Hearing Review__publication By Dr Tarek Khrais_ Medics Index Member
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The Journal of Laryngology & Otology (2006), 120, 366–370. # 2006 JLO (1984) Limited doi:10.1017/S002221510600332X Printed in the United Kingdom First published online 24 March 2006
Hearing preservation surgery in vestibular schwannoma TAREK KHRAIS, FRCS(I), DHSM, MARIO SANNA, MD*
Abstract Objectives: To study the effect of pre-operative hearing level and tumour size on the hearing outcome of hearing preservation surgery for vestibular schwannoma. Study design and setting: A review of literature conducted at Gruppo Otologico, a tertiary referral centre for neurotology and skull base surgery. Results: A total of 1993 patients in 16 publications addressing the topic of hearing preservation surgery in vestibular schwannoma were analysed. The American Academy of Otolaryngology–Head and Neck Surgery hearing classification system was the classification upon which we based our analysis. Conclusion: Defining hearing preservation as class-A hearing, there was a strong inverse relationship between pre-operative hearing and post-operative hearing levels and between tumour size and postoperative hearing levels. Key words: Acoustic Neuroma; Otological Surgical Procedures; Post-operative Complications; Hearing
divided the papers into groups according to the classification system used. Those papers that presented a complete account of the hearing data, both pre- and post-operative, and of the vestibular schwannoma size were kept as a separate group, to be classified and later added to the group with the largest number of patients. Data were analysed according to the American Academy of Otolaryngology–Head and Neck Surgeons (AAO-HNS) hearing classification system (Table I). Although some papers were published before the publication of this AAO-HNS system, data in these papers were amenable to analysis either because they used a similar classification or because they were sufficiently detailed. Tumour size was divided into four groups: intra-canalicular tumours, 0– 0.9 mm tumours, 1 – 1.9 mm tumours and .1.9 mm tumours. All 16 publications presented their data such that the intra-canalicular tumour component measurements were separate from the extra-canalicular tumour component measurements. We were eventually able to collect 16 papers with similar data, to be analysed for the relationship between pre-operative and post-operative hearing. Only seven papers were useful to investigate the relationship between size and post-operative hearing, all of which were used for the first part of our review. Patients were not categorized according to the surgical approach used, because such categorization produced many groups each containing a very small
Introduction Since the first report on hearing preservation surgery for vestibular schwannoma, by Elliott and McKissock1 almost five decades ago, surgeons have striven to improve the hearing outcome of vestibular schwannoma surgery. In spite of the fact that technology had helped markedly in improving results, this particular domain is still in its infancy and much work is required before hearing preservation surgery reaches the levels of success of other types of vestibular schwannoma surgery. Materials and methods A Mednet search of the English literature was performed using the key words ‘vestibular schwannoma’, ‘hearing preservation surgery’, ‘middle cranial fossa approach’ and ‘retro sigmoid approach’. The search results were limited to papers published during the last 10 years. A total of 261 papers were found. Of these, we selected the papers in which both pre-operative and post-operative data were presented in a complete and comparable manner. Sixteen publications were thus selected, presenting a total of 1993 patients. Because of the diversity of data reporting and the wide variety of hearing classification systems used, we did not predetermine which hearing classification systems would be admissible. The only factor that determined selection was availability. We first
From the ENT Department, Jordan University of Science & Technology, Irbid, Jordan, and the Gruppo Otologico, Piacenza– Rome, Italy. Accepted for publication: 29 September 2005. 366
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HEARING PRESERVATION IN VESTIBULAR SCHWANNOMA
TABLE I AMERICAN ACADEMY OF HEAD AND NECK SURGEONS CLASSIFICATION OF HEARING PRESERVATION SURGERY FOR VESTIBULAR SCHWANNOMA
Class A B C D
Pure-tone threshold
Speech discrimination (%)
30 dB .30 dB, 50 dB .50 dB Any level
70 50 50 ,50
8.7 per cent had class-C hearing and 7.2 per cent had class-D hearing. Post-operatively, 18.7 per cent of these patients had class-A hearing, 18.8 per cent had class-B hearing, 8.9 per cent had class-C hearing and 53.6 per cent had class-D hearing. The Chi-square test showed no trend towards a better chance of hearing preservation or improvement with better pre-operative hearing for patients with classes A, B and C hearing.
Classes A, B and C require both the pure-tone threshold and speech discrimination criteria to be met
number of cases, rendering the review and the subsequent analysis insignificant. This approach was also taken by some of the papers reviewed. The statistical analysis was done using the Chisquare and Fischer’s exact tests; statistical significance was set at p ¼ 0.05. Results In the 16 publications analysed,2 – 17 data from 1993 patients were reported. All of these patient data were used to analyse the relationship between preoperative and post-operative hearing. Data from 1048 patients, reported in seven publications, were used to analyse the relationship between tumour size and post-operative hearing.3 – 6,15 – 17 Pre-operative versus post-operative hearing Table II shows the overall relationship between pre-operative and post-operative hearing for the 1993 cases analysed by this review. Almost half of these patients (50.3 per cent) had class-A hearing pre-operatively, 33.8 per cent had class-B hearing,
Tumour size versus post-operative hearing Tables III to VI show the relationship between tumour size and hearing preservation. Class-A hearing was preserved in 25.7 per cent of patients with intra-canalicular tumours, 21.8 per cent of those with 0– 0.9 mm tumours, 9.8 per cent of those with 1 –1.9 mm tumours and 2.9 per cent of those with .1.9 mm tumours. The trend towards better post-operative hearing with smaller tumour size was statistically significant (p , 0.0001, Chi-square test). For patients with pre-operative hearing in classes B, C and D, those with intra-canalicular tumours showed an 8.5 per cent improvement, those with ,0.9 cm tumours showed a 6.5 per cent improvement, those with 1 –1.9 cm tumours showed a 1.3 per cent and those with .1.9 cm tumours showed a 1.6 per cent improvement ( p ¼ 0.0026, Chi-square test). For patients in each tumour size group, we found the following rates of improvement up to class-A hearing: 5.4 per cent for those with intra-canalicular tumours, 3.6 per cent for those with ,0.9 cm tumours, 1.3 per cent for those with 1– 1.9 cm tumours and 0.0 per cent for those with .1.9 cm tumours ( p ¼ 0.0114, Chi-square test).
