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Acoustic neuroma surgery as an interdisciplinary approach
  1. D G HARDY
  1. Department of Neurosurgery, Box 166, Level 2, Block A, Addenbrooke's Hospital, Hills Road, Cambridge CB2 2QQ, UK

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    For such a relatively rare tumour, acoustic neuroma continues to hold a remarkable fascination for both neurosurgeons and neuro-otologists. The Third International Conference on Acoustic Neuroma in Rome last June continued for 5 days!

    The early controversies in the management of acoustic neuromas were largely about the surgical approaches which might be used and about the outcome of facial nerve function. In this period the improved outcomes which could be achieved by utilising the combined expertise of otologists and neurosurgeons, were clearly demonstrated. Likewise, the advantages to be gained by monitoring facial nerve function were also firmly established. More recently, controversy has shifted to the question of hearing preservation and, in particular, to the unresolved problem of what constitutes “useful” hearing. The place of intraoperative brain stem auditory evoked response (BAER) audiometry in improving hearing outcomes is still uncertain, largely because of the known difficulties in obtaining reliable recordings. However, on empirical grounds it is likely that if hearing preservation rates are to improve, BAER audiometry will play a significant part in this improvement. The paper1 by Tonn et al in this issue (pp 161–166) once more emphasises the benefits of interdisciplinary teamworking. It also indicates that BAER monitoring may indeed have a part to play in improved hearing outcomes. However, it also raises other perhaps more interesting questions. The series is large and the analysis of the patient material indicates that 78.5% of the series had “good” hearing preoperatively (grade 1–3 on the Gardner-Robertson scale). This is a remarkably high proportion of patients with “good” preoperative hearing. In the Cambridge series (now 725 patients) the number of patients who have “good” preoperative hearing are in a substantial minority. Most of our patients have had either “dead” ears or very poor hearing. This is a significant difference and I suspect that it reflects the unsatisfactory level of delay inherent in current United Kingdom practice for the management of acoustic neuromas. In this country, when patients first become aware that something may be wrong, they go in the first instance to their general practitioners, then, often after a substantial wait, are referred to and eventually seen by an ear, nose, and throat surgeon. By the time the necessary investigations have been performed, the various results assembled, and an appointment made further time has elapsed. Referral onwards to the “acoustic team” may involve significant further delay. When a decision to operate has eventually been made, a further period of delay on a waiting list may then occur. By the time the patient eventually comes to surgery the hearing has not infrequently by then deteriorated to the level at which any efforts directed to its preservation are usually pointless. This is clearly very unsatisfactory. In Germany, as in most developed countries elsewhere, they do things differently and such delays are not inherent in their systems. The system we have adopted in the United Kingdom is often euphemistically described as “gatekeeping” but in fact acts as a covert form of “rationing” and is clearly to the detriment of our patients. If in the United Kingdom we are to improve our rate of hearing preservation, a first step must be to treat the continuing risk to hearing as a matter of some urgency. It must be better for our patients if we are able to eliminate the various delays between initial presentation and surgery. Wherever possible we should be able to intervene while acceptable levels of hearing are still present.

    The controversy about how to measure “acceptable” hearing continues. The use of the term “good” or “useful” hearing is no longer acceptable and, if used in scientific papers, a clear definition of what is meant by the term should also be set out. In our paper,2 the difficulties of comparative assessment of hearing results are set out. It is now, I think, generally accepted that concepts, such as “serviceable hearing” or “good functional hearing” are insufficiently accurate to serve as useful comparators for results. It is generally agreed among British otologists and neurosurgeons that a less than 30 dB loss on pure tone audiogram and a speech discrimination score of 70% or more represents the best definition of “good”, “serviceable”, “good functional” or “socially useful” hearing and I would make a plea for this definition to be accepted as the gold standard for these terms. If such criteria are used then the number of cases with “good” or “socially acceptable” preoperative hearing is likely to be much fewer than reported in most recent series and the postoperative outcomes will be correspondingly somewhat worse. Unless preoperative and postoperative hearing results are reported in this objective manner comparison of hearing outcomes becomes very difficult. All papers which do not report their results in this manner should now perhaps carry a “government health warning”.

    In our series, under these strict criteria, our postoperative hearing preservation rate is poor (less than 5%). The only preoperative factor that predicted a favourable hearing preservation outcome was the presence of normal preoperative BAER morphology. The outcomes in the paper by Tonn et al seem substantially better but direct comparisons are not possible as audiological and speech discrimination results are not explicitly given. However, it may nevertheless be correct that our hearing preservation results are indeed poorer than those of our more progressive neighbours. In surgery great technical breakthroughs are rare: the usual method of progress is by incremental improvements applied to a multiplicity of separate factors but it is much easier to identify those factors which might count if we have clear and comparable reporting criteria beforehand. It is also true that we should not first shoot ourselves in the foot by accepting such long delays before embarking on our surgery so that the exercise has already become pointless.


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