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Acoustic neuroma: an investigation of associations between tumor size and diagnostic delays, facial weakness, and surgical complications.

Abstract

We conducted a retrospective case review to ascertain the clinical characteristics associated with acoustic neuromas and their treatment. Our study population was made up of 96 patients--41 men and 55 women, aged 17 to 84 years (mean: 54)--who had undergone treatment for acoustic neuromas and for whom necessary data were available. We compiled data on presenting symptoms, the interval from symptom onset to diagnosis, tumor size at diagnosis, facial weakness, the interval from diagnosis to surgery, the type of surgical approach, and surgical complications. Our primary goals were to determine if tumor size was correlated to (1) the interval from symptom onset to diagnosis, (2) the degree of preoperative facial weakness, and (3) surgical complications. We also sought to document various other clinical characteristics of these cases. The mean interval from the first symptom to diagnosis was 4.5 years; the time to diagnosis did not correlate with tumor size. Nor was tumor size correlated with the degree of preoperative facial weakness as determined by facial electroneurography. Surgical complications occurred in 15 of the 67 patients who underwent surgery (22.4%), and they did correlate with tumor size. The most common complications were postoperative facial weakness (13.4% of operated patients), cerebrospinal fluid leak (6.0%), and infection (3.0%). Since tumors typically grow about 2 mm per year and since larger tumors are associated with more severe symptoms and surgical complications, we expected that the time to diagnosis would correlate with tumor size, but we found no significant association.

Introduction

Acoustic neuromas (vestibular schwannomas) are benign neoplasms that usually arise on the superior vestibular portion of the auditory nerve (cranial nerve [CN] VIII); larger acoustic neuromas can involve other nerves, including the facial nerve (CN VII). These lesions account for 8 to 10% of all intracranial tumors and more than 90% of all cerebellopontine angle tumors. (1) Although they are benign, acoustic neuromas can cause considerable morbidity if left untreated because of their location in the internal auditory canal and cerebellopontine angle.

Most acoustic neuromas are idiopathic, while others occur as an autosomal dominant form that manifests as neurofibromatosis type 2 (NF2). (2) NF2 is caused by a mutation on the NF2 gene on the long arm of chromosome 22. Patients with NF2 often develop bilateral tumors.

The annual incidence of acoustic neuromas was recently reported as 1.1 per 100,000 population. (3) It is interesting that there has been a substantial change in the reported incidence over time, probably due, at least in part, to technologic improvements. According to Stangerup et al, 0.31 cases per 100,000 population were diagnosed in 1976,2.28/100,000 were diagnosed in 2004, and 1.94/100,000 were diagnosed in 2008. (4)

Anderson et al reviewed 24,246 magnetic resonance imaging (MRI) scans and reported that the prevalence of asymptomatic acoustic neuromas found incidentally was 0.07%. (5)

In a review of socioeconomic data, Schuz et al made an interesting finding, suggesting that acoustic neuromas are less common in people who are not highly educated, who are unemployed, and who retire early. (6)

Common presenting symptoms include unilateral sensorineural hearing loss, tinnitus, and disequilibrium. If left untreated, large masses can compress not only other cranial nerves but also the fourth ventricle and cause hydrocephalus. Acoustic neuromas of the facial nerve can cause ipsilateral facial weakness.

On average, acoustic neuromas are believed to grow at a rate of about 2 mm per year, although individual rates vary substantially. (1) However, while some tumors continue to grow, many stop growing at some point. Martin et al reviewed 276 cases of acoustic neuroma and found that 22% of them grew; their mean annual growth rate was 4 mm (range: 0.5 to 17). (7) Some 35% of these tumors grew rapidly (5 to 17 mm per year). Approximately 90% of all the growing tumors were recognized as such within 3 years of diagnosis.

Battaglia et al reviewed the literature and found that 18% of acoustic neuromas grew at least 1 mm per year. (8) Other extensive literature reviews in which large numbers of patients were evaluated found that at least 50% of tumors did not grow, and the growth rate for all tumors (factoring in those that did not grow) was between 1 and 2 mm per year; for only those tumors that did grow, the rate was generally between 2 and 4 mm per year. (9,10)

Both Martin et al (7) and Battaglia et al (8) noted that some tumors actually regress and that some grow at a rate greater than 18 mm per year.

