Assessment of visualization of structures in the middle ear via Tos modified canal wall-up mastoidectomy versus classic canal wall-up and canal wall-down mastoidectomies

Abstract

The aim of this prospective study is to evaluate the differences in the ability to view structures in the middle ear between Tos modified canal wall-up mastoidectomy and classic canal wall-up (CWU) and canal wall-down (CWD) mastoidectomies. Eighteen temporal bones of 10 cadaver heads were used. Six bones were randomly selected for each surgical technique (Tos' technique, CWU and CWD mastoidectomies) and fixed on an operating table. In the Tos' technique: (1) transmeatal posterior tympanotomy with drilling of the supero-posterior bony annulus, (2) transmeatal atticotomy with preservation of the bony bridge and (3) cortical mastoidectomy were performed. In the classic CWU mastoidectomy, cortical mastoidectomy and posterior atticotympanotomy (facial recess approach) were performed. Incus and posterior half of the tympanic membrane were removed from all temporal bones. An independent specialist performing otologic surgery evaluated all of the temporal bones and approved the proper extent of dissections. Two another independent observers blinded to the purpose of the study were asked to point five anatomic structures and locations (sinus tympani, anterior attic, posterior crus, lateral attic and the Eustachian tube orifice) in two different sessions. Observers were allowed to rotate the operating table as it has been done during otologic surgery, and the line of view for the observers was both transmastoid and transcanal. The ability to view these structures was recorded as "correct/visible" or "incorrect/invisible". These records were also verified after removing the posterior and superior walls of the outer ear canal in temporal bones of the Tos and CWU groups at the end of the study. Significant differences were found in the ability to view middle ear structures between the Tos' technique and CWU mastoidectomy as well as between CWU and CWD mastoidectomies, with the Tos' and CWD techniques almost equally showing superiority to CWU (p<.0001). Of the five locations, sinus tympani and anterior attic were observed more frequently with the Tos' technique versus CWU (p=.001). Sinus tympani (p<.005), anterior attic (p=.001) and posterior crus (p<.05) were observed more frequently with CWD versus CWU. There was no significant difference in the ability to observe lateral attic and the Eustachian tube orifice among the three techniques. In addition, there was no significant difference in the ability to visualize all the five locations between the Tos' and CWD technique. Statistical analysis showed good reproducibility of this randomised, blinded study. Tos' modified CWU mastoidectomy, in which most part of the canal wall is intact, showed similar advantage of the CWD in viewing structures in the middle ear. The Tos' technique and CWD mastoidectomy provided better visualization of sinus tympani and anterior attic that are the most frequent places of residual cholesteatoma in the classic CWU mastoidectomy.