MAIN ARTICLE
The Journal of Laryngology & Otology (2014), 128, 406–415. © JLO (1984) Limited, 2014 doi:10.1017/S0022215114000541
Factors affecting final facial nerve outcome following vestibular schwannoma surgery D A MOFFAT1, R A PARKER2, D G HARDY3, R MACFARLANE3 1
Neuro-otology and Skull Base Surgery Department, Addenbrookes Hospital, Cambridge University Teaching Hospitals NHS Trust, 2Centre for Applied Medical Statistics, University of Cambridge, and 3Neurosurgery Department, Addenbrookes Hospital, Cambridge University Teaching Hospitals NHS Trust, UK
Abstract Objective: To determine factors affecting facial nerve outcome of vestibular schwannoma surgery. Methods: This retrospective cohort study comprised 652 patients. The outcome measure was House–Brackmann classification at two years post-operatively. Univariate and multivariate analyses were carried out to determine the factors affecting facial nerve outcome. The incidence rates of hemifacial spasm, metallic taste and crocodile tear syndrome were recorded. Results: For tumours less than 1.5 cm, 95 per cent of outcomes were normal, 100 per cent were satisfactory (House–Brackmann grades I–III) and 0 per cent were unsatisfactory (grades IV–VI). For tumours 1.5–2.4 cm, 83 per cent of outcomes were normal, 99 per cent were satisfactory and 1 per cent were unsatisfactory. For tumours 2.5–3.4 cm, 68 per cent of outcomes were normal, 96 per cent were satisfactory and 4 per cent were unsatisfactory. For tumours 3.5–4.4 cm, 52 per cent of outcomes were normal, 80 per cent were satisfactory and 20 per cent were unsatisfactory. For tumours larger than 4.4 cm, 50 per cent of outcomes were normal, 72 per cent were satisfactory and 28 per cent were unsatisfactory. Conclusion: Tumour size and operation year were significant predictors of facial nerve outcome. The surgical learning curve was steepest for the first 50 patients. Key words: Vestibular Schwannoma; Facial Nerve; Otologic Surgical Procedures; Prognosis
Introduction The first successful preservation of the facial nerve during complete excision of a vestibular schwannoma has been attributed to Sir Hugh Cairns, who reported the procedure in 1931.1 McKissock reported a remarkable series of facial and cochlear nerve preservation in 1965 without the aid of magnification.2 However, the introduction of the operating microscope around the same year by William House was an important milestone in vestibular schwannoma surgery.3 Microsurgical advances paved the way to fulfilling the primary goal of vestibular schwannoma surgery, which is complete tumour removal with minimal morbidity and mortality.4 Many centres throughout the world now achieve high rates of facial nerve preservation and good postoperative facial nerve function.5–12 Unfortunately, anatomical continuity of the facial nerve does not always result in good long-term facial recovery. Any corrective surgery should be undertaken relatively early for the most favourable results. It is important when counselling patients preoperatively to inform them of the likely outcome with
regard to facial nerve function, including nervus intermedius function,13 as this is an important pre-determinant of post-operative quality of life. It will also form part of an evidence base for the surgical modality of management in comparison with the other two modern modalities of observation with interval imaging and stereotactic radiotherapy. It is not only important for the surgeon to be able to quote his or her own facial nerve outcome figures, but also to be cognisant of the predictive factors which influence facial nerve outcome in vestibular schwannoma surgery. This detailed study of a large series of patients over three decades was an attempt to identify patient and surgical variables which influence facial nerve outcome and quality of life after vestibular schwannoma excision.
