The patterns and risk factors of hearing loss following microvascular decompression for hemifacial spasm.
OBJECTIVE
The aim of this study was to reveal the risk factors including intraoperative brain stem auditory evoked potential (BAEP) changes and to define parameter and warning values of BAEP beyond which the probability of hearing impairment rises significantly.


METHODS
From April 1997 to February 2009, 1156 patients underwent microvascular decompression (MVD) for hemifacial spasm (HFS) and their medical records and audiologic data. The intraoperative BAEP monitoring was performed in all operations during surgery from the time of administration of general anesthesia until the time of skin closure. Pure tone audiometry (PTA) and Speech Discrimination Score (SDS) were performed on all patients before and after surgery for categorizing the patterns of hearing loss. There were 825 females and 331 males with a mean age of 48.7 years (range 17-75 years). The mean symptom duration was 67.8 months (range 1-420 months).


RESULTS
At the 1-year follow-up examination, 1091 (94.4%) patients of the total 1156 patients exhibited a cured state, and 65 (5.6%) patients had residual spasms. Hearing loss occurred in 46 patients (3.9%). In 26 patients, PTA was decreased more than 15 dB with a proportional decrease of the SDS. In 10 patients, poor SDS without hearing loss occurred. Total deafness was developed in 10 patients. A higher incidence of BAEP change and a poor recovery especially amplitude in wave V during surgery was observed in patients with poor SDS (eight patients) and total deafness (seven patients) (p =  0.000). Reduction of amplitude more than 50% in wave V was a strong indicator for a worse outcome of the hearing capacity. The difference in other risk factors according to hearing loss pattern was not statistically significant (p  >  0.05). Only female was significant (p = 0.005).


CONCLUSIONS
The intraoperative BAEP change and a poorer recovery, especially reduction of amplitude more than 50% in wave V, was a strong indicator for a worse outcome of the hearing capacity. Vigilant intraoperative monitoring of the BAEP and adequate steps for recovery of the BAEP change could prevent hearing loss after MVD for HFS.
Department of Neurosurgery, Samsung Medical Center, Sungkyunkwan University School of Medicine, 50, Irwon-dong, Gangnam-gu, Seoul, 135-710, South Korea.
Kwang-Wook
KW
Jo
Jong-Won
JW
Kim
Doo-Sik
DS
Kong
Sung-Hwa
SH
Hong
Kwan
K
Park
D000293:Adolescent; D000328:Adult; D000368:Aged; D000369:Aged, 80 and over; D019299:Decompression, Surgical / Q000009:adverse effects* / Q000401:mortality; D005260:Female; D034381:Hearing Loss / Q000209:etiology* / Q000503:physiopathology / Q000517:prevention & control; D019569:Hemifacial Spasm / Q000503:physiopathology / Q000601:surgery*; D006801:Humans; D008297:Male; D008866:Microsurgery / Q000009:adverse effects* / Q000401:mortality; D008875:Middle Aged; D019635:Neurosurgical Procedures / Q000009:adverse effects* / Q000401:mortality; D012189:Retrospective Studies; D014656:Vascular Surgical Procedures / Q000009:adverse effects* / Q000401:mortality; D055815:Young Adult