The role of preoperative computerized tomography in a safe posterior tympanotomy for cochlear implant surgery

Abstract

A posterior tympanotomy is a technique performed to access round window area to insert cochlear implant electrode into round window membrane or through cochleostomy. In this study, we aimed to classify and evaluate the anatomical relationships between the facial nerve (FN) (vertical segment), chorda tympani nerve, and facial recess (FR) pneumatization in an axial temporal bone computerized tomography (CT) to be safe when performing a posterior tympanotomy. We performed a retrospective analytic study of temporal bone CT scans. A cohort of 51 patients who underwent cochlear implantation with classical mastoidectomy with posterior tympanotomy were included. All patients had preoperative diagnostic CT of the temporal bone from January 2014 to November 2015. Anatomical correlations were classified according to several parameters including protrusion of the FN into the antrum, FR pneumatization, and status of the facial canal. Anatomical relationships between the vertical segment and posterior tympanotomy were classified into three types: type 1, the FN has no protrusion with a regular facial canal with pneumatized FR; type 2, the FN has protrusion into the antrum with a regular facial canal and/or poorly pneumatized FR; and type 3, the FN has sclerotic mastoid with no FR pneumatization. These results enable preoperative evaluation of the FN’s status and difficulty while performing posterior tympanotomy, providing basic knowledge to prevent injury of the FN while performing a posterior tympanotomy.