Acoustic neuroma

Radiotherapy has long been used in benign conditions, e.g. glomus tumours and angiofibroma of the nasopharynx. More recently, radiotherapy has been used in the treatment of acoustic tumours. An external beam can be accurately focussed using a stereotactic system, to which the names gamma knife or x-knife are given, depending on the radiation source. Proponents of this system refer to it as radiosurgery and to themselves as radiosurgeons.

It is the purpose of this article to review the current literature and to compare the reported results of radiotherapy with the results of surgery carried out by one surgeon working with various co-surgeons* at St Vincent's Hospital, Sydney over a 12 month period, namely January to December, 1997.

Materials and Methods

A retrospective review was made of cases of internal auditory canal (IAC) and cerebello-pontine angle (CPA) tumours operated as a co-surgeon or wholly by the senior author (PAF) during the period January 1997 - December 1997. Facial function and hearing results were assessed and the complications of surgery tabulated.

The great majority of acoustic tumour surgery was carried out using the translabyrinthine approach. Middle fossa surgery and retrosigmoid surgery were reserved for small tumours with good hearing.

The period of review was chosen to coincide in part with the Fellowship at St Vincent's Hospital of one of the authors (SAA).

Results

Sixty seven patients had surgery for tumours of the cerebello-pontine angle and internal auditory canal. In 53 of these, the diagnosis was acoustic neuroma (AN). There were 4 patients with meningioma and 10 with other diagnoses (Table 1).

The size distribution of the acoustic tumour group is shown in Figure 1. Tumour size was graded as intracanalicular, small (cerebello-pontine angle (CPA) extension less than 1.5cm), medium (CPA extension 1.5 cm to less than 3.0cm), and large (3.0cm +). Overall, there were only 6 intracanalicular tumours and 9 less than l.5cm in the CPA. The largest tumour measured 5.Scm in the CPA and the mean tumour size was 2.3cm. Of the total, 23 extended 2.4cm or more into the CPA.

Facial nerve results are illustrated in Figures 2, 3, 4 and 5. The anatomical integrity of the facial nerve was maintained in 100% of cases. Overall, 48 cases (90%) were House and Brackmann Grades I and II and 4 cases (8%) were Grade III. There was only one patient with a House and Brackmann Grade IV result (Figure 6). This patient's tumour measured 3.Ocm in the cerebello-pontine angle.

With small tumours (less than l.Scm in the CPA), there was no long term facial result worse than House and Brackmann Grade II. One patient in the intracanalicular group, where hearing was normal after surgery, had a House and Brackmann Grade III result at 12 months.

Hearing preservation was attempted in 10 patients. These were intracanalicular or small tumours. Hearing preservation is defined as being within 15dB of the preoperative level in the speech frequencies, with speech discrimination above 75% (Table II). Five patients (50%) fulfilled these criteria.

One patient, after middle fossa surgery, developed minimal temporal lobe symptoms which resolved with steroid treatment and short-term anti-convulsants. There was one pulmonary embolus with no sequelae. One patient, with a 5.Scm tumour, had a radial nerve palsy following prolonged anaesthesia. Complete recovery occurred.

There were five CSF leaks (9%) of which four were managed conservatively with lumbar drainage and one required re-exploration. There were no other major neurological sequelae.

Discussion In the management of benign tumour, it is important to know the natural history of the untreated disease. In the past, tumours presented with signs of papilloedema and raised intracranial pressure (House 1964) and small tumours were rarely diagnosed. The devastation wrought by large tumours is best depicted by Sir Charles Bell (Bell 1830) who described the march of symptoms from the fifth and seventh cranial nerves, to headache of classic raised pressure type to the death of the patient "from difficult respiration and want of the power of swallowing".

The post mortem incidence of small acoustic tumours is of the order of 1% (Leonard and Talbot 1970, Stewart et al 1975) but even with modern imaging, the clinical incidence of diagnosed acoustic tumour is only about 12 per million (Tos and Thomsen 1991).

