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Acta Oto-Laryngologica, 2011; 131: 351–357 ORIGINAL ARTICLE Correlations between CT scan findings and hearing thresholds in otosclerosis MATHIEU MARX1, SEBASTIEN LAGLEYRE1, BERNARD ESCUDÉ2, JULIE DEMESLAY1, TARIK ELHADI1, OLIVIER DEGUINE1 & BERNARD FRAYSSE1 1 Department of Otology-Neurotology and Skull Base Surgery, Purpan University Hospital, Toulouse and 2Department of Neuroradiology, Clinique Pasteur, Toulouse, France Abstract Conclusion: High-resolution computed tomography (CT) scan may reveal an isolated fenestral form of otosclerosis, and an extensive form, which involves multiple foci around the otic capsule. Pre- and postoperative hearing thresholds are poorer in patients with extensive otosclerosis and their chance of overclosure is reduced by 90%. Objectives: To evaluate the relationship between CT scan extension of otosclerotic foci and hearing thresholds in the operated ear, before and after stapedotomy. Methods: A preoperative CT scan was performed in 200 patients suspected of having otosclerosis. CT scan findings were categorized as negative, isolated fenestral otosclerosis, and extensive otosclerosis. Preoperative and 2 months postoperative air-conduction (AC) and bone-conduction (BC) thresholds were collected. Results: In the operated ear, 150 CT scans (75%) revealed an isolated fenestral otosclerosis; 35 (17.5%) were classified as extensive otosclerosis. Mean preoperative BC was significantly poorer in extensive otosclerosis (30.3 dB) than in isolated fenestral otosclerosis (24.6 dB). Mean postoperative BC remained lower in extensive otosclerosis (30.3 dB) than in isolated fenestral otosclerosis (21.2 dB). An overclosure greater than 10 dB was found in 20% of isolated fenestral otoscleroses and in 2.85% of extensive otoscleroses (chi-square: 5.5; p = 0.02). Keywords: Bone conduction, cochlear endosteum, otosclerosis Introduction Otosclerosis is typically defined as a primary dystrophy affecting the otic capsule bone and represents a common etiology of conductive hearing loss. It may sometimes display a sensorineural pattern, although its involvement in such a hearing loss entity remains controversial. For instance, in Schuknecht’s temporal bone studies [1–3], sensorineural hearing loss was generally due to different pathologies but not to otosclerosis. Only rare cases of severe sensorineural hearing loss may be related to extensive otosclerotic foci involving the endosteum of more than one cochlear spiral turn. However, according to some authors [4], the impact of endosteal lesions on hearing thresholds appears to be more common and may manifest in more limited foci cases. High-resolution computed tomography (HRCT) scan can be used as an additional diagnostic tool for otosclerosis when clinical symptoms are not indicative enough. In most cases, it reveals a hypodensity in the anterior part of the footplate [5]. Nevertheless, several other anatomic locations may coexist, such as pericochlear, cochlear endosteum, and internal auditory canal wall. The first aim of our study was to evaluate the relationship between otosclerotic foci extension on CT scan and pure tone audiometry (PTA) thresholds. Our second aim was to assess hearing progression characteristics in the operated ear and in the Correspondence: Mathieu Marx MD, Department of Otology-Neurotology and Skull Base Surgery, Purpan University Hospital, Place du Docteur Baylac, 31059 Toulouse, France. Tel: +33 5 61 77 22 11. Fax: +33 5 61 7721 49. E-mail: [email protected] (Received 6 September 2010; accepted 14 November 2010) ISSN 0001-6489 print/ISSN 1651-2251 online 2011 Informa Healthcare DOI: 10.3109/00016489.2010.549841 352 M. Marx et al. nonoperated one, considering audiometric and CT scan findings. Material and methods This was a retrospective study, performed in a tertiary referral center between 2004 and 2006. All patients suspected of having otosclerosis and scheduled for a surgical middle ear exploration were included. Suspicion of otosclerosis was based upon conductive or mixed hearing loss with normal tympanic membrane and abnormal stapedial reflex in at least one ear. In all, 200 patients matching the inclusion criteria were found in the database. Clinical, audiological, and radiological data were collected. Surgical data were also gathered. In our institution, HRCT scan is systematically performed in the preoperative assessment in cases of mixed or conductive hearing loss with normal