3.2 Surgery findings
Five ears underwent CI using traditional retroauricular straight incision 3∼3.5cm in length. Four ears were performed using conventional facial recess and round window approach(Table 2). Case 3 underwent simultaneous bilateral CI surgery. Left ear used retrofacial approach due to anteromedially displaced mastoid segment FN.
Individually, full electrode array insertion and excellent intraoperative electrically Evoked Compound action potential was achieved in right ear of Case 1. Case 2 had right aural atresia but normal cochlear nerve dimensions in the operation ear (Figure 1). Since the mastoid was completely sclerotic, and the semicircular canal was aplasia, only the dura and sigmoid sinus were used as anatomical landmarks during mastoidectomy. Drilling out of the superficial mastoid bone exposed a strip-like fibrous tissue resembling the vertical segment of the facial nerve, but facial nerve monitoring ruled out the possibility (Figure 1). The mastoid segment of the facial nerve was exposed gradually by removing the overlying bone with a fine diamond drill in the deep part of the mastoid, with the assistance of facial nerve monitoring. Covert round window niche was identified in front of the nerve and after removing the overhanging bone and fibrous tissue, the round window was exposed. 7 of the 12 electrodes were inserted through the enlarged round window. Congenital dehiscent facial canal of the tympanic and pyramid segment were confirmed in the right ear, which had facial paralysis postoperatively. The patient underwent a secondary exploratory operation 7 days later, and the main trunk of facial nerve demonstrated no reaction to monitoring probe. facial paralysis recovered to Brackmann Level Ⅰ about 1 year later. Only partial insertion was achieved in left ear of case 4.