Tieleman et al reported that, overall, the size of tumors has steadily decreased over time. (11) They found that in 1991, the mean tumor size at the time of diagnosis was 30 mm; by 2008, it was only 10 mm. In the review by Anderson et al, 8 of 17 unsuspected acoustic neuromas were smaller than 1 cm, 6 were between 1 and 2 cm, and 3 were 2 cm or larger. (5) According to Schuz et al, socioeconomic factors were not associated with tumor size. (6)

There is no universal agreement on the optimal approach to diagnosing acoustic neuromas. In addition to a good clinical examination, common diagnostic tests include audiometry and auditory brainstem response (ABR) testing. However, these are generally regarded as screening tools, and controversies remain regarding their sensitivity and specificity.

Gadolinium-enhanced MRI of the internal auditory canals is considered to be the standard confirmatory test. If a patient is unable for medical reasons to receive gadolinium, an unenhanced MRI may be sufficient, especially if it is performed on high-resolution equipment. If a patient cannot undergo MRI, computed tomography (CT) with contrast or air-contrast CT may be used to detect the lesion.

Management options include watchful waiting with symptomatic treatment, focused radiation (stereotactic radiosurgery), and surgical excision. Surgery can be performed via several different approaches, depending on tumor size, the degree of hearing loss, and the surgeon's experience. The translabyrinthine approach does not preserve hearing, while the retrosigmoid approach might. The middle fossa approach can preserve hearing, but it is usually reserved for small tumors that are confined to the internal auditory canal.

In this article, we describe our study of patients with acoustic neuromas to determine whether tumor size was correlated with various factors.

Patients and methods

For this retrospective study, we examined the available office charts of patients diagnosed with an acoustic neuroma who had been seen at our tertiary care neurotologic referral center. Our primary goals were to determine if tumor size was correlated to (1) the interval from onset of symptoms to diagnosis, (2) the degree of preoperative facial weakness, and (3) surgical complications. We also sought to document various other clinical characteristics of these cases.

We found sufficient usable data on 96 patients--41 men and 55 women, aged 17 to 84 years (mean: 54). All patients had undergone observation, surgery, or stereotactic radiosurgery. All surgeries, including stereotactic radiosurgeries, had been performed by the senior author (R.T.S.).

In addition to demographic information, we compiled pre-, intra-, and postoperative data, de-identified them, entered them into a computerized database, and analyzed the results. These data included detailed information on presenting symptoms, the interval from symptom onset to diagnosis, tumor size at diagnosis, facial weakness, the interval from diagnosis to surgery, the type of surgical approach, and surgical complications.

Facial nerve function was measured by electroneurography (ENoG), which had been performed with bipolar electrodes placed 18 mm apart. Square-wave impulses were generated in front of the tragus. Summation potentials from the facial muscles were recorded through electrodes placed adjacent to the alar rim and corner of the mouth. Maximal responses were used for calculation. All patients had clinically normal facial motion preoperatively.

We used the criteria described by Schmidt et al to define ABR results. (12) Results were considered to be abnormal if:

* the interaural difference in wave I-V delay was greater than 0.2 ms;

* the interaural difference in absolute wave V latency was greater than 0.2 ms;

* wave I could not be identified with certainty in one or both ears, with the Brackmann correction factor applied for ears with hearing loss greater than 50 dB at 4.0 kHz; and

* there were no identifiable waves.

Data were collected in a custom-designed Access database (Microsoft; Redmond, Wash.) and exported into individual Microsoft Excel spreadsheets. Statistical analysis--including generation of graphs, regression tests, and the Student t test--was performed with Microsoft Excel. Statistical significance was set at p < 0.05.

Approval for the study was granted by the Institutional Review Board at the Drexel University College of Medicine.