tympanic membrane. Therefore, an institutional review board was not required. Axial and coronal cuts were obtained with 0.6 mm slice thickness in 121 patients (60.5%) and 1 mm in the remaining 79 cases (39.5%). CT scans were analyzed by a single neuroradiologist. Three categories of CT scan results were defined based on the site and the extension of otosclerotic lesions. (1) Negative CT scan: absence of otosclerotic foci or any other middle and/or inner ear abnormalities (including tympanosclerosis, ossicular chain fixation, superior canal dehiscence, modiolus dysplasia, and enlarged vestibular acqueduct). (2) Isolated fenestral otosclerosis, i.e. either foci limited to the oval window area, such as anterior fenestral hypodensity (Figure 1) and/or complete thickening of the footplate; or doubtful small lesions, such as isolated partial thickening of the anterior part of the footplate or triangular enlargement of the anterior crus of the stapes. (3) Extensive otosclerosis with one or several hypodensities involving the pericochlea, the internal auditory canal, and/or the round window (Figure 2). Fenestral lesions extended to the cochlear endosteum or to the vestibule were also included in this category. CT scan sensitivity and specificity were evaluated by comparing CT scan results to the surgical findings. Positive surgical diagnosis of otosclerosis was confirmed by the presence of macroscopic otosclerotic foci on the oval window, with stapes fixation. In confirmed otosclerosis cases, stapedotomy was performed using argon laser and skeeter microdrill. Air-conduction (AC) and bone-conduction (BC) thresholds were measured in all patients the day before surgery and 2 months later in the same double-walled soundproof room. Audiometric data were collected and compared as recommended by the Figure 1. CT, axial cut, showing an isolated fenestral otosclerosis, characterized by a hypodensity immediately adjacent to the anterior margin of the oval window, including the anterior branch of the stapes. guidelines published in 1995 by the Committee on Hearing and Equilibrium of the American Academy of Otolaryngology-Head and Neck Surgery (AAOHNS) [6]. Thus, AC and BC thresholds were averaged on 0.5, 1, 2, and 3 kHz frequencies. Air–bone gap (ABG) was calculated using same time AC and BC measurements. Sensorineural hearing level (SNHL) was estimated by averaging the BC thresholds in 1, 2, and 4 kHz frequencies. A positive change in postoperative SNHL was referred as an overclosure and a negative change was considered as a surgically induced hearing loss. Figure 2. CT, axial cut, showing an internal auditory canal hypodensity on the internal auditory meatus associated with a large anterior fenestral hypodensity. CT findings and hearing thresholds in otosclerosis The second aim of this study was to evaluate hearing evolution in the nonoperated ears, particularly those with normal hearing. Three years of follow-up (mean 46 months, SD 8.7) was available for 77 patients (39.5%), including 37 patients with initially normal hearing in the opposite ear. The number of patients in this subgroup was adapted for running comparative analyses. Surgical events such as revision surgery or contralateral stapedotomy were reported. Pure tone audiometry was performed and results were compared to those collected preoperatively. Statistical analysis was performed using Statview software. Nonparametric and classic bivariate tests were used according to the distribution features. These tests included one-way analysis of variance (ANOVA) to compare the values of a continuous variable between categories and the Mann-Whitney U test. The threshold of significance was 0.05. Results Operated ear Description (Table I). The mean age was 47.3 years, ranging from 17 to 77 years. The sex ratio was 2.44. The mean BC threshold was 25.4 dB (SD = 13.42) and mean preoperative ABG was 27.8 dB (SD = 10). Concerning CT scan findings, 15 CT scans (7.2%) did not show any temporal bone abnormality and were classified as negative; an isolated fenestral otosclerosis was found in 150 cases and 35 patients had extensive otosclerosis. Among the 150 CT scans (75%) showing isolated fenestral otosclerosis, 4 had thickened footplate, 9 had both anterior hypodensity and thickening of the footplate, and 137 had isolated anterior fenestral hypodensities. In the last subgroup, 18 (8.6%) cases 353 appeared as a triangular widening of the anterior crus (15) or as a minor malformation of