained temporal bone CT scan. Tympanometric data were also recorded for each ear. The methods were compared using a linear mixed effect model. Results EAC volume was compared between tympanometrically calculated volumes and CT measured volumes. It was found that CT measured volumes are, on average, smaller (1.12 cm3, SE = 0.04) than tympanometry volumes (1.27 cm3, SE = 0.04 cm3). There was a significant difference in CT measured volume between genders (p = 0.0125), with males having larger measured volumes (1.23 cm3, SD = 0.28 cm3) than females (1.06 cm3, SD = 0.20 cm3). There was a significant difference in average circumference between ear laterality (p = 0.0071), with the right ear having a slightly larger average circumference (2.49 cm, SD = 0.23 cm) than the left ear (2.44 cm, SD = 0.50 cm).There was also a significant difference in minimum circumference between age groups (p = 0.0448), with patients younger than 60 years having larger minimum circumferences (1.89 cm, SD = 0.21 cm) than older patients (1.78 cm, SD = 0.25 cm). Conclusions This study demonstrates that CT analysis can provide more information about EAC dimensions than traditional techniques. Moreover, slight but statistically significant differences are associated with age, gender and laterality. Accurate estimation of EAC dimensions is important for the development of hearing aids and personal protective equipment and can also be helpful for surgical planning, specifically otoendoscopy. Future research will focus on simplifying computation, developing cross-cultural cohort comparisons, and application to otoendoscopic procedures.