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Original Research—Otology and Neurotology Acoustic Reflex Screening of Conductive Hearing Loss for Third Window Disorders Robert S. Hong, MD, PhD1,2,3,4, Christopher M. Metz, DO5, Dennis I. Bojrab, MD1,2,3,4, Seilesh C. Babu, MD1,2,3,4, John Zappia, MD1,2,3,4, Eric W. Sargent, MD1,2,3,4, Eleanor Y. Chan, MD1,2,3,4, Ilka C. Naumann, MD1,2,3,4, and Michael J. LaRouere, MD1,2,3,4 No sponsorships or competing interests have been disclosed for this article. Abstract Objective. This study examines the effectiveness of acoustic reflexes in screening for third window disorders (eg, superior semicircular canal dehiscence) prior to middle ear exploration for conductive hearing loss. Study Design. Case series with chart review. Setting. Outpatient tertiary otology center. Subjects and Methods. A review was performed of 212 ears with acoustic reflexes, performed as part of the evaluation of conductive hearing loss in patients without evidence of chronic otitis media. The etiology of hearing loss was determined from intraoperative findings and computed tomography imaging. The relationship between acoustic reflexes and conductive hearing loss etiology was assessed. Results. Eighty-eight percent of ears (166 of 189) demonstrating absence of all acoustic reflexes had an ossicular etiology of conductive hearing loss. Fifty-two percent of ears (12 of 23) with at least 1 detectable acoustic reflex had a nonossicular etiology. The positive and negative predictive values for an ossicular etiology were 89% and 57% when acoustic reflexes were used alone for screening, 89% and 39% when third window symptoms were used alone, and 94% and 71% when reflexes and symptoms were used together, respectively. Otolaryngology– Head and Neck Surgery 2016, Vol. 154(2) 343–348 Ó American Academy of Otolaryngology—Head and Neck Surgery Foundation 2015 Reprints and permission: sagepub.com/journalsPermissions.nav DOI: 10.1177/0194599815620162 http://otojournal.org Received August 19, 2015; revised October 14, 2015; accepted November 10, 2015. T he acoustic reflex refers to the contraction of the stapedius muscle in response to an intense acoustic stimulus. It can be indirectly measured in the clinical setting by means of an impedance bridge. The reflex arc consists of sound stimulating the cochlea, resulting in stimulation of the eighth cranial nerve, ventral cochlear nuclei, superior olive, and facial nerve and, ultimately, contraction of the stapedius muscle.1 It involves crossed and uncrossed pathways, whereby stimulation of 1 ear with a high-level sound stimulus will result in contraction of the stapedius muscles of both ears in a individual with normal physiology. The majority of patients with significant conductive hearing loss, with otherwise normal otoscopic examination results, will have an ossicular etiology of hearing loss. However, there have been reports of patients undergoing middle ear exploration with the intraoperative finding of a normal ossicular chain, despite a significant conductive hearing loss.2,3 For many years, these patients were considered as having an ‘‘inner ear conductive hearing loss.’’4-6 More recently, it has been found that third window disorders, such as superior semicircular canal dehiscence and a dilated vestibular aqueduct, can also cause a conductive hearing loss,7-9 and many patients 1 Michigan Ear Institute, Farmington Hills, Michigan, USA Department of Otolaryngology–Head and Neck Surgery, Wayne State University, Detroit, Michigan, USA 3 Neurotology Division, St John Providence Health System, Novi, Michigan, USA 4 Department of Surgery, Oakland University William Beaumont School of Medicine, Rochester, Michigan, USA 5 Osteopathic Division, St John Providence Health System, Madison Heights, Michigan, USA 2 Conclusion. Acoustic reflex testing is an effective means of screening for third window disorders in patients with a conductive hearing loss. Questioning for third window symptoms should complement screening. The detection of even 1 acoustic reflex or third window symptom (regardless of reflex status) should prompt further workup prior to middle ear exploration. Keywords acoustic reflex, otosclerosis, superior semicircular canal dehiscence, conductive hearing loss, third window This article was presented at the 2015 AAO-HNSF Annual Meeting & OTO EXPO; September 27-30, 