The shape of the osseous external auditory canal and its relationship to chronic external otitis

In literature and based on clinical observations, the shape of the osseous external auditory canal (OEAC) has often been suggested to be an etiologic factor in chronic otitis externa (COE). However, to date, no evidence has been presented to confirm this correlation. The aim of this study was to see whether evidence of such a correlation exists, and if so, what shape of the OEAC is related to COE.

Using CT scans of 2 groups of patients (with and without COE), a novel and easy to use method was introduced to measure 2 dimensions of the OEAC: the pretympanic recess (the depth (DPTR) and anterior curvature (ACPTR)). In addition, a descriptive classification of the entire OAEC was introduced.

The proposed method was demonstrated to be useful as excellent interobserver agreements were found (r = 0.89). No significant differences in the descriptive classifications of the OEAC were observed between COE and the non-COE patients. The DPTR was significantly deeper in COE patients. For the ACPTR, no significant differences were observed.

Based on a new method of determining the DPTR, we demonstrate that the DPTR is significantly deeper in COE patients and that the shape of the OEAC is thus of importance in the pathogenesis of COE.