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Sudden hearing loss in acoustic neuroma patients
Sudden hearing loss in acoustic neuroma patients JAMES E. SAUNDERS, MD, WILLIAM M. LUXFORD, MD, K. KAY DEVGAN, MD, and BRUCE L. FEI"rERMAN,MD,
Los Angeles, California Patients with acoustic neuroma m a y have sudden sensorineural hearing loss. Most patients with sudden hearing loss seek medical attention promptly, but the diagnosis of an acoustic neuroma m a y be delayed for months or years because sudden hearing loss is an unusual initial symptom of an acoustic neuroma. In a retrospective review of 836 cases of sudden hearing loss, we found t 3 patients with acoustic neuromas. The prevalence of acoustic neuromas for those screened with auditory brain stem response or magnetic resonance imaging was 2.5%. In addition to these t3 patients, 79 acoustic neuroma patients treated in our clinic had well-documented sudden hearing loss as the initial symptom. Hearing loss in these 92 patients ranged from mild to profound. Associated symptoms of pain, facial paresthesia, or unilateral tinnitus preceding the sudden hearing loss were suggestive of an acoustic neuroma, as was a midfrequency [U-shaped) hearing loss. A history of other diseases or events that might explain the sudden hearing loss, a normal electronystagmogram, or recovery of hearing does not eliminate the possibility of a tumor. Because there are no clinical findings that clearly distinguish those patients with acoustic neuromas from other patients with sudden hearing loss, we recommend either an evaluation with auditory brain stem response or gadolinium-enhanced magnetic resonance imaging for any patient with sudden hearing loss. [OTOLARYNGOLHEAD NECK SURG 1995;113:23-31 .}
| n his 1917 monograph on the diagnosis and management of acoustic tumors, Cushing I described two patients with sudden hearing loss (SHL). Since that time there have been numerous reports of SHL in acoustic neuroma (AN) patients. 2-17 According to Moffat et al., ~7 10.2% of A N patients have SHL as their primary symptom, making SHL the second most common initial symptom in A N patientsJ 7 Although most patients with SHL will seek medical attention promptly, some patients may ignore this initial symptom. When asked retrospectively about their symptoms, more than one fourth of tumor patients will relate some episode of SHL during their clinical courseJ 5 Many tumors in patients with SHL may not be diagnosed for more than a year after the SHL eventJ 3 All too often patients with
From the House Ear Clinic and House Ear Institute (Drs. Saunders and Luxford) and the Universityof Southern California Medical Center (Drs. Devgan and Fetterman). Presented at the Annual Meeting of the American Academy of Otolaryngology-Head and Neck Surgery, San Diego, Calif., Sept. 18-21, 1994. Received for publication Oct. 24, 1994; accepted Jan. 20, 1995. Reprint requests: William M. Luxford, MD, House Ear Clinic, 2100 West Third St., First Floor, Los Angeles, CA 90059. Copyright © 1995by the American Academyof OtolaryngologyHead and Neck Surgery Foundation, Inc. 0194-5998/95/$3.00 + 0 23/l/63547
SHL from an A N (SHL/AN) are treated by physicians who are either unaware of the possibility of an acoustic tumor in this setting or who elect not to evaluate these patients because the frequency of ANs in SHL is believed to be extremely low. To address this problem, we set out to define the prevalence of ANs in patients with SHL, to determine whether there are any clinical features that could distinguish these patients, and to clarify the pathophysiology of SHL in A N patients. The prevalence of ANs in patients with SHL is unclearJ 8 Hallberg 19 found one patient with an AN in a large series of patients with SHL (178 cases) in 1956. Jaffe, 2° however, did not identify ANs as a potential cause of SHL in his review of 143 patients. Nedzelski and Dufour 4 subsequently reported a tumor prevalence of 3% in a series of 63 patients with SHL, but they suggested that this overestimated the actual rate. In their series of 1220 SHL patients, Shaia and Sheehy 5 found 10 ANs, for a prevalence in this population of 0.8%. Despite this low frequency, the authors strongly recommended that all patients with SHL should be evaluated to rule out an AN. Welling et al. 2~proposed a cost-effective approach to the diagnosis of an AN that is based on the probability of finding a tumor in a given clinical situation. They estimated the probability of an acoustic tumor in SHL to be 5% to 30% and thus recommended a 23
24
Otolaryngology Head and Neck Surgery July 1995
SAUNDERSet al.
100
NS
[~. SHL w/AN
90
SHL
80 c
70 60
IX.
"6
50
NS~
¢o
o_
p<.01
40 30
20
p_<,.05
p_<.01
p<.001
10 Tinnitus
Tinnitus Before
Dizzy
Fullness
Otalgia Paresthesia
Symptoms Fig. t. Symptoms of patients with SIlL/AN and SHL. Statistical differences between the groups are indicated. (Reprinted with permission of House Ear Institute.)
gadolinium-enhanced magnetic resonance imaging (MRI/Gd) scan to evaluate these patients. Their estimate of tumor prevalence was based on the clinical experience of the authors and a higher detection rate with the use of MRI/Gd. The actual prevalence of ANs in SHL patients evaluated with auditory brain stem response (ABR) and MRI/Gd has not been reported. Several studies have attempted to identify clinical features that distinguish SHL/AN patients from those with other causes of SHL5 '12 Most of these studies are based on relatively small series of patients, and there is little consensus between studies. Nedzelski and Dufour4 concluded that SHL/AN patients will generally have abnormal caloric electronystagmography (ENG) and poor hearing recovery. There have been numerous recent reports, however, of SHL recovery in patients with an AN. 1°,11,~4 Likewise, ENG findings in SHL/AN have varied between studies. Yoshimoto 12found canal paresis in all patients with SHL/AN, whereas Ogawa et al. ~3 suggested that a trough or U-shaped audiogram and a normal ENG are typical of SHL/AN patients. 9,~3 Other studies have reported a more heterogeneous array of audiogram shapes, v'17 Pensak et al. 7 were unable to identify any distinguishing audiologic features of these patients. Furthermore, there have been conflicting reports of tumor size in patients with SHL/AN. A disproportionate number of small tumors have been suggested by some, ~3'~6whereas others report that larger tumors are more common. 12 In addition, the pathophysiology of SHL in AN patients is not well understood. In general, ANs
grow very slowly.22How these slow-growing tumors cause an abrupt onset of symptoms is unclear. The mechanisms of vascular compromise, neuronal conduction block, rapid tumor growth, and immune or toxic effects on the cochlea have all been considered. 3'7'1°'13 Because of the distribution of the labyrinthine blood supply, an acute vascular occlusion has been postulated to result in a low-frequency or flat hearing loss and vestibular dysfunction.3,1° One patient with a known vascular cause of SHL from an internal auditory artery aneurysm has been described (Roberson J, Luxford WM. Internal auditory artery aneurysm. Submitted to OTOLARYNGOLHEAD NEcI~ SURG, 1994). SHL from tumor compression on the cochlear nerve (conduction block) is believed to result in a trough or U-shaped audiogram with normal vestibular function. 13 Small tumors of the inferior vestibular nerve, because of their juxtaposition to the cochlear nerve, might be more likely to cause a cochlear nerve conduction block than superior vestibular nerve tumors? 3 Finally, rapid tumor expansion could cause SHL and might be associated with the pathologic findings of hemorrhage, cystic degeneration, or necrosis. We present a detailed study of a large series of patients with SHL/AN. The purposes of this study are (1) to define the prevalence of ANs in the SHL population with the current diagnostic techniques (ABR and MRI/Gd), (2) to identify the typical clinical findings in SHL/AN patients and compare these features with those from other patients with SHL, and (3) to evaluate the proposed theories of SHL/AN pathophysiology by
Otolaryngology Head and Neck Surgery Volume 113 Number I
SAUNDERSet al.
25
100 [-] SHL w/AN
90
SHL
80 ¢O3
70 6O p<.05
CI.
"5 E O ,o
50 4O
O
13.
