The question pertains to the ''Gardner-Robertson Hearing Scale'' used to grade hearing after gamma knife radiosurgery for acoustic neuromas.
Please realize that the Gardner-Robertson Hearing Scale is one of many such tools used to evaluate any treatment for acoustic neuromas, including observation only with MRI follow-up, gamma knife radiosurgery, or the gold-standard microsurgical removal of these tumors.
This scale is very simple, easy to employ, and can be used to compare various treatment modalities. The most important factor in the evaluation of hearing after the gamma knife, or any type of radiotherapy, is the timing of the hearing assessment. While changes in hearing, related to microsurgery, occur from the time of surgery to a few months, the effects of radiation on the cochlear nerve or the cochlear blood supply may be delayed for months or even years. Thus, the use of the Gardner-Robertson Scale to evaluate hearing results after gamma knife treatment of acoustic neuromas must be serial, and over a long (7 years) period of time. This holds true for any treatment modality rendered.