Tumour Size

It is known that some tumours do not progress (Cox 1993) and some authors have elected to pursue a conservative course with serial imaging (Glasscock et al 1997, Wiet et al 1995). These authors have shown that over periods of up to nine years, there was no growth in 20 out of 34 (76%) and in 32 out of 53 (60%) respectively. Bederson et al (1991) found that in 70 patients followed for one year, there was no detectable growth on CT scan in 49%. Of these, 18 were followed for a second year and only one of these showed tumour growth.

In the most recent study on tumour growth (Fucci et al awaiting publication), an expectant policy was adopted in 119 patients. Of these, 36 (30%) showed continued growth but 79 (66%) showed no growth over periods ranging from five months to eight years. Tumours greater than 20mm in diameter at presentation had a much greater likelihood of growth than did smaller tumours and of these, growth was noted early during the period of observation. These authors therefore recommend that if an expectant policy is to be adopted, the first imaging takes place at six months and thereafter at longer intervals. Rapid tumour growth is rare but is well documented (Forer and Fagan 1987).

Further, it is known that some tumours, perhaps as many as 8%, spontaneously involute (Luetje et al 1988, Charabi et al 1995, Strasnick et al 1994, Rosenberg et al 1993). This is summarised in Table III.

Tumour growth rates can be measured by immunohistochemical methods (Lesser et al 1991) and by Flow Cytometric analysis (Kesterton et al 1993). These studies confirm that tumour growth rates can vary to a great degree and that some exhibit no growth over long periods.

An early report from the Karolinska Institute (Noren et al 1983) showed that after radiotherapy 57% of tumours were reduced in size by amounts as little as lmm. In 21%, the tumours increased in size and 14% showed no change. Radiotherapy dosages in this study were large (25-35 Gy to the tumour margin). Such a radiation dose is associated with an unacceptably high rate of cranial nerve lesions and other complications (Pollock et al 1995). Further, brainstem injuries have been reported (Brackmann and Kwartler 1990). It was these experiences and the knowledge that complications were related to radiotherapy dose and treatment volume which lead to dosage reduction both at the periphery and centrally (Noren et al 1992, 1993, Linskey et al 1992). The initial results of these later series, with regard to progression in tumour size, are similar to earlier reports but no intermediate or long-term follow-up is available.

The effect of radiotherapy on tumour size is documented in Table IV and is to be compared to the changes in untreated tumours (Table III).

In a recent publication (Tomasevic et al 1998), 34 tumours were treated by radiotherapy and 26 of 27 patients showed no progression with a follow-up period between 0 and 65 months. These authors initially used a dosage of 14-20.5 Gy, later reduced to 16-18 Gy. They refer to associated brainstem complications, not discussed. They state that, in future, tumours abutting the brainstem will be treated with fractionated stereotactic radiation, that is, multiple treatments which deliver the same total dosage.

Radiotherapy has been suggested as a treatment for small tumours. Most surgical authorities measure that portion of the tumour which is in the cerebello-pontine angle, unless the tumour is confined to the internal auditory canal when it is called intracanalicular and the dimensions can be given. On the other hand, most radiotherapists (Sekhar et al 1996), including Tomasevic et al (1988) include the length of the internal auditory canal in tumour measurement. The internal auditory canal measures some 10.6mm +/-2.2mm (Sakashita and Sando 1995) and is shown measured in Figure 7. In Figure 8, a medium tumour, measuring 2.1cm in the cerebellopontine angle, is shown. When the length of the internal auditory canal is included, this small tumour assumes the more formidable dimensions of 3.2cm (Figure 9).

Smee (1995) has advocated radiotherapy for tumours as large as 3.Scms. When, however, allowance for the IAC is made, such a tumour will have a projection of 2.4cm in the CPA which is little bigger than the mean tumour size (2.3cm) of the series under review. In the present series, 23 were 2.4cm (CPA) or larger.