20 10 0
) High Frequency
p<.001 NS
Flat
Low Frequency
Mid Frequency
Profound
Audiogram Configuration Fig. 2. Audiogram configuration in patients with SHL/ANand SHL.Statistical differences between the groups are indicated. (Reprinted with permission of House Ear Institute,)
comparing SHL/AN patients with data from other AN patients. An appreciation of the clinical characteristics of SHL/AN patients may improve our general understanding of how acoustic tumors affect the cochlear system and our ability to diagnose these tumors early. METHODS
This study includes data that were retrospectively collected from the clinic charts of two groups of patients. The first group is comprised of 836 patients with well-documented SHL seen at the House Ear Clinic from January 1989 to December 1993 (SHL group). The second group includes data from 1487 patients with AN treated at the House Ear Clinic for a 10-year period (January 1982 to March 1993). Ninety-two patients with ANs and well-documented SHL were identified in these two patient groups (13 in the SHL group and 79 in the AN group). This combined group of 92 patients with SHL/AN are the main focus of the study. SHL was defined as any rapid change in hearing with evidence of elevated pure-tone thresholds (> 25 dB HL). Two patients with AN who had a sudden change in speech discrimination with normal pure-tone thresholds were excluded from this study. The vast majority of patients had hearing loss immediately or on awakening, and only patients with SHL occurring in less than 48 hours were included. This group included 45 men and 47 women. The mean age was 48 years, with a range from 26 to 81 years. Data collected included
demographic data, symptoms at the time of onset, treatment rendered, time elapsed between presentation and tumor diagnosis (diagnostic delay), audiometry and ABR results, ENG results, radiographic findings, surgical findings, tumor size, and pathologic findings. The assessment of hearing recovery was based both on the subjective impression of the patient or the treating physician and on an objective audiologic measure when these data were available. Audiologic improvement was defined as a decrease in pure-tone average (PTA) of 10 dB or a 15% improvement in speech discrimination. The clinical findings for the SHL/AN patients were compared with the data from the 836 patients with SHL (SHL group) and with data from the 1487 patients in the AN database (AN group). Statistical differences between groups were assessed with a two-tailed Z test of the difference between proportions and a two-tailed Student's t test. The criterion for statistical significance was set at p _< 0.05. RESULTS P r e v a l e n c e of ANs in SHL
The estimated tumor prevalence rates are shown in Table I. To accurately estimate the prevalence of ANs in the SHL population, it is necessary to consider SHL patients independently from patients referred with ANs. In our review of 836 charts seen primarily for SHL, only 13 tumors were found (1.5%). The workup of these patients was variable. Only 523 patients were evaluated with ABR and/or
26
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SAUNDERS et al.
T a b l e I . P r e v a l e n c e of AN in p a t i e n t s with SHL Group
No. of AN found
No. of SHL patients
Prevalence [%]
SHL as primary diagnosis SHL patients screened with ABR or MRI/Gd SHL patients screened with MRI All House Ear Clinic SHL patients (1/89-12/92)
13 13 13 40
836 523 431 740
1.5 2,5 2,7 5.4
MRI/Gd, for a tumor prevalence of 2.5% if only these patients are included. Because all tumor patients eventually had an MRI/Gd scan, the prevalence rate for patients who were evaluated with MRI/Gd (431 patients) was 2,7%. Of the 1487 ANs treated at the House Ear Clinic from January 1982 to March 1993, a description of the initial symptoms was available in 1204 cases. SHL was recorded as the initial symptom in 116 of these 1204 patients (9.6%). Thirty-seven of these 116 cases were excluded from this study because, on further review, they did not meet our criteria for SHL. The 79 remaining cases all had a well-documented episode of SHL, comprising slightly more than 5% (79 of 1204) of our AN patients. Of these 79 cases, 27 patients were treated during a 4-year period (January 1989 to December 1992) that coincided with our 5-year review of SHL patients. If these 27 cases are combined with our 13 patients from the SHL group, a total of 40 patients with SHL/AN were seen at the House Ear Clinic from January 1989 to December 1992. During this 4-year period, 740 patients with SHL were seen. Therefore, if all patients with SHL/AN are included, the AN prevalence in the SHL population at our clinic would be 5.4% (40 of 740). This rate does not account for those SHL patients who were determined by outside physicians not to have an acoustic tumor and therefore were not referred. This figure may be considered, however, as an estimate of the tumor frequency is a neurotology referral practice. Characteristics of SHL in AN Patients
The clinical findings of the combined group of 92 patients with SHL/AN were analyzed and compared with the findings in the SHL and AN groups. No significant differences were found between these groups for age, sex, or affected side. Information on other symptoms at the time of SHL was available in 89 SHL/AN patients and 739 patients with SHL (Fig. 1). Unilateral tinnitus wascommon in both groups, but 15.4% of patients with SHL/AN related some tinnitus in the affected ear preceding the SHL event; this symptom was rare (3.7%) in the SHL
population (p _< 0.01). No significant difference was found in the percentage of patients with vestibular symptoms between SHL/AN patients (34.1%) and the SHL group (42.7%). Unlike tinnitus that preceded the SHL event, balance problems before the SHL were rare for both groups (8.0% for SHL/AN, 5.3% for SHL). Otalgia and facial paresthesia were significantly more frequent in those patients with SHL/AN than in the SHL group (p _ 0.05 and p _< 0.001, respectively). In contrast, aural fullness or pressure was more common in the patients with SHL than in those with SHL/AN (p _< 0.01). Many of the patients in the SHL/AN group had other diseases or "precipitating" events that could be considered to contribute to SHL, thus confounding the tumor diagnosis (Table 2). The mean PTA and speech discrimination score (SDS) for each study group are shown in Table 3. No significant difference was found in these audiometric parameters between the SHL/AN group and other patients with ANs. Surprisingly, the PTA and SDS for the SHL/AN group were significantlybetter than for the SHL group. Audiogram configuration data were available on 89 patients with SHL/AN and 451 patients from the SHL group (Fig. 2). All audiogram shapes were represented in both the SHL/AN and SHL groups. Midfrequency (U-shaped) and high-frequency sloping hearing loss were more common in SHL patients with tumors than in the overall SHL group (p _< 0.01 andp _ 0.05, respectively). In contrast, only one patient in the SHL/AN group had a low-frequency pattern, whereas 25.2% of the SHL group had this configuration (p _< 0.001). Of the 30 patients evaluated with ENG in the SHL/AN group, abnormal ENG findings ( > 30% reduced vestibular response) were noted in 60% (Fig. 3). This rate is not significantly different from that of the AN group (69.9%) but is significantly higher than that of the SHLgroup (42.8%,p <_ 0.05). Most tumors in patients with SHL/AN were diagnosed within 6 months of the SHL event. If the diagnosis is not made within the first 6 months, however, there is a tendency for the diagnosis to go unrecognized. The mean interval between SHL and
Otoloryngology Head and Neck Surgery Volume 113 Number I
tumor diagnosis was just under 2 years (22 months), and almost 20% of patients were not diagnosed for more than 2 years after the SHL event. ABR was obtained in 38 patients in the SHL/AN group and was abnormal in 36 patients (sensitivity, 94.7%). Prolonged wave V latency was noted in 22 patients, and no response was found in 14 patients. Both patients with normal ABR had small tumors ( _<1 cm) and moderate high-frequency (2 to 4 kHz) SHL. When the ABR was obtained 1 month after the initial SHL, the hearing had returned to normal (PTA < 25 dB HL). One of these patients had a repeat ABR 18 months later that was abnormal, with an interaural wave V delay of 0.6 milliseconds. Many patients in the SHL/AN group received treatment for SHL before the tumor diagnosis. In some cases treatment was initiated while the evaluation was underway, but often patients were treated without plans for a diagnostic workup. Forty-two (53%) patients with SHL/AN received some type of medical treatment, and the average duration of treatment was just under 2 months (54 days). As is characteristic of SHL management, a wide variety of treatments were used, and most patients received more than one treatment. The most common treatment used was steroids (25 patients), followed by niacin (15 patients), antibiotics (13 patients), histamine (5 patients), and miscellaneous vasodilator agents (4 patients). One patient underwent an exploratory tympanotomy for repair of a possible perilymph fistula. Of the 42 patients treated, 20 (47.6%) had subjective improvement in hearing that was presumed to be due to treatment. Subjective hearing improvement in this population was confirmed with audiologic data when available. A significant relationship was found between subjective improvement and a reduction of PTA by 10 dB HL or 15% improvement in speech discrimination (p ___ 0.05). In addition, four patients had spontaneous recovery of hearing without treatment. There was no relationship between hearing recovery and the type of treatment used, the use of steroids, the degree of hearing loss, the audiogram shape, the presence of vestibular symptoms, or the ENG results. Hearing recovery was seen for all tumor sizes, and there was no relationship between the recovery of hearing and tumor size. Surgical and Pathologic Findings
Tumor size data were available in 56 cases in the SHL/AN group and in 1479 cases in the AN group (Fig. 4). Most tumors in the SHL/AN group were medium (1 to 3 cm), and the mean tumor size was 2.1
SAUNDERS et al.