Results

Presenting symptoms. A total of 71 patients (74.0%) presented with hearing loss, 56 (58.3%) presented with tinnitus, and 30 (31.3%) presented with dizziness. Some 54 patients (56.3%) had a chief complaint of hearing loss, 25 (26.0%) cited tinnitus, 14 (14.6%) complained primarily of dizziness, and 3 (3.1%) initially complained of other symptoms.

Hearing loss. Of the 71 patients with hearing loss, 70 (98.6%) had asymmetric hearing loss. Of the 70 patients with asymmetric hearing loss, 58 (82.9%) had worse hearing on the side of the acoustic neuroma. Symmetrical hearing loss was defined as no more than a 15-dB difference in average hearing thresholds from 0.5 to 8.0 kHz. Data on the severity of asymmetric hearing loss are shown in table 1.

ABR testing on the tumor side was performed on 71 of the 96 patients (74.0%). The remaining 27 patients did not undergo testing because their hearing loss was too severe to permit ABR recordings. Many of the tested patients had no abnormality on ABR (table 2).

Tinnitus. The 56 patients who reported tinnitus were asked to describe its character, volume, and severity (table 3).

Onset to diagnosis. At the initial evaluation, the senior author established the approximate time when each patient experienced his or her first symptom by meticulous questioning, keeping in mind the possibility of recall bias. This questioning revealed that the interval from symptom onset to diagnosis ranged from 0 to 47 years (mean: 4.5).

Tumor size at diagnosis. Tumor size at diagnosis ranged from 0.5 mm to 60 mm (mean: 16.8). For tumors 15 mm and smaller, the average time to diagnosis was 3.3 years, and for those larger than 15 mm, the interval was 4.8 years. There was no significant correlation between tumor size and the time to diagnosis (figure 1).

Facial weakness. ENoG testing for facial nerve function was performed soon after the first visit on 68 patients. Some patients declined ENoG because of problems with insurance coverage. Of this group, 30 patients (44.1%) were found to have an ipsilateral ENoG reduction of 10% or more, another 26 patients (38.2%) had an ipsilateral ENoG reduction of 25% or more, and the remaining 12 patients had either no reduction or a reduction of less than 10%. There was no significant correlation between tumor size at diagnosis and preoperative facial weakness as measured by ENoG (figure 2).

Diagnosis to surgery. The interval from diagnosis to surgery ranged from 2 months to 12 years (mean: 3.6 yr). Some patients who were only observed at first later underwent surgery because of documented tumor growth.

Type of surgery. Surgery was recommended for 68 patients and performed on 67 (table 4). The most commonly used surgical route was the translabyrinthine approach, which was used in 53 of the 67 cases (79.1%).

Complications of surgery. Surgical complications occurred in 15 of the 67 patients who underwent surgery (22.4%). They occurred in 11 of 53 patients (20.8%) who underwent translabyrinthine surgery and in 4 of 8 (50.0%) who underwent surgery via a combined retrosigmoid and transtemporal approach (table 4).

Tumor size was correlated with surgical complications. The average tumor size was 27.4 mm in patients who experienced surgical complications, and 13.7 mm in those who did not, representing a 100% increase in size in the former group.

The most common complication was postoperative facial weakness, which occurred in 9 of the 15 patients (60.0%) (table 5). Of these 9 patients, preoperative ENoG data were available for 7 patients. The mean ENoG response was 49.71% for the 7 patients who experienced postoperative palsy and 39.78% for the 60 patients who did not. The difference between these two groups was not statistically significant.

All 9 of the patients who experienced postoperative facial nerve weakness did so in the immediate postoperative period. On the House-Brackmann scale, 6 were graded as VI/VI, 2 as V/VI, and 1 as I-II/VI. One year after surgery, follow-up data were available on 8 of the 9 patients. All but 1 of these 8 patients experienced an improvement in facial nerve function (5 patients were graded as House-Brackmann III/VI or better).

Finally, there was no statistically significant association between the incidence of postoperative facial weakness and the interval from symptom onset to diagnosis. The time to diagnosis was 6 years among patients with postoperative palsy and 5.76 years for those without.