Materials and methods This study involved a retrospective case note analysis of a series of patients with a unilateral sporadic vestibular schwannoma and pre-operatively normal facial nerve function (House–Brackmann grade I). Patients were treated surgically, using either a translabyrinthine
Presented Orally at the Sixth International Conference on Acoustic Neuroma, 28–30 June 2011, Los Angeles, California, USA. Accepted for publication 5 August 2013 First published online 31 March 2014
407
FACIAL NERVE OUTCOME OF VESTIBULAR SCHWANNOMA SURGERY
or a retrosigmoid approach. Surgery was carried out by the senior authors (DAM, with either DGH or RM) between the years 1981 and 2010 at Addenbrookes, Cambridge University Teaching Hospital. Clinical data were collected from a 250-point database using Filemaker Pro 6 initially and more recently Filemaker Pro 10 software. Patients with neurofibromatosis type 2, those receiving pre-operative stereotactic radiotherapy and those patients with recurrent tumour referred from other units were excluded from this analysis. Patients The surgical series consisted of 652 patients with histologically proven, sporadic, unilateral vestibular schwannomas. There were 321 male patients and 331 females. The age range was 13 to 86 years, with a mean of 53.8 years and a standard deviation of 12.6 years. The age distribution in decades can be seen in Figure 1. Tumour size was assessed in terms of the maximum diameter of the mediolateral tumour including the intracanalicular portion; the series extends back to 1981 and this was the method used at that time. The authors are cognisant of the more recent measure of maximum intracranial tumour diameter,14 where solely intracanalicular tumours (vestibular schwannoma = 0 mm) are stated as such. For the sake of consistency, we used the former measurement method throughout. Maximum tumour size was measured in centimetres for each individual tumour and also classified in increments (i.e. less than 1.5 cm, 1.5–2.4 cm, 2.5–3.4 cm, 3.5–4.4 cm and 4.5 cm or larger) (Figure 2). There were 563 (86 per cent) translabyrinthine and 89 (14 per cent) retrosigmoid operations performed. Outcome measures Facial nerve function was assessed at three months, and at one, two and five years post-operatively. The final facial nerve outcome was recorded at two years postoperatively for this data analysis. Facial nerve function was assessed using the House–Brackmann grading system.15 Totally normal
FIG. 1 Age distribution in decades (n = 652).
FIG. 2 Tumour size (n = 652).
function is classified as House–Brackmann grade I; however, in line with some recently reported series, grades I and II were both considered normal. Grades I–III were classified as a satisfactory outcome and grades IV–VI as unsatisfactory at 24 months after surgery. An analysis of the facial nerve outcome at 24 months post-operatively for the translabyrinthine approach and separately for the retrosigmoid approach was carried out for each tumour size increment (i.e. less than 1.5 cm, 1.5–2.4 cm, 2.5–3.4 cm, 3.5–4.4 cm and 4.5 cm or larger), both in total numbers and percentages. Facial nerve outcome for both approaches was tabulated based on the percentages of patients with House–Brackmann grades I and II, I–III, and IV–VI. The rate of facial nerve anatomical preservation was recorded, and the type of facial reconstruction and functional outcome was documented in those few cases where the facial nerve was lost. Nervus intermedius function and aberrant regeneration of the facial nerve, in the form of altered taste and crocodile tear incidence rates, were assessed at 3 and 24 months post-operatively, along with the rates of symptom development and recovery. Magnetic resonance imaging was performed at two and five years post-operatively. Chi-square tests for trend were used to determine the individual effects of gender, tumour size (categorical) and operation approach on facial nerve outcome. (A chi-square test for trend is a version of the ordinary Pearson’s chi-square test that takes into account the ordinal nature of the facial nerve outcome variable.) A chi-square test for trend was also used to compare House–Brackmann grading in the first decade (1981–1990) with that in the second and third decades (1991–2010). Data on exact tumour size were available for 652 out of 1018 patients on the database (64 per cent); this was used to confirm the results using categories of tumour size. In order to determine whether there was a significant relationship between House–Brackmann grading and tumour size, a linear regression model was applied to the exact tumour size data, with facial
408
D A MOFFAT, R A PARKER, D G HARDY et al.
nerve outcome entering the model as a predictor variable. Similarly, a linear regression method was used to evaluate the effect of age on facial nerve outcome. Multivariate analysis was used (in the form of a multiple logistic regression) to investigate predictors of satisfactory facial nerve outcome (House–Brackmann grades I–III), and to determine if variables found to be significant univariately remained so after adjusting for other important variables. A multiple logistic regression model was fitted to facial nerve outcome, with sex, age, operative approach and years of operation after 1981 included as exploratory variables in the model. Tumour size was also included in the model as an exploratory factor variable, wherein different levels corresponded to the predefined tumour size groups, with a tumour size of less than 1.5 cm as the reference category. The results were also analysed using exact tumour size. A male group was used as the reference group for gender. The translabyrinthine approach was used as the reference group for operative approach. Odds ratios were presented with 95 per cent confidence intervals (CIs) and p-values. It was important to determine if there was a trend in improvement over time, particularly in relation to a surgical learning curve. Outcome was thus also analysed in the form of a bar chart with three-year surgical segments, and by an assessment of facial nerve outcome according to tumour size increments for the most recent six years of surgery, in tabloid form. The extent of the excision was classified as total, near total, subtotal or partial. Total removal was complete excision of the tumour. Near total was defined as complete excision apart from tiny remnants of capsule on a cranial nerve or brainstem. Subtotal excision meant that greater than 95 per cent of the tumour had been removed and partial excision referred to cases where less than 95 per cent of the tumour had been removed. The categorisation of the extent of tumour excision can be seen in Figure 3. The facial nerve outcome (quantified as normal, satisfactory or unsatisfactory, as previously defined), was determined in relation to the extent of the excision.