The aim of radiotherapy is cessation of tumour growth. Viable cells with the potential for growth probably always remain (Anniko et al 1981) so that the final word can be written only after 20 years, or more, of follow up. It must therefore be concluded that the current reports of the effect of radiotherapy on progression of tumour size are presently meaningless in the context of the studies of the natural history of the growth of acoustic neuromata and must await long term follow up. Further, when a comparison of results, particularly of the facial nerve, is made, it should be between tumours of similar size, and allowance must be made for different methods of tumour measurement.

Facial Nerve Function

Most surgeons use the House and Brackmann grading of facial function (House and Brackmann 1985), but not all radiotherapists are so specific, using terms such as neuropathy, which is of uncertain meaning.

In an early report (Noren et al 1983), in which a large dose of radiation was used in some 14 patients, facial nerve dysfunction occurred in 38%. As radiation dose was reduced (Noren et al 1993), facial nerve weakness occurred in 17%, but there were still 7% in Grade IV and 4% in Grades V-VI.

Mendenhall et al (1994) report that of 32 patients, 5 developed a facial paralysis. Three made a partial recovery and 2 made no recovery. If this is so, it means that 6% of this series of small tumours had a final House and Brackmann Grade VI result.

Pollock et al (1995), using a reduced dosage, reports 83% Grade I and 9% Grade II for a total Grades I and II of 91% but there were 6% Grade III and 2% Grade IV. Tomasevic et al (1998) do not report their House and Brackmann grading but there is a reported incidence of facial neuropathy in some 24% of patients. Final results are not given.

Ito et al has reported a 22% incidence of facial palsy (Ito et al 1996). These authors noted that, unlike surgery, a facial nerve paralysis is of late onset and does not improve with time, which experience differs from that of Tomasevic et al who report that "neuropathies often improved, at least to some extent".

It would seem from these results that with the possible exception of one series (Pollock 1995) which deals with smaller tumours, all other radiotherapy results are worse than those in the present surgically treated series of tumours of all sizes. This experience does not differ from those reported in other specialised surgical centres (Uziel et al 1993, Slattery and Brackmann, 1995). However, it is to be noted that the follow up period in recent publications where a low dosage of radiotherapy is used is, of necessity, short. As radiotherapy induced facial paralysis is of late onset and probably does not improve with time, it will be necessary to ascertain long term facial results before a valid comparison can be made. Further, the facial nerve results of surgery, after failed radiotherapy, would seem to be very poor (Slattery and Brackmann 1995, Thomsen and Tos 1997). It is likely therefore that long term radiotherapy results will be significantly worse than those currently published.

It is well known that facial weakness after surgery, almost always of rapid onset, continues to improve for 18 months. In the series presented, follow up is not complete and it is likely that the worst results (House and Brackmann Grades III and IV) will improve further.

The results of surgery for large tumours should be particularly noted. There were 13 such tumours in the present series. The worst facial nerve result was a single House and Brackmann Grade IV, and 11 were House and Brackmann Grades I and II (85%). The MR studies of two of these patients are shown (Figures 10 and 11). In particular the gross hydrocephalus seen in Figure 11 is to be noted. Following tumour excision in each case, facial function is normal and apart from the expected total hearing loss, there were no other permanent neurological sequelae.

Hearing Preservation

Claims for hearing preservation are made in radiotherapy publications. Noren et al (1992) report that in patients with good hearing, at 4 years 11% had adequate hearing. Tomasevic et al (1998) have shown that 26% of patients lost hearing immediately after radiotherapy. No other follow up is given nor is there any audiological data.

It is very difficult to compare hearing preservation results because of a lack of uniformity in reporting. Further, claims of hearing preservation are made even when hearing is as bad as 90dB pre-treatment (Noren 1993). These authors show that 22% were unchanged at one year. Linskey et al (1992), in a series of 87 patients, had 20 with hearing of Grade I and II (Gardner and Robinson classification 1988) prior to treatment. After treatment, there were 7 patients (35%) in these grades and indeed only 4 of 12 (33%) in Grade I which is 0-30dB. Most otologists would not regard Gardner and Robinson Grade II (31-50dB) as a satisfactory result, especially if it is to be compared to a normal contra-lateral ear.

