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 cross-sectional 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.