Morphology and anatomical variability of the external auditory canal: A population-based MRI study

Background: The external auditory canal (EAC) exhibits a complex morphology and strong inter-individual variations. However, these have not yet been comprehensively described in the literature. Purpose: This study aims to determine the width, height and cross-sectional area of the cartilaginous portion of the EAC and to describe the three-dimensional morphology and variability of different EACs. Methods: Magnetic resonance imaging was performed on 870 subjects (401 male, 469 female, resulting in 1740 EACs) who participated in the longitudinal, population-based cohort study 'Study of Health in Pomerania-START-3'. The height and width were measured in the cartilaginous part of the EAC, between the first and second bend. The variability of the EAC morphology was visualized in three-dimensional models. Results: The mean height (vertical length) of the EAC was 8.62 mm (SD = 2.42) on the right, 8.47 mm (SD = 2.36) on the left. The width (horizontal length) was 4.08 mm (SD = 1.6) on the right, 3.93 mm (SD = 1.64) on the left. The EAC cross-section was 28.6 mm2 (SD = 15.19) on the right, 27.15 mm2 (SD = 14.33) on the left. The average cross-sectional area of the EAC in men was higher than in women. Subjects with larger body size had larger crosssectional areas. Subjects with higher body mass index tended to have smaller cross-sections. Although the average EAC had an oval shape, a three-dimensional comparison of different EACs revealed strong individual variation in morphology. Conclusion: This study enhances the understanding of otolaryngologists and anatomists regarding the complex morphology and variability of the cartilaginous portion of the EAC.