Weber and Gantz (1996) reported that in patients operated on via the middle cranial fossa approach, there was a hearing preservation rate of some 60%. Similarly, Slattery et al (1997) had a hearing preservation rate of 68% in some 151 patients. In Neurofibromatosis Type II (NFI) when tumours are small, hearing preservation is of the order of 65% with 48% of the total being within 15dB (PTA) of the pre-operative level and within 15% of the pre-operative speech discrimination score (Slattery et al 1998).

In the present series of some 10 patients with very good hearing who underwent a hearing preservation procedure, either by the middle cranial fossa or posterior fossa approach, hearing was preserved in 5 (45%) and this experience is similar to previous studies (Beaumont and Fagan 1989).

Radiotherapy has been advanced as a treatment for patients in an only hearing ear and in Neurofibromatosis (Tomasevich et al 1988).

When small tumours with good hearing are treated surgically, at least 30% and up to 50% of the patients will lose hearing. The hearing results after radiotherapy are at least as poor and the risk of total hearing loss one year after treatment can be 65% (Flickinger et al 1993). Given this, to advocate any immediate treatment in a small tumour in an only hearing ear is contentious at best. Tomasevic et al (1998) have treated three patients with NFII. The size of these tumours is not given nor is it reported if any of these patients have been rendered anacoustic by their treatment.

Complications

Post-treatment hydrocephalus occurs in a significant number of tumours after radiotherapy. The number of patients requiring ventriculo-peritoneal shunting has been variously reported by Noren et al (1983) as 14% and Pollock et al (1995) as 13%. Others report lower rates (Noren 1993 3%, Linskey et al 1992 5%). The need for shunting after microsurgical removal is virtually unknown (Thomsen et al 1990).

Trigeminal nerve dysfunction has a significant incidence after radiosurgery (Noren et al 1992 20%; Mendenhall et al 1994 19%; Flickinger et al 1991 29%; Linskey et al 1992 32%). Subarachnoid and intraventricular haemorrhage have also been reported (Park et al 1995) but the outcome of this major event is not discussed. Further, these authors report a death from the complications of hydrocephalus. Balance dysfunction also persists in up to 31% of patients after radiosurgery (Linskey 1992).

Brainstem Implantation

Of recent times, a world-wide trial of the Auditory Brainstem Implant (ABI) has been undertaken (Portillo et al 1993, Otto et al 1990, Otto and Staller 1995, Laszig et al 1995). Results are very encouraging (Briggs et al 1994), being similar to those obtained with the early Cochlear Implant, the single-channel House/3M device (Rosen et al 1989). In those patients in whom the ABI has been used following failed radiotherapy, none have been successful (Slattery and Brackmann 1995) so that prior radiotherapy has become an accepted contraindication to the use of the Auditory Brainstem Implant.

Recurrences and Further Surgery

The claimed advantages of radiotherapy are the short hospital stay, hearing preservation, no mortality and decreased facial nerve morbidity but, with the exception of the first, the claims do not stand examination. Further, initial equipment costs, the very long follow up needed, and repeated short interval imaging makes claims of decreased cost hard to substantiate. This point is of particular importance as there is no long term follow up available for those patients treated with reduced doses of radiation, and subsequent surgery may well be required. This possible requirement for surgery after failed radiotherapy is to be contrasted with the recurrence rate of acoustic tumour after translabyrinthine surgery. Slattery and Brackmann (1995) report a recurrence rate of only 0.2% in over 3,000 tumours. Results of the St Vincent's Department mirror this experience on a smaller scale.

The experiences of Thomsen and Tos (1997) also bear consideration. Ten patients were referred for radiotherapy, 4 with unilateral tumours and six with bilateral. Three of the unilateral tumours continued to grow, lost the hearing, and had to be operated with poor facial results. The fourth lost the hearing, developed hydocephalus and required shunting. Of the 12 tumours in the NFII group, 2 had growth arrested. Of the 12 ears involved, 11 lost hearing, all but 2 tumours continued to grow, and 1 patient developed a malignant transformation.