TABLE II OVERALL PRE-OPERATIVE HEARING AND POST-OPERATIVE HEARING PRESERVATION
Pre-operative hearing class A B C D Total
Total (n)
1003 (50.3%) 673 (33.8%) 174 (8.7%) 143 (7.2%) 1993 (100%)
Post-operative hearing class (n) A
B
C
D
344 24 2 2 372 (18.7%)
170 183 13 8 374 (18.8%)
49 85 41 2 177 (8.9%)
440 381 118 131 1070 (53.6%)
Assessed by the American Association of Otolaryngology –Head & Neck Surgery hearing classification system
TABLE III PRE-OPERATIVE HEARING AND POST-OPERATIVE HEARING PRESERVATION FOR INTRA-CANALICULAR TUMOURS
Pre-operative hearing class A B C D Total
Total (n)
166 (56.1%) 92 (31.1%) 22 (7.4%) 16 (5.4%) 296 (100%)
Post-operative hearing class (n) A
B
C
D
69 6 1 0 76 (25.7%)
30 34 2 0 66 (22.3%)
9 15 10 2 36 (12.1%)
58 37 9 14 118 (39.9%)
Assessed by the American Association of Otolaryngology –Head & Neck Surgery hearing classification system
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TABLE IV PRE-OPERATIVE HEARING AND POST-OPERATIVE HEARING PRESERVATION FOR
Pre-operative hearing class A B C D Total
Total (n)
156 (48%) 110 (33.8%) 43 (13.3%) 16 (4.9%) 325 (100%)
0– 0.9 CM
TUMOURS
Post-operative hearing class (n) A
B
C
D
65 5 1 0 71 (21.8%)
26 33 5 0 64 (19.7%)
9 22 8 0 39 (12%)
56 50 29 16 151 (46.5%)
Assessed by the American Association of Otolaryngology – Head & Neck Surgery hearing classification system
TABLE V PRE-OPERATIVE HEARING AND POST-OPERATIVE HEARING PRESERVATION FOR
Pre-operative hearing class A B C D Total
Total (n)
167 (51.4%) 100 (30.8%) 32 (9.8%) 26 (8%) 325 (100%)
1– 1.9 CM
TUMOURS
Post-operative hearing class (n) A
B
C
D
30 2 0 0 32 (9.8%)
25 24 0 0 49 (15%)
9 12 3 0 24 (7.4%)
103 62 29 26 220 (67.8%)
Assessed by the American Association of Otolaryngology – Head & Neck Surgery hearing classification system
TABLE VI PRE-OPERATIVE HEARING AND POST-OPERATIVE HEARING PRESERVATION FOR
Pre-operative hearing class A B C D Total
Total (n)
40 (39.3%) 34 (33.3%) 13 (12.7%) 15 (14.7%) 102 (100%)
.1.9 CM
TUMOURS
Post-operative hearing class (n) A
B
C
D
3 0 0 0 3 (2.9%)
5 4 0 1 10 (9.8%)
3 3 1 0 7 (6.9%)
29 27 12 14 82 (80.4%)
Assessed by the American Association of Otolaryngology – Head & Neck Surgery hearing classification system
Discussion Hearing preservation surgery is probably one of the most difficult and controversial aspects of vestibular neuroma surgery. Published studies on this topic have lacked uniform reporting and management strategies. This problem was evident throughout our review. Indications for hearing preservation surgery for vestibular schwannoma differed markedly; some authors attempted hearing preservation surgery in the presence of tumours of any size and pre-operative hearing of any level,16,18 – 21 while others undertook such surgery only in patients with small tumours and good hearing.13,14,22,23 Controversy also raged over the definition of the terms ‘small’ and ‘good’. The situation was no clearer regarding the reporting of results; the line of demarcation between preserved and lost hearing was ambiguous, and results criteria were extremely dissimilar. One of the main reasons for such disputes is the lack of large studies presenting comprehensive data and avoiding such confounding factors as single authorship. Recently, there has been growing interest in establishing the predictive factors for success in hearing
preservation. Pre-operative hearing level and tumour size are the two such factors most commonly mentioned in the literature and are also the most objective. Again, in the majority of published studies, a salient limitation was the relatively small number of cases involved. In our review, we tried to overcome this barrier by analysing a larger, more homologous group of patients with the least possible number of confounding variables. Unfortunately, because of the problems mentioned earlier, we were only able to match the reports of 16 authorial groups, which assessed a total of 1993 procedures. The vast majority of vestibular schwannoma patients present with unilateral hearing loss, with the contra-lateral hearing being (if altered) better than that of the affected ear. Hence, the rationale for hearing preservation should be to preserve the affected ear’s ability to participate in binaural hearing, which enables sound localization and suppression of background noise, facilitating speech comprehension in noisy conditions.24 For functional binaural hearing, the inter-aural hearing difference should not exceed 20 dB.25 Regarding background noise, the head shadow effect, added to the signal
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HEARING PRESERVATION IN VESTIBULAR SCHWANNOMA
to noise ratio, will lead to a 20 dB hearing loss with sound frequencies .2000 Hz, which is the range of speech.26 In addition, retro-cochlear pathologies have been shown to have an especially deleterious effect on binaural hearing performance.27 In our analysis of the relationship between preand post-operative hearing, we found that the majority of patients (50.3 per cent) had class-A preoperative hearing and the rest had hearing distributed amongst classes B, C and D. Post-operatively, the situation was reversed, in that 53.6 per cent of patients showed class-D hearing. One of our major concerns was whether there was a relationship between pre-operative hearing level and postoperative hearing preservation. We calculated the number of patients in hearing classes A, B and C whose post-operative hearing was maintained at the same level or improved. (We did not include patients in hearing class D in this calculation, as this group contained, in addition to patients whose hearing was preserved at the same level, those whose preoperative hearing was completely lost, giving a false impression of post-operative hearing preservation.) Thus, hearing was maintained or improved for 34.3 per cent of patients with class-A hearing, 30.7 per cent of those with class-B hearing and 32.2 per cent of those with class-C hearing. Using the Chi-square test for this trend gave p ¼ 0.2299, signifying no statistical