2015; Dallas, Texas. Corresponding Author: Robert S. Hong, MD, PhD, Michigan Ear Institute, 30055 Northwestern Hwy, #101, Farmington Hills, MI 48334, USA. Email: [email protected] Downloaded from oto.sagepub.com at SOCIEDADE BRASILEIRA DE CIRUR on February 2, 2016 344 Otolaryngology–Head and Neck Surgery 154(2) with previously unclear causes of conductive hearing loss have been found to have such a third window disorder.10-13 One potential way to avoid middle ear surgery in patients whose hearing loss is caused by a third window disorder is to obtain high-resolution computed tomography (CT) imaging of the temporal bone.14 However, this is not performed routinely, due to the high rates of success of middle ear exploration and to the added cost and radiation involved with imaging. An alternative that may be considered to assess for a third window disorder is to obtain acoustic reflexes prior to middle ear exploration. In patients considering surgical correction of conductive hearing loss, one would expect acoustic reflexes to be absent in the affected ear if the etiology is secondary to otosclerosis.15,16 In contrast, in patients with conductive hearing loss due to a third window disorder, the acoustic reflex should remain present, as the ossicles are normal.9 For patients whose reflexes are not consistent with an ossicular etiology, imaging can be ordered to assess for a third window disorder. At our institution, we routinely measure acoustic reflexes at 4 stimulus frequencies (500, 1000, 2000, and 4000 Hz) for each ear. Thus, a total of 8 measurements of acoustic reflex threshold are relevant when one is evaluating the likelihood of an ossicular etiology of a particular ear’s conductive hearing loss. What are ill defined are the exact criteria that should be used to trigger further workup for a third window disorder. How many acoustic reflexes need to be present to recommend imaging for a third window disorder? Does the magnitude of the acoustic reflex threshold matter, when present? Is it possible for all acoustic reflexes to be absent and still have a third window disorder responsible for the conductive hearing loss? If so, are there other factors to consider to mitigate the risk of unnecessary middle ear exploration? In addressing these questions, we hope to improve our ability to avoid middle ear surgery for patients whose conductive hearing loss is not due to an ossicular etiology. Methods The cases of 720 consecutive patients who had acoustic reflexes performed at a tertiary otology center from July 2011 to April 2014 were screened in a retrospective review. The study was approved by the Providence Hospital and Medical Centers Institutional Review Board (study No. 636292). From these, 192 patients contributing 212 ears were included in the study, based on the following inclusion and exclusion criteria. Inclusion criteria included the following: Acoustic reflexes obtained in context of consideration of middle ear exploration for conductive hearing loss Evidence of etiology of conductive hearing loss— including (1) middle ear surgery documenting the status of the ossicles AND postoperative documentation of hearing status or (2) high-resolution CT imaging of temporal bone Exclusion criteria were as follows: Prior middle ear surgery on the ear with the conductive hearing loss Chronic otitis media, including tympanic membrane perforation or cholesteatoma (based on history, physical examination, or imaging findings) Incomplete acoustic reflex data relevant for a particular ear’s conductive hearing loss Given the above, the majority of patients who were excluded from this study were those with a conductive hearing loss who did not have surgical exploration of the ear and did not have CT imaging, as the etiology of the hearing loss could not be determined. Classification of conductive hearing loss. The etiology of conductive hearing loss was separated into the following categories: (1) ossicular abnormalities, (2) third window disorders, (3) both ossicular and third window etiologies, (4) other etiology, and (5) unknown etiology. To be classified as having an ossicular etiology, an ear needed to meet 1 of the following criteria. First, if an ear underwent middle ear surgery, there needed to be an intraoperative finding of an ossicular abnormality (eg, ossicular fixation or discontinuity) deemed responsible for the hearing