Malignant transformation

Malignant schwannoma is extremely rare with only 4 cases being reported up to 1994 (Gruber et al 1994). However, Chang and Kamerer (1997), report what is probably a malignant transformation. A 3cm tumour treated with 34 Gy significantly decreased in size and lay dormant for some six years until the patient rapidly developed facial paralysis. A 4cm tumour was found on imaging. The histological specimen was characterised by high cellularity and high mitotic activity. The authors believe that this was malignant from the outset, but histological proof is lacking. This may be the same case reported by Comey et al (1998) from the University of Pittsburg. However, Chang and Kamerer are not acknowledged in the later presentation. Comey et al (1998) report a further unpublished case presented by Kurita et al at the 1997 Meeting of the International Stereotactic Radiosurgery Society in Madrid, Spain.

Conclusions

1. Radiotherapy, advocated as a means of treatment for small acoustic tumours, produces facial nerve results which are inferior to those of surgery.

2. Long term facial nerve results after radiotherapy are worse than the published figures due to the noninclusion of those patients who require salvage surgery.

3. Surgery leads to cure by total disease removal. After radiotherapy, life long follow up is required.

4. There is, by consensus, no place for radiotherapy in the treatment of large tumours.

5. No intermediate or long term follow up is available for patients treated with reduced dosage radiotherapy.

6. Cases suggestive of malignant transformation after radiotherapy have been reported.

7. There is a definite place for an expectant policy in small tumours. Small tumours in the older age group are particularly likely to remain stable.

8. If an expectant policy is adopted, the first imaging study should be carried out at six months.

9. Hearing preservation results after radiotherapy are at least as bad as surgery and are probably worse.

10. Radiotherapy is contraindicated in patients with NFII. Those with serviceable hearing are likely to lose it. Prior radiotherapy is a contraindication to the ABI.

11. Proponents of radiotherapy are urged to include audiological data and an accepted facial nerve classification e.g. House and Brackmann in reporting their results.

In summary, the authors of the present paper agree with Tomasevic et al (1998) and with the National Institutes of Health Consensus Conference on Acoustic Neuroma (1994) that microsurgical removal is the treatment of choice. Radiotherapy should be limited to those few cases where treatment is required, but where the surgical risks are considered to be excessive, the exception being very large tumours. However, if a tumour is small, a valid question is whether treatment is warranted. In the light of the natural history as discussed, it may well eventuate that many more patients with small tumours will undergo a period of observation before treatment of any sort, is undertaken.

References

ANNIKO M., ARNDT J., NOREN G. (1981) The Human Acoustic Tumour in Organ Culture II. ACTA Otolaryngol. 91, 223-235.

BEAUMONT C.I., FAGAN P.A. (1989) Hearing Preservation in Cerebello-Pontine Angle Surgery: An ongoing Study. In Neurological Surgery of the Ear and Skull Base, Proceedings of Sixth International Symposium, Zurich. Ed. by Fisch U., Valvanis A., Yasargil M.G., Kugler, Gherdini. Amsterdam. 217-226.

BEDERSON J.B., VON AMMON K., WERNER W.W.,

YASERGIL M.G. (1991) Conservative Treatment of Patients with Acoustic Tumours. Neurosurg. 28, 646-651. BELL C. (1830) The Nervous System of the Human Body. Appendix of Cases, London. In ed Cushing H. (1917) Tumours of the Nervous Acousticus and the Syndrome of the cerebello-pontine angle. W.B. Saunders Company, Philadel.

BRACKMANN D., KWARTLER J.A. (1990) Treatment of

Acoustic Tumours with Radiotherapy. Arch. Otolaryngol. Head Neck Surg. 116, 161-162.

BRIGGS R.J., BRACKMANN D.E., BASER M.E., HITSELBERGER W.E. (1994) Comprehensive management of bilateral acoustic neuromas. Arch. Otolaryngol. Head Neck Surg. 120, 1307-1314.