FIG. 3 Extent of tumour excision (n = 652).
various increments of tumour size, can be seen in Table I. A summary of the outcomes for translabyrinthine cases in terms of House–Brackmann grades I and II classified as normal, grades I–III classified as satisfactory, and grades IV–VI classified as unsatisfactory can be seen in Table II. For tumours less than 1.5 cm in size, 79 per cent of translabyrinthine cases had a normal functional outcome, 96 per cent were satisfactory and only 4 per cent unsatisfactory. For tumours 1.5–2.4 cm in size, 68 per cent of cases had a normal outcome, 94 per cent were satisfactory and 6 per cent unsatisfactory. For tumours 2.5–3.4 cm in size, the rates dropped to 52 per cent for normal outcomes, 84 per cent for satisfactory outcomes and 16 per cent for unsatisfactory outcomes. For tumours 3.5–4.4 cm in size, 45 per cent of cases had normal outcomes, 76 per cent were satisfactory and 24 per cent were unsatisfactory. For very large tumours greater than 4.4 cm in size, 43 per cent of cases had a normal outcome, 74 per cent were satisfactory and 26 per cent were unsatisfactory. The results of a similar analysis conducted for the smaller number of retrosigmoid cases are shown in Table III. It is important to note that we reserve the retrosigmoid approach for patients with smaller tumours who have opted for hearing preservation surgery; the numbers of tumours sized 3.5–4.4 cm, or 4.5 cm or larger were too small to be meaningfully analysed.
Results The 24-month post-operative functional facial nerve outcomes following translabyrinthine surgery, for the
TABLE I TRANSLABYRINTHINE SURGERY OUTCOME: HB GRADE BY TUMOUR SIZE∗ Tumour size (cm) 4.4 ∗
n 97 195 126 98 47
HB I (n (%)) 64 93 44 23 11
(66.0) (47.7) (34.9) (23.5) (23.4)
HB II (n (%)) 13 40 21 21 9
(13.4) (20.5) (16.7) (21.4) (19.2)
HB III (n (%)) 16 51 41 30 15
(16.5) (26.2) (32.5) (30.6) (31.9)
Refers to outcomes at 24 months (total n = 563). HB = House–Brackmann
HB IV (n (%)) 3 3 6 5 3
(3.1) (1.5) (4.8) (5.1) (6.4)
HB V (n (%)) 0 (0) 1 (0.5) 2 (1.6) 2 (2.0) 1 (2.1)
HB VI (n (%)) 1 7 12 17 8
(1) (3.6) (9.5) (17.3) (17.0)
409
FACIAL NERVE OUTCOME OF VESTIBULAR SCHWANNOMA SURGERY
TABLE II TRANSLABYRINTHINE SURGERY OUTCOME: HB CATEGORY BY TUMOUR SIZE∗
TABLE IV RETROSIGMOID SURGERY OUTCOME: HB CATEGORY BY TUMOUR SIZE∗
Tumour size (cm)
n
HB I & II normal (%)
HB I–III satisfactory (%)
HB IV–VI unsatisfactory (%)
Tumour size (cm)
n
HB I & II normal (%)
HB I–III satisfactory (%)
HB IV–VI unsatisfactory (%)
4.4
97 195 126 98 47
79 68 52 45 43
96 94 84 76 74
4 6 16 24 26
4.4
OR
95% CI
p
0.782 0.983 1.741 1.151
0.463–1.319 0.963–1.003 0.638–4.750 1.098–1.206
0.36 0.09 0.28
The Journal of Laryngology & Otology (2014), 128, 406–415. © JLO (1984) Limited, 2014 doi:10.1017/S0022215114000541
Factors affecting final facial nerve outcome following vestibular schwannoma surgery D A MOFFAT1, R A PARKER2, D G HARDY3, R MACFARLANE3 1
Neuro-otology and Skull Base Surgery Department, Addenbrookes Hospital, Cambridge University Teaching Hospitals NHS Trust, 2Centre for Applied Medical Statistics, University of Cambridge, and 3Neurosurgery Department, Addenbrookes Hospital, Cambridge University Teaching Hospitals NHS Trust, UK