loss. Furthermore, if surgical correction of this abnormality was attempted, there needed to be confirmation of hearing improvement postoperatively, in the form of either closure of the average air-bone gap (ABG) after surgery to \20 dB or documentation of subjective hearing improvement (in a few instances where the audiogram not available). Second, if an ear did not undergo surgery, it needed to have a highresolution CT scan of the temporal bone that demonstrated either evidence of otosclerosis or lack of evidence of a third window disorder. To be classified as having a third window disorder, an ear needed to demonstrate semicircular canal dehiscence or a dilated vestibular aqueduct on CT imaging. Diagnosis of these entities was based on review of the local neuroradiologist’s report of CT findings, followed by review of images by the attending otologist during the patient encounter as documented in the patient chart. With respect to the diagnosis of superior semicircular canal dehiscence, all scans obtained at our home institution had the recommended views in the Stenvers and Poschl planes; CT scans obtained from outside institutions were reformatted by the attending otologist at the time of the patient visit using OsiriX software (Pixmeo Sarl, Bernex, Switzerland) in the Stenvers and Poschl planes if such views were not already available. To be classified under other etiology, there needed to be a clearly defined alternative etiology for conductive hearing loss, as was true in one case of an encephalocele (seen on CT imaging and intraoperatively). To be classified as having an unknown etiology, there needed to be a lack of evidence of ossicular etiology (ie, intraoperative finding of normal ossicles and/or lack of Downloaded from oto.sagepub.com at SOCIEDADE BRASILEIRA DE CIRUR on February 2, 2016 Hong et al 345 improvement in hearing postoperatively despite attempted surgical correction) and lack of evidence of a third window disorder (ie, normal CT temporal bone). Audiometry. All testing was performed in a soundproof booth. Pure tone audiometry was performed from 250 to 8000 Hz for air conduction and 250 to 4000 Hz for bone conduction, with masking as appropriate. Conductive hearing loss was calculated from the 4-tone average ABG measured at 500, 1000, 2000, and 4000 Hz. Acoustic reflex thresholds were measured at 500, 1000, 2000, and 4000 Hz for each ear with both ipsilateral and contralateral presentation of the sound stimulus. Reflexes were assessed with the GSI Tympstar Middle Ear Analyzer (Grason-Stadler, Eden Prairie, Minnesota). All stimuli were presented with the auto-timing GSI default setting, with a train of 8 repeated pure tones over 1.5 seconds. Stimuli were initially presented at 80 dB and increased in 5-dB increments up to 120 dB, until a reflex was measured. If an acoustic reflex was not detected at 120 dB, then the acoustic reflex was regarded as not being present. A total of 8 acoustic reflexes were relevant for evaluating the conductive hearing loss in a given ear. For example, for right conductive hearing loss, reflexes were relevant at each frequency for the right ipsilateral condition (sound stimulus to right ear, probe in right ear) and left contralateral condition (sound stimulus to left ear, probe in right ear). Results A total of 192 patients contributing 212 ears met inclusion criteria for the study, with 20 patients contributing both ears. Their average age was 47.5 years, and there were 121 women and 91 men. The laterality of the ears was 110 left and 102 right ears. The average ABG prior to any surgical intervention for all ears in this study was 22.8 dB, with those with an ossicular etiology having a statistically significantly larger ABG (23.8 dB) than those with a third window disorder (17.2 dB; t test, P = .003). The etiology of conductive hearing loss is shown in Table 1. Of the ears included in this study, 186 of 212 underwent middle ear surgery, which included several ears where the diagnosis of a nonossicular etiology of hearing loss was not obtained until after surgery. Out of 212 ears, 189 demonstrated no response to all acoustic reflexes, and 23 had at least 1 detectable acoustic reflex. Of the ears found to have absent acoustic reflexes at all frequencies tested, an ossicular etiology of hearing loss was found in 88% (166 of 189 ears) and a third window etiology in 10% (18 