significance for the rate of same-level hearing preservation. From a clinical view point, however, this argument does not hold true; in the case of class-A patients, 34.3 per cent had their hearing preserved at a good level (30 dB and 70 per cent speech discrimination score (SDS)) while, in the majority of other cases, hearing preservation rates signified that hearing was preserved at the same poor pre-operative level (in a minority of cases, hearing was improved). However, since preserving poor hearing weakens the overall apparent effect of hearing preservation surgery in vestibular schwannoma, the strength of the above p value is immensely attenuated. To reveal the substantial effect of this, we calculated the rates of preserved hearing as bad as class C for the same groups; the results were 56.1 per cent for class A, 43.4 per cent for class B and 32.2 per cent for class D. Statistical analysis (using the same test) gave p , 0.0001, signifying a strong tendency towards better hearing preservation with better preoperative hearing. Another effect we investigated was the overall rate of preserving class-A post-operative hearing and the contribution to this from each pre-operative hearing class. Out of the 1993 patients, 372 (18.7 per cent) had class-A post-operative hearing. Of these, 344 patients (92.5 per cent) had class-A hearing preoperatively, 24 (6.5 per cent) had class B, two (0.5 per cent) had class C and two (0.5 per cent) had class D. These figures allowed us to calculate the percentage of patients in each hearing class for whom post-operative class-A hearing was achieved. The figures were 34.3 per cent for patients with class-A pre-operative hearing, 3.6 per cent for those with class B, 1.1 per cent for those with class C and
1.4 per cent for those with class D. The Chi-square test for this trend gave p , 0.0001, signifying a very strong tendency towards a reduced rate of class-A post-operative hearing preservation with poorer pre-operative hearing levels. The purpose behind all these calculations was to clarify what effect changing the criteria for successful hearing preservation would have on the reported rate of post-operative hearing preservation. Whilst loose criteria are convenient for the self-esteem of the surgeon, they tend to harm patients by masking the problem of low rates of hearing preservation, hindering the efforts of those seeking improved outcomes. We would have liked to add yet another category to the results of the review where the rate of preserving a normal hearing could not be calculated in all of the papers. In our previous publication,17 however, we calculated the rate of preserving normal hearing from eight prior studies plus our own cases, making a total of 641 cases. The result was a reduction from 11.4 per cent in the class-A hearing group (AAO-HNS classification) to 5.1 per cent in the normal hearing group (group A modified Sanna classification). In our opinion, for reasons given earlier, this is the actual fraction that should be considered as successful hearing preservation, whether the patient’s pre-operative hearing was class-A or worse. When we began the other part of our review, i.e. the relationship between tumour size and hearing preservation, we found that the diversity in classifying tumour size was even greater. A total of 1048 cases were analogous. Tables II to V show the preand post-operative hearing of these patients after dividing them into tumour size groups. The first element we analysed was the rate of class-A hearing preservation in relation to tumour size; these rates were 25.7 per cent for patients with intra-canalicular tumours, 21.8 per cent for those with ,1 cm tumours, 9.8 per cent for those with 1– 1.9 cm tumours and 2.9 per cent for those with .1.9 cm tumours. The Chi-square test gave p , 0.0001, indicating that the reduction in hearing preservation rate as tumour size increased was statistically significant. Numerically, the data showed a constant decrease in the rates of hearing preservation, reaching a minimum with 2 cm tumours. This result supported our own strategy of limiting hearing preservation surgery in cases of vestibular schwannoma to patients with ,2 cm tumours. Another element we analysed was the rate of postoperative hearing improvement in relation to tumour size. First, we calculated the percentage of any postoperative hearing improvement for patients with pre-operative hearing levels in classes B, C and D, for each tumour size group. (Class A was not included because the data provided in the studies were frequently not sufficient to calculate the percentage of cases experiencing post-operative hearing improvement.) The results were 8.5 per cent for patients with intra-canalicular tumours, 6.5 per cent for those with ,1 cm tumours, 1.3 per cent for those with 1– 1.9 cm tumours and 1.6 per cent for those with .1.9 cm tumours. We found a statistically
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significant trend towards reduction of the hearing improvement rate as tumour size increased ( p ¼ 0.0026, Chi-square test). The next step was calculating the post-operative hearing improvement to class-A hearing for patients with class-B, -C and -D pre-operative hearing, for each tumour size category alone. Further reduction was noticed, and the results were 5.4 per cent for patients with intracanalicular tumours, 3.6 per cent for those with ,0.9 cm tumours, 1.3 per cent for those with 1– 1.9 cm tumours and 0.0 per cent for those with .1.9 cm tumours ( p ¼ 0.0114, Chi-square test). In addition to the fact that these data as a whole are feeble, the rate of improvement still decreased with poorer pre-operative hearing levels. Conclusion The results of analysing a large number of hearing preservation procedures revealed the presence of a strong inverse relationship between pre-operative and post-operative hearing levels, and between tumour size and post-operative hearing levels. However, this relationship could be unintentionally concealed by the use of loose criteria to define preserved hearing. References 1 Elliott FA, McKissock W. Acoustic neuroma; early diagnosis. Lancet 1954;6850:1189 – 91. 