Discussion

Our finding that the three most common presenting symptoms were asymmetric hearing loss, tinnitus, and dizziness is consistent with other reports in the literature.

[FIGURE 1 OMITTED]

Hearing loss was a presenting symptom in 74.0% of our patients and the chief complaint in 56.3%. This is comparable to the 87 and 65% reported by Chandrasekhar et al in 1995. (13) In our study, audiometry showed that hearing loss was generally mild across the frequencies required to hear speech and more acute at the higher frequencies.

In our study, tinnitus was reported by 58.3% of patients, and it was a chief complaint in 26.0%. These rates are roughly comparable to the 80 and 16% rates reported by Chandrasekhar et al. (13)

Dizziness was reported by 31.3% of our patients, and it was the chief complaint of 14.6%. Chandrasekhar et al reported rates of 57 and 10%, respectively. (13)

The large proportion of patients who presented with hearing loss, tinnitus, and/or dizziness in our study and in others underscores the importance of these symptoms in the diagnosis of acoustic neuromas. A minority of patients will present with all three symptoms. However, the initial presentation of acoustic neuroma is highly variable, and other patients will present with less common symptoms (e.g., facial weakness, headaches, and nystagmus) and some will have no symptoms at all. This variability may contribute to the long interval between the onset of symptoms and diagnosis. Time to diagnosis was not significantly correlated with tumor size in our study, nor were ABR results.

The sometimes complex presentation of acoustic neuroma can pose a diagnostic quandary for primary care physicians, who may not identify these symptoms as necessitating a referral, MRI, or even audiometry. Most of our patients with long delays in diagnosis had been under the care of a primary care physician who was aware of their complaints for years before the diagnosis was established. The problem of diagnostic delays can be exacerbated by a lack of medical insurance coverage among a significant portion of the general population and the refusal of insurance organizations to provide reimbursement for certain diagnostic tests.

In our study, preoperative facial ENoG revealed a reduction in ipsilateral amplitude of 10% or more in 44.1 % of patients and a reduction in ipsilateral amplitude of 25% or more in another 38.2%. The former figure is much lower than that found in a study by Kartush et al (14) (85%), and the latter is much higher than that reported in a study by Syms et al (18%). (15) We found no correlation between preoperative ENoG-measured facial nerve function and tumor size. This finding calls into question the value of ENoG as a diagnostic tool. Still, ENoG might be useful in establishing a baseline level of facial nerve function for comparison purposes following subsequent surgery or other management.

[FIGURE 2 OMITTED]

Surgical complications occurred in 22.4% of the patients who underwent resection. Complications did have a positive correlation with tumor size; on average, the tumors in those with complications were twice as large as the tumors in those who did not have complications. This significant difference illustrates at least one benefit of earlier diagnosis.

The combined retrosigmoid and transtemporal approach represented only 10.4% of all surgeries but 26.7% of all complications. We believe this disparity is probably attributable to larger tumor size rather than the surgical technique itself. Our complication rates were similar to those in previously reported series. (16,17)

We expected that the interval from the onset of symptoms to the diagnosis would be a significant factor in our study, since larger tumors have been associated with more severe symptoms and surgical complications. However, we found that tumor size was not correlated with the time to diagnosis. This might be because the delays were generally not extremely long (mean: 4.5 yr) or because our sample size was too small to yield a correlation.

Overall, diagnostic delays seem to be under-reported in the existing literature. Given the efficacy of modern MRI technology and the common symptom presentation of most acoustic neuroma patients (i.e., asymmetric sensorineural hearing loss, tinnitus, and dizziness), it should be possible to reduce the time from first symptom to diagnosis. Moreover, given the increased efficacy and diminished morbidity associated with current treatment modalities, a reduction in diagnostic lead time should clearly be a goal worth achieving. Strategies for improving this situation should be pursued, and the consequences of diagnostic delays should be studied further in larger, multi-institutional investigations.

