Otology & Neurotology 35:338Y343 Ó 2014, Otology & Neurotology, Inc.
Superior Canal Dehiscence: Can We Predict the Diagnosis? Lina Zahra Benamira, Musaed Alzahrani, and Issam Saliba From the Division of OtolaryngologyYHead and Neck Surgery, Montreal University Hospital Center (CHUM), Otology and Neurotology, University of Montreal, Montreal, Quebec, Canada.
Objective: Identify independent clinical and audiometric factors to predict a positive high-resolution computed tomography (HRCT) scan for superior canal dehiscence (SCD). Study Design: Retrospective chart review. Setting: Tertiary referral center. Patients: Patients presenting SCD. Intervention(s): Audiogram, VEMP, temporal bone HRCT, and SCD symptoms and signs chart. Main Outcome Measure(s): ABG, VEMP threshold, and symptoms and signs. Results: Approximately 106 patients with SCD symptoms were included: 62 had a positive and 44 had a negative CT scan. The positive scan group showed a higher average of cochlear symptoms than the negative CT scan group (4.3 versus 2.6) ( p G 0.001), but no statistical difference for vestibular symptoms (2.2 versus 1.8) was identified. CVEMP thresholds of the positive and negative CT scan groups were of 66 and 81 dB, respectively ( p G 0.001). The positive CT scan group showed higher ABGs at 250 Hz (24 versus 14 dB) and 500 Hz
(17 versus 8 dB) ( p = 0.008 and p = 0.008, resectively). No statistical significance was found when comparing both groups for air and bone conduction thresholds. Approximately 23% of the positive CT scan group showed a Valsalva-induced vertigo against 2.3% of the negative scan group ( p = 0.003); 27% of the positive CT scan group showed speculum-induced vertigo but none of the negative scan patients ( p G 0.001). Using logistic regression, we found that each 10-dB unit increase in the 250 Hz ABG is associated to an increase odd of having SCD of 51% (OR, 1.51; 95% CI, 1.10Y2.08). Conclusion: Nature and number of cochlear symptoms, Valsalva and pneumatic speculum-induced vertigo, VEMP thresholds, and ABGs seem to correlate with a positive HRCT. The ABG at 250 Hz is the most accurate predictor of SCD. Key Words: Air-bone gapsVHearing lossV HyperacusisVPneumatic speculumYinduced vertigoVSuperior semicircular canal dehiscenceVVestibular evoked myogenic potential. Otol Neurotol 35:338Y343, 2014.
Superior canal dehiscence (SCD) is a clinical and radiologic entity in which a defect in the bone covering the superior semicircular canal leads to sound- and/or pressure-induced vertigo and oscillopsia (1Y4). Precise anatomo-physiologic explanatory model remains unclear, but manifestations can be explained by the third-window hypothesis. In this theory, the presence of a dehiscence in the superior canal creates a third mobile window in addition to the oval and round windows in the inner ear system, which allows sound- and/or pressure-induced motion of the stapes to produce a flow of lymph in the superior canal (1,3,5,6). Audiometric evaluation is often
abnormal with bone conduction less than 0 dB nHL, as well as low frequency conductive hearing loss resulting in the characteristic air-bone gap (ABG) (3,4,7,8). Moreover, patients presenting superior canal dehiscence syndrome (SCDS) commonly demonstrate lower vestibular evoked myogenic potential (VEMP) thresholds (8Y10). Until recently, SCD was pictured as an underdiagnosed condition that needed to be promoted in the medical community (9,11,12). However, as clinicians become more aware to keep this syndrome in mind, they are facing a new challenge: clinical distinction of SCD from a large family of close auditory and vestibular pathologies (10,11,13). It even deserved to this syndrome the title of ‘‘The great otologic mimicker.’’ (9) For instance, certain patients may present with pure cochlear or vestibular symptoms, whereas others experience both (9,14). Cases of superior canal dehiscence simulating otosclerosis have been reported in literature (12Y14). This kind of misdiagnosis can lead to inappropriate management, such as nonindicated stapes surgery and failure to improve hearing loss (15,16).
Address correspondence and reprint requests to Issam Saliba, M.D., F.R.C.S.C., Montreal University Hospital Center (CHUM), Notre-Dame Hospital, Division of OtolaryngologyYHead and Neck Surgery, 1560 Sherbrooke Street East, Montreal, Qc - H2L 4M1, Canada; E-mail: [email protected] Sources of financial support or funding: none. No funding received for this work from any of the following organizations: National Institutes of Health, Welcome Trust, Howard Hughes Medical Institute, or other.
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FACTORS TO PREDICT SCD Thus, the myriad of clinical presentations, which may arise from this syndrome, can make it difficult for one to be confident about this diagnosis before radiologic confirmation. High-resolution computed tomography (HRCT) scan of the temporal bone with reconstruction in the plane of the superior canal is actually the gold standard to visualize superior canal dehiscence. However, HRCT is not only very costly but also exposes patients to radiation, which makes it an unfavorable screening test despite its high sensitivity. Currently, there is no specific tool that enables clinicians to assess the need to request further investigation regarding the clinical presentation only and the degree of suspicion for a dehiscence syndrome. We hypothesize that we can identify independent clinical and audiometric predictors of SCD. Identification of such predictors could help the clinical assessment and management of these cases, avoid unnecessary imaging, and be more cost effective. METHODS Patients Studied A retrospective study was performed examining charts of 106 patients who were referred for HRCT on the basis of clinically suspected superior canal dehiscence syndrome at our tertiary care center between February 2007 and June 2012. This study was approved by the local research ethics committee. Of the 106 patients studied, 62 had a positive HRCT, whereas 44 had a negative HRCT for superior canal dehiscence. Demographic pattern and clinical presentation, including cochleovestibular signs and symptoms, were also collected.