27
Table 2. Other diagnoses and events in SHL patients with AN Other diagnosis
No. of
or event
patients
Viral illness Vascular disease Pregnancy Airplane flight Infectious disease history, (HIV, syphilis, encephalitis, tuberculosis) Rheumatic fever Head trauma Heavy lifting
12 7 3 2 4 1 1 1
cm. Patients with SHL/AN had a significantly higher proportion of medium tumors than did the AN group (_< 0.01), and there were fewer small (1 cm) tumors in the SHL/AN group (p _< 0.01). The site of tumor origin in SHL/AN patients could be determined in 47 cases at the time of surgery. Inferior vestibular nerve tumors were resPonsible for SHL in 27 cases, and superior vestibular nerve tumors were found in 20 cases. These proportions are not significantly different than those of the AN group. The pathologic reports of 69 SHL/AN patients were reviewed for the presence of cystic degeneration, tumor necrosis, or hemorrhage within the lesion and compared with reports from 69 randomly selected AN patients with progressive hearing loss. Cystic degeneration and tumor necrosis were rare in both groups, and no significant differences were found between SHL/AN patients and our randomly selected AN patients. There was, however, a significantly higher rate of patients with tumor hemorrhage in the SHL/AN group (34.8%) than in the other AN patients (18.8%, p _< 0.05). DISCUSSION
Prevalence of ANs in SIlL
In his 1956 report "Sudden Deafness of Obscure Origin," Hallberg asserted that SHL should be considered a "symptom, not a disease. ''19Although most cases of SHL are idiopathic, many authors have echoed the need always to rule out an underlying cause. 5,2°The otolaryngologist should recognize the possibility of an AN as one cause of SHL and request appropriate studies to rule out a tumor. Our data indicate that if a tumor is not diagnosed within the first 6 months, it may go unrecognized for more than 2 years. The patient may subsequently have additional symptoms associated with larger tumors before the diagnosis is recognized,z3The importance of early recognition of acoustic tumors in reducing
28
Otolaryngology Head and Neck Surgery July 1995
SAUNDERS et al.
100 (.9 z LU
90
-~ E
80 •
O
c ..Q < ~-
70
~
50
c
60
40
a_
30
E
20
o
0
SHL
SHL with AN
Acoustic Neuroma
Patient Groups
Fig. 3. ENG findings in the SHL/AN, SHL, and AN groups. The percent of patients with abnormal ENG findings (_> 30% reduced vestibular response) in each group are shown. A statistically significant difference was found between the SHL/AN and SHL groups (p _< 0.05). (Reprinted with permission of House Ear Institute.)
Table 3. Audiometric data SHL
Mean PTA (n, SD) Mean SDS (n, SD)
65.6 dB (431, 35.4) 44.7% (386, 41.5)
SHL/AN
p _< 0.001 p _< 0,001
operative morbidity and treatment cost has been emphasized by Moffat et al. 24 Diagnostic strategies should, therefore, consider the cost of delayed diagnosis and the relative risk of an AN. The risk of an AN in a patient with SHL can be estimated by the prevalence of the disease in the SHL population. The most conservative way to estimate tumor prevalence is to consider only those patients who have been screened with MRI/Gd, thus essentially eliminating the possibility of a missed tumor in the study population. With this approach, our results indicate the tumor frequency in SHL to be 2.7%. The increase in tumor prevalence in SHL patients seen at the House Ear Clinic compared with that reported by Shaia and Sheehy5 is likely due to improvements in tumor detection with the use of MRI/Gd and ABR. We believe that this rate realistically reflects the risk of AN in the general SHL population. Characteristics of SHL in AN Patients
Certain clinical features may suggest which SHL patients will have an AN. Although otalgia and facial paresthesia were much more frequent in SHL
45.9 dB (89, 32.0) 62.8% (85, 35,9)
AN
NS NS
51.4 dB (1196, 34,76) 55.0% (1127, 38,9)
patients with tumors, the overall incidence of these symptoms was low for both groups. Likewise, unilateral tinnitus before the SHL event is suggestive of a tumor, but only 15% of patients with SHL/AN will have this characteristic. The value of these associated symptoms in predicting which SHL patients will have acoustic tumors underscores the need for a complete and thorough history in all patients with SHL; however, their absence does not eliminate the possibility of a tumor. Our analysis of the audiogram configuration in SHL reveals that a midfrequency (U-shaped) hearing loss and high-frequency hearing loss are more common in patients with SHL/AN. Conversely, lowfrequency hearing loss was rare in those patients with tumors and relatively common in the SHL patients. Some of these audiometric findings in SHL may be used to predict the risk of an AN. For example, of 29 SHL patients with midfrequency hearing loss who were evaluated with either ABR or MRI/Gd, 4 had acoustic tumors. The relative risk in a patient with a midfrequency loss would therefore be more than 13% in this study population. On the
Otolaryngology Head and Neck Surgery Volume 113 Number t
SAUNDERS et al.
29
100 [~ SHL w/AN
90
Acoustic Neuroma
80 ¢9 C
70 60
n
50 ¢-
40 12.
30 20 10 0
Small
Medium
Large
Tumor Size Fig. 4. Tumor size categories for SHL/AN and AN groups, showing percentage of patients with small ( _<1 cm), medium (I to 3 cm), and large ( > 3 cm) tumors. A statistical difference was found between groups for each size category (p -< 0.05). (Reprinted with permission of House Ear Institute.)
other hand, because high-frequency SHL is also common in patients without tumors, the risk of a tumor in patients with high-frequency SHL is still less than 5% (5 tumors in 135 patients screened). ENG abnormalities were also statistically more common in the SHL/AN patients than their SHL counterparts. However, many patients in both groups will have abnormal ENG findings, and 40% of the SHL/AN patients tested had normal ENG findings. Therefore we do not recommend ENG to rule out an AN. MRI/Gd is widely recognized as the gold standard in the diagnosis of ANs. Currently, ABR is less expensive than MRI/Gd, but it is also less sensitive. A recent study of patients at the House Ear Clinic (Chandrasekhar SS, Brackmann DE, Devgan KK. Utility of auditory brainstem response audiometry in diagnosis of acoustic neuromas. Submitted to Am J Otol) cited an overall ABR sensitivity of 92.3%, but the sensitivity fell to 83.1% for small tumors ( < 1 cm). The overall sensitivity of ABR in the SHL/AN patients was 94.7%. Welling et al? 1 proposed a cost-effective approach to the diagnosis of AN on the basis of the probability of a tumor in a given clinical setting. Although high- and intermediate-risk patients were evaluated directly with MRI/Gd, an initial screening ABR was recommended for any patient whose risk of an AN was less than 5%. Our results indicate that the risk of AN in SHL patients is
within this range, providing the patient does not have any additional risk factors. Because of the relatively low probability of SHL patients having an acoustic tumor, ABR can be used to evaluate many of these patients. However, the clinician may need to consider other factors besides tumor risk. Both of the patients with false-negative ABRs in this study had small tumors ( _<1 cm) and had recovered normal hearing at the time of the ABR examination. One of these patients had a repeat ABR that was abnormal. The clinician should, therefore, be cautious in interpreting ABR results from patients with normal hearing recovery. Prior studies have emphasized the potential for false-negative ABR in tumor patients with good hearing. 25In addition, many of these patients may be poor candidates for ABR testing. More than one fourth of patients in this series had thresholds greater than 70 dB HL at 4 kHz. SHL patients with associated otalgia, paresthesia, or unilateral tinnitus before the SHL should be evaluated with MRI/Gd. SHL with a midfrequency (U-shaped) hearing loss is rare in the SHL population and may be an indication for MRI/Gd evaluation. The patient's age and ability to return for follow-up are also important considerations. We prefer to use ABR for elderly patients in whom the consequences of missing a small tumor are minimal. Finally, the cost difference between ABR and MRI/Gd has been reduced in recent years. It is possible that a screening, low-cost
30
SAUNDERS et al.