Diagnostic methodology and treatment options have changed over time, particularly the use of MRI and stereotactic radiosurgery, and further advances are anticipated. (18) Continued evaluation of diagnostic tools, their sensitivity, specificity, and efficacy is necessary as imaging becomes more refined and cost-effective, as is assessment of treatments.

References

(1.) Brackmann DE, Arriaga MA. Posterior fossa skull base neoplasms. In: Cummings CW, Frederickson J, Krause C, Schuller D, eds. Cummings Otolaryngology-Head and Neck Surgery. 4th ed. St. Louis: Mosby; 2005:2514-15.

(2.) Xiao GH, Chernoff J, Testa JR. NF2: The wizardry of merlin. Genes Chromosomes Cancer 2003;38(4):389-99.

(3.) Gal TJ, Shinn J, Huang B. Current epidemiology and management trends in acoustic neuroma. Otolaryngol Head Neck Surg 2010;142(5):677-81.

(4.) Stangerup SE, Tos M, Thomsen J, Caye-Thomasen P. True incidence of vestibular schwannoma? Neurosurgery 2010;67(5):1335-40.

(5.) Anderson TD, Loevner LA, Bigelow DC, Mirza N. Prevalence of unsuspected acoustic neuroma found by magnetic resonance imaging. Otolaryngol Head Neck Surg 2000;122(5):643-6.

(6.) Schuz J, Steding-Jessen M, Hansen S, et al. Sociodemographic factors and vestibular schwannoma: A Danish nationwide cohort study. Neuro Oncol 2010;12(12):1291-9.

(7.) Martin TP, Senthil L, Chavda SV, et al. A protocol for the conservative management of vestibular schwannomas. Otol Neurotol 2009;30(3):381-5.

(8.) Battaglia A, Mastrodimos B, Cueva R. Comparison of growth patterns of acoustic neuromas with and without radiosurgery. Otol Neurotol 2006;27(5):705-12.

(9.) Fortnum H, O'Neill C, Taylor R, et al. The role of magnetic resonance imaging in the identification of suspected acoustic neuroma: A systemic review of clinical and cost effectiveness and natural history. Health Technol Assess 2009;13(18):iii-v, ix-xi, 1-154.

(10.) Nikolopoulos TP, Fortnum H, O'Donoghue G, Baguley D. Acoustic neuroma growth: A systematic review of the evidence. Otol Neurotol 2010;31(3):478-85.

(11.) Tieleman A, Casselman JW, Somers T, et al. Imaging of intralabyrinthine schwannomas: A retrospective study of 52 cases with emphasis on lesion growth. AJNR Am J Neuroradiol 2008;29(5):898-905.

(12.) Schmidt RJ, Sataloff RT, Newman J, et al. The sensitivity of auditory brainstem response testing for the diagnosis of acoustic neuromas. Arch Otolaryngol Head Neck Surg 2001;127(1):19-22.

(13.) Chandrasekhar SS, Brackmann DE, Devgan KK. Utility of auditory brainstem response audiometry in diagnosis of acoustic neuromas. Am J Otol 1995;16(1):63-7.

(14.) Kartush JM, Graham MD, Kemink JL. Electroneurography: Preoperative facial nerve assessment in acoustic neuroma surgery: A preliminary study. Am J Otol 1986;7(5):322-5.

(15.) Syms CA III, House JR III, Luxford WM, Brackmann DE. Preoperative electroneuronography and facial nerve outcome in acoustic neuroma surgery. Am J Otol 1997;18(3):401-3.

(16.) Sanna M, Taibah A, Russo A, et al. Perioperative complications in acoustic neuroma (vestibular schwannoma) surgery. Otol Neurotol 2004;25(3):379-86.

(17.) Slattery WH III, Francis S, House KC. Perioperative morbidity of acoustic neuroma surgery. Otol Neurotol 2001;22(6):895-902.

(18.) Kondziolka D, Mousavi SH, Kano H, et al. The newly diagnosed vestibular schwannoma: Radiosurgery, resection, or observation? Neurosurg Focus 2012;33(3):E8.