Audiometric Evaluation Each patient’s audiometric evaluation was assessed using pure-tone audiometry to obtain air conduction and bone conduction thresholds. Bone conduction was masked and measured in the supranormal (-5 and -10 dB). Air-bone gaps (ABG) were calculated for each frequency: from 250 to 4,000 Hz. The VEMP was evoked using a Blackman Tone Burst Generator with a rarefaction tone burst at 500 Hz. Cervical VEMP (cVEMP) testing was performed in all patients, whereas ocular VEMP (oVEMP) thresholds were measured on only 20 of the positive HRCT patients and 2 of negative HRCT group.
CT imaging and Measurements Patients underwent HRCT scan of the temporal bone with 0.55-mm collimation with a pitch of 1 at 360 mAs and 120kV. Images were acquired in axial plane and reformatted at 0.6 mm every 0.4 mm using a kernel of 80. The presence of superior canal dehiscence was first assessed on coronal images by a first observer. If the bony covering of the superior canal was found to be dehiscent on one or more coronal slices, the HRCT was reformatted in the plane of the superior semicircular canal (Poschl’s plane) to rule out false-positive cases. Reconstructed images were evaluated by the first observer and again by a second observer to ensure reliability. In this study, dehiscence was defined as the complete absence of a portion of the bone overlying the superior semicircular canal. Thus, thinning of the superior canal did not meet our criteria for dehiscence. All CT scans were evaluated on a DS3000 Agfa diagnostic PACS station by the same 2 investigators blinded to the patients’ clinical history.
339 Statistical Analysis
Groups description was performed using frequency for categorical data and mean, whereas standard deviation and maximum and minimum were used for continuous characteristics. The difference between both groups for presence of cochleovestibular signs and symptoms was studied with Pearson’s chisquared test. Student’s t test was used to compare VEMP thresholds and ANOVA for repeated measures with 2 factors (group and frequencies) to study ABGs and air and bone conduction thresholds. We analyzed prediction of SCD with multivariate logistic regression (forward stepwise based on likelihood ratio). All analyses were done with SPSS 20 and a significance level of 5%.
RESULTS Symptoms and Signs A total of 106 patients were referred for temporal bone HRCT to confirm or rule out SCD. From these, 62 (32 male and 30 female subjects) had a positive HRCT. The age range at the time of diagnosis in this group went from 27 to 74 years, with a mean of 47 years (T12 standard deviation). Only the right ear was affected in 21 patients, only the left ear in 25, whereas 15 patients presented bilateral SCD. On the other hand, HRCT excluded SCD in 44 patients (17 male and 27 female subjects) among the total 106 for whom we had clinical suspicion of SCD, which represents 41.5%. Mean age in this category was 44 years (T13 years standard deviation), ranging from 21 to 73 years. There was no statistically significant difference between the 2 groups for age at radiologic diagnosis ( p = 0.287) nor for sex ( p = 0.250). Average dehiscence size in the positive scan group was of 4.2 mm (range, 1.3Y8.0 mm) with a standard deviation of 1.6 mm. The symptoms and signs that were present in these patients are summarized in Table 1. SCD group presented an average of 4.2 cochlear symptoms of the 11 we assessed at initial evaluation, whereas the negative HRCT subjects showed an average of 2.6, which was statistically significant ( p G 0.001). However, groups did not show a significant difference when compared for the average number of vestibular symptoms at presentation (positive scan group, 2.2; negative scan group, 1.8; p 9 0.05). Tinnitus was the most prevalent symptom in both groups affecting 75.8% (42 of 62) and 75.0% (33 of 44) of positive and negative scan group patients, respectively. Both groups showed comparable rates of tinnitus ( p = 0.059). On the other hand, pulsatile tinnitus revealed a significant association with SCD ( p G 0.001), with 51.6% (32 of 62) of the positive scan patients presenting this symptom against 18.8% (8 of 44) of dehiscence-free patients. Hypoacousis and hyperacusis were both common complaints in our cohort of patients screened for SCD. Thirty-nine of the 62 patients with SCD (62.9%) reported hypoacousis, which was significantly higher than the rate of 45.5% (20 of 44) found in the negative scan group ( p = 0.035). Our results show that all forms of hyperacusis (autophony, tympanophony, oversensitivity to one’s footsteps or eating sounds, oculophony, and sense of vibration) mainly go together with superior canal dehiscence. For instance, Otology & Neurotology, Vol. 35, No. 2, 2014
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L. Z. BENAMIRA ET AL. TABLE 1.