Abstract Objective: To determine factors affecting facial nerve outcome of vestibular schwannoma surgery. Methods: This retrospective cohort study comprised 652 patients. The outcome measure was House–Brackmann classification at two years post-operatively. Univariate and multivariate analyses were carried out to determine the factors affecting facial nerve outcome. The incidence rates of hemifacial spasm, metallic taste and crocodile tear syndrome were recorded. Results: For tumours less than 1.5 cm, 95 per cent of outcomes were normal, 100 per cent were satisfactory (House–Brackmann grades I–III) and 0 per cent were unsatisfactory (grades IV–VI). For tumours 1.5–2.4 cm, 83 per cent of outcomes were normal, 99 per cent were satisfactory and 1 per cent were unsatisfactory. For tumours 2.5–3.4 cm, 68 per cent of outcomes were normal, 96 per cent were satisfactory and 4 per cent were unsatisfactory. For tumours 3.5–4.4 cm, 52 per cent of outcomes were normal, 80 per cent were satisfactory and 20 per cent were unsatisfactory. For tumours larger than 4.4 cm, 50 per cent of outcomes were normal, 72 per cent were satisfactory and 28 per cent were unsatisfactory. Conclusion: Tumour size and operation year were significant predictors of facial nerve outcome. The surgical learning curve was steepest for the first 50 patients. Key words: Vestibular Schwannoma; Facial Nerve; Otologic Surgical Procedures; Prognosis
Introduction The first successful preservation of the facial nerve during complete excision of a vestibular schwannoma has been attributed to Sir Hugh Cairns, who reported the procedure in 1931.1 McKissock reported a remarkable series of facial and cochlear nerve preservation in 1965 without the aid of magnification.2 However, the introduction of the operating microscope around the same year by William House was an important milestone in vestibular schwannoma surgery.3 Microsurgical advances paved the way to fulfilling the primary goal of vestibular schwannoma surgery, which is complete tumour removal with minimal morbidity and mortality.4 Many centres throughout the world now achieve high rates of facial nerve preservation and good postoperative facial nerve function.5–12 Unfortunately, anatomical continuity of the facial nerve does not always result in good long-term facial recovery. Any corrective surgery should be undertaken relatively early for the most favourable results. It is important when counselling patients preoperatively to inform them of the likely outcome with
regard to facial nerve function, including nervus intermedius function,13 as this is an important pre-determinant of post-operative quality of life. It will also form part of an evidence base for the surgical modality of management in comparison with the other two modern modalities of observation with interval imaging and stereotactic radiotherapy. It is not only important for the surgeon to be able to quote his or her own facial nerve outcome figures, but also to be cognisant of the predictive factors which influence facial nerve outcome in vestibular schwannoma surgery. This detailed study of a large series of patients over three decades was an attempt to identify patient and surgical variables which influence facial nerve outcome and quality of life after vestibular schwannoma excision.
