[Stapedotomy and anatomical variations of the facial nerve]

Among the 595 stapedotomies performed between 1992 and 1999 (surgeon R. Häusler), there were 40 cases (6.7%) where the facial nerve had an abnormal course. In 32, a partial nerve prolapse over the oval window was noted with (6 cases, 1 being a duplicated nerve around the oval window) or without (26 cases) dehiscence in the long bony canal. In 8 cases, there was a total prolapse of the nerve over the oval window, with 2 special cases: facial nerve having an inferior course over the oval window and the promontory; facial nerve being widely spread over the oval window and the promontory. Concomitant anomalies of the stapes were seen and several patients had dysmorphic syndromes with conductive hearing loss since early childhood. Stapedotomy was performed in 39 patients. In the 32 cases of partial nerve prolapse, a small piston (0.4 mm) was placed in the lower part of the oval window which was sometimes enlarged towards the promontory, except when the nerve was duplicated: the prosthesis was placed into the footplate between the nerve branches. In the 8 patients with total facial nerve prolapse, the prosthesis was either placed directly in a burr hole into the promontory just below the oval window (6 cases), or, when the nerve ran over the promontory and over the oval window, the prosthesis was placed above the oval window at the site where the facial nerve is usually located (1 case). In the case where the nerve was spread widely over the oval window and the promontory, no prosthesis was placed. In the 39 patients where a stapedotomy was performed, the average hearing level gain ranged from -15 dB to 40 dB (average: 18 dB) at 0.5, 1, 2 and 4 kHz. The average residual air-bone gap was < 30 dB in 36 patients (92.3%), < 20 dB in 30 (77%) and < 10 dB in 16 (41%). A post-operative additional hearing loss > or = 10 dB occurred in 3 cases (10, 12.5 and 12.5 dB). There were no cases of post-operative deafness or facial palsy. This analysis shows that in many cases with an aberrant course of the facial nerve, stapedotomy using adequate and sometimes non-conventional techniques can give post-operative hearing improvement.