2 Lassaletta L, Fontes L, Melcon E, Sarria MJ, Gavillan J. Hearing preservation with the retrosigmoid approach for vestibular schwannoma: myth or reality? Otolaryngol Head Neck Surg 2003;129:397 –401 3 Satar B, Jackler RK, Oghalai J, Pitts LH, Yates PD. Riskbenefit analysis of using the middle fossa approach for acoustic neuromas with .10 mm cerebellopontine angle component. Laryngoscope 2002;112:1500 – 6 4 Somers T, Casselman J, de Ceulaer G, Govaerts P, Offeciers E. Prognostic value of magnetic resonance imaging findings in hearing preservation surgery for vestibular schwannoma. Otol Neurotol 2001;22:87 –94 5 Gjuric M, Wigand ME, Wolf SR. Enlarged middle fossa vestibular schwannoma surgery: experience with 735 cases. Otol Neurotol 2001;22:223 –30 (discussion 230–1) 6 Staecker H, Nadol JB Jr, Ojeman R, Ronner S, McKennia MJ. Hearing preservation in acoustic neuroma surgery: middle fossa versus retrosigmoid approach. Am J Otol 2000;21:399 –404 7 Mazzoni A, Calabrese V, Danesi G. A modified retrosigmoid approach for direct exposure of the fundus of the internal auditory canal for hearing preservation in acoustic neuroma surgery. Am J Otol 2000;21:98 –109 8 Brackmann DE, Owens RM, Friedman RA, Hitselberger WE, De la Cruz A, House JW et al. Prognostic factors for hearing preservation in vestibular schwannoma surgery. Am J Otol 2000;21:417 –24 9 Moffat DA, da Cruz MJ, Baguley DM, Beynon GJ, Hardy DG. Hearing preservation in solitary vestibular schwannoma surgery using the retrosigmoid approach. Otolaryngol Head Neck Surg 1999;121:781 –8 10 Noguchi Y, Komatsuzaki A, Nishida H. Cochlear microphonics for hearing preservation in vestibular schwannoma surgery. Laryngoscope 1999;109:1982 –7 11 Kanzaki J, Ogawa K, Inoue Y, Shiobara R, Toya S. Quality of hearing preservation in acoustic neuroma surgery. Am J Otol 1998;19:644 –8
12 Irving RM, Jackler RK, Pitts LH. Hearing preservation in patients undergoing vestibular schwannoma surgery: comparison of middle fossa and retrosigmoid approaches. J Neurosurg 1998;88:840– 5 13 Arriaga MA, Chen DA, Fukushima T. Individualizing hearing preservation in acoustic neuroma surgery. Laryngoscope 1997;107:1043– 7 14 Weber PC, Gantz BJ. Results and complications from acoustic neuroma excision via middle cranial fossa approach. Am J Otol 1996;17:669 –75 15 Post KD, Eisenberg MB, Catalano PJ. Hearing preservation in vestibular schwannoma surgery: what factors influence outcome? J Neurosurg 1995;83:191– 6 16 Cohen NL, Lewis WS, Ransohoff J. Hearing preservation in cerebellopontine angle tumour surgery: the NYU experience 1974 – 1991. Am J Otol 1993;14:423– 33 17 Sanna M, Khrais T, Russo A, Piccirillo E, Argurio A. Hearing preservation surgery in vestibular schwannoma: the hidden truth. Ann Otol Rhinol Laryngol 2004;113: 1156– 63 18 Nadol JB Jr, Chiong CM, Ojemann RG, McKenna MJ, Martuza RL, Montgomery WW et al. Preservation of hearing and facial nerve function in resection of acoustic neuroma. Laryngoscope 1992;102:1153– 8 19 Fischer G, Fischer C, Remond J. Hearing preservation in acoustic neurinoma surgery. J Neurosurg 1992;76:910– 17 20 Umezu H, Aiba T. Preservation of hearing after surgery for acoustic schwannomas: correlation between cochlear nerve function and operative findings. J Neurosurg 1994;80:844– 8 21 Samii M, Matthies C. Management of 1000 vestibular schwannomas (acoustic neuromas): hearing function in 1000 tumor resections. Neurosurgery 1997;40:248– 60 (discussion 260–2) 22 Slattery WH 3rd, Brackmann DE, Hitselberger W. Middle fossa approach for hearing preservation with acoustic neuromas. Am J Otol 1997;18:596 –601 23 Rowed DW, Nedzelski JM. Hearing preservation in the removal of intracanalicular acoustic neuromas via the retrosigmoid approach. J Neurosurg 1997;86:456 –61 24 Persson P, Harder H, Arlinger S, Magnuson B. Speech recognition in background noise: monaural versus binaural listening conditions in normal-hearing patients. Otol Neurotol 2001;22:625 –30 25 Hall JW 3rd, Derlacki EL. Effect of conductive hearing loss and middle ear surgery on binaural hearing. Ann Otol Rhinol Laryngol 1986;95:525 –30 26 Valente M, Valente M, Enrietto J, Layton KM. Fitting strategies for patients with unilateral hearing loss. In: Valente M, ed. Strategies for Selecting and Verifying Hearing Aid Fittings. New York, Stuttgart: Thieme, 2002; 253–71 27 Hausler R, Colburn S, Marr E. Sound localization in subjects with impaired hearing. Spatial discrimination and interaural discrimination tests. Acta Otolaryngol Suppl 1983;400:1–62
Address for correspondence: Tarek Khrais, ENT Department, King Abdullah University Hospital, Jordan University of Science & Technology, Irbid 21110, Jordan. Fax: 00962 2 7247850 E-mail: [email protected] Dr T Khrais takes responsibility for the integrity of the content of the paper. Competing interests: None declared
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The Journal of Laryngology & Otology (2006), 120, 366–370. # 2006 JLO (1984) Limited doi:10.1017/S002221510600332X Printed in the United Kingdom First published online 24 March 2006
Hearing preservation surgery in vestibular schwannoma TAREK KHRAIS, FRCS(I), DHSM, MARIO SANNA, MD*
Abstract Objectives: To study the effect of pre-operative hearing level and tumour size on the hearing outcome of hearing preservation surgery for vestibular schwannoma. Study design and setting: A review of literature conducted at Gruppo Otologico, a tertiary referral centre for neurotology and skull base surgery. Results: A total of 1993 patients in 16 publications addressing the topic of hearing preservation surgery in vestibular schwannoma were analysed. The American Academy of Otolaryngology–Head and Neck Surgery hearing classification system was the classification upon which we based our analysis. Conclusion: Defining hearing preservation as class-A hearing, there was a strong inverse relationship between pre-operative hearing and post-operative hearing levels and between tumour size and postoperative hearing levels. Key words: Acoustic Neuroma; Otological Surgical Procedures; Post-operative Complications; Hearing