CHANG C.Y.J., KAMERER D.B. (1997) Stereotactic Radiosurgery for Acoustic Neuromas. In Acoustic Tumours: Diagnosis and Management. 2nd Ed. House W.F., Luetje C., Doyle K.J. Eds. Singular Publishing Group Inc., San Diego, London 309-346.

CHARABI S., THOMSEN J., MANTONI M., CHARABI B.,

JORGENSEN B., BORGENSEN S.E., GYLDENSTED C., TOS M. (1995) Acoustic Neuroma (Vestibular Schwannoma): Growth and Surgical and Non-Surgical Consequences of the Wait and See Policy. Otolaryngol. Head Neck Surg. 113, 5-14.

COMEY C.H., McLAUGHLIN M.R., JHO H.D., MARTINEZ A.J., LUNSFORD L.D. (1998) Death from a Malignant Cerebello-pontine Angle Triton Tumour, Despite Stereotactic Radiosurgery. J. Neurosurg. 89, 653-658.

COX G.J. (1993) Intra-canalicular acoustic neuromas: a conservative approach. Clin. Otolaryngol. 18, 153-154.

FLICKINGER J.C., LUNSFORD L.D., COFFEY R.J., LINSKEY M.E., BISSONETTE D.J., MAITZ A.H., KONDZIOLKA D. (1991) Radiosurgery of Acoustic Neuromas. Cancer 67, 345-353.

FLICKINGER J.C., LUNSFORD L.D., LINSKEY M.E. (1993) Gamma Knife Radiosurgery for Acoustic Tumours: Multivariate Analysis of Four Year Results. Radiother. Oncol. 27, 91-98.

FORER M., FAGAN P.A. (1987) Acoustic Tumour in a Young Adult : Documented Growth Rate. AJO 8:2, 108-110.

FUCCI M.J., BUCKMAN C.A., BRACKMANN D.E., BERLINER K.I. (awaiting publication) Acoustic Tumour Growth: Implications for Treatment Choices. American Neuro-Otologic Society, West Palm Beach, Florida 10/5/98.

GARDNER G., ROBERTSON J.H. (1988) Hearing Preservation in Unilateral Acoustic Neuroma Surgery. Am. Otol. Rhinol. Laryngol. 97, 55-66.

GLASSCOCK M.E. III, PAPPAS Jr. D.G., MANOLIDIS S., VON DOERSTEN P.G., JACKSON C.G., STORPER I.S. (1997) Management of Acoustic Neuroma in the Elderly Population. Am. J. Otol. 18, 236-242.

GRUBER B., PETCHENIK L., WILLIAMS M., THOMAS C., LUKEN M.G. (1994) Malignant Vestibular Schwannoma. Skull Base Surgery 4, 227-231.

HOUSE J.W., BRACKMANN D.E. (1985) Facial Nerve Grading System. Otolaryng. Head Neck Surg. 93, 146-147. HOUSE W.F. (1964) Acoustic Neuroma (Monograph) Arch. Otolaryngol. Head Neck Surg. 80, 598-757.

ITO K., KURITA H., SUGASAWA K., OKUNO T., MIZUNO M., SASAKI T. (1996) Neuro-otological findings after radiosurgery for acoustic neurimonas. Arch. Otolaryngol. Head Neck Surg. 122(11), 1229-33.

KESTERSON L., SHELTON C., DRESSLER L., BERLINER K.I. (1993) Clinical behaviour of acoustic tumours. A flow Cytometric analysis. Arch. Otolaryngol. Head Neck Surg. 119(3), 269-71.

LASZIG R., SOLLMANN W.P., MARANGOS N., CHARACHON R., RAMSDEN R. (1995) Nucleus 20-channel and 21-channel auditory brain stem implants: first European experiences. Ann. Otol. Rhinol. Laryngol. Supplement. 166, 28-30.

LEONARD J.R., TALBOT M.L. (1970) Asymtomatic acoustic neurilemmoma. Arch. Otolaryngol. 91, 117-124.