Clinical signs and symptoms at initial evaluation No. of patients
Symptoms Hypoacusis Tympanophony Autophony Tinnitus Pulsatile tinnitus Phonophobia Aural fullness Other forms of hyperacusis Footstep sound Eating sound Oculophony Sense of vibration Vestibular Vertigo symptoms Vertigo with effort Imbalance/dizziness Motion dizziness Tullio phenomenon Oscillopsia At rest With walking With effort Signs Tunning fork at malleolus Pneumatic speculum induced vertigo Valsalva maneuver Hennebert Cochlear symptoms
footsteps and eating hyperacusis were both present in only 2 of 44 patients, which was significantly lower than what was reported in subjects showing SCD, in whom both symptoms were present in 27.4% (17 of 62) of the population ( p = 0.008 and p = 0.007, respectively). Most of the vestibular symptoms assessed were comparable between both groups (Table 1). Of the 8 vestibular symptoms evaluated, oscillopsia with effort was the only one showing a significant difference, with none (0 of 44) of the non-SCD patients reporting this symptom versus 22.6% (14 of 62) of subjects with superior canal dehiscence. Four signs were evaluated in our series of patients: Tuning fork at malleolus, pneumatic speculumYinduced vertigo, Valsalva-induced vertigo, and Hennebert sign; 22.6% of patients with SCD presented vertigo when performing Valsalva maneuver, against 2.3% of subjects with a negative HRCT ( p = 0.003). None of the patients in the latter group experienced vertigo induced by pneumatic speculum, whereas 27.4% of patients in SCD group did. Tuning fork at malleolus and Hennebert sign failed to demonstrate a statistically significant difference between the 2 groups ( p = 0.137 and p = 0.393, respectively). Audiometric Evaluation Figure 1 displays the audiograms for the patients in this study. We compared air and bone conduction thresholds between the 2 groups at 250, 500, 1,000, 2,000, 3,000, and 4,000 Hz frequencies. There was no statistically significant difference between our groups for air and bone conduction thresholds regardless of the frequency eval-
Ratio of patients (%)
Positive scan group (n = 62)
Negative scan group (n = 44)
Positive scan group (n = 62)
Negative scan group (n = 44)
p value
39 13 37 42 32 34 36 17 17 21 16 16 11 41 26 19 14 10 14
20 2 13 33 8 21 13 2 2 3 0 17 2 26 18 13 3 2 0
62.9 2.1 59.7 75.8 51.6 54.8 58.1 27.4 27.4 33.9 25.8 25.8 17.7 66.1 41.9 30.6 22.6 16.1 22.6
45.5 4.5 29.5 75.0 18.8 47.7 29.5 3.2 4.5 4.5 0 38.6 4.5 59.0 40.9 29.5 6.8 4.5 0
0.035 0.051 G0.001 0.059 G0.001 G0.001 0.003 0.008 0.007 0.003 0.001 0.321 0.089 0.018 0.200 0.132 0.055 0.104 0.003
12 17 14 1
4 0 1 0
19.4 27.4 22.6 1.6
9.1 0 2.3 0
0.137 G0.001 0.003 0.393
uated ( p = 0.286 and p = 0.214, respectively). The ABG was calculated for the same frequencies, as well as an average of ABG at the low frequencies (between 250 and 1,000 Hz). The averages of ABGs in symptomatic ears for both groups are presented in Table 2. Association between significantly higher ABGs and the presence of SCD was shown to be positive at 250 and 500 Hz, with an average difference of 10 and 9 dB, respectively, between both groups ( p = 0.008 and p = 0.008, respectively). The average low-frequency ABG was of 24 dB (T15 SD) in the positive scan group and 17 dB (T13 SD) in the negative scan group, which was not significantly different ( p = 0.311). Cervical VEMP (cVEMP) testing was performed in all our patients, whereas ocular VEMP (oVEMP) was recorded for 20 symptomatic SCD confirmed ears and for 2 patients with intact superior canal. Our results show that mean cVEMP threshold was of 66 dB in the dehiscent ears and 81 dB in non-SCD ears, a statistically significant difference ( p G 0.001). Ocular VEMP thresholds were also significantly lower in SCD ears with a mean threshold of 64 dB, whereas the second group showed an average of 90 dB ( p G 0.001) Predicting SCD Using forward stepwise based on likelihood ratio, we found the number of cochlear symptoms and the ABG at 250 Hz to be the best predictors of SCD. However, because of multicollinearity and our sample size, both variables could not be included. The logistic regression
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FACTORS TO PREDICT SCD
FIG. 1. Mean audiogram of superior canal dehiscent (A) and nonsuperior canal dehiscent (B) patients.
model using the ABG at 250 Hz was found to be the best predictor of SCD. In this model, for each 10 dB unit increase in the 250 Hz ABG, we expect to see an increase odd of having SCD of 51% (OR, 1.51; 95% CI, 1.10Y2.08). DISCUSSION Although research has been conducted to better understand superior canal dehiscence syndrome, some aspects remain unclear. Clinical features of patients with SCD vary, and it is still unexplained why some patients present with exclusively auditory symptoms, some exclusively vestibular symptoms, and others with both (17). TABLE 2. Frequency (Hz) 250 500 1,000 2,000 3,000 4,000
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Hence, clinical diagnosis of SCD with a high index of certitude is challenging, and indications of requesting HRCT are not clearly established. This is further illustrated by our results indicating that as much as 41.5% (44 of 106) of suspected cases of superior semicircular canal dehiscence had a negative HRCT scan. This is, to our knowledge, the first study to explore the possibility of bringing out independent clinical and audiometric factors to predict superior canal dehiscence. In our series of patients who were investigated for superior canal dehiscence, we studied the prevalence of cochlear and vestibular symptoms in each group to find out which among them were associated with a positive HRCT. According to our results, cochlear symptoms are more associated to SCD than vestibular symptoms. We pointed out the fact that some forms of hyperacusis were almost absent in non-SCD patients, for instance, hypersensitivity to one’s own eating and/or footsteps sounds. On the other hand, vestibular symptoms seemed to display no difference between studied groups, which suggests that it may be misleading to rely on vestibular symptoms to make the distinction between SCD and other otologic pathologies. Although this tendency puts forward the potential value of cochlear symptoms in SCD prediction, the size of our population