divided the papers into groups according to the classification system used. Those papers that presented a complete account of the hearing data, both pre- and post-operative, and of the vestibular schwannoma size were kept as a separate group, to be classified and later added to the group with the largest number of patients. Data were analysed according to the American Academy of Otolaryngology–Head and Neck Surgeons (AAO-HNS) hearing classification system (Table I). Although some papers were published before the publication of this AAO-HNS system, data in these papers were amenable to analysis either because they used a similar classification or because they were sufficiently detailed. Tumour size was divided into four groups: intra-canalicular tumours, 0– 0.9 mm tumours, 1 – 1.9 mm tumours and .1.9 mm tumours. All 16 publications presented their data such that the intra-canalicular tumour component measurements were separate from the extra-canalicular tumour component measurements. We were eventually able to collect 16 papers with similar data, to be analysed for the relationship between pre-operative and post-operative hearing. Only seven papers were useful to investigate the relationship between size and post-operative hearing, all of which were used for the first part of our review. Patients were not categorized according to the surgical approach used, because such categorization produced many groups each containing a very small
Introduction Since the first report on hearing preservation surgery for vestibular schwannoma, by Elliott and McKissock1 almost five decades ago, surgeons have striven to improve the hearing outcome of vestibular schwannoma surgery. In spite of the fact that technology had helped markedly in improving results, this particular domain is still in its infancy and much work is required before hearing preservation surgery reaches the levels of success of other types of vestibular schwannoma surgery. Materials and methods A Mednet search of the English literature was performed using the key words ‘vestibular schwannoma’, ‘hearing preservation surgery’, ‘middle cranial fossa approach’ and ‘retro sigmoid approach’. The search results were limited to papers published during the last 10 years. A total of 261 papers were found. Of these, we selected the papers in which both pre-operative and post-operative data were presented in a complete and comparable manner. Sixteen publications were thus selected, presenting a total of 1993 patients. Because of the diversity of data reporting and the wide variety of hearing classification systems used, we did not predetermine which hearing classification systems would be admissible. The only factor that determined selection was availability. We first
From the ENT Department, Jordan University of Science & Technology, Irbid, Jordan, and the Gruppo Otologico, Piacenza– Rome, Italy. Accepted for publication: 29 September 2005. 366
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HEARING PRESERVATION IN VESTIBULAR SCHWANNOMA
TABLE I AMERICAN ACADEMY OF HEAD AND NECK SURGEONS CLASSIFICATION OF HEARING PRESERVATION SURGERY FOR VESTIBULAR SCHWANNOMA
Class A B C D
Pure-tone threshold
Speech discrimination (%)
30 dB .30 dB, 50 dB .50 dB Any level
70 50 50 ,50
8.7 per cent had class-C hearing and 7.2 per cent had class-D hearing. Post-operatively, 18.7 per cent of these patients had class-A hearing, 18.8 per cent had class-B hearing, 8.9 per cent had class-C hearing and 53.6 per cent had class-D hearing. The Chi-square test showed no trend towards a better chance of hearing preservation or improvement with better pre-operative hearing for patients with classes A, B and C hearing.
Classes A, B and C require both the pure-tone threshold and speech discrimination criteria to be met
number of cases, rendering the review and the subsequent analysis insignificant. This approach was also taken by some of the papers reviewed. The statistical analysis was done using the Chisquare and Fischer’s exact tests; statistical significance was set at p ¼ 0.05. Results In the 16 publications analysed,2 – 17 data from 1993 patients were reported. All of these patient data were used to analyse the relationship between preoperative and post-operative hearing. Data from 1048 patients, reported in seven publications, were used to analyse the relationship between tumour size and post-operative hearing.3 – 6,15 – 17 Pre-operative versus post-operative hearing Table II shows the overall relationship between pre-operative and post-operative hearing for the 1993 cases analysed by this review. Almost half of these patients (50.3 per cent) had class-A hearing pre-operatively, 33.8 per cent had class-B hearing,
Tumour size versus post-operative hearing Tables III to VI show the relationship between tumour size and hearing preservation. Class-A hearing was preserved in 25.7 per cent of patients with intra-canalicular tumours, 21.8 per cent of those with 0– 0.9 mm tumours, 9.8 per cent of those with 1 –1.9 mm tumours and 2.9 per cent of those with .1.9 mm tumours. The trend towards better post-operative hearing with smaller tumour size was statistically significant (p , 0.0001, Chi-square test). For patients with pre-operative hearing in classes B, C and D, those with intra-canalicular tumours showed an 8.5 per cent improvement, those with ,0.9 cm tumours showed a 6.5 per cent improvement, those with 1 –1.9 cm tumours showed a 1.3 per cent and those with .1.9 cm tumours showed a 1.6 per cent improvement ( p ¼ 0.0026, Chi-square test). For patients in each tumour size group, we found the following rates of improvement up to class-A hearing: 5.4 per cent for those with intra-canalicular tumours, 3.6 per cent for those with ,0.9 cm tumours, 1.3 per cent for those with 1– 1.9 cm tumours and 0.0 per cent for those with .1.9 cm tumours ( p ¼ 0.0114, Chi-square test).
