Revision stapedectomy.

During the past decade, the evolution of surgical techniques and philosophy for revision surgery after stapedectomy has accelerated. Lasers, new surgical techniques, and new prostheses now permit the precise identification and reliable correction of the conductive problem, while reducing the risk of postoperative sensorineural hearing loss that plagued nonlaser revision techniques.

Causes of conductive hearing loss after stapedectomy or stapedotomy: a prospective study of 279 consecutive surgical revisions.

OBJECTIVE: To analyze the causes for residual or recurrent conductive hearing loss following stapedectomy or stapedotomy and then propose surgical techniques to avoid these complications. STUDY DESIGN: Prospective study of 279 consecutive stapedectomy or stapedotomy revisions performed by the author. SETTING: Tertiary referral center. PATIENTS: The study included 260 patients who presented with a 20 dB or greater average air-bone gap in the speech frequencies 1 month to 35 years following stapedectomy or stapedotomy (19 patients were explored for possible oval window perilymph fistula). INTERVENTION: Stapedectomy (stapedotomy) surgical revision. MAIN OUTCOME MEASURES: Microscopic inspection and palpation assessed the mobility and continuity of the malleus, incus, and prosthesis. Infrared laser vaporization thinned the oval window neomembrane to identify the precise depth and margins of the oval window, the presence of residual stapes footplate, and finally, the relationship of the prosthesis to the fenestra into the vestibule. RESULTS: Prosthesis displacement out of the oval window fenestration with fixation of the prosthesis against the residual stapes footplate or otic capsule margin was demonstrated in 81% (211/260) of the patients. Of these patients, 31% had complete incus erosion, and an additional 60% demonstrated partial incus erosion, usually on the undersurface of the incus. Residual fixed stapes footplate was found in 14%, and malleus fixation in 4%. Incus dislocation was found in 4%, and incus fixation in 2%. CONCLUSIONS: Prosthesis migration and subsequent fixation caused the majority of stapedectomy failures. Collagen contracture of the oval window neomembrane lifts the prosthesis out of the oval window fenestration. Prosthesis displacement then results from adhesions pulling the prosthesis or mechanical forces further tilting the prosthesis. Incus erosion results from vibration against the fixed prosthesis. Six specific stapedotomy recommendations are made to minimize postoperative prosthesis migration.

Preservation of auditory brainstem response thresholds after cochleostomy and titanium microactuator implantation in the lateral wall of cat scala tympani.

HYPOTHESIS: The safety of implanting a titanium microactuator into the lateral wall of cat scala tympani was assessed by comparing preoperative and postoperative auditory brainstem response (ABR) thresholds for 1 to 3 months. BACKGROUND: The safety of directly stimulating cochlear perilymph with an implantable hearing system requires maintaining preoperative hearing levels. This cat study is an essential step in the development of the next generation of fully implantable hearing devices for humans. METHODS: Following GLP surgical standards, a 1-mm cochleostomy was drilled into the lateral wall of the scala tympani, and a nonfunctioning titanium anchor/microactuator assembly was inserted in 8 cats. The scala media was damaged in the 1 cat. ABR thresholds with click and 4- and 8-kHz stimuli were measured preoperatively and compared with postoperative thresholds at 1, 2, and 3 months. Nonimplanted ear thresholds were also measured to establish statistical significance for threshold shifts (>28.4 dB). Two audiologists independently interpreted thresholds. RESULTS: Postoperatively, 7 cats implanted in the scala tympani demonstrated no significant ABR threshold shift for click stimulus; one shifted ABR thresholds to 4- and 8-kHz stimuli. The eighth cat, with surgical damage to the scala media, maintained stable click threshold but had a significant shift to 4- and 8-kHz stimuli. CONCLUSION: This cat study provides no evidence of worsening hearing thresholds after fenestration of the scala tympani and insertion of a titanium anchor/microactuator, provided there is no surgical trauma to the scala media and the implanted device is securely anchored in the cochleostomy. These 2 issues have been resolved in the development of a fully implantable hearing system for humans. The long-term hearing stability (combined with histologic studies) reaffirm that the microactuator is well tolerated by the cat cochlea.