Electrode Misdirection into the Superior Semicircular Canal: Complication of Cochlear Implantation by Round Window Approach

Abstract

OBJECTIVE:The purposes of this study were to investigate the misdirection of the electrode into the superior semicircular canal during cochlear implantation and to suggest surgical principles for correct electrode insertion through the round window membrane. MATERIALS and METHODS:In this retrospective case review, operative records and postoperative images of cochlear implantations performed at a tertiary care facility from 1988 to 2010 were reviewed. RESULTS:In 3 out of 629 cases, electrode insertion into the superior semicircular canal was found. All 3 cases occurred in cochlear implantations using the round window approach, and none was found when using the cochleostomy approach. Insufficient exposure of the round window membrane and intra-cochlear soft tissue were regarded as the cause of misdirection of the electrode. The electrodes were repositioned appropriately into the cochlea with revision surgery in all 3 cases. CONCLUSION:In order to prevent electrode misdirection during cochlear implantation through the round window, the round window membrane needs to be clearly visualized by sufficiently drilling bony overhangs and removing soft tissues around the round window.

Anatomy of the Round Window Region With Relation to Selection of Entry Site Into the Scala Tympani

“…This means that the ST superior to the horizontal part of the RWM is very narrow, and any attempt to enter the ST in this area will damage the OSL/BM and probably result in an SV insertion or even risk the electrode array entering the vestibule and possibly the semicircular canal. 31 Scala tympani. The ST initially extends inferiorly, anteriorly, and medially to the RWM vertical portion ( Figs.…”