TABLE II OVERALL PRE-OPERATIVE HEARING AND POST-OPERATIVE HEARING PRESERVATION
Pre-operative hearing class A B C D Total
Total (n)
1003 (50.3%) 673 (33.8%) 174 (8.7%) 143 (7.2%) 1993 (100%)
Post-operative hearing class (n) A
B
C
D
344 24 2 2 372 (18.7%)
170 183 13 8 374 (18.8%)
49 85 41 2 177 (8.9%)
440 381 118 131 1070 (53.6%)
Assessed by the American Association of Otolaryngology –Head & Neck Surgery hearing classification system
TABLE III PRE-OPERATIVE HEARING AND POST-OPERATIVE HEARING PRESERVATION FOR INTRA-CANALICULAR TUMOURS
Pre-operative hearing class A B C D Total
Total (n)
166 (56.1%) 92 (31.1%) 22 (7.4%) 16 (5.4%) 296 (100%)
Post-operative hearing class (n) A
B
C
D
69 6 1 0 76 (25.7%)
30 34 2 0 66 (22.3%)
9 15 10 2 36 (12.1%)
58 37 9 14 118 (39.9%)
Assessed by the American Association of Otolaryngology –Head & Neck Surgery hearing classification system
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TABLE IV PRE-OPERATIVE HEARING AND POST-OPERATIVE HEARING PRESERVATION FOR
Pre-operative hearing class A B C D Total
Total (n)
156 (48%) 110 (33.8%) 43 (13.3%) 16 (4.9%) 325 (100%)
0– 0.9 CM
TUMOURS
Post-operative hearing class (n) A
B
C
D
65 5 1 0 71 (21.8%)
26 33 5 0 64 (19.7%)
9 22 8 0 39 (12%)
56 50 29 16 151 (46.5%)
Assessed by the American Association of Otolaryngology – Head & Neck Surgery hearing classification system
TABLE V PRE-OPERATIVE HEARING AND POST-OPERATIVE HEARING PRESERVATION FOR
Pre-operative hearing class A B C D Total
Total (n)
167 (51.4%) 100 (30.8%) 32 (9.8%) 26 (8%) 325 (100%)
1– 1.9 CM
TUMOURS
Post-operative hearing class (n) A
B
C
D
30 2 0 0 32 (9.8%)
25 24 0 0 49 (15%)
9 12 3 0 24 (7.4%)
103 62 29 26 220 (67.8%)
Assessed by the American Association of Otolaryngology – Head & Neck Surgery hearing classification system
TABLE VI PRE-OPERATIVE HEARING AND POST-OPERATIVE HEARING PRESERVATION FOR
Pre-operative hearing class A B C D Total
Total (n)
40 (39.3%) 34 (33.3%) 13 (12.7%) 15 (14.7%) 102 (100%)
.1.9 CM
TUMOURS
Post-operative hearing class (n) A
B
C
D
3 0 0 0 3 (2.9%)
5 4 0 1 10 (9.8%)
3 3 1 0 7 (6.9%)
29 27 12 14 82 (80.4%)
Assessed by the American Association of Otolaryngology – Head & Neck Surgery hearing classification system
Discussion Hearing preservation surgery is probably one of the most difficult and controversial aspects of vestibular neuroma surgery. Published studies on this topic have lacked uniform reporting and management strategies. This problem was evident throughout our review. Indications for hearing preservation surgery for vestibular schwannoma differed markedly; some authors attempted hearing preservation surgery in the presence of tumours of any size and pre-operative hearing of any level,16,18 – 21 while others undertook such surgery only in patients with small tumours and good hearing.13,14,22,23 Controversy also raged over the definition of the terms ‘small’ and ‘good’. The situation was no clearer regarding the reporting of results; the line of demarcation between preserved and lost hearing was ambiguous, and results criteria were extremely dissimilar. One of the main reasons for such disputes is the lack of large studies presenting comprehensive data and avoiding such confounding factors as single authorship. Recently, there has been growing interest in establishing the predictive factors for success in hearing
preservation. Pre-operative hearing level and tumour size are the two such factors most commonly mentioned in the literature and are also the most objective. Again, in the majority of published studies, a salient limitation was the relatively small number of cases involved. In our review, we tried to overcome this barrier by analysing a larger, more homologous group of patients with the least possible number of confounding variables. Unfortunately, because of the problems mentioned earlier, we were only able to match the reports of 16 authorial groups, which assessed a total of 1993 procedures. The vast majority of vestibular schwannoma patients present with unilateral hearing loss, with the contra-lateral hearing being (if altered) better than that of the affected ear. Hence, the rationale for hearing preservation should be to preserve the affected ear’s ability to participate in binaural hearing, which enables sound localization and suppression of background noise, facilitating speech comprehension in noisy conditions.24 For functional binaural hearing, the inter-aural hearing difference should not exceed 20 dB.25 Regarding background noise, the head shadow effect, added to the signal
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to noise ratio, will lead to a 20 dB hearing loss with sound frequencies .2000 Hz, which is the range of speech.26 In addition, retro-cochlear pathologies have been shown to have an especially deleterious effect on binaural hearing performance.27 In our analysis of the relationship between preand post-operative hearing, we found that the majority of patients (50.3 per cent) had class-A preoperative hearing and the rest had hearing distributed amongst classes B, C and D. Post-operatively, the situation was reversed, in that 53.6 per cent of patients showed class-D hearing. One of our major concerns was whether there was a relationship between pre-operative hearing level and postoperative hearing preservation. We calculated the number of patients in hearing classes A, B and C whose post-operative hearing was maintained at the same level or improved. (We did not include patients in hearing class D in this calculation, as this group contained, in addition to patients whose hearing was preserved at the same level, those whose preoperative hearing was completely lost, giving a false impression