MRI/Gd protocol could be developed to further reduce the cost of this test. Although there were some differences between the SHL/AN and SHL groups, none of these clinical features were found in all SHL/AN patients. These features cannot be reliably used to distinguish SHL patients with tumors from other SHL patients. Recognizing which SHL patients will have an acoustic tumor is complicated by the fact that many SHL/AN patients will have a history that is suggestive of another cause of the SHL, and many patients will have hearing recovery. Therefore, we strongly recommend that all patients with SHL be evaluated with at least an ABR. Patients with associated symptoms (tinnitus before SHL, pain, or paresthesia) or midfrequency hearing loss should be evaluated with MRI/Gd. Pathophysiology of SHL in AN Patients
Our analysis of SHL/AN patients failed to reveal a uniform pattern that supports any single mechanism of SHL from ANs. On the contrary, the findings in these patients were variable and may represent several different mechanisms of SHL. Advocates of a vascular cause have proposed that an occlusion of the internal auditory artery in the internal auditory canal is the most likely site of vascular compression from an AN? Because this arterial system supplies the vestibular labyrinth as well as the cochlea, a high rate of vestibular abnormalities has been expected in these patients. Furthermore, because the apical turn of the cochlea is a distal "watershed" region of cochlear blood flow, low-frequency hearing loss should be common in patients with vascular interruption of the cochlear blood flow. 1°Our data do not support these experiences. Vestibular symptoms are usually not present in SHL/AN patients, and 40% of patients will have a normal ENG. Furthermore, the audiogram configuration of patients with SHL from an AN suggests that low-frequency hearing is usually preserved. Animal studies have demonstrated that vascular occlusion may result in a variable distribution of histologic damage in the cochlea and vestibular labyrinth, especially with temporary interruption of flow.26The horizontal ampulla is affected in only 50% to 70% of animals with permanent arterial occlusion and even less commonly in animals with temporary or venous obstruction. 26'27 Furthermore, Roberson and Luxford (submitted to OTOI~ARY~OL HEAD NECK SURG, 1994) have identified a case of SHL from an internal auditory artery aneurysm with predominantly high-frequency hearing loss and a normal ENG. The clinical findings in patients with
Otolaryngology Head a n d Neck Surgery July 1995
acute vascular interruption from a tumor may therefore be more variable than expected. SHL from AN could also be the result of a conduction block of the cochlear nerve action potential. The cochlear nerve is tonotopically organized so that the high-frequency and midfrequency fibers lie on the outer surface of the cochlear nerveY Apical (low-frequency) fibers are found deep in the central core of the nerve. Ogawa et al. 13 proposed that small inferior vestibular nerve tumors would be expected to preferentially affect the midfrequency fibers of the cochlear nerve. Midfrequency hearing loss was present in 18 patients in our series. These 18 tumors included all tumor sizes, and there was an equal distribution of inferior and superior vestibular nerve tumors in this group. Pensak et a15 and Selesnick and Jackler 15reported an equal distribution of small, medium, and large tumors in patients with SHL, whereas Yanagihara and Asai 16 reported a disproportionate number of small tumors in patients with SHL. Most tumors in our SHL/AN patients were 1 to 3 cm, and small tumors were less common than with other AN patients (Fig. 4). Nerve conduction block from larger tumors might affect any frequency range. However, the low,frequency fibers should be relatively protected from compression effects because of their position within the nerve. This might account for the rare occurrence of low-frequency hearing loss in SHL/AN patients. Another possible explanation of SHL/AN is rapid tumor growth.3,1° ANs usually grow very slowly, although a variable growth rate is possible. 22 Cystic degeneration, necrosis, and hemorrhage are some of the factors that might be associated with rapid tumor expansion. In our review of pathologic reports, tumor hemorrhage was more common in SHL/AN tumors than in tumors from patients with progressive symptoms. This observation, along with the relative lack of small tumors in the SHL/AN group, is consistent with tumor hemorrhage and rapid tumor expansion as a possible cause of SHL in some patients. There have been previous case reports of hemorrhage into an AN and subarachnoid hemorrhage from a n A N . 29'30 Finally, it is possible that the AN may predispose the cochlear system to biomechanical change, such as a membrane rupture, or to an inflammatory process that causes a precipitous decline in hearing. Our understanding of the rapid deterioration of hearing in patients with ANs is still poor. It is possible that several different mechanisms may independently result in SHL.
Otolaryngology Head a n d Neck Surgery Volume 113 Number I
CONCLUSIONS 1. Approximately 3 of 100 patients with SHL will have an AN. Therefore all patients with SHL should be evaluated with either A B R or MRI/Gd. 2. The associated symptoms of pain, facial paresthesia, or unilateral tinnitus preceding the SHL were suggestive of an AN. A midfrequency (U-shaped) hearing loss in an SHL patient is also suggestive of an AN. Patients with these associated symptoms and signs should be evaluated with MRI/Gd. 3. The otolaryngologist should n o t be dissuaded from obtaining an A B R or MRI/Gd because of a history of other diseases or events that might explain the SHL. Likewise, a normal E N G or recovery of hearing does not eliminate the possibility of a tumor. 4. Although the clinical findings in SHL/AN patients are mixed, aspects of our data support the possibility of a nerve conduction block or rapid tumor expansion in the pathogenesis of SHL in tumor patients. We cannot rule out the possibility of a vascular occlusion as the cause of SHL in some tumor patients. We would like to thank Karen Berliner, PhD, for her editorial comments and statistical analysis of the data. We are also grateful to A n n Masuda, MA, and Stacy Dorcas for their help in data entry and to our librarian, Liz Gnerre. REFERENCES
1. Cushing H. Tumors of the nervus acusticus and the syndrome of the cerebellopontine angle. Philadelphia: WB Saunders, 1917. 2. Stroud MH, Thalmann R. Unusual audiological and vestibular problems in the diagnosis of cerebellopontine angle lesions. Laryngoscope 1969;79:171-200. 3. Higgs WA. Sudden deafness as the presenting symptom of acoustic neurinoma. Arch Otolaryngol 1973;98:73-6. 4. Nedzelski JM, Dufour JJ. Acoustic neurinomas presenting as sudden deafness. ORL J Otorhinolaryngol Relat Spec 1975; 37:271-9. 5. Shaia FT, Sheehy JL. Sudden sensori-neural hearing impairment: a report of 1,220 cases, Laryngoscope 1976;86:38998. 6. Terry RM. An unusual presentation of acoustic neuroma. J Laryngol Otol 1985;99:593-5. 7. Pensak ML, Glasscock ME III, Josey AF, Jackson CG, Gulya AJ. Sudden hearing loss and cerebellopontine angle tumors. Laryngoscope 1985;95:1188-93. 8. Sataloff RT, Davies B, Myers DL. Acoustic neuromas presenting as sudden deafness. Am J Otol 1985;6:349-52.