the stapes (3) and were thus defined as doubtful. Thirty-five CT scans (17.5%) revealed extensive otosclerosis. Lesions were multifocal in 32 cases, affecting the pericochlea in 17 cases, the internal auditory canal wall in 15 cases, the round window in 6 cases, and the cochlear endosteum in 7 cases. Two isolated pericochlear foci and one isolated internal auditory canal focus were also identified. For the six cases with round window lesions, four involved the round window niche edge with a normal round window membrane and two were completely obliterating it. CT scan findings and surgical diagnosis. Otosclerosis was confirmed during surgery in all ears with positive CT scan findings. The 18 ears with doubtful hypodensity revealed 17 positive diagnoses of otosclerosis during surgery and 1 minor malformation of the stapes. Among the 15 negative CT scans, we found 10 false-negative cases diagnosed as otosclerosis during surgery, 4 minor malformations of the ossicular chain, and 1 fracture of the stapes. Seven of the falsenegative CT scans were obtained with 1 mm thickness slices and three with 0.6 mm thickness slices. Sensitivity of HRCT in the diagnosis of otosclerosis in this series was 95% and specificity was 99.1%. Relationship between CT scan findings and audiometric data (Figure 3). Extension of otosclerotic lesions was found to have an effect on preoperative PTA. In fact, PTA thresholds were significantly poorer in cases of extensive otosclerosis. Mean preoperative AC and BC were respectively 44.2 dB (SD 12.61) and 22.6 dB (SD 14.01) in patients with negative CT scans, 49.9 dB (SD 14.68) and 24.6 dB (SD 11.83) in Table I. Patients’demographic and audiometric data according to the CT scan findings. Parameter Negative CT scan Isolated fenestral otosclerosis Extensive otosclerosis No. of patients 15 150 35 Mean age, years (SD) 51.2 (8,4) 47 (10.4) 46.8 (10.9) Side 10R, 5L 81R, 69L 19R, 16L Mean preoperative BC (SD) 22.6 dB (14) 24.6 dB (12.1) 30.3 dB (18.1) Mean preoperative AC (SD) 44.2 dB (12.6) 49.9 dB (14.9) 59.9 dB (22.4) Mean preoperative ABG (SD) 23.2 dB (6.93) 27.3 (9.91) 31.7 (10.46) Mean postoperative BC (SD) 20.4 dB (12.31) 21.2 dB (11.08) 30.3 dB (19.46) Mean postoperative AC (SD) 31.2 dB (8.08) 29 dB (14.64) 39.2 dB (23.72) Mean overclosure (SD) 2.9 dB (4.81) 3 dB (9.14) 0.5 dB (6.88) SD, standard deviation; R, right ear; L, left ear. 354 M. Marx et al. 90 90 80 80 70 60 *p = 0.02 50 NS 40 30 20 10 Mean post op BC (dBHL) B 100 Mean pre op BC (dBHL) A 100 70 60 *p = 0.016 50 NS 40 30 20 10 0 0 Negative CT Isolated fenestral otosclerosis Extensive otosclerosis Negative CT Isolated fenestral otosclerosis Extensive otosclerosis Figure 3. Mean preoperative bone conduction BC (A) and postoperative BC (B) in the operated ear for patients with negative CT scans, isolated fenestral otosclerosis, and extensive otosclerosis. patients with isolated fenestral otosclerosis, and 59.9 dB (SD 22.44) and 30.3 dB (SD 18.12) in cases of extensive otosclerosis. PTA thresholds were poorer (ANOVA, p = 0.0012 for AC, p = 0.02 for BC) and the ABG was significantly larger (ANOVA, p = 0.025) in the group with extensive otosclerosis. BC thresholds were within normal limits in 6 patients (40%) with negative CT scans, 55 patients (36.6%) with isolated fenestral otosclerosis, and 5 patients (14%) with extensive otosclerosis. Similarly, postoperative PTA results were found to be correlated to the degree of otosclerosis extension. Patients with negative CT scan (AC 31.2 dB, SD 8.08 and BC 20.4 dB, SD 12.31) or isolated fenestral otosclerosis (AC 29 dB, SD 14.64 and BC, 21.2 dB, SD 11.08) showed better thresholds than patients with extensive otosclerosis (AC 39.2 dB, SD 23.72 and BC 30.3 dB, SD 19.46) (ANOVA, p = 0.01 for AC, p = 0.012 for BC). Regarding the SNHL, we considered clinically significant changes of BC thresholds to highlight the differences between groups. Among patients with negative CT scans, there was no worsening of BC more than 5 dB and one patient showed an improvement above 10 dB. A decrease of mean BC greater than 5 dB was more frequently observed in patients with extensive otosclerosis (6 patients, i.e. 17.1%) than in patients with negative or isolated fenestral otosclerosis (18 patients, 10.9%). Risk of worsening BC thresholds tended to be higher in extensive otosclerosis, although this trend did not reach statistical significance (chi-square = 3.8; odds ratio = 2.8; CI 95% = 0.99–7.88; p = 0.054). SNHL improvements