Herniation of the Mastoid Segment of the Facial Nerve During Cochlear Implantation Surgery.

Background: We aim to report a rare case of a herniated mastoid segment of the facial nerve that was accidently discovered during cochlear implantation surgery and how altering the surgery plan could achieve the implantation while preserving the nerve.

Case presentation: A four-year-old girl presented with profound bilateral sensorineural hearing loss that did not completely resolve after 2 years of using hearing aids was scheduled for cochlear implantation surgery in the right ear. During surgery, a herniated mastoid segment of the facial nerve took an anterior course and obstructed the access to the round window.

Conclusion: When a traditional posterior tympanotomy approach in cochlear implantation surgery is limited in cases of a herniated facial nerve, a tunnel created near the inferior part of the posterior wall of the auditory canal provided safe insertion of the electrode. It also permitted placement of a piece of fascia between the electrode and the facial nerve, therefore, protecting the facial nerve from electrical stimuli.