Materials and methods This study involved a retrospective case note analysis of a series of patients with a unilateral sporadic vestibular schwannoma and pre-operatively normal facial nerve function (House–Brackmann grade I). Patients were treated surgically, using either a translabyrinthine
Presented Orally at the Sixth International Conference on Acoustic Neuroma, 28–30 June 2011, Los Angeles, California, USA. Accepted for publication 5 August 2013 First published online 31 March 2014
407
FACIAL NERVE OUTCOME OF VESTIBULAR SCHWANNOMA SURGERY
or a retrosigmoid approach. Surgery was carried out by the senior authors (DAM, with either DGH or RM) between the years 1981 and 2010 at Addenbrookes, Cambridge University Teaching Hospital. Clinical data were collected from a 250-point database using Filemaker Pro 6 initially and more recently Filemaker Pro 10 software. Patients with neurofibromatosis type 2, those receiving pre-operative stereotactic radiotherapy and those patients with recurrent tumour referred from other units were excluded from this analysis. Patients The surgical series consisted of 652 patients with histologically proven, sporadic, unilateral vestibular schwannomas. There were 321 male patients and 331 females. The age range was 13 to 86 years, with a mean of 53.8 years and a standard deviation of 12.6 years. The age distribution in decades can be seen in Figure 1. Tumour size was assessed in terms of the maximum diameter of the mediolateral tumour including the intracanalicular portion; the series extends back to 1981 and this was the method used at that time. The authors are cognisant of the more recent measure of maximum intracranial tumour diameter,14 where solely intracanalicular tumours (vestibular schwannoma = 0 mm) are stated as such. For the sake of consistency, we used the former measurement method throughout. Maximum tumour size was measured in centimetres for each individual tumour and also classified in increments (i.e. less than 1.5 cm, 1.5–2.4 cm, 2.5–3.4 cm, 3.5–4.4 cm and 4.5 cm or larger) (Figure 2). There were 563 (86 per cent) translabyrinthine and 89 (14 per cent) retrosigmoid operations performed. Outcome measures Facial nerve function was assessed at three months, and at one, two and five years post-operatively. The final facial nerve outcome was recorded at two years postoperatively for this data analysis. Facial nerve function was assessed using the House–Brackmann grading system.15 Totally normal
FIG. 1 Age distribution in decades (n = 652).
FIG. 2 Tumour size (n = 652).
function is classified as House–Brackmann grade I; however, in line with some recently reported series, grades I and II were both considered normal. Grades I–III were classified as a satisfactory outcome and grades IV–VI as unsatisfactory at 24 months after surgery. An analysis of the facial nerve outcome at 24 months post-operatively for the translabyrinthine approach and separately for the retrosigmoid approach was carried out for each tumour size increment (i.e. less than 1.5 cm, 1.5–2.4 cm, 2.5–3.4 cm, 3.5–4.4 cm and 4.5 cm or larger), both in total numbers and percentages. Facial nerve outcome for both approaches was tabulated based on the percentages of patients with House–Brackmann grades I and II, I–III, and IV–VI. The rate of facial nerve anatomical preservation was recorded, and the type of facial reconstruction and functional outcome was documented in those few cases where the facial nerve was lost. Nervus intermedius function and aberrant regeneration of the facial nerve, in the form of altered taste and crocodile tear incidence rates, were assessed at 3 and 24 months post-operatively, along with the rates of symptom development and recovery. Magnetic resonance imaging was performed at two and five years post-operatively. Chi-square tests for trend were used to determine the individual effects of gender, tumour size (categorical) and operation approach on facial nerve outcome. (A chi-square test for trend is a version of the ordinary Pearson’s chi-square test that takes into account the ordinal nature of the facial nerve outcome variable.) A chi-square test for trend was also used to compare House–Brackmann grading in the first decade (1981–1990) with that in the second and third decades (1991–2010). Data on exact tumour size were available for 652 out of 1018 patients on the database (64 per cent); this was used to confirm the results using categories of tumour size. In order to determine whether there was a significant relationship between House–Brackmann grading and tumour size, a linear regression model was applied to the exact tumour size data, with facial
408
D A MOFFAT, R A PARKER, D G HARDY et al.
nerve outcome entering the model as a predictor variable. Similarly, a linear regression method was used to evaluate the effect of age on facial nerve outcome. Multivariate analysis was used (in the form of a multiple logistic regression) to investigate predictors of satisfactory facial nerve outcome (House–Brackmann grades I–III), and to determine if variables found to be significant univariately remained so after adjusting for other important variables. A multiple logistic regression model was fitted to facial nerve outcome, with sex, age, operative approach and years of operation after 1981 included as exploratory variables in the model. Tumour size was also included in the model as an exploratory factor variable, wherein different levels corresponded to the predefined tumour size groups, with a tumour size of less than 1.5 cm as the reference category. The results were also analysed using exact tumour size. A male group was used as the reference group for gender. The translabyrinthine approach was used as the reference group for operative approach. Odds ratios were presented with 95 per cent confidence intervals (CIs) and p-values. It was important to determine if there was a trend in improvement over time, particularly in relation to a surgical learning curve. Outcome was thus also analysed in the form of a bar chart with three-year surgical segments, and by an assessment of facial nerve outcome according to tumour size increments for the most recent six years of surgery, in tabloid form. The extent of the excision was classified as total, near total, subtotal or partial. Total removal was complete excision of the tumour. Near total was defined as complete excision apart from tiny remnants of capsule on a cranial nerve or brainstem. Subtotal excision meant that greater than 95 per cent of the tumour had been removed and partial excision referred to cases where less than 95 per cent of the tumour had been removed. The categorisation of the extent of tumour excision can be seen in Figure 3. The facial nerve outcome (quantified as normal, satisfactory or unsatisfactory, as previously defined), was determined in relation to the extent of the excision.