did not allow the integration of this factor in our predictive model. Careful physical exam should never be underestimated, especially when evaluating a patient with unspecific complaints. Our results highlighted the accuracy of pneumatic speculum-induced vertigo and Valsalva maneuver in directing SCD diagnosis. It is now evidence based that SCD can result in a significant conductive hearing loss, and thus, patients manifesting SCD in a purely cochlear fashion are prone to be misdiagnosed with middle ear pathologies such as otosclerosis (4,6,8). Consistently with literature, SCD patients demonstrated increased ABGs at low frequencies (8,9). ABGs in SCD can be explained by the ‘‘third window,’’ which allows acoustic energy to be shunted away from the cochlea to the vestibules, thus increasing air conduction thresholds and impedance discrepancy of the cochlear partition causing supranormal bone conduction thresholds (9,18). Our results confirm the use of ABGs in superior canal dehiscence syndrome diagnosis. Average air-bone gaps at 250 and 500 Hz were of 24 and 18 dB in patients with SCD, whereas they were under 10 in nonSCD patients. Although ABG was traditionally associated
Mean air-bone gaps of positive and negative high-resolution computed tomographic scan for superior canal dehiscence and mean difference between the 2 groups of air-bone gaps Mean ABG of positive HRCT patients (dBT SD) (n = 56)
Mean ABG of negative HRCT patients (dBT SD) (n = 40)
24 T 15 17 T 13 12 T 10 4T7 7T9 10 T 10
14 T 19 8 T 15 8 T 11 1T8 5T8 8 T 11
Mean ABG difference (dBT SD) 10 T 9T 4T 3T 2T 2T
4 2 1 1 1 1
p value 0.008 0.008 0.097 0.207 0.250 0.572
ABG indicates air-bone gap; HRCT, high-resolution computed tomography; SD, standard deviation. Otology & Neurotology, Vol. 35, No. 2, 2014
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with middle ear pathologies (6,16,19), its usefulness may have been underestimated in SCD diagnosis. In fact, our study shows that, among all the factors analyzed, the ABG at 250 Hz is the best predictor of SCD. We firmly believe that this univariate model could be improved by adding other factors, such as VEMP results or cochlear symptoms, but again, statistical analysis was limited by the number of subjects included in this study. Although this 5-year study conducted in a tertiary-care center reports one of the largest SCD database in literature, it will be of utmost importance to further extend it to recruit more cases. VEMP testing is a relatively recent way of assessing vestibular function and thus screening SCD. CVEMP consists in a saccule-mediated reflex triggered by acoustic stimuli, which results in an inhibitory signal traveling through vestibulo-spinal tracts and eliciting ipsilateral sternocleidomastoid muscle relaxation (18,20). Previous work has been conducted to determine the diagnosis value of VEMP testing. We know for instance that lowered VEMP thresholds are described in SCD but can also be attenuated in other pathologies, as later stages of Me´nie`re’s disease (20). Zuniga and colleagues (21) matched SCD ears with healthy controls whose cVEMP thresholds have been evaluated. They found that a cutoff value of 85 dB nHL and lesser gave the combination of best sensitivity (86%) and specificity (90%). Also, cVEMP thresholds were abnormally low in our SCD patients (average, 66 T 13 dB) and significantly lower than non-SCD patient thresholds (average, 81 T 10 dB). The gap between our cutoff value and the one suggested in the latter study can be explained by the control group selection. In fact, Zuniga et al. compared their SCD patients with healthy individuals with no previous history of neurologic complaints, whereas we considered clinically relevant to form our control group with patients for which we falsely suspected SCD and thus requested a CT scan. Examining each patient cVEMP threshold individually, we find that only 2 of the 44 negative scan group patients displayed a cVEMP threshold lower than 75 dB, and only one of the 62 patients in the positive scan group displayed a threshold higher than 75 dB. However, the main issue arising from using 75 dB as a cutoff value to better predict SCD is the fact that many of our patients presented a threshold of exactly 75 dB (15 cases in the positive scan group and 5 in the negative scan group). Also, we failed to find a reliable cutoff value to maximize sensitivity and specificity, given that our sample size was too small, and thus, the confidence intervals were too large. Finally, it would have been interesting to compare cVEMP and oVEMP thresholds, but oVEMP testing has not been preformed for enough patients to draw reliable conclusions out of it.
CONCLUSION Superior canal dehiscence syndrome can present with variables features and may mislead clinicians because of its ability to mimic several vestibulocochlear pathologies. It is the first study which aims is to bring to the fore
specific clinical and audiometric factors to predict SCD. According to our results, the ABG at 250 Hz is the most accurate predictor of SCD. Besides, other factors, including cochlear symptoms and VEMP results, have been found to be strongly associated with SCD. In light of these results, we believe that a multivariate predictive model could be drawn, but long-term studies with larger populations will need to be conducted to do so. Acknowledgments: The authors thank Miguel Chagnon, M.Sc., Department of Mathematics and Statistics, University of Montreal; Me´lanie Benoit, Department of Audiology, Montreal University Hospital Center (CHUM), University of Montreal; and Ve´ronique Montreuil-Jacques, Department of Audiology, Montreal University Hospital Center (CHUM), University of Montreal, for the assistance and logistical support.
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FACTORS TO PREDICT SCD 16. Lehmann M, Ebmeyer J, Upile T, et al. Superior canal dehiscence in patients with three failed stapedectomy operations for otosclerosis: a case report. J Med Case Rep 2011;5:47Y9. 17. Chi F, Ren D, Dai C. Variety of audiologic manifestations in patients with superior canal dehiscence. Otol Neurotol 2009;31:2Y10. 18. Zhou G, Poe D, Quinton G. Clinical use of vestibular evoked myogenic potentials in the evaluation of patients with air-bone gaps. Otol Neurotol 2012;33:1368Y74.
