Human Auricles Are Not Symmetrical: A Comparative Study Using Landmark-Based and Surface-Based Software

To evaluate the outcome of ear reconstruction, the contralateral auricle is often used as a reference. Literature has shown that auricles are symmetric on a group level, but it is unknown if this is also true on an individual level. In this paper, the authors quantify bilateral symmetry of the auricle and hypothesize that quantifying bilateral differences on an individual level requires a technique that is more precise than conventional manual measurement methods.

CT sinus scans of 42 healthy volunteers were used to determine the bilateral symmetry of the auricle using conventional manual measurement techniques and a high-precision computer-assisted surface-based technique with a high precision of measurement. Bilateral symmetry was evaluated for the following geometric auricle parameters: length, width, protrusion distance, auriculocephalic angle, inclination angle, posteroanterior and superoinferior position difference. Bilateral differences exceeding the reliability threshold, based on the precision of measurement for the manual and automated approaches, were considered true differences.

In both the manual and automated measurements, the authors found no statistically significant differences in bilateral auricle parameters at the group level when evaluating a group of L versus R ears. At the individual level, however, the automated algorithm established bilateral differences in auricle parameters in 74% to 100% of the cases, whereas manual measurements could only detect bilateral differences in 7% to 64% of the cases.

The high-precision surface-based technique shows that human auricles are generally not symmetric on the individual level. Future research is needed to investigate which discrepancies are acceptable from a technical point of view and which left-right differences are considered acceptable from a cosmetic and reconstructive point of view.