FIG. 3 Extent of tumour excision (n = 652).
various increments of tumour size, can be seen in Table I. A summary of the outcomes for translabyrinthine cases in terms of House–Brackmann grades I and II classified as normal, grades I–III classified as satisfactory, and grades IV–VI classified as unsatisfactory can be seen in Table II. For tumours less than 1.5 cm in size, 79 per cent of translabyrinthine cases had a normal functional outcome, 96 per cent were satisfactory and only 4 per cent unsatisfactory. For tumours 1.5–2.4 cm in size, 68 per cent of cases had a normal outcome, 94 per cent were satisfactory and 6 per cent unsatisfactory. For tumours 2.5–3.4 cm in size, the rates dropped to 52 per cent for normal outcomes, 84 per cent for satisfactory outcomes and 16 per cent for unsatisfactory outcomes. For tumours 3.5–4.4 cm in size, 45 per cent of cases had normal outcomes, 76 per cent were satisfactory and 24 per cent were unsatisfactory. For very large tumours greater than 4.4 cm in size, 43 per cent of cases had a normal outcome, 74 per cent were satisfactory and 26 per cent were unsatisfactory. The results of a similar analysis conducted for the smaller number of retrosigmoid cases are shown in Table III. It is important to note that we reserve the retrosigmoid approach for patients with smaller tumours who have opted for hearing preservation surgery; the numbers of tumours sized 3.5–4.4 cm, or 4.5 cm or larger were too small to be meaningfully analysed.
Results The 24-month post-operative functional facial nerve outcomes following translabyrinthine surgery, for the
TABLE I TRANSLABYRINTHINE SURGERY OUTCOME: HB GRADE BY TUMOUR SIZE∗ Tumour size (cm) 4.4 ∗
n 97 195 126 98 47
HB I (n (%)) 64 93 44 23 11
(66.0) (47.7) (34.9) (23.5) (23.4)
HB II (n (%)) 13 40 21 21 9
(13.4) (20.5) (16.7) (21.4) (19.2)
HB III (n (%)) 16 51 41 30 15
(16.5) (26.2) (32.5) (30.6) (31.9)
Refers to outcomes at 24 months (total n = 563). HB = House–Brackmann
HB IV (n (%)) 3 3 6 5 3
(3.1) (1.5) (4.8) (5.1) (6.4)
HB V (n (%)) 0 (0) 1 (0.5) 2 (1.6) 2 (2.0) 1 (2.1)
HB VI (n (%)) 1 7 12 17 8
(1) (3.6) (9.5) (17.3) (17.0)
409
FACIAL NERVE OUTCOME OF VESTIBULAR SCHWANNOMA SURGERY
TABLE II TRANSLABYRINTHINE SURGERY OUTCOME: HB CATEGORY BY TUMOUR SIZE∗
TABLE IV RETROSIGMOID SURGERY OUTCOME: HB CATEGORY BY TUMOUR SIZE∗
Tumour size (cm)
n
HB I & II normal (%)
HB I–III satisfactory (%)
HB IV–VI unsatisfactory (%)
Tumour size (cm)
n
HB I & II normal (%)
HB I–III satisfactory (%)
HB IV–VI unsatisfactory (%)
4.4
97 195 126 98 47
79 68 52 45 43
96 94 84 76 74
4 6 16 24 26
4.4
OR
95% CI
p
0.782 0.983 1.741 1.151
0.463–1.319 0.963–1.003 0.638–4.750 1.098–1.206
0.36 0.09 0.28
