Patterns of hearing loss after microvascular decompression for hemifacial spasm

Background: The purpose of this study was to analyse audiological data after microvascular decompression (MVD) for hemifacial spasm (HFS), and to compare the data with hearing before surgery. Methods: Auditory functions were studied before and after surgery in 698 patients who underwent an MVD of the intracranial portion of the facial nerve for HFS. The results were expressed as the average of pure tone audiometry (PTA) and speech discrimination score (SDS). Results: 668 patients (95.7%) had no hearing loss immediately after surgery (group 1). 17 patients (2.4%) had a postoperative decrease in PTA exceeding 15 dB and a decrease in SDS which was proportional to the postoperative PTA thresholds (group 2). Eight patients (1.2%) had poor SDS that appeared to be out of proportion to the degree of hearing loss depicted by the postoperative PTA thresholds, suggesting retrocochlear or cochlear nerve pathology (group 3). Five patients (0.7%) had total deafness after surgery (group 4). In group 2, 12 patients (70.6%) returned to their preoperative hearing capacity. However, among the eight patients in group 3 and five in group 4, only two (25%) and none (0%) have returned to their preoperative hearing status, respectively. Conclusion: In this large study, permanent hearing loss occurred in 16 patients (2.2%). Patients with a mild hearing loss with a good SDS (cochlear type) demonstrated much better prognosis than those with poor SDS (retrocochlear type) or total deafness. In addition, total deafness after surgery had no chance of recovery to preoperative hearing capacity.