Resumen de Facial nerve canal dehiscence: evaluation of a new middle eardissection technique and digitalized image analysis
Abdulaziz Alomiery, Lulwah Alturki, Christopher S.G. Thompson
The tympanic segment (TS) of the facial nerve (FN) runs in a protective bony canal in the medial wall of the middle ear. Facial nerve canal dehis-cence (FND) represents a breach in the bony ca-nal covering the FN. Full exposure of the TS great-ly aids visualisation and therefore the gross inves-tigation of middle and inner ear pathologies, but the existing literature provides minimal guidance on dissection and measurement techniques. The aim of this study was to develop a dissection ap-proach for the middle ear, investigate the inci-dence of FND in fresh- frozen and embalmed ca-davers, and finally, to grade/measure FND using a digitalized image analysis software (ImageJ). Twenty-two temporal bones were investigated (59% [n = 13] were fresh-frozen [six males, seven females], and 40% [n = 9] embalmed [six males, three females]). Dissection was conducted in the anatomy teaching laboratory of the University of Edinburgh (regulated by the Human Tissue [Scotland] Act 2006). Dissection and analysis pro-cedure involved five main stages: preparation, ex-posure, sectioning of the horizontal segment, grad-ing of the canal’s dehiscence, and measurementand analysis. The overall dehiscence rate was 41% (n = 9): 23% (n = 3) in fresh-frozen cadavers and 66% (n = 6) in embalmed cadavers. Of 22 temporal bones, 36% were graded as fully de-hisced in different locations. Our dissection suc-cessfully achieved full exposure of both the medial wall of the middle ear and the FN’s TS. Analysis of the curved TS was performed with ImageJ soft-ware and allowed a more accurate measurement of the TS’s length and any associated FND. Attain-ing a clear and systematic dissection approach for the middle ear is of fundamental importance for future anatomical research that investigates FND, as well as for the provision of teaching materials in the form of anatomical specimens.