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Otology & Neurotology, Vol. 35, No. 2, 2014
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Superior Canal Dehiscence: Can We Predict the Diagnosis? Lina Zahra Benamira, Musaed Alzahrani, and Issam Saliba From the Division of OtolaryngologyYHead and Neck Surgery, Montreal University Hospital Center (CHUM), Otology and Neurotology, University of Montreal, Montreal, Quebec, Canada.
Objective: Identify independent clinical and audiometric factors to predict a positive high-resolution computed tomography (HRCT) scan for superior canal dehiscence (SCD). Study Design: Retrospective chart review. Setting: Tertiary referral center. Patients: Patients presenting SCD. Intervention(s): Audiogram, VEMP, temporal bone HRCT, and SCD symptoms and signs chart. Main Outcome Measure(s): ABG, VEMP threshold, and symptoms and signs. Results: Approximately 106 patients with SCD symptoms were included: 62 had a positive and 44 had a negative CT scan. The positive scan group showed a higher average of cochlear symptoms than the negative CT scan group (4.3 versus 2.6) ( p G 0.001), but no statistical difference for vestibular symptoms (2.2 versus 1.8) was identified. CVEMP thresholds of the positive and negative CT scan groups were of 66 and 81 dB, respectively ( p G 0.001). The positive CT scan group showed higher ABGs at 250 Hz (24 versus 14 dB) and 500 Hz
(17 versus 8 dB) ( p = 0.008 and p = 0.008, resectively). No statistical significance was found when comparing both groups for air and bone conduction thresholds. Approximately 23% of the positive CT scan group showed a Valsalva-induced vertigo against 2.3% of the negative scan group ( p = 0.003); 27% of the positive CT scan group showed speculum-induced vertigo but none of the negative scan patients ( p G 0.001). Using logistic regression, we found that each 10-dB unit increase in the 250 Hz ABG is associated to an increase odd of having SCD of 51% (OR, 1.51; 95% CI, 1.10Y2.08). Conclusion: Nature and number of cochlear symptoms, Valsalva and pneumatic speculum-induced vertigo, VEMP thresholds, and ABGs seem to correlate with a positive HRCT. The ABG at 250 Hz is the most accurate predictor of SCD. Key Words: Air-bone gapsVHearing lossV HyperacusisVPneumatic speculumYinduced vertigoVSuperior semicircular canal dehiscenceVVestibular evoked myogenic potential. Otol Neurotol 35:338Y343, 2014.
Superior canal dehiscence (SCD) is a clinical and radiologic entity in which a defect in the bone covering the superior semicircular canal leads to sound- and/or pressure-induced vertigo and oscillopsia (1Y4). Precise anatomo-physiologic explanatory model remains unclear, but manifestations can be explained by the third-window hypothesis. In this theory, the presence of a dehiscence in the superior canal creates a third mobile window in addition to the oval and round windows in the inner ear system, which allows sound- and/or pressure-induced motion of the stapes to produce a flow of lymph in the superior canal (1,3,5,6). Audiometric evaluation is often
abnormal with bone conduction less than 0 dB nHL, as well as low frequency conductive hearing loss resulting in the characteristic air-bone gap (ABG) (3,4,7,8). Moreover, patients presenting superior canal dehiscence syndrome (SCDS) commonly demonstrate lower vestibular evoked myogenic potential (VEMP) thresholds (8Y10). Until recently, SCD was pictured as an underdiagnosed condition that needed to be promoted in the medical community (9,11,12). However, as clinicians become more aware to keep this syndrome in mind, they are facing a new challenge: clinical distinction of SCD from a large family of close auditory and vestibular pathologies (10,11,13). It even deserved to this syndrome the title of ‘‘The great otologic mimicker.’’ (9) For instance, certain patients may present with pure cochlear or vestibular symptoms, whereas others experience both (9,14). Cases of superior canal dehiscence simulating otosclerosis have been reported in literature (12Y14). This kind of misdiagnosis can lead to inappropriate management, such as nonindicated stapes surgery and failure to improve hearing loss (15,16).
Address correspondence and reprint requests to Issam Saliba, M.D., F.R.C.S.C., Montreal University Hospital Center (CHUM), Notre-Dame Hospital, Division of OtolaryngologyYHead and Neck Surgery, 1560 Sherbrooke Street East, Montreal, Qc - H2L 4M1, Canada; E-mail: [email protected] Sources of financial support or funding: none. No funding received for this work from any of the following organizations: National Institutes of Health, Welcome Trust, Howard Hughes Medical Institute, or other.
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FACTORS TO PREDICT SCD Thus, the myriad of clinical presentations, which may arise from this syndrome, can make it difficult for one to be confident about this diagnosis before radiologic confirmation. High-resolution computed tomography (HRCT) scan of the temporal bone with reconstruction in the plane of the superior canal is actually the gold standard to visualize superior canal dehiscence. However, HRCT is not only very costly but also exposes patients to radiation, which makes it an unfavorable screening test despite its high sensitivity. Currently, there is no specific tool that enables clinicians to assess the need to request further investigation regarding the clinical presentation only and the degree of suspicion for a dehiscence syndrome. We hypothesize that we can identify independent clinical and audiometric predictors of SCD. Identification of such predictors could help the clinical assessment and management of these cases, avoid unnecessary imaging, and be more cost effective. METHODS Patients Studied A retrospective study was performed examining charts of 106 patients who were referred for HRCT on the basis of clinically suspected superior canal dehiscence syndrome at our tertiary care center between February 2007 and June 2012. This study was approved by the local research ethics committee. Of the 106 patients studied, 62 had a positive HRCT, whereas 44 had a negative HRCT for superior canal dehiscence. Demographic pattern and clinical presentation, including cochleovestibular signs and symptoms, were also collected.