LESSER T.H.J., JANZER R.C., KLEIHUES P., FISCH U. (1991) Clinical Growth Rate of Acoustic Schwannomas, Correlation with

the growth fraction as defined by the monoclonal antibody Ki-67. Skull Base Surgery 1, 1-15.

LINSKEY M.E., LUNSFORD L.D., FLICKINGER J.C., KONDZIOLKA D. (1992) Stereotactic radiosurgery for acoustic tumours. Neurosurg. Clin. North Am. 3, 191-205.

LUETJE C.M., WHITTAKER C.K., DAVIDSON K.C., VERGARA G.G. (1988) Spontaneous Acoustic Tumour Involution. OtolaryngoL Head Neck Surg. 98, 95-97.

MENDENHALL W.M., FRIEDMAN W.A., BOVA F.J. (1994) Linear Accelerator-based Radiosurgery for Acoustic Schwannomas. Int. J. Radiat. OncoL Biol. Phys. 28, 803-810. National Institutes of Health Consensus Development Conference Statement, December 1994, Arch. Neurol. 51:2, 201-207.

NOREN G., ARNDT J., HINDMARSH T. (1983) Stereotactic radiosurgery in cases of acoustic neurinoma : further experiences. Neurosurg 13, 12-22.

NOREN G., GREITZ D., HIRSCH A., LAX I. (1992) Gamma knife radiosurgery in acoustic neurinomas. In: Tos M., Thomsen J. eds. Proceedings of the first International Conference on Acoustic Neuroma. Amsterdam: Kugler: 289-92.

NOREN G., GREITZ D., HIRSCH A., LAX I. (1993) Gamma knife surgery in acoustic neuromas. Acta Neurochi. SuppL (wein) 58, 104-7.

OGUNRINDE O.K., LUNSFORD L.D., FLICKINGER J.C., KONDZIOLKA D. (1994) Facial Nerve Preservation and Tumour Control after Gamma Knife Radiosurgery of Unilateral Acoustic Tumours. Skull Base Surg. 4, 87-92.

OTTO S.R., HOUSE W.F., BRACKMANN D.E., HITSELBERGER W.E., NELSON R.A. (1990) Auditory brain stem implant: effect of tumour size and preoperative hearing level on function. Ann. Otol. Rhinol. Laryngol. 99 (10 Pt 1), 789-90.

OTTO S., STALLER S. (1995) Multichannel auditory brain stem implant: case studies comparing fitting strategies and results. Ann. Otol. Rhinol. Laryngol. - Supplement 166, 36-9.

PARK Y.G., CHUNG S.S., KIM D.I., CHANG J.W., CHO J. (1995) Complications following Gamma Knife Radiosurgery. Proceedings of the 1994 meeting of the Leksell Gamma Knife Society, Kyoto, Japan published in Stereotact. Funct. Neurosurg. 64: (Suppl 1), 239-48 Karger A.G. Basel.

POLLOCK B.E., LUNSFORD L.D., KONDZIOLKA D., FLICKINGER J.C., BISSONETTE D.J., KELSEY S.F., JANNETTA P.J. (1995) Outcome Analysis of Acoustic Neuroma Management: A Comparison of Microsurgery and Stereotactic Radiosurgery. Neurosurg. 36, 215-229.

PORTILLO F., NELSON R.A., BRACKMANN D.E., HITSELBERGER W.E., SHANNON R.V., WARING M.D., MOORE J.K. (1993) Auditory brain stem implant: electrical stimulation of the human cochlear nucleus. Adv. Oto-RhinoLaryngoL 48, 248-52.

ROSEN S., WALLIKER J., BRIMACOMBE J.A., EDGERTON B.J. (1989) Prosodic and segmental aspects of speech perception

with the House/3M single-channel implant. J. Speech Hearing Res. 32(1), 93-111.

ROSENBERG S., SILVERSTEIN H., GORDON M., FLANZER J., WILLCOX T., SILVERSTEIN J. (1993) A Comparison of Growth Rates of Acoustic Neuromas: Non-surgical Patients vs Subtotal Resection. Otolaryngol. Head Neck Surg. 109, 482-487.