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3t
9. Chow JM, Garcia J. Acoustic neuroma presenting as sudden hearing loss. Am J Otolaryngol 1985;6:115-9. 10. Berg HM, Cohen NL, Hammerschlag PE, Waltzman SB. Acoustic neuroma presenting as sudden hearing loss with recovery. OTOI~ARYNOOLHEAD NECK SURG 1986;94:15-22. 11. Mineta H, Nozue M, Ito H, Nozawa O, Nanba T. Acoustic tumor with hearing loss of sudden onset and recovery. Auris Nasus Larynx (Tokyo) 1986;13(suppl):S123-9. 12. Yoshimoto Y. Clinico-statistical study on acoustic tumors with sudden hearing loss. Auris Nasus Larynx (Tokyo) 1988; 15:165-71. 13. Ogawa K, Kanzaki J, Ogawa S, Tsuchihashi N, Inoue Y. Acoustic neuromas presenting as sudden hearing loss. Acta Otolaryngol (Stockh) 1991;(suppl 487):138-43. 14. Berenholz LP, Eriksen C, Hirsh FA. Recovery from repeated sudden hearing loss with corticosteroid use in the presence of an acoustic neuroma. Ann Otol Rhinol Laryngol 1992;101: 827-31. 15. Selesnick SH, Jackler RK. Atypical hearing loss in acoustic neuroma patients. Laryngoscope 1993;103:437-41. 16. Yanagihara N, Asai M. Sudden hearing loss induced by acoustic neuroma: significance of small tumors. Laryngoscope 1993;103:308-11. 17. Moffat DA, Baguley DM, yon Blumenthal H, Irving RM, Hardy DG. Sudden deafness in vestibular schwannoma. J Laryngol Otol 1994;108:116-9. 18. Mangham CA. Acoustic neuroma: cost-effective approach [Letter]. OTOLARVNGOI.HEAD NECK Su~o 1992;106:315-6. 19. Hallberg OE. Sudden deafness of obscure origin. Laryngoscope 1956;66:1237-65. 20. Jaffe BF. Sudden deafness: an otologic emergency. Arch Otolaryngol 1967;86:81-6. 21. Welling DB, Glasscock ME III, Woods CI, Jackson CG. Acoustic ncuroma: a cost-effective approach. OTOtaRVNOOI. HEAD NECK SURe 1990;103:364-70. 22. Lanser M J, Sussman SA, Frazer K. Epidemiology, pathogenesis, and genetics of acoustic tumors. Otolaryngol Clin North Am 1992;25:499-520. 23. Selesnick SH, Jackler RK. Clinical manifestations and audiologic diagnosis of acoustic neuromas. Otolaryngol Clin North Am 1992;25:521-51. 24. Moffat DA, Hardy DG, Baguley DM. Strategy and benefits of acoustic neuroma searching. J Laryngol Otol 1989;103: 51-9. 25. Josey AF, Jackson CG, Glasscock ME III. Brainstem evoked response audiometry in confirmed eighth nerve tumors. Am J Otolaryngol 1980;1:285-90. 26. Kimura RS. Animal models of inner ear vascular disturbances. Am J Otolaryngol 1986;7:130-9. 27. Kimura R, Perlman HB. Arterial obstruction of the labyrinth. Part I. Cochlear changes. Ann Otol Rhinol Laryngol 1958; 67:5-40. 28. Schuknecht HF. Pathology of the ear. 2nd ed. Philadelphia: Lea & Febiger, 1993. 29. Castilto R, Watts C, Pulliam M. Sudden hemorrhage in an acoustic neuroma. J Neurosurg 1982;56:416-9. 30. Yonemitsu T, Niizuma H, Kodama N, Fujiwara S, Suzuki J. Acoustic neurinoma presenting as subarachnoid hemorrhage. Surg Neurol 1983;20:125-30.
Los Angeles, California Patients with acoustic neuroma m a y have sudden sensorineural hearing loss. Most patients with sudden hearing loss seek medical attention promptly, but the diagnosis of an acoustic neuroma m a y be delayed for months or years because sudden hearing loss is an unusual initial symptom of an acoustic neuroma. In a retrospective review of 836 cases of sudden hearing loss, we found t 3 patients with acoustic neuromas. The prevalence of acoustic neuromas for those screened with auditory brain stem response or magnetic resonance imaging was 2.5%. In addition to these t3 patients, 79 acoustic neuroma patients treated in our clinic had well-documented sudden hearing loss as the initial symptom. Hearing loss in these 92 patients ranged from mild to profound. Associated symptoms of pain, facial paresthesia, or unilateral tinnitus preceding the sudden hearing loss were suggestive of an acoustic neuroma, as was a midfrequency [U-shaped) hearing loss. A history of other diseases or events that might explain the sudden hearing loss, a normal electronystagmogram, or recovery of hearing does not eliminate the possibility of a tumor. Because there are no clinical findings that clearly distinguish those patients with acoustic neuromas from other patients with sudden hearing loss, we recommend either an evaluation with auditory brain stem response or gadolinium-enhanced magnetic resonance imaging for any patient with sudden hearing loss. [OTOLARYNGOLHEAD NECK SURG 1995;113:23-31 .}
| n his 1917 monograph on the diagnosis and management of acoustic tumors, Cushing I described two patients with sudden hearing loss (SHL). Since that time there have been numerous reports of SHL in acoustic neuroma (AN) patients. 2-17 According to Moffat et al., ~7 10.2% of A N patients have SHL as their primary symptom, making SHL the second most common initial symptom in A N patientsJ 7 Although most patients with SHL will seek medical attention promptly, some patients may ignore this initial symptom. When asked retrospectively about their symptoms, more than one fourth of tumor patients will relate some episode of SHL during their clinical courseJ 5 Many tumors in patients with SHL may not be diagnosed for more than a year after the SHL eventJ 3 All too often patients with
From the House Ear Clinic and House Ear Institute (Drs. Saunders and Luxford) and the Universityof Southern California Medical Center (Drs. Devgan and Fetterman). Presented at the Annual Meeting of the American Academy of Otolaryngology-Head and Neck Surgery, San Diego, Calif., Sept. 18-21, 1994. Received for publication Oct. 24, 1994; accepted Jan. 20, 1995. Reprint requests: William M. Luxford, MD, House Ear Clinic, 2100 West Third St., First Floor, Los Angeles, CA 90059. Copyright © 1995by the American Academyof OtolaryngologyHead and Neck Surgery Foundation, Inc. 0194-5998/95/$3.00 + 0 23/l/63547
SHL from an A N (SHL/AN) are treated by physicians who are either unaware of the possibility of an acoustic tumor in this setting or who elect not to evaluate these patients because the frequency of ANs in SHL is believed to be extremely low. To address this problem, we set out to define the prevalence of ANs in patients with SHL, to determine whether there are any clinical features that could distinguish these patients, and to clarify the pathophysiology of SHL in A N patients. The prevalence of ANs in patients with SHL is unclearJ 8 Hallberg 19 found one patient with an AN in a large series of patients with SHL (178 cases) in 1956. Jaffe, 2° however, did not identify ANs as a potential cause of SHL in his review of 143 patients. Nedzelski and Dufour 4 subsequently reported a tumor prevalence of 3% in a series of 63 patients with SHL, but they suggested that this overestimated the actual rate. In their series of 1220 SHL patients, Shaia and Sheehy 5 found 10 ANs, for a prevalence in this population of 0.8%. Despite this low frequency, the authors strongly recommended that all patients with SHL should be evaluated to rule out an AN. Welling et al. 2~proposed a cost-effective approach to the diagnosis of an AN that is based on the probability of finding a tumor in a given clinical situation. They estimated the probability of an acoustic tumor in SHL to be 5% to 30% and thus recommended a 23
24
Otolaryngology Head and Neck Surgery July 1995
SAUNDERSet al.
100
NS
[~. SHL w/AN
90
SHL
80 c
70 60
IX.
"6
50
NS~
¢o
o_
p<.01
40 30
20
p_<,.05
p_<.01
p<.001
10 Tinnitus
Tinnitus Before
Dizzy
Fullness
Otalgia Paresthesia
Symptoms Fig. t. Symptoms of patients with SIlL/AN and SHL. Statistical differences between the groups are indicated. (Reprinted with permission of House Ear Institute.)