Audiometric Evaluation Each patient’s audiometric evaluation was assessed using pure-tone audiometry to obtain air conduction and bone conduction thresholds. Bone conduction was masked and measured in the supranormal (-5 and -10 dB). Air-bone gaps (ABG) were calculated for each frequency: from 250 to 4,000 Hz. The VEMP was evoked using a Blackman Tone Burst Generator with a rarefaction tone burst at 500 Hz. Cervical VEMP (cVEMP) testing was performed in all patients, whereas ocular VEMP (oVEMP) thresholds were measured on only 20 of the positive HRCT patients and 2 of negative HRCT group.
CT imaging and Measurements Patients underwent HRCT scan of the temporal bone with 0.55-mm collimation with a pitch of 1 at 360 mAs and 120kV. Images were acquired in axial plane and reformatted at 0.6 mm every 0.4 mm using a kernel of 80. The presence of superior canal dehiscence was first assessed on coronal images by a first observer. If the bony covering of the superior canal was found to be dehiscent on one or more coronal slices, the HRCT was reformatted in the plane of the superior semicircular canal (Poschl’s plane) to rule out false-positive cases. Reconstructed images were evaluated by the first observer and again by a second observer to ensure reliability. In this study, dehiscence was defined as the complete absence of a portion of the bone overlying the superior semicircular canal. Thus, thinning of the superior canal did not meet our criteria for dehiscence. All CT scans were evaluated on a DS3000 Agfa diagnostic PACS station by the same 2 investigators blinded to the patients’ clinical history.
339 Statistical Analysis
Groups description was performed using frequency for categorical data and mean, whereas standard deviation and maximum and minimum were used for continuous characteristics. The difference between both groups for presence of cochleovestibular signs and symptoms was studied with Pearson’s chisquared test. Student’s t test was used to compare VEMP thresholds and ANOVA for repeated measures with 2 factors (group and frequencies) to study ABGs and air and bone conduction thresholds. We analyzed prediction of SCD with multivariate logistic regression (forward stepwise based on likelihood ratio). All analyses were done with SPSS 20 and a significance level of 5%.
RESULTS Symptoms and Signs A total of 106 patients were referred for temporal bone HRCT to confirm or rule out SCD. From these, 62 (32 male and 30 female subjects) had a positive HRCT. The age range at the time of diagnosis in this group went from 27 to 74 years, with a mean of 47 years (T12 standard deviation). Only the right ear was affected in 21 patients, only the left ear in 25, whereas 15 patients presented bilateral SCD. On the other hand, HRCT excluded SCD in 44 patients (17 male and 27 female subjects) among the total 106 for whom we had clinical suspicion of SCD, which represents 41.5%. Mean age in this category was 44 years (T13 years standard deviation), ranging from 21 to 73 years. There was no statistically significant difference between the 2 groups for age at radiologic diagnosis ( p = 0.287) nor for sex ( p = 0.250). Average dehiscence size in the positive scan group was of 4.2 mm (range, 1.3Y8.0 mm) with a standard deviation of 1.6 mm. The symptoms and signs that were present in these patients are summarized in Table 1. SCD group presented an average of 4.2 cochlear symptoms of the 11 we assessed at initial evaluation, whereas the negative HRCT subjects showed an average of 2.6, which was statistically significant ( p G 0.001). However, groups did not show a significant difference when compared for the average number of vestibular symptoms at presentation (positive scan group, 2.2; negative scan group, 1.8; p 9 0.05). Tinnitus was the most prevalent symptom in both groups affecting 75.8% (42 of 62) and 75.0% (33 of 44) of positive and negative scan group patients, respectively. Both groups showed comparable rates of tinnitus ( p = 0.059). On the other hand, pulsatile tinnitus revealed a significant association with SCD ( p G 0.001), with 51.6% (32 of 62) of the positive scan patients presenting this symptom against 18.8% (8 of 44) of dehiscence-free patients. Hypoacousis and hyperacusis were both common complaints in our cohort of patients screened for SCD. Thirty-nine of the 62 patients with SCD (62.9%) reported hypoacousis, which was significantly higher than the rate of 45.5% (20 of 44) found in the negative scan group ( p = 0.035). Our results show that all forms of hyperacusis (autophony, tympanophony, oversensitivity to one’s footsteps or eating sounds, oculophony, and sense of vibration) mainly go together with superior canal dehiscence. For instance, Otology & Neurotology, Vol. 35, No. 2, 2014
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L. Z. BENAMIRA ET AL. TABLE 1.