of post-operative hearing preservation.) Thus, hearing was maintained or improved for 34.3 per cent of patients with class-A hearing, 30.7 per cent of those with class-B hearing and 32.2 per cent of those with class-C hearing. Using the Chi-square test for this trend gave p ¼ 0.2299, signifying no statistical significance for the rate of same-level hearing preservation. From a clinical view point, however, this argument does not hold true; in the case of class-A patients, 34.3 per cent had their hearing preserved at a good level (30 dB and 70 per cent speech discrimination score (SDS)) while, in the majority of other cases, hearing preservation rates signified that hearing was preserved at the same poor pre-operative level (in a minority of cases, hearing was improved). However, since preserving poor hearing weakens the overall apparent effect of hearing preservation surgery in vestibular schwannoma, the strength of the above p value is immensely attenuated. To reveal the substantial effect of this, we calculated the rates of preserved hearing as bad as class C for the same groups; the results were 56.1 per cent for class A, 43.4 per cent for class B and 32.2 per cent for class D. Statistical analysis (using the same test) gave p , 0.0001, signifying a strong tendency towards better hearing preservation with better preoperative hearing. Another effect we investigated was the overall rate of preserving class-A post-operative hearing and the contribution to this from each pre-operative hearing class. Out of the 1993 patients, 372 (18.7 per cent) had class-A post-operative hearing. Of these, 344 patients (92.5 per cent) had class-A hearing preoperatively, 24 (6.5 per cent) had class B, two (0.5 per cent) had class C and two (0.5 per cent) had class D. These figures allowed us to calculate the percentage of patients in each hearing class for whom post-operative class-A hearing was achieved. The figures were 34.3 per cent for patients with class-A pre-operative hearing, 3.6 per cent for those with class B, 1.1 per cent for those with class C and
1.4 per cent for those with class D. The Chi-square test for this trend gave p , 0.0001, signifying a very strong tendency towards a reduced rate of class-A post-operative hearing preservation with poorer pre-operative hearing levels. The purpose behind all these calculations was to clarify what effect changing the criteria for successful hearing preservation would have on the reported rate of post-operative hearing preservation. Whilst loose criteria are convenient for the self-esteem of the surgeon, they tend to harm patients by masking the problem of low rates of hearing preservation, hindering the efforts of those seeking improved outcomes. We would have liked to add yet another category to the results of the review where the rate of preserving a normal hearing could not be calculated in all of the papers. In our previous publication,17 however, we calculated the rate of preserving normal hearing from eight prior studies plus our own cases, making a total of 641 cases. The result was a reduction from 11.4 per cent in the class-A hearing group (AAO-HNS classification) to 5.1 per cent in the normal hearing group (group A modified Sanna classification). In our opinion, for reasons given earlier, this is the actual fraction that should be considered as successful hearing preservation, whether the patient’s pre-operative hearing was class-A or worse. When we began the other part of our review, i.e. the relationship between tumour size and hearing preservation, we found that the diversity in classifying tumour size was even greater. A total of 1048 cases were analogous. Tables II to V show the preand post-operative hearing of these patients after dividing them into tumour size groups. The first element we analysed was the rate of class-A hearing preservation in relation to tumour size; these rates were 25.7 per cent for patients with intra-canalicular tumours, 21.8 per cent for those with ,1 cm tumours, 9.8 per cent for those with 1– 1.9 cm tumours and 2.9 per cent for those with .1.9 cm tumours. The Chi-square test gave p , 0.0001, indicating that the reduction in hearing preservation rate as tumour size increased was statistically significant. Numerically, the data showed a constant decrease in the rates of hearing preservation, reaching a minimum with 2 cm tumours. This result supported our own strategy of limiting hearing preservation surgery in cases of vestibular schwannoma to patients with ,2 cm tumours. Another element we analysed was the rate of postoperative hearing improvement in relation to tumour size. First, we calculated the percentage of any postoperative hearing improvement for patients with pre-operative hearing levels in classes B, C and D, for each tumour size group. (Class A was not included because the data provided in the studies were frequently not sufficient to calculate the percentage of cases experiencing post-operative hearing improvement.) The results were 8.5 per cent for patients with intra-canalicular tumours, 6.5 per cent for those with ,1 cm tumours, 1.3 per cent for those with 1– 1.9 cm tumours and 1.6 per cent for those with .1.9 cm tumours. We found a statistically