greater than 10 dB were found in 30 patients with isolated fenestral otosclerosis (i.e. 20%), in only 1 patient with extensive otosclerosis (i.e. 2.85%). We measured the chance of getting more than 10 dB SNHL improvement and found it to be 90% lower in extensive foci than in isolated fenestral focus (chi-square = 5.5; odds ratio = 0.11; CI 95% = 0.01–0.84; p = 0.02). The mean ABG closure was significantly different between negative CT scans (11.3 dB, SD 7.4) and positive CT scans for otosclerosis (ANOVA, p = 0.02). ABG closure was found to have a tendency to be better (p = 0.07) in extensive otosclerosis (20.6 dB, SD 10.42) than in isolated fenestral otosclerosis (17.2 dB, SD 10.86). Follow-up of the operated ear. Between 2004 and 2009, 4 of the 200 patients underwent a revision surgery for the operated ear. The four revision procedures revealed a lateralized piston. Three patients had an extensive form of otosclerosis and one had an isolated fenestral otosclerosis. Concerning the long-term results, 77 of the 200 patients included in this study completed a 3-year follow-up after surgery (mean follow-up, 46 months, SD 8.7; n = 77). The comparative analyses that we conducted did not show any statistical difference between groups, for any auditory threshold (p > 0.05). Mean AC, BC, and ABG were respectively 23.4 dB (SD 6.07), 14.6 dB (SD 6.29), and 10.1 (SD 8.38) in patients with negative CT scans. In patients with isolated fenestral otosclerosis (n = 59), mean AC was 29.8 (SD 15.53), mean BC was 25.1 dB (SD 14.61), and mean ABG was 5.9 dB (SD 5.24). Concerning the group of patients with extensive otosclerosis (n = 13), mean AC, BC, and ABG were 33.3 dB (SD 20.49), 27 dB (SD 19.89) and 6.3 dB (SD 4.06), respectively. CT findings and hearing thresholds in otosclerosis Nonoperated ear Description. Concerning the 200 opposite ears, we determined 2 groups from the initial PTA. Group 1 had initially normal contralateral hearing (AC £20 dB and ABG £10 dB) and included 68 patients. Mean threshold values were respectively: 12 dB (SD 4.87) for AC, 8.4 dB (SD 4.00) for BC, and 3.7 dB (SD 2.71) for ABG. Among this group, 38 CT scans (55.9%) found 29 isolated fenestral otoscleroses and 8 extensive otoscleroses (Table II). Seven of the 29 fenestral otoscleroses presented as an isolated widening of the anterior crus of the stapes and were thus defined as doubtful. Extensive otosclerosis was multifocal in six patients (two pericochlear foci, two anterior fenestral foci, three foci localized to the cochlear endosteum, six foci to the internal auditory canal) and three patients with solely involvement of the internal auditory canal. The other 30 CT scans were described as negative (30, 44.1%). Group 2 had initially abnormal hearing (AC >20 dB and/or an ABG ‡10 dB) and included 132 patients. Mean threshold values were respectively: 35.1 dB (SD 15.88) for AC, 23.1 dB (SD 14.36) for BC and 12.2 dB (SD 9.53) for ABG. In all, 80 patients had conductive or mixed hearing loss, and 52 had pure sensorineural hearing loss. A total of 111 CT scan examinations (84.1%) showed 81 isolated fenestral involvements and 31 extensive otosclerosis. The extensive lesions were mainly multifocal (29 CT scans) and involved pericochlea in 15 patients, cochlear endosteum in 7 cases, and internal auditory canal in 14 patients. Four patients had round window foci, localized at the edge of the round window niche, sparing the membrane. CT scan was found to be negative in 20 patients (15.1%). Comparing both groups, we found more negative CT scans in group 1 than in group 2 (Mann-Whitney U test, p < 0.001). Extensive otosclerosis ratio was significantly higher in group 2 (23.5%) than in group 1 (11.7%) (Mann-Whitney U test, p = 0.002). Relationship between location of otosclerotic hypodensities and PTA results. Similarly to the operated ear, analysis Table II. CT scan findings with respect to initial hearing status in the nonoperated ear. Parameter Normal hearing No. of patients 68 Isolated fenestral otosclerosis 29 (42.6%) Extensive otosclerosis CT scan negative Hearing loss 132 81 (61.4) 9 (13.2%) 31 (23.5%) 30 (44.1%) 20 (15.9%) 355 of CT scans revealed a significant impact of otosclerosis extension on PTA results according to all the nonoperated ears whether hearing level was normal or not (groups 1 and 2). Actually, mean AC and BC were significantly poorer in cases of extensive otosclerosis (36.6 dB and 27.2 dB) than in cases of isolated fenestral otosclerosis (28.1 dB and 17.5 dB) (ANOVA, p = 0.006 for AC; p = 0.001 for BC). Patients with negative CT scans presented mean AC and BC (18.7 dB and 12.8 dB) within normal values. The mean ABG was lower in patients with negative CT scans (5.9 dB, SD 5.22) than in patients with fenestral (10.7 dB, SD 8.79) or extensive otosclerosis (9.5 dB, SD 11.31). The impact of foci extension was greater in group 2, with mean AC and BC of respectively 29.8 dB (SD 8.48) and 20.7 dB (SD 10.64) in patients with negative CT scan, 33.8 dB (SD 13.51) and 20.8B (SD 10.29) in patients with isolated fenestral involvement, and 42 dB (SD 22.67) and 31.1 dB (SD 21.53) in patients with severe locations. Progression of hearing in the nonoperated ear: relationship with CT scan findings. In all, 77 of the 200 patients included in this prospective study had a complete 3-year follow-up (mean follow-up 46 months, SD 8.72). Evolution of hearing in the nonoperated ear was evaluated based on the comparison of 3-year PTA data with initial audiograms. At 3 years, data were available for 37 patients in group 1 and 40 patients in group 2. A decrease in AC and BC was observed in both groups (–4.4 and –6.6 dB, respectively). The ABG remained stable at 3 years in group 1 compared to the initial values (mean ABG evolution: –1 dB, SD 6.40). During the 3-year follow-up, stapedotomy in opposite ears was performed in 12 patients in group 2, whereas none of the patients in group 1 presented a hearing evolution justifying a contralateral stapedotomy. Mean interval between both stapedotomies was 22 months (SD 9.5) for patients who underwent bilateral surgery. Before the second stapedotomy, mean AC, BC, and ABG were respectively 48.25 dB (SD 3.61), 23.35 dB (SD 6.48), and 26.3 dB (SD 3.79). In group 2, patients who did not undergo revision surgery revealed increased BC and AC thresholds at 3 years, with a mean aggravation of 8.8 dB (SD 15.92) and 5.3 dB (SD 8.57). With regard to CT scan findings, the impact of foci extension observed at inclusion was logically demonstrated at 3-year follow-up. Patients with extensive otosclerosis showed poorer AC and BC thresholds than patients with isolated fenestral lesions. Patients 356 M. Marx et al. with negative CT scan showed better AC and BC thresholds than patients with positive findings. The ABG was greater in patients with extensive otosclerosis (mean ABG 9.3 dB, SD 9.62) and isolated fenestral otosclerosis (mean ABG 10.8, SD 9.41) than in patients with negative CT scans (mean ABG 3 dB, SD 3.10; ANOVA, p = 0.03). Nevertheless, worsening of AC, BC, and ABG was not related to the location of the otosclerotic lesions: evolution of these thresholds did not significantly differ from one group to another. Symmetry in CT findings Finally, CT scans of both ears were analyzed in terms of bilaterality of the lesions. For the 15 negative CT scans in the operated ear, we found 13 contralateral negative CT scans. The contralateral findings for the 158 ears with isolated fenestral otosclerosis were 108 contralateral fenestral otosclerotic foci (68.35%), 14 extensive otosclerosis (8.8%), and 36 negative CT scans (22.8%). For the 35 operated ears with extensive otosclerosis, we found 28 contralateral extensive lesions (77.5%), 5 isolated fenestral otosclerosis, and 2 negative CT scans. Extensive otosclerosis provided significantly more bilateral positive findings than isolated fenestral otosclerosis (chi-square = 5.28, p = 0.025). Discussion The relationship between the location of otosclerotic foci and hearing thresholds has mainly been evaluated in histological studies. As mentioned above, this topic has generated several conflicting reports. Based upon various temporal bone studies, Schuknecht and his co-workers always stated that association between otosclerosis and sensorineural hearing loss was rather uncommon. For instance, Schuknecht and Barber [3] studied 48 temporal bones with clinical otosclerosis and did not observe any association between bone conduction thresholds and the size of the lesion, the activity of the lesion, the cochlear endosteum or the round window involvement. In another study on 263 temporal bones of subjects with progressive sensorineural hearing loss [1], 21 temporal bones presented otosclerotic lesions with only 3 endosteal involvements. Elonka and Applebaum [7] evaluated this relationship in 29 temporal bones with clinical otosclerosis and according to them, the strict correlation between endosteal involvement