Clinical signs and symptoms at initial evaluation No. of patients
Symptoms Hypoacusis Tympanophony Autophony Tinnitus Pulsatile tinnitus Phonophobia Aural fullness Other forms of hyperacusis Footstep sound Eating sound Oculophony Sense of vibration Vestibular Vertigo symptoms Vertigo with effort Imbalance/dizziness Motion dizziness Tullio phenomenon Oscillopsia At rest With walking With effort Signs Tunning fork at malleolus Pneumatic speculum induced vertigo Valsalva maneuver Hennebert Cochlear symptoms
footsteps and eating hyperacusis were both present in only 2 of 44 patients, which was significantly lower than what was reported in subjects showing SCD, in whom both symptoms were present in 27.4% (17 of 62) of the population ( p = 0.008 and p = 0.007, respectively). Most of the vestibular symptoms assessed were comparable between both groups (Table 1). Of the 8 vestibular symptoms evaluated, oscillopsia with effort was the only one showing a significant difference, with none (0 of 44) of the non-SCD patients reporting this symptom versus 22.6% (14 of 62) of subjects with superior canal dehiscence. Four signs were evaluated in our series of patients: Tuning fork at malleolus, pneumatic speculumYinduced vertigo, Valsalva-induced vertigo, and Hennebert sign; 22.6% of patients with SCD presented vertigo when performing Valsalva maneuver, against 2.3% of subjects with a negative HRCT ( p = 0.003). None of the patients in the latter group experienced vertigo induced by pneumatic speculum, whereas 27.4% of patients in SCD group did. Tuning fork at malleolus and Hennebert sign failed to demonstrate a statistically significant difference between the 2 groups ( p = 0.137 and p = 0.393, respectively). Audiometric Evaluation Figure 1 displays the audiograms for the patients in this study. We compared air and bone conduction thresholds between the 2 groups at 250, 500, 1,000, 2,000, 3,000, and 4,000 Hz frequencies. There was no statistically significant difference between our groups for air and bone conduction thresholds regardless of the frequency eval-
Ratio of patients (%)
Positive scan group (n = 62)
Negative scan group (n = 44)
Positive scan group (n = 62)
Negative scan group (n = 44)
p value
39 13 37 42 32 34 36 17 17 21 16 16 11 41 26 19 14 10 14
20 2 13 33 8 21 13 2 2 3 0 17 2 26 18 13 3 2 0
62.9 2.1 59.7 75.8 51.6 54.8 58.1 27.4 27.4 33.9 25.8 25.8 17.7 66.1 41.9 30.6 22.6 16.1 22.6
45.5 4.5 29.5 75.0 18.8 47.7 29.5 3.2 4.5 4.5 0 38.6 4.5 59.0 40.9 29.5 6.8 4.5 0
0.035 0.051 G0.001 0.059 G0.001 G0.001 0.003 0.008 0.007 0.003 0.001 0.321 0.089 0.018 0.200 0.132 0.055 0.104 0.003
12 17 14 1
4 0 1 0
19.4 27.4 22.6 1.6
9.1 0 2.3 0
0.137 G0.001 0.003 0.393
uated ( p = 0.286 and p = 0.214, respectively). The ABG was calculated for the same frequencies, as well as an average of ABG at the low frequencies (between 250 and 1,000 Hz). The averages of ABGs in symptomatic ears for both groups are presented in Table 2. Association between significantly higher ABGs and the presence of SCD was shown to be positive at 250 and 500 Hz, with an average difference of 10 and 9 dB, respectively, between both groups ( p = 0.008 and p = 0.008, respectively). The average low-frequency ABG was of 24 dB (T15 SD) in the positive scan group and 17 dB (T13 SD) in the negative scan group, which was not significantly different ( p = 0.311). Cervical VEMP (cVEMP) testing was performed in all our patients, whereas ocular VEMP (oVEMP) was recorded for 20 symptomatic SCD confirmed ears and for 2 patients with intact superior canal. Our results show that mean cVEMP threshold was of 66 dB in the dehiscent ears and 81 dB in non-SCD ears, a statistically significant difference ( p G 0.001). Ocular VEMP thresholds were also significantly lower in SCD ears with a mean threshold of 64 dB, whereas the second group showed an average of 90 dB ( p G 0.001) Predicting SCD Using forward stepwise based on likelihood ratio, we found the number of cochlear symptoms and the ABG at 250 Hz to be the best predictors of SCD. However, because of multicollinearity and our sample size, both variables could not be included. The logistic regression
Otology & Neurotology, Vol. 35, No. 2, 2014
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FACTORS TO PREDICT SCD
FIG. 1. Mean audiogram of superior canal dehiscent (A) and nonsuperior canal dehiscent (B) patients.