of 189). This excludes 4 ears that had evidence of both etiologies and 1 ear that had evidence of neither. Of the ears found to have at least 1 detectable acoustic reflex, an ossicular etiology of hearing loss was present in 48% (11 of 23 ears), and a third window abnormality was present in 39% (9 of 23). This excludes 1 ear that had evidence of both, 1 ear that had evidence of neither, and 1 ear that had an encephalocele as the source of the conductive hearing loss. Thus, overall, for patients with at least 1 detectable acoustic reflex, a nonossicular etiology Table 1. Etiology of Conductive Hearing Loss. Conductive Hearing Loss Etiology Ossicular abnormality Otosclerosis Other ossicular abnormality Third window disorder Superior semicircular canal dehiscence Dilated vestibular aqueduct Both ossicular and third window disorder (including above) Other (eg, encephalocele) Unknown Ears, n 171 11 29 3 5 1 2 was present in 52% (12 of 23 ears). The number of detectable acoustic reflexes for ears with only an ossicular abnormality and those with only a third window disorder are shown in Figure 1. There was no statistical correlation found between either the number of detectable reflexes or the magnitude of these reflexes, when detected, and the etiology of conductive hearing loss. For patients with no response to any acoustic reflexes, the prevalence of symptoms suggestive of third window disorders was examined. No such symptoms were found in 82% (155 of 189 ears), including 144 ears with an ossicular etiology, 8 ears with a third window etiology, 2 ears with both etiologies, and 1 ear with an unknown etiology. The symptom of dizziness was found in 14% (26 of 189 ears), including 17 ears with an ossicular etiology, 8 ears with a third window disorder, and 1 ear with both. The symptom of pulsatile tinnitus was present in 7% (13 of 189 ears), including 8 ears with an ossicular etiology, 4 ears with a third window disorder, and 1 ear with both. The symptom of autophony was present in 2% (3 of 189 ears), including 1 ear with an ossicular etiology and 2 ears with a third window disorder. Overall, 35% (12 of 34) of ears with dizziness, pulsatile tinnitus, and/or autophony and no response to any acoustic reflex were found to have a nonossicular etiology of conductive hearing loss. For patients with at least 1 detectable acoustic reflex, the prevalence of symptoms suggestive of third window disorders was also examined. No such symptoms were found in 83% (19 of 23 ears), including 10 ears with an ossicular etiology, 6 ears with a third window etiology, 1 ear with both etiologies, 1 ear with an unknown etiology, and 1 ear with an encephalocele. The symptom of dizziness was found in 13% (3 of 23 ears), with all 3 ears with a third window disorder. The symptom of pulsatile tinnitus was present in 4% (1 of 23 ears), with this ear having an ossicular etiology. The symptom of autophony was not found in any ears. Overall, 75% (3 of 4) of ears with dizziness, pulsatile tinnitus, and/or autophony and at least 1 detectable acoustic reflex were found to have a third window disorder. In summary, the results presented in Table 2 demonstrate the value of acoustic reflexes as compared with the Downloaded from oto.sagepub.com at SOCIEDADE BRASILEIRA DE CIRUR on February 2, 2016 346 Otolaryngology–Head and Neck Surgery 154(2) Figure 1. Number of acoustic reflexes present. The number of acoustic reflexes detected (of 8) per ear is shown for those with conductive hearing loss secondary to an ossicular abnormality and a third window disorder. Table 2. Performance of Acoustic Reflexes vs Third Window Symptoms as a Screening Tool for Conductive Hearing Loss (in Percentages). Positive predictive value Negative predictive value Sensitivity Specificity Acoustic Reflexes Third Window Symptoms Both 89 57 94 36 89 39 87 43 94 71 94 69 use of third window symptoms as a screening tool for determining that an ossicular abnormality is solely responsible for conductive hearing loss. A true positive is defined as a correct determination of an ossicular etiology of hearing loss. A true negative is defined as a correct determination that an ossicular etiology is not solely responsible for hearing loss. From the table, it can be seen that the use of third window symptoms alone in screening is almost as effective as using acoustic reflexes alone. However, the most effective