Marc Olshan, MD, MBA; Visish M. Srinivasan, MD; Tre Landrum, DO; Robert T. Sataloff, MD, DMA, FACS

From the Department of Internal Medicine, University of Miami-Jackson Memorial Hospital, Miami (Dr. Olshan); the Department of Neurosurgery, Baylor College of Medicine, Houston (Dr. Srinivasan); the Department of Otolaryngology-Head and Neck Surgery, Valley View Regional Hospital, Ada, Okla. (Dr. Landrum); and the Department of Otolaryngology-Head and Neck Surgery, Drexel University College of Medicine, Philadelphia (Dr. Sataloff). This study was conducted at the Drexel University College of Medicine.

Corresponding author: Robert T. Sataloff, MD, DMA, FACS, Department of Otolaryngology-Head and Neck Surgery, Drexel University College of Medicine, 1721 Pine St., Philadelphia, PA 19103. Email: RTSataloff@PhillyENT.com
Table 1. Severity of asymmetric hearing loss

                                   Frequency (kHz)

Asymmetry, dB      0.25       0.5       1.0       2.0        3.0

Range             5 to 75   5 to 85   5 to 85   5 to 105   5 to 100
Mean                24        28        35         39         38
Median              20        20        35         40         40
Mode                 5         5        40         10         20

                         Frequency (kHz)

Asymmetry, dB       4.0       6.0       8.0

Range             5 to 95   5 to 90   5 to 95
Mean                36        38        35
Median              35        40        30
Mode                50        35        10

Table 2. Results of auditory brainstem response
testing (n = 71)

Measurement                                   n (%) *

11.1 pps long absolute wave V                27 (38.0)
(>6.04 ms)

11.1 pps long absolute wave 1-V              19(26.8)
(>4.31 ms)

57.7 pps long absolute wave V                17(23.9)
(>6.52 ms)

57.7 pps long absolute wave l-V               2 (2.8)
(>4.72 ms)

Interaural difference                        12 (16.9)
(>0.2ms)

* Some patients had more than one abnormality.

Table 3. Character, volume, and severity of tinnitus
(n = 56)

Variable                  n (%)

Character
  Ringing               13(23.2)
  Seashell              11 (19.6)
  Buzzing               10 (17.9)
  Heartbeat              4 (7.1)
  Hissing                3 (5.4)
  Voices                 2 (3.6)
  Crickets               2 (3.6)
  Whistling              1 (1.8)

Not characterized       10 (17.9)
  Volume
  Soft whisper          20 (35.7)
  Electric fan          16 (28.6)
  Diesel truck motor     3 (5.4)
  Jet taking off         1 (1.8)
  Other                  1 (1.8)
  Not characterized     15 (26.8)

Severity
  Mild                  19 (33.9)
  Moderate              15 (26.8)
  Severe                8 (14.3)
  Very severe            4 (7.1)
  Not characterized     10 (17.9)

Table 4. Surgical approaches (n = 67)

Approach             Recommended,     Performed,
                          n              n (%)

Translabyrinthine         53           53 (79.1)
Retrosigmoid and
  transtemporal            8           7 (10.4)
Middle fossa               4            4 (6.0)
Suboccipital               2               0
Stereotactic
  radiosurgery             1            3 (4.5)

Approach            Complications,    Mean tumor
                         n (%)           size

Translabyrinthine      11 (20.8)        23.8 mm
Retrosigmoid and
  transtemporal        4 (57.1)         38.3 mm
Middle fossa               0
Suboccipital              --
Stereotactic
  radiosurgery             0

Table 5. Surgical complications (n = 15)

Complication                                  n (%)

Facial weakness                              9 (60.0)
CSF leak                                     4 (26.7)
Infection                                    2 (13.3)
Unexpected hearing loss                         0
Prolonged vertigo                               0
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Title Annotation:ORIGINAL ARTICLE
Author:Olshan, Marc; Srinivasan, Visish M.; Landrum, Tre; Sataloff, Robert T.
Publication:Ear, Nose and Throat Journal
Article Type:Report
Date:Aug 1, 2014
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