gadolinium-enhanced magnetic resonance imaging (MRI/Gd) scan to evaluate these patients. Their estimate of tumor prevalence was based on the clinical experience of the authors and a higher detection rate with the use of MRI/Gd. The actual prevalence of ANs in SHL patients evaluated with auditory brain stem response (ABR) and MRI/Gd has not been reported. Several studies have attempted to identify clinical features that distinguish SHL/AN patients from those with other causes of SHL5 '12 Most of these studies are based on relatively small series of patients, and there is little consensus between studies. Nedzelski and Dufour4 concluded that SHL/AN patients will generally have abnormal caloric electronystagmography (ENG) and poor hearing recovery. There have been numerous recent reports, however, of SHL recovery in patients with an AN. 1°,11,~4 Likewise, ENG findings in SHL/AN have varied between studies. Yoshimoto 12found canal paresis in all patients with SHL/AN, whereas Ogawa et al. ~3 suggested that a trough or U-shaped audiogram and a normal ENG are typical of SHL/AN patients. 9,~3 Other studies have reported a more heterogeneous array of audiogram shapes, v'17 Pensak et al. 7 were unable to identify any distinguishing audiologic features of these patients. Furthermore, there have been conflicting reports of tumor size in patients with SHL/AN. A disproportionate number of small tumors have been suggested by some, ~3'~6whereas others report that larger tumors are more common. 12 In addition, the pathophysiology of SHL in AN patients is not well understood. In general, ANs
grow very slowly.22How these slow-growing tumors cause an abrupt onset of symptoms is unclear. The mechanisms of vascular compromise, neuronal conduction block, rapid tumor growth, and immune or toxic effects on the cochlea have all been considered. 3'7'1°'13 Because of the distribution of the labyrinthine blood supply, an acute vascular occlusion has been postulated to result in a low-frequency or flat hearing loss and vestibular dysfunction.3,1° One patient with a known vascular cause of SHL from an internal auditory artery aneurysm has been described (Roberson J, Luxford WM. Internal auditory artery aneurysm. Submitted to OTOLARYNGOLHEAD NEcI~ SURG, 1994). SHL from tumor compression on the cochlear nerve (conduction block) is believed to result in a trough or U-shaped audiogram with normal vestibular function. 13 Small tumors of the inferior vestibular nerve, because of their juxtaposition to the cochlear nerve, might be more likely to cause a cochlear nerve conduction block than superior vestibular nerve tumors? 3 Finally, rapid tumor expansion could cause SHL and might be associated with the pathologic findings of hemorrhage, cystic degeneration, or necrosis. We present a detailed study of a large series of patients with SHL/AN. The purposes of this study are (1) to define the prevalence of ANs in the SHL population with the current diagnostic techniques (ABR and MRI/Gd), (2) to identify the typical clinical findings in SHL/AN patients and compare these features with those from other patients with SHL, and (3) to evaluate the proposed theories of SHL/AN pathophysiology by
Otolaryngology Head and Neck Surgery Volume 113 Number I
SAUNDERSet al.
25
100 [-] SHL w/AN
90
SHL
80 ¢O3
70 6O p<.05
CI.
"5 E O ,o
50 4O
O
13.
20 10 0
) High Frequency
p<.001 NS
Flat
Low Frequency
Mid Frequency
Profound
Audiogram Configuration Fig. 2. Audiogram configuration in patients with SHL/ANand SHL.Statistical differences between the groups are indicated. (Reprinted with permission of House Ear Institute,)
comparing SHL/AN patients with data from other AN patients. An appreciation of the clinical characteristics of SHL/AN patients may improve our general understanding of how acoustic tumors affect the cochlear system and our ability to diagnose these tumors early. METHODS
This study includes data that were retrospectively collected from the clinic charts of two groups of patients. The first group is comprised of 836 patients with well-documented SHL seen at the House Ear Clinic from January 1989 to December 1993 (SHL group). The second group includes data from 1487 patients with AN treated at the House Ear Clinic for a 10-year period (January 1982 to March 1993). Ninety-two patients with ANs and well-documented SHL were identified in these two patient groups (13 in the SHL group and 79 in the AN group). This combined group of 92 patients with SHL/AN are the main focus of the study. SHL was defined as any rapid change in hearing with evidence of elevated pure-tone thresholds (> 25 dB HL). Two patients with AN who had a sudden change in speech discrimination with normal pure-tone thresholds were excluded from this study. The vast majority of patients had hearing loss immediately or on awakening, and only patients with SHL occurring in less than 48 hours were included. This group included 45 men and 47 women. The mean age was 48 years, with a range from 26 to 81 years. Data collected included
demographic data, symptoms at the time of onset, treatment rendered, time elapsed between presentation and tumor diagnosis (diagnostic delay), audiometry and ABR results, ENG results, radiographic findings, surgical findings, tumor size, and pathologic findings. The assessment of hearing recovery was based both on the subjective impression of the patient or the treating physician and on an objective audiologic measure when these data were available. Audiologic improvement was defined as a decrease in pure-tone average (PTA) of 10 dB or a 15% improvement in speech discrimination. The clinical findings for the SHL/AN patients were compared with the data from the 836 patients with SHL (SHL group) and with data from the 1487 patients in the AN database (AN group). Statistical differences between groups were assessed with a two-tailed Z test of the difference between proportions and a two-tailed Student's t test. The criterion for statistical significance was set at p _< 0.05. RESULTS P r e v a l e n c e of ANs in SHL
The estimated tumor prevalence rates are shown in Table I. To accurately estimate the prevalence of ANs in the SHL population, it is necessary to consider SHL patients independently from patients referred with ANs. In our review of 836 charts seen primarily for SHL, only 13 tumors were found (1.5%). The workup of these patients was variable. Only 523 patients were evaluated with ABR and/or
26
Otolaryngology Head and Neck Surgery July 1995
SAUNDERS et al.
T a b l e I . P r e v a l e n c e of AN in p a t i e n t s with SHL Group
No. of AN found
No. of SHL patients
Prevalence [%]
SHL as primary diagnosis SHL patients screened with ABR or MRI/Gd SHL patients screened with MRI All House Ear Clinic SHL patients (1/89-12/92)
13 13 13 40
836 523 431 740
1.5 2,5 2,7 5.4
MRI/Gd, for a tumor prevalence of 2.5% if only these patients are included. Because all tumor patients eventually had an MRI/Gd scan, the prevalence rate for patients who were evaluated with MRI/Gd (431 patients) was 2,7%. Of the 1487 ANs treated at the House Ear Clinic from January 1982 to March 1993, a description of the initial symptoms was available in 1204 cases. SHL was recorded as the initial symptom in 116 of these 1204 patients (9.6%). Thirty-seven of these 116 cases were excluded from this study because, on further review, they did not meet our criteria for SHL. The 79 remaining cases all had a well-documented episode of SHL, comprising slightly more than 5% (79 of 1204) of our AN patients. Of these 79 cases, 27 patients were treated during a 4-year period (January 1989 to December 1992) that coincided with our 5-year review of SHL patients. If these 27 cases are combined with our 13 patients from the SHL group, a total of 40 patients with SHL/AN were seen at the House Ear Clinic from January 1989 to December 1992. During this 4-year period, 740 patients with SHL were seen. Therefore, if all patients with SHL/AN are included, the AN prevalence in the SHL population at our clinic would be 5.4% (40 of 740). This rate does not account for those SHL patients who were determined by outside physicians not to have an acoustic tumor and therefore were not referred. This figure may be considered, however, as an estimate of the tumor frequency is a neurotology referral practice. Characteristics of SHL in AN Patients
The clinical findings of the combined group of 92 patients with SHL/AN were analyzed and compared with the findings in the SHL and AN groups. No significant differences were found between these groups for age, sex, or affected side. Information on other symptoms at the time of SHL was available in 89 SHL/AN patients and 739 patients with SHL (Fig. 1). Unilateral tinnitus wascommon in both groups, but 15.4% of patients with SHL/AN related some tinnitus in the affected ear preceding the SHL event; this symptom was rare (3.7%) in the SHL
