Vestibular schwannoma

C P Yu 余仲平, S C L Leung 梁昌倫

Dear Editor,

We read with interest the article entitled "Vestibular schwannoma" published in the Volume 22 December 2000 issue of The Hong Kong Practitioner. We strongly disagree with the author's view that "the role of stereotactic radiosurgery in the management of vestibular schwannoma is not yet defined".

For acoustic neuromas (synonymous with vestibular schwannoma), the role of Gamma Knife radiosurgery has been well documented by large scale clinical studies with scientific methodology and long term follow up as published in prestigious peer reviewed journals.^2-7,9

It is now clear that Gamma Knife radiosurgery using high resolution neuro-imaging and sophisticated planning sofeware has raised the bar of excellence. Recent studies, including one from Hong Kong, confirm Gamma Knife induces tumour shrinkage or negative growth rather than by growth control alone.^6,9 The most recent analysis as published in the January 2001 issue of Journal of Neurosurgery, entitled "current results of radiosurgery for acoustic neuromas" summarises the current status: tumour control, 97%; facial neuropathy, 1%; trigeminal neuropathy, 2.6%; hearing preservation, 91%, with zero mortality and procedural related morbidity.²

We strongly believe microsurgery and Gamma Knife radiosurgery are complimentary to each other. For small tumours, advocates of open surgery must show their results are at least as good as those of Gamma Knife radiosurgery. Best results of open surgery come from centres of excellence where hundreds of patients are treated per year. In this context, direct comparison of published local experience is much more relevant.

Finally, we also disagree with the suggestions of conservative treatment of symptomatic acoustic neuromas. Most reports on natural history of acoustic neuromas used linear rather than 3D volume measurements. These studies showed tumours either do not grow or grow at a "very slow rate of 1 mm per year". We argue that their methodology underestimated the growth rate. For a 1 cm tumour, an increase in linear dimension by 1 mm equates to 30% increase in volume.⁹ There is also evidence to suggest conservative management of acoustic neuromas stands the risk of losing serviceable hearing.^1,8 At present, both microsurgery (not the trans-labyrinth approach which destroys hearing) and Gamma Knife radiosurgery have preservation of hearing as a realistic goal. The minimal invasive Gamma Knife approach may be preferred as compared to conservative treatment in selected patients who cannot afford to lose their hearing.

Authors' Reply

M C F Tong 唐志輝, J M K Lam 藍明權, C A van Hasselt 尹懷信, W S Poon 潘偉生

Dear Editor,

The Update Article on "Vestibular Schwannoma" was presented to The Hong Kong Practitioner for readers who seldom encounter the condition aiming to raise awareness and consequent timely diagnosis of a common but easily missed tumour. Details of management, surgical approaches and controversies were deliberately set aside.

The senior authors (M C F Tong and C A van Hasselt) welcome comments from colleagues with experience of managing these patients, particularly in the local setting, and acknowledge the success and popularity achieved with the gamma knife programme in Hong Kong. Dr Yu and Dr Leung have correctly alluded to three controversial areas in the management of these patients, namely the use of stereotatic radiosurgery (in the form of gamma knife or the more recently available linear accelerator based delivery system), the surgical approach and conservat ive management in selected patients.

As pointed out in our article, the management of vestibular schwannomas continues to evolve with the passage of time. Centres with recognised expertise with whom we have close communication, have over the years developed certain well defined approaches and outcomes that have inspired us to attempt to achieve the same level of excellence in Hong Kong. Firstly, a multidisciplinary approach cannot be dismissed. Secondly, the availability of multi-modal therapy for these patients has to be acknowledged as advantageous. Thirdly, surveillance and audit of long-term follow-ups in these patients is extremely important and are being undertaken in these centres.

In the Prince of Wales Hospital, a team involving neurosurgeons, otologists, neuroradiologists, radiation oncologists, neuro-anaesthesiologists, audiologists, speech therapists and other supporting staff work together with the primary objective to achieve the best outcomes for these patients. All management modalities including hearing preservation and translabyrinthine surgery, stereotatic radiosurgery and observation of tumour growth are available and selected based upon a patient-centred approach. In many fields of medicine, particularly so in surgery, the same disease can well be managed by different approaches with very similar overall outcomes. This is no different in the management of patients with vestibular schwannoma especially with the increasing ease of diagnosis. There are always both advantages and disadvantages for each treatment modality. We are of the opinion that The Hong Kong Practitioner is not the appropriate vehicle in which to detail the management of vestibular schwannoma. As members of the management team we are always willing to provide information to patients with the condition. We suggest interested readers search the available literature to find evidence relevant to management on the subject. We feel that the team approach for the management of this condition should be strongly promoted, but not a single treatment modality.