screening method is to use a combination of acoustic reflexes and the presence of third window symptoms to screen, where a CT scan is obtained for all patients that have either at least 1 detectable acoustic reflex or third window symptom (regardless of acoustic reflex result). Ordering imaging in these cases would allow us to increase the positive predictive value to 94%, as we would correctly diagnose the etiology of conductive hearing loss in 12 additional ears (Table 2). The cost of such an algorithm would be that a negative CT scan would be ordered in 12%, as 22 ears with an ossicular abnormality and absence of all acoustic reflexes also had dizziness, pulsatile tinnitus, and/or autophony. Discussion This study demonstrates that it is important to obtain acoustic reflexes and inquire about the presence of third window symptoms in all patients prior to middle ear exploration. While reflexes alone and history alone can serve as screening tools for third window disorders, the combination of the two is most effective in minimizing the risk of unnecessary middle ear surgery. The results of this study suggest that the detection of even 1 acoustic reflex relevant to a particular ear’s conductive hearing loss should prompt further workup with CT imaging. Furthermore, it is important to realize that it is possible for all acoustic reflexes to be absent and still have a third window disorder responsible for the conductive hearing loss. Asking about third window symptoms and obtaining a CT scan when such symptoms are present help to mitigate the risk of a negative middle ear exploration in such a scenario. It has been suggested that vestibular evoked myogenic potentials may also play a role in the screening process for third window disorders prior to middle ear exploration.17 Additional research is required to determine what combination of history, acoustic reflexes, and/or vestibular evoked myogenic potentials is most effective for screening for third window disorders in such patients. With ossicular etiologies of conductive hearing loss, acoustic reflexes change as the disease progresses. With otosclerosis as an example, the reflexes may be initially normal. As stapes fixation progresses, reflex amplitudes will decrease, and thresholds will increase, until eventually the Downloaded from oto.sagepub.com at SOCIEDADE BRASILEIRA DE CIRUR on February 2, 2016 Hong et al 347 reflexes can no longer be detected.16 In this study, all patients had advanced-enough disease (average ABG = 22.8 dB) where surgical exploration was considered and where one may have reasonably expected all reflexes to be absent. Nevertheless, some ears with ossicular etiologies had detectable acoustic reflexes, so reflex testing is not infallible. At our institution, we do not routinely assess for the presence of the biphasic ‘‘negative on/off ’’ effect that has been described with early otosclerosis.18 It is possible that the addition of this assessment may further improve the value of acoustic reflexes in differentiating among etiologies of conductive hearing loss. The retrospective nature of this study requires that the results be interpreted with a degree of caution. First, the number of patients with third window symptoms may be underestimated. In particular, patients who present with hearing loss where an ossicular etiology is highly suspected may not always have documented if they experience autophony or pulsatile tinnitus. Second, given that we practice at a tertiary otology referral center, the CT scans obtained came from a large number of different facilities and were of variable quality. This may have introduced variability in the accuracy of the radiologic diagnosis of ossicular and third window disorders. Third, the number of patients with third window disorders and thus combined etiologies may be underestimated. In this study, the majority of patients with otosclerosis did not have a CT scan performed. It was assumed that if they had an intraoperative finding of stapes fixation, postoperative hearing improvement, and no CT scan, the cause of their hearing loss was due solely to an ossicular etiology. However, the prevalence of third window disorders in the general population has been reported to be between 3% and 9%.19-21 Thus, we suspect that if every patient received imaging prior to middle ear exploration, we would find a higher rate than the 