population (p _< 0.01). No significant difference was found in the percentage of patients with vestibular symptoms between SHL/AN patients (34.1%) and the SHL group (42.7%). Unlike tinnitus that preceded the SHL event, balance problems before the SHL were rare for both groups (8.0% for SHL/AN, 5.3% for SHL). Otalgia and facial paresthesia were significantly more frequent in those patients with SHL/AN than in the SHL group (p _ 0.05 and p _< 0.001, respectively). In contrast, aural fullness or pressure was more common in the patients with SHL than in those with SHL/AN (p _< 0.01). Many of the patients in the SHL/AN group had other diseases or "precipitating" events that could be considered to contribute to SHL, thus confounding the tumor diagnosis (Table 2). The mean PTA and speech discrimination score (SDS) for each study group are shown in Table 3. No significant difference was found in these audiometric parameters between the SHL/AN group and other patients with ANs. Surprisingly, the PTA and SDS for the SHL/AN group were significantlybetter than for the SHL group. Audiogram configuration data were available on 89 patients with SHL/AN and 451 patients from the SHL group (Fig. 2). All audiogram shapes were represented in both the SHL/AN and SHL groups. Midfrequency (U-shaped) and high-frequency sloping hearing loss were more common in SHL patients with tumors than in the overall SHL group (p _< 0.01 andp _ 0.05, respectively). In contrast, only one patient in the SHL/AN group had a low-frequency pattern, whereas 25.2% of the SHL group had this configuration (p _< 0.001). Of the 30 patients evaluated with ENG in the SHL/AN group, abnormal ENG findings ( > 30% reduced vestibular response) were noted in 60% (Fig. 3). This rate is not significantly different from that of the AN group (69.9%) but is significantly higher than that of the SHLgroup (42.8%,p <_ 0.05). Most tumors in patients with SHL/AN were diagnosed within 6 months of the SHL event. If the diagnosis is not made within the first 6 months, however, there is a tendency for the diagnosis to go unrecognized. The mean interval between SHL and
Otoloryngology Head and Neck Surgery Volume 113 Number I
tumor diagnosis was just under 2 years (22 months), and almost 20% of patients were not diagnosed for more than 2 years after the SHL event. ABR was obtained in 38 patients in the SHL/AN group and was abnormal in 36 patients (sensitivity, 94.7%). Prolonged wave V latency was noted in 22 patients, and no response was found in 14 patients. Both patients with normal ABR had small tumors ( _<1 cm) and moderate high-frequency (2 to 4 kHz) SHL. When the ABR was obtained 1 month after the initial SHL, the hearing had returned to normal (PTA < 25 dB HL). One of these patients had a repeat ABR 18 months later that was abnormal, with an interaural wave V delay of 0.6 milliseconds. Many patients in the SHL/AN group received treatment for SHL before the tumor diagnosis. In some cases treatment was initiated while the evaluation was underway, but often patients were treated without plans for a diagnostic workup. Forty-two (53%) patients with SHL/AN received some type of medical treatment, and the average duration of treatment was just under 2 months (54 days). As is characteristic of SHL management, a wide variety of treatments were used, and most patients received more than one treatment. The most common treatment used was steroids (25 patients), followed by niacin (15 patients), antibiotics (13 patients), histamine (5 patients), and miscellaneous vasodilator agents (4 patients). One patient underwent an exploratory tympanotomy for repair of a possible perilymph fistula. Of the 42 patients treated, 20 (47.6%) had subjective improvement in hearing that was presumed to be due to treatment. Subjective hearing improvement in this population was confirmed with audiologic data when available. A significant relationship was found between subjective improvement and a reduction of PTA by 10 dB HL or 15% improvement in speech discrimination (p ___ 0.05). In addition, four patients had spontaneous recovery of hearing without treatment. There was no relationship between hearing recovery and the type of treatment used, the use of steroids, the degree of hearing loss, the audiogram shape, the presence of vestibular symptoms, or the ENG results. Hearing recovery was seen for all tumor sizes, and there was no relationship between the recovery of hearing and tumor size. Surgical and Pathologic Findings
Tumor size data were available in 56 cases in the SHL/AN group and in 1479 cases in the AN group (Fig. 4). Most tumors in the SHL/AN group were medium (1 to 3 cm), and the mean tumor size was 2.1
SAUNDERS et al.
27
Table 2. Other diagnoses and events in SHL patients with AN Other diagnosis
No. of
or event
patients
Viral illness Vascular disease Pregnancy Airplane flight Infectious disease history, (HIV, syphilis, encephalitis, tuberculosis) Rheumatic fever Head trauma Heavy lifting
12 7 3 2 4 1 1 1
cm. Patients with SHL/AN had a significantly higher proportion of medium tumors than did the AN group (_< 0.01), and there were fewer small (1 cm) tumors in the SHL/AN group (p _< 0.01). The site of tumor origin in SHL/AN patients could be determined in 47 cases at the time of surgery. Inferior vestibular nerve tumors were resPonsible for SHL in 27 cases, and superior vestibular nerve tumors were found in 20 cases. These proportions are not significantly different than those of the AN group. The pathologic reports of 69 SHL/AN patients were reviewed for the presence of cystic degeneration, tumor necrosis, or hemorrhage within the lesion and compared with reports from 69 randomly selected AN patients with progressive hearing loss. Cystic degeneration and tumor necrosis were rare in both groups, and no significant differences were found between SHL/AN patients and our randomly selected AN patients. There was, however, a significantly higher rate of patients with tumor hemorrhage in the SHL/AN group (34.8%) than in the other AN patients (18.8%, p _< 0.05). DISCUSSION
Prevalence of ANs in SIlL
In his 1956 report "Sudden Deafness of Obscure Origin," Hallberg asserted that SHL should be considered a "symptom, not a disease. ''19Although most cases of SHL are idiopathic, many authors have echoed the need always to rule out an underlying cause. 5,2°The otolaryngologist should recognize the possibility of an AN as one cause of SHL and request appropriate studies to rule out a tumor. Our data indicate that if a tumor is not diagnosed within the first 6 months, it may go unrecognized for more than 2 years. The patient may subsequently have additional symptoms associated with larger tumors before the diagnosis is recognized,z3The importance of early recognition of acoustic tumors in reducing
28
Otolaryngology Head and Neck Surgery July 1995
SAUNDERS et al.
100 (.9 z LU
90
-~ E
80 •
O
c ..Q < ~-
70
~
50
c
60
40
a_
30
E
20
o
0
SHL
SHL with AN
Acoustic Neuroma
Patient Groups
Fig. 3. ENG findings in the SHL/AN, SHL, and AN groups. The percent of patients with abnormal ENG findings (_> 30% reduced vestibular response) in each group are shown. A statistically significant difference was found between the SHL/AN and SHL groups (p _< 0.05). (Reprinted with permission of House Ear Institute.)
Table 3. Audiometric data SHL
Mean PTA (n, SD) Mean SDS (n, SD)
65.6 dB (431, 35.4) 44.7% (386, 41.5)
SHL/AN
p _< 0.001 p _< 0,001
operative morbidity and treatment cost has been emphasized by Moffat et al. 24 Diagnostic strategies should, therefore, consider the cost of delayed diagnosis and the relative risk of an AN. The risk of an AN in a patient with SHL can be estimated by the prevalence of the disease in the SHL population. The most conservative way to estimate tumor prevalence is to consider only those patients who have been screened with MRI/Gd, thus essentially eliminating the possibility of a missed tumor in the study population. With this approach, our results indicate the tumor frequency in SHL to be 2.7%. The increase in tumor prevalence in SHL patients seen at the House Ear Clinic compared with that reported by Shaia and Sheehy5 is likely due to improvements in tumor detection with the use of MRI/Gd and ABR. We believe that this rate realistically reflects the risk of AN in the general SHL population. Characteristics of SHL in AN Patients
Certain clinical features may suggest which SHL patients will have an AN. Although otalgia and facial paresthesia were much more frequent in SHL
45.9 dB (89, 32.0) 62.8% (85, 35,9)
AN
NS NS
51.4 dB (1196, 34,76) 55.0% (1127, 38,9)
patients with tumors, the overall incidence of these symptoms was low for both groups. Likewise, unilateral tinnitus before the SHL event is suggestive of a tumor, but only 15% of patients with SHL/AN will have this characteristic. The value of these associated symptoms in predicting which SHL patients will have acoustic tumors underscores the need for a complete and thorough history in all patients with SHL; however, their absence does not eliminate the possibility of a tumor. Our analysis of the audiogram configuration in SHL reveals that a midfrequency (U-shaped) hearing loss and high-frequency hearing loss are more common in patients with SHL/AN. Conversely, lowfrequency hearing loss was rare in those patients with tumors and relatively common in the SHL patients. Some of these audiometric findings in SHL may be used to predict the risk of an AN. For example, of 29 SHL patients with midfrequency hearing loss who were evaluated with either ABR or MRI/Gd, 4 had acoustic tumors. The relative risk in a patient with a midfrequency loss would therefore be more than 13% in this study population. On the
Otolaryngology Head and Neck Surgery Volume 113 Number t
SAUNDERS et al.
29
100 [~ SHL w/AN
90
Acoustic Neuroma
80 ¢9 C
70 60
n
50 ¢-
40 12.