model using the ABG at 250 Hz was found to be the best predictor of SCD. In this model, for each 10 dB unit increase in the 250 Hz ABG, we expect to see an increase odd of having SCD of 51% (OR, 1.51; 95% CI, 1.10Y2.08). DISCUSSION Although research has been conducted to better understand superior canal dehiscence syndrome, some aspects remain unclear. Clinical features of patients with SCD vary, and it is still unexplained why some patients present with exclusively auditory symptoms, some exclusively vestibular symptoms, and others with both (17). TABLE 2. Frequency (Hz) 250 500 1,000 2,000 3,000 4,000
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Hence, clinical diagnosis of SCD with a high index of certitude is challenging, and indications of requesting HRCT are not clearly established. This is further illustrated by our results indicating that as much as 41.5% (44 of 106) of suspected cases of superior semicircular canal dehiscence had a negative HRCT scan. This is, to our knowledge, the first study to explore the possibility of bringing out independent clinical and audiometric factors to predict superior canal dehiscence. In our series of patients who were investigated for superior canal dehiscence, we studied the prevalence of cochlear and vestibular symptoms in each group to find out which among them were associated with a positive HRCT. According to our results, cochlear symptoms are more associated to SCD than vestibular symptoms. We pointed out the fact that some forms of hyperacusis were almost absent in non-SCD patients, for instance, hypersensitivity to one’s own eating and/or footsteps sounds. On the other hand, vestibular symptoms seemed to display no difference between studied groups, which suggests that it may be misleading to rely on vestibular symptoms to make the distinction between SCD and other otologic pathologies. Although this tendency puts forward the potential value of cochlear symptoms in SCD prediction, the size of our population did not allow the integration of this factor in our predictive model. Careful physical exam should never be underestimated, especially when evaluating a patient with unspecific complaints. Our results highlighted the accuracy of pneumatic speculum-induced vertigo and Valsalva maneuver in directing SCD diagnosis. It is now evidence based that SCD can result in a significant conductive hearing loss, and thus, patients manifesting SCD in a purely cochlear fashion are prone to be misdiagnosed with middle ear pathologies such as otosclerosis (4,6,8). Consistently with literature, SCD patients demonstrated increased ABGs at low frequencies (8,9). ABGs in SCD can be explained by the ‘‘third window,’’ which allows acoustic energy to be shunted away from the cochlea to the vestibules, thus increasing air conduction thresholds and impedance discrepancy of the cochlear partition causing supranormal bone conduction thresholds (9,18). Our results confirm the use of ABGs in superior canal dehiscence syndrome diagnosis. Average air-bone gaps at 250 and 500 Hz were of 24 and 18 dB in patients with SCD, whereas they were under 10 in nonSCD patients. Although ABG was traditionally associated
Mean air-bone gaps of positive and negative high-resolution computed tomographic scan for superior canal dehiscence and mean difference between the 2 groups of air-bone gaps Mean ABG of positive HRCT patients (dBT SD) (n = 56)
Mean ABG of negative HRCT patients (dBT SD) (n = 40)
24 T 15 17 T 13 12 T 10 4T7 7T9 10 T 10
14 T 19 8 T 15 8 T 11 1T8 5T8 8 T 11
Mean ABG difference (dBT SD) 10 T 9T 4T 3T 2T 2T
4 2 1 1 1 1
p value 0.008 0.008 0.097 0.207 0.250 0.572
ABG indicates air-bone gap; HRCT, high-resolution computed tomography; SD, standard deviation. Otology & Neurotology, Vol. 35, No. 2, 2014
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with middle ear pathologies (6,16,19), its usefulness may have been underestimated in SCD diagnosis. In fact, our study shows that, among all the factors analyzed, the ABG at 250 Hz is the best predictor of SCD. We firmly believe that this univariate model could be improved by adding other factors, such as VEMP results or cochlear symptoms, but again, statistical analysis was limited by the number of subjects included in this study. Although this 5-year study conducted in a tertiary-care center reports one of the largest SCD database in literature, it will be of utmost importance to further extend it to recruit more cases. VEMP testing is a relatively recent way of assessing vestibular function and thus screening SCD. CVEMP consists in a saccule-mediated reflex triggered by acoustic stimuli, which results in an inhibitory signal traveling through vestibulo-spinal tracts and eliciting ipsilateral sternocleidomastoid muscle relaxation (18,20). Previous work has been conducted to determine the diagnosis value of VEMP testing. We know for instance that lowered VEMP thresholds are described in SCD but can also be attenuated in other pathologies, as later stages of Me´nie`re’s disease (20). Zuniga and colleagues (21) matched SCD ears with healthy controls whose cVEMP thresholds have been evaluated. They found that a cutoff value of 85 dB nHL and lesser gave the combination of best sensitivity (86%) and specificity (90%). Also, cVEMP thresholds were abnormally low in our SCD patients (average, 66 T 13 dB) and significantly lower than non-SCD patient thresholds (average, 81 T 10 dB). The gap between our cutoff value and the one suggested in the latter study can be explained by the control group selection. In fact, Zuniga et al. compared their SCD patients with healthy individuals with no previous history of neurologic complaints, whereas we considered clinically relevant to form our control group with patients for which we falsely suspected SCD and thus requested a CT scan. Examining each patient cVEMP threshold individually, we find that only 2 of the 44 negative scan group patients displayed a cVEMP threshold lower than 75 dB, and only one of the 62 patients in the positive scan group displayed a threshold higher than 75 dB. However, the main issue arising from using 75 dB as a cutoff value to better predict SCD is the fact that many of our patients presented a threshold of exactly 75 dB (15 cases in the positive scan group and 5 in the negative scan group). Also, we failed to find a reliable cutoff value to maximize sensitivity and specificity, given that our sample size was too small, and thus, the confidence intervals were too large. Finally, it would have been interesting to compare cVEMP and oVEMP thresholds, but oVEMP testing has not been preformed for enough patients to draw reliable conclusions out of it.
CONCLUSION Superior canal dehiscence syndrome can present with variables features and may mislead clinicians because of its ability to mimic several vestibulocochlear pathologies. It is the first study which aims is to bring to the fore
specific clinical and audiometric factors to predict SCD. According to our results, the ABG at 250 Hz is the most accurate predictor of SCD. Besides, other factors, including cochlear symptoms and VEMP results, have been found to be strongly associated with SCD. In light of these results, we believe that a multivariate predictive model could be drawn, but long-term studies with larger populations will need to be conducted to do so. Acknowledgments: The authors thank Miguel Chagnon, M.Sc., Department of Mathematics and Statistics, University of Montreal; Me´lanie Benoit, Department of Audiology, Montreal University Hospital Center (CHUM), University of Montreal; and Ve´ronique Montreuil-Jacques, Department of Audiology, Montreal University Hospital Center (CHUM), University of Montreal, for the assistance and logistical support.
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