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significant trend towards reduction of the hearing improvement rate as tumour size increased ( p ¼ 0.0026, Chi-square test). The next step was calculating the post-operative hearing improvement to class-A hearing for patients with class-B, -C and -D pre-operative hearing, for each tumour size category alone. Further reduction was noticed, and the results were 5.4 per cent for patients with intracanalicular tumours, 3.6 per cent for those with ,0.9 cm tumours, 1.3 per cent for those with 1– 1.9 cm tumours and 0.0 per cent for those with .1.9 cm tumours ( p ¼ 0.0114, Chi-square test). In addition to the fact that these data as a whole are feeble, the rate of improvement still decreased with poorer pre-operative hearing levels. Conclusion The results of analysing a large number of hearing preservation procedures revealed the presence of a strong inverse relationship between pre-operative and post-operative hearing levels, and between tumour size and post-operative hearing levels. However, this relationship could be unintentionally concealed by the use of loose criteria to define preserved hearing. References 1 Elliott FA, McKissock W. Acoustic neuroma; early diagnosis. Lancet 1954;6850:1189 – 91. 2 Lassaletta L, Fontes L, Melcon E, Sarria MJ, Gavillan J. Hearing preservation with the retrosigmoid approach for vestibular schwannoma: myth or reality? Otolaryngol Head Neck Surg 2003;129:397 –401 3 Satar B, Jackler RK, Oghalai J, Pitts LH, Yates PD. Riskbenefit analysis of using the middle fossa approach for acoustic neuromas with .10 mm cerebellopontine angle component. Laryngoscope 2002;112:1500 – 6 4 Somers T, Casselman J, de Ceulaer G, Govaerts P, Offeciers E. Prognostic value of magnetic resonance imaging findings in hearing preservation surgery for vestibular schwannoma. Otol Neurotol 2001;22:87 –94 5 Gjuric M, Wigand ME, Wolf SR. Enlarged middle fossa vestibular schwannoma surgery: experience with 735 cases. Otol Neurotol 2001;22:223 –30 (discussion 230–1) 6 Staecker H, Nadol JB Jr, Ojeman R, Ronner S, McKennia MJ. Hearing preservation in acoustic neuroma surgery: middle fossa versus retrosigmoid approach. Am J Otol 2000;21:399 –404 7 Mazzoni A, Calabrese V, Danesi G. A modified retrosigmoid approach for direct exposure of the fundus of the internal auditory canal for hearing preservation in acoustic neuroma surgery. Am J Otol 2000;21:98 –109 8 Brackmann DE, Owens RM, Friedman RA, Hitselberger WE, De la Cruz A, House JW et al. Prognostic factors for hearing preservation in vestibular schwannoma surgery. Am J Otol 2000;21:417 –24 9 Moffat DA, da Cruz MJ, Baguley DM, Beynon GJ, Hardy DG. Hearing preservation in solitary vestibular schwannoma surgery using the retrosigmoid approach. Otolaryngol Head Neck Surg 1999;121:781 –8 10 Noguchi Y, Komatsuzaki A, Nishida H. Cochlear microphonics for hearing preservation in vestibular schwannoma surgery. Laryngoscope 1999;109:1982 –7 11 Kanzaki J, Ogawa K, Inoue Y, Shiobara R, Toya S. Quality of hearing preservation in acoustic neuroma surgery. Am J Otol 1998;19:644 –8
12 Irving RM, Jackler RK, Pitts LH. Hearing preservation in patients undergoing vestibular schwannoma surgery: comparison of middle fossa and retrosigmoid approaches. J Neurosurg 1998;88:840– 5 13 Arriaga MA, Chen DA, Fukushima T. Individualizing hearing preservation in acoustic neuroma surgery. Laryngoscope 1997;107:1043– 7 14 Weber PC, Gantz BJ. Results and complications from acoustic neuroma excision via middle cranial fossa approach. Am J Otol 1996;17:669 –75 15 Post KD, Eisenberg MB, Catalano PJ. Hearing preservation in vestibular schwannoma surgery: what factors influence outcome? J Neurosurg 1995;83:191– 6 16 Cohen NL, Lewis WS, Ransohoff J. Hearing preservation in cerebellopontine angle tumour surgery: the NYU experience 1974 – 1991. Am J Otol 1993;14:423– 33 17 Sanna M, Khrais T, Russo A, Piccirillo E, Argurio A. Hearing preservation surgery in vestibular schwannoma: the hidden truth. Ann Otol Rhinol Laryngol 2004;113: 1156– 63 18 Nadol JB Jr, Chiong CM, Ojemann RG, McKenna MJ, Martuza RL, Montgomery WW et al. Preservation of hearing and facial nerve function in resection of acoustic neuroma. Laryngoscope 1992;102:1153– 8 19 Fischer G, Fischer C, Remond J. Hearing preservation in acoustic neurinoma surgery. J Neurosurg 1992;76:910– 17 20 Umezu H, Aiba T. Preservation of hearing after surgery for acoustic schwannomas: correlation between cochlear nerve function and operative findings. J Neurosurg 1994;80:844– 8 21 Samii M, Matthies C. Management of 1000 vestibular schwannomas (acoustic neuromas): hearing function in 1000 tumor resections. Neurosurgery 1997;40:248– 60 (discussion 260–2) 22 Slattery WH 3rd, Brackmann DE, Hitselberger W. Middle fossa approach for hearing preservation with acoustic neuromas. Am J Otol 1997;18:596 –601 23 Rowed DW, Nedzelski JM. Hearing preservation in the removal of intracanalicular acoustic neuromas via the retrosigmoid approach. J Neurosurg 1997;86:456 –61 24 Persson P, Harder H, Arlinger S, Magnuson B. Speech recognition in background noise: monaural versus binaural listening conditions in normal-hearing patients. Otol Neurotol 2001;22:625 –30 25 Hall JW 3rd, Derlacki EL. Effect of conductive hearing loss and middle ear surgery on binaural hearing. Ann Otol Rhinol Laryngol 1986;95:525 –30 26 Valente M, Valente M, Enrietto J, Layton KM. Fitting strategies for patients with unilateral hearing loss. In: Valente M, ed. Strategies for Selecting and Verifying Hearing Aid Fittings. New York, Stuttgart: Thieme, 2002; 253–71 27 Hausler R, Colburn S, Marr E. Sound localization in subjects with impaired hearing. Spatial discrimination and interaural discrimination tests. Acta Otolaryngol Suppl 1983;400:1–62
Address for correspondence: Tarek Khrais, ENT Department, King Abdullah University Hospital, Jordan University of Science & Technology, Irbid 21110, Jordan. Fax: 00962 2 7247850 E-mail: [email protected] Dr T Khrais takes responsibility for the integrity of the content of the paper. Competing interests: None declared
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