2% (5 of 212 ears) of concurrent ossicular and third window disorders found in this study. One question brought up by this study is how to address patients with significant conductive hearing loss for whom there is evidence (eg, from a preoperative CT scan) for both otosclerosis and a third window disorder. In this study, 5 ears were found to fit into this category, all of which had concurrent otosclerosis and superior semicircular canal dehiscence. Of these ears, 2 underwent stapedectomy surgery and had a successful postoperative hearing outcome; 1 underwent middle ear surgery with no postoperative change in hearing; and 2 did not have surgery because of the concurrent presence of a third window disorder. When one considers middle ear exploration for concurrent otosclerosis and third window disorders, there are 2 relevant issues to address. The first is if hearing can be improved significantly with middle ear surgery, given the concurrent presence of a third window disorder. The literature is sparse but supports our findings that in some cases, significant closure of the ABG can be achieved.22,23 The second issue is whether there is an increased risk of sensorineural hearing loss following stapedectomy because of a concurrent third window disorder. We are not aware of any reports of sensorineural hearing loss following stapedectomy attributed to semicircular canal dehiscence. There are a few case reports linking intraoperative stapes gusher and postoperative sensorineural hearing loss to dilated vestibular aqueduct,24,25 but most of these cases had other inner ear malformations present. Therefore, it seems reasonable to offer middle ear exploration to patients with concurrent otosclerosis and third window disorders, as long as they are counseled that there may not be complete closure of the ABG after surgery. Acknowledgments We thank Nancy M. Jackson, PhD, for her help with statistical analysis. Author Contributions Robert S. Hong, design of study, analysis of data, drafting of work, final approval of version to be published, agreement to be accountable; Christopher M. Metz, acquisition of data, drafting of work, final approval of version to be published, agreement to be accountable; Dennis I. Bojrab, design of study, critical revision, final approval of version to be published, agreement to be accountable; Seilesh C. Babu, design of study, critical revision, final approval of version to be published, agreement to be accountable; John Zappia, design of study, critical revision, final approval of version to be published, agreement to be accountable; Eric W. Sargent, design of study, critical revision, final approval of version to be published, agreement to be accountable; Eleanor Y. Chan, design of study, critical revision, final approval of version to be published, agreement to be accountable; Ilka C. Naumann, design of study, critical revision, final approval of version to be published, agreement to be accountable; Michael J. LaRouere, design of study, critical revision, final approval of version to be published, agreement to be accountable. Disclosures Competing interests: None. Sponsorships: None. Funding source: None. References 1. Borg E. On the neuronal organization of the acoustic middle ear reflex: a physiological and anatomical study. Brain Res. 1973;49:101-123. 2. Bess FH, Miller GW, Glasscock ME, Bratt GW. Unexplained conductive hearing-loss. South Med J. 1980;73:335-338. 3. House JW, Sheehy JL, Antunez JC. Stapedectomy in children. Laryngoscope. 1980;90:1804-1809. 4. Al Muhaimeed H, El Sayed Y, Rabah A, Al-Essa A. 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Pritchett CV, Spector ME, Kileny PR, Heidenreich KD, ElKashlan HK. Surgical treatment of hearing loss when otosclerosis coexists with superior semicircular canal dehiscence syndrome. Otol Neurotol. 2014;35:1163-1167. 23. Hope A, Fagan P. Latent superior canal dehiscence syndrome unmasked by stapedotomy for otosclerosis. J Laryngol Otol. 2010;124:428-430. 24. Shirazi A, Fenton JE, Fagan PA. Large vestibular aqueduct syndrome and stapes fixation. J Laryngol Otol. 1994;108:989-990. 25. Talbot JM, Wilson DF. Computed tomographic diagnosis of X-linked congenital mixed deafness, fixation of the stapedial footplate, and perilymphatic gusher. Am J Otol. 1994; 15:177-182. Downloaded from oto.sagepub.com at SOCIEDADE BRASILEIRA DE CIRUR on February 2, 2016