30 20 10 0
Small
Medium
Large
Tumor Size Fig. 4. Tumor size categories for SHL/AN and AN groups, showing percentage of patients with small ( _<1 cm), medium (I to 3 cm), and large ( > 3 cm) tumors. A statistical difference was found between groups for each size category (p -< 0.05). (Reprinted with permission of House Ear Institute.)
other hand, because high-frequency SHL is also common in patients without tumors, the risk of a tumor in patients with high-frequency SHL is still less than 5% (5 tumors in 135 patients screened). ENG abnormalities were also statistically more common in the SHL/AN patients than their SHL counterparts. However, many patients in both groups will have abnormal ENG findings, and 40% of the SHL/AN patients tested had normal ENG findings. Therefore we do not recommend ENG to rule out an AN. MRI/Gd is widely recognized as the gold standard in the diagnosis of ANs. Currently, ABR is less expensive than MRI/Gd, but it is also less sensitive. A recent study of patients at the House Ear Clinic (Chandrasekhar SS, Brackmann DE, Devgan KK. Utility of auditory brainstem response audiometry in diagnosis of acoustic neuromas. Submitted to Am J Otol) cited an overall ABR sensitivity of 92.3%, but the sensitivity fell to 83.1% for small tumors ( < 1 cm). The overall sensitivity of ABR in the SHL/AN patients was 94.7%. Welling et al? 1 proposed a cost-effective approach to the diagnosis of AN on the basis of the probability of a tumor in a given clinical setting. Although high- and intermediate-risk patients were evaluated directly with MRI/Gd, an initial screening ABR was recommended for any patient whose risk of an AN was less than 5%. Our results indicate that the risk of AN in SHL patients is
within this range, providing the patient does not have any additional risk factors. Because of the relatively low probability of SHL patients having an acoustic tumor, ABR can be used to evaluate many of these patients. However, the clinician may need to consider other factors besides tumor risk. Both of the patients with false-negative ABRs in this study had small tumors ( _<1 cm) and had recovered normal hearing at the time of the ABR examination. One of these patients had a repeat ABR that was abnormal. The clinician should, therefore, be cautious in interpreting ABR results from patients with normal hearing recovery. Prior studies have emphasized the potential for false-negative ABR in tumor patients with good hearing. 25In addition, many of these patients may be poor candidates for ABR testing. More than one fourth of patients in this series had thresholds greater than 70 dB HL at 4 kHz. SHL patients with associated otalgia, paresthesia, or unilateral tinnitus before the SHL should be evaluated with MRI/Gd. SHL with a midfrequency (U-shaped) hearing loss is rare in the SHL population and may be an indication for MRI/Gd evaluation. The patient's age and ability to return for follow-up are also important considerations. We prefer to use ABR for elderly patients in whom the consequences of missing a small tumor are minimal. Finally, the cost difference between ABR and MRI/Gd has been reduced in recent years. It is possible that a screening, low-cost
30
SAUNDERS et al.
MRI/Gd protocol could be developed to further reduce the cost of this test. Although there were some differences between the SHL/AN and SHL groups, none of these clinical features were found in all SHL/AN patients. These features cannot be reliably used to distinguish SHL patients with tumors from other SHL patients. Recognizing which SHL patients will have an acoustic tumor is complicated by the fact that many SHL/AN patients will have a history that is suggestive of another cause of the SHL, and many patients will have hearing recovery. Therefore, we strongly recommend that all patients with SHL be evaluated with at least an ABR. Patients with associated symptoms (tinnitus before SHL, pain, or paresthesia) or midfrequency hearing loss should be evaluated with MRI/Gd. Pathophysiology of SHL in AN Patients
Our analysis of SHL/AN patients failed to reveal a uniform pattern that supports any single mechanism of SHL from ANs. On the contrary, the findings in these patients were variable and may represent several different mechanisms of SHL. Advocates of a vascular cause have proposed that an occlusion of the internal auditory artery in the internal auditory canal is the most likely site of vascular compression from an AN? Because this arterial system supplies the vestibular labyrinth as well as the cochlea, a high rate of vestibular abnormalities has been expected in these patients. Furthermore, because the apical turn of the cochlea is a distal "watershed" region of cochlear blood flow, low-frequency hearing loss should be common in patients with vascular interruption of the cochlear blood flow. 1°Our data do not support these experiences. Vestibular symptoms are usually not present in SHL/AN patients, and 40% of patients will have a normal ENG. Furthermore, the audiogram configuration of patients with SHL from an AN suggests that low-frequency hearing is usually preserved. Animal studies have demonstrated that vascular occlusion may result in a variable distribution of histologic damage in the cochlea and vestibular labyrinth, especially with temporary interruption of flow.26The horizontal ampulla is affected in only 50% to 70% of animals with permanent arterial occlusion and even less commonly in animals with temporary or venous obstruction. 26'27 Furthermore, Roberson and Luxford (submitted to OTOI~ARY~OL HEAD NECK SURG, 1994) have identified a case of SHL from an internal auditory artery aneurysm with predominantly high-frequency hearing loss and a normal ENG. The clinical findings in patients with
Otolaryngology Head a n d Neck Surgery July 1995
acute vascular interruption from a tumor may therefore be more variable than expected. SHL from AN could also be the result of a conduction block of the cochlear nerve action potential. The cochlear nerve is tonotopically organized so that the high-frequency and midfrequency fibers lie on the outer surface of the cochlear nerveY Apical (low-frequency) fibers are found deep in the central core of the nerve. Ogawa et al. 13 proposed that small inferior vestibular nerve tumors would be expected to preferentially affect the midfrequency fibers of the cochlear nerve. Midfrequency hearing loss was present in 18 patients in our series. These 18 tumors included all tumor sizes, and there was an equal distribution of inferior and superior vestibular nerve tumors in this group. Pensak et a15 and Selesnick and Jackler 15reported an equal distribution of small, medium, and large tumors in patients with SHL, whereas Yanagihara and Asai 16 reported a disproportionate number of small tumors in patients with SHL. Most tumors in our SHL/AN patients were 1 to 3 cm, and small tumors were less common than with other AN patients (Fig. 4). Nerve conduction block from larger tumors might affect any frequency range. However, the low,frequency fibers should be relatively protected from compression effects because of their position within the nerve. This might account for the rare occurrence of low-frequency hearing loss in SHL/AN patients. Another possible explanation of SHL/AN is rapid tumor growth.3,1° ANs usually grow very slowly, although a variable growth rate is possible. 22 Cystic degeneration, necrosis, and hemorrhage are some of the factors that might be associated with rapid tumor expansion. In our review of pathologic reports, tumor hemorrhage was more common in SHL/AN tumors than in tumors from patients with progressive symptoms. This observation, along with the relative lack of small tumors in the SHL/AN group, is consistent with tumor hemorrhage and rapid tumor expansion as a possible cause of SHL in some patients. There have been previous case reports of hemorrhage into an AN and subarachnoid hemorrhage from a n A N . 29'30 Finally, it is possible that the AN may predispose the cochlear system to biomechanical change, such as a membrane rupture, or to an inflammatory process that causes a precipitous decline in hearing. Our understanding of the rapid deterioration of hearing in patients with ANs is still poor. It is possible that several different mechanisms may independently result in SHL.
Otolaryngology Head a n d Neck Surgery Volume 113 Number I
CONCLUSIONS 1. Approximately 3 of 100 patients with SHL will have an AN. Therefore all patients with SHL should be evaluated with either A B R or MRI/Gd. 2. The associated symptoms of pain, facial paresthesia, or unilateral tinnitus preceding the SHL were suggestive of an AN. A midfrequency (U-shaped) hearing loss in an SHL patient is also suggestive of an AN. Patients with these associated symptoms and signs should be evaluated with MRI/Gd. 3. The otolaryngologist should n o t be dissuaded from obtaining an A B R or MRI/Gd because of a history of other diseases or events that might explain the SHL. Likewise, a normal E N G or recovery of hearing does not eliminate the possibility of a tumor. 4. Although the clinical findings in SHL/AN patients are mixed, aspects of our data support the possibility of a nerve conduction block or rapid tumor expansion in the pathogenesis of SHL in tumor patients. We cannot rule out the possibility of a vascular occlusion as the cause of SHL in some tumor patients. We would like to thank Karen Berliner, PhD, for her editorial comments and statistical analysis of the data. We are also grateful to A n n Masuda, MA, and Stacy Dorcas for their help in data entry and to our librarian, Liz Gnerre. REFERENCES
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