Pre-operative assessment of facial recess width in paediatric cochlear implant recipients: a radiological study

Background The location of the vertical segment of the facial nerve varies greatly among patients undergoing otological surgery. Its position relative to the incus determines facial recess width, which has implications for ease of cochlear implantation. Objective To investigate the variation in facial nerve depth, relative to the incus, on pre-operative computed tomography in patients undergoing cochlear implantation. Methods A retrospective cohort study was conducted of paediatric patients undergoing cochlear implantation at a tertiary referral centre. Distance between the incus short process and facial nerve, in the transverse (medial-lateral) dimension, was measured at six imaging slices, ranging from 1.25 to 7.25 mm below the tip of the incus short process. Results Facial nerve depth relative to the incus short process demonstrated significant variability. Among all subjects and at all measurements taken inferior to the incus, the mean dimension between the facial nerve and the incus short process was 1.71 mm. Conclusion This paper presents a rapid, repeatable technique to assess the depth of the facial nerve vertical segment on pre-operative computed tomography, as measured relative to the tip of the incus short process. This allows the surgeon to anticipate facial recess width and round window access during cochlear implantation.