SAKASHITA T., SANDO I. (1995) Postnatal Development of The Internal Auditory Canal Studied by Computer-Aided ThreeDimensional Reconstruction and Measurement. Ann. Otol. Rhinol. Laryngol. 104, 469-475.

SEKHAR L.N., GORMLEY W.B., WRIGHT D.C. (1996) The Best Treatment for Vestibular Schwannoma (Acoustic Neuroma): Microsurgery or Radiosurgery? Am. J. Otol. 17, 676-682.

SLATTERY W.H. III, BRACKMANN D.E. (1995) Results of Surgery Following Stereotactic Irradiation for Acoustic Tumours. Am. J. Otol. 16, 315-319.

SLATTERY W.H. III, BRACKMANN D.E., HITSELBERGER W. (1998) Hearing Preservation in Neurofibromatosis Type 2. Am. J. Otol. 19, 638-643.

SLATTERY W.H. III, BRACKMANN D.E., HITSELBERGER W. (1997) Middle Fossa Approach for hearing Preservation with Acoustic Neuromas. Am. J. Otol. 18, 596-601.

SMEE R. (1995) Stereotatic Radiosurgery. Proceedings of Acoustic Neuroma Association of Australia. Oct, 1995: 2-6. STEWART T.J., LII.AND J., SCHUKNECHT H.F. (1975) Occult Schwannomas of the Vestibular Nerve. Arch. Otolaryngol. 101, 91-95. STRASNICK B., GLASSCOCK M.E., HAYNES D., McMENOMEY S.O., MINOR L.B. (1994) The Natural History of Untreated Acoustic Neuroma. Laryngoscope 104, 1115 IS-1124. THOMSEN J., TOS M. (1997) Radiosurgery: A Referring Surgeon's Experience. Presented Third European Skull Base Conference, London, 1997.

THOMSEN J., TOS M., BORGESEN S.E. (1990) Gamma Knife: Hydrocephalus as a complication of stereotactic radiosurgical treatment of an acoustic neuroma. AJO 11, 330-333. TOMASEVIC P., HOOK C., SMEE R. (1998) Stereotactic Radiosurgery as a Treatment Option for Selected Acoustic Neuroma Patients. Aust. J. Otolaryng. 31, 7-11. TOS M., THOMSEN J. (1991) Management of Acoustic Neuromas. Arch. Otolaryngol. 111, 616-632.

UZIEL A., BENZECH J., FREREBEAU P. (1993) Intraoperative Facial Nerve Monitoring in Posterior Fossa Acoustic Neuroma Surgery. Arch. Otolaryngol. Head Neck Surg. 108, 126-134. WEBER P.C., GANTZ B.J. (1996) Results and Complications from Acoustic Neuroma Excision via Middle Cranial Fossa Approach. AJO 17, 669-675.

WIET R.J., ZAPPIA J.J., HECHT C.S., O'CONNOR C.A. (1995) Conservative Management of Patients with Small Acoustic Tumours. Laryngoscope 105, 795-800.

St. Vincent's Hospital

Sydney, New South Wales

Saleh Al-Abdulwahed M.D., F.R.C.S.C.

Department of Otolaryngology

Security Forces Hospital

Riyadh, Saudia Arabia

Paul A. Fagan M.D., F.R.A.C.S.

Department of Otolaryngology/Skull Base Surgery

St Vincent's Hospital

Sydney, NSW Australia

Correspondence:

Dr. P. Fagan

352 Victoria Street

Darlinghurst NSW 2010

Australia

Tel: (02) 9380 5900

Fax: (02) 9360 5419

*The authors would like to acknowledge the efforts and skills of the various co-surgeons involved with this surgery - Dr John Sheehy, Dr John Tonkin and Dr Marcus Atlas for whom, over many years, the senior author has had the greatest respect and gratitude.

Copyright Australian Society of Otolaryngology Head & Neck Surgery Ltd. Jan 1999
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