Preservation of hearing is an important goal for many patients with acoustic neuromas. The Gardner Robertson classification is a useful way to measure hearing, and is based on the Speech Discrimination Score (the percent of words identified on the hearing test at a certain volume), and the Pure Tone Average. We have classified our results on hearing preservation after Gamma knife radiosurgery in three different ways. These included
- maintenance of hearing within the same hearing class,
- preservation of hearing at a "useful" or "serviceable" level (Gardner-Robertson score of 1 or 2), and
- maintenance of some measureable hearing function.
Among 121 patients with testable hearing and >3 years of follow-up, hearing preservation rates were: 71% for Gardner-Robertson hearing level (1-4) preservation (keeping within the same hearing class), 74% for serviceable hearing (Gardner-Robertson 1 or 2), and 95% for any testable hearing.
Patients with the smaller, intracanalicular tumors tend to present with better hearing at the outset, and have a higher opportunity for hearing preservation. In this review, 25 patients with intracanalicular tumors had hearing preservation rates of 84 % for preservation of the same Gardner-Robertson hearing level, and 92 % for preservation of serviceable hearing.
Over time, there was some drop-off in hearing preservation in patients who were 10 or more years after radiosurgery. Serviceable or useful hearing (Class 1-2) was preserved in 60 of 106 evaluable patients with a 10-year actuarial preservation rate of 53.8 + 6.8%. Drop from Gardner Robertson grade 1 to grade 2 levels of hearing were seen in two patients beyond this timeframe (at 116 and 128 months after radiosurgery). Hearing improved by one class, 4 to 24 months post-radiosurgery in 5 patients. In one of these patients, hearing was eventually lost on later follow up. One patient improved in hearing from GR class 3 to GR class 1 at 19 months. Two patients who maintained class 1 serviceable hearing noted a subjective improvement in speech discrimination after radiosurgery. Preservation of any testable hearing by pure tone audiometry was accomplished in 174 of 184 patients with a 10-year actuarial preservation-rate for any testable hearing of 80.4 + 6.8%.
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