and bone conduction thresholds was poor. However, incidence of sensorineural hearing loss was greater in the subgroup of 15 temporal bones with severe otosclerotic extension affecting cochlear endosteum in 2 sites or more. In contrast, Hueb et al. [4] showed a positive correlation in 37 temporal bones when the size of the lesions, the activity, and the degree of cochlear endosteal involvement were compared to BC thresholds. In the same way, Parahy and Linthicum [8] put in evidence an association between cochlear endosteum involvement and elevated BC thresholds. The sensorineural component in otosclerosis would be due to spiral ligament hyalinization adjacent to the active endosteal foci. In their study, the group with hyalinization of the spiral ligament presented a mean BC of 71.8 dB whereas mean BC in the group without hyalinization was 33.6 dB. This hyalinization would support a protein release, interfering with terminal auditory nerve fibers. Histological studies provide an incomparable description of otosclerotic lesions but their validity in audiometric correlations seems limited by the delay between patients’ last audiogram and patients’ death; CT studies may yield a better temporal matching for audio-radiological correlations. A CT scan study by Shin et al. [9] compared patients with isolated fenestral otosclerosis and patients with pericochlear extension. The authors showed that BC thresholds were poorer in a subgroup of patients with endosteal involvement compared with BC in patients with fenestral otosclerosis. Kawase et al. [10] evaluated the relationship between a determined cut-off Hounfsield unit and PTA thresholds. They found a significant correlation between the density in the area anterior to the oval window and the hearing thresholds (both AC and BC) on 500 and 1000 Hz. Our results emphasize the auditory consequences of otosclerosis extension. AC and BC thresholds were worse in cases of extensive otosclerotic foci. In fact, BC thresholds were significantly higher when the disease involved the pericochlea, the cochlear endosteum, the round window or the internal auditory canal wall. Further, our findings regarding the SNHL indicate higher risk of aggravation and poorer chance of improvement in extensive otosclerosis. Multifocality of otosclerotic lesions should thus be considered as a sign of severe prognosis in otosclerosis. Otosclerosis is known as a bilateral osteodystrophy but a significant amount of patients present only a unilateral conductive or mixed hearing loss. In these cases, the opposite ear should systematically be considered because hearing evolution and a subsequent contralateral stapedotomy are recurrent questions from patients. Our study found 68/200 patients (34%) with strictly normal hearing in the nonoperated ear. In this population, CT scans revealed a large proportion of negative CT scans for the opposite ear (44.1%), which significantly exceeded the rate of negative CT scans when contralateral hearing was abnormal (15.1%). Thirty-seven patients with normal CT findings and hearing thresholds in otosclerosis initial contralateral hearing were followed up for more than 3 years and did not show any worsening in the ABG (–1 dB, SD 6.02). In other words, no patient with initial normal PTA thresholds decreased contralateral hearing enough to suggest a stapedotomy. Some of these patients might be affected with strictly unilateral otosclerosis but the follow-up duration was undeniably short if we consider the slowly progressive pattern of the disease. Furthermore, the possible dissociation between histological and clinical otosclerosis should not be discarded. The study of temporal bones by Hueb et al. [4] revealed a higher rate of bilateral histological otosclerosis compared with bilateral clinical otosclerosis, confirmed by stapes fixation. They found bilateral otosclerotic foci in 75.6% of the cases while 45.8% of ears had clinical otosclerosis. In a CT scan study, Vicente et al. [11] found bilateral hypodensities in 68.5% of patients with a surgical diagnosis of otosclerosis. In Lee et al.’s series [12], 84% of patients had bilateral foci but they did not report any surgical confirmation. The present study reports bilateral positive findings in 77.5% of patients and emphasizes the role of foci extension. Bilateral otosclerosis was more frequently found in the extensive form of the disease, in which symmetry of lesions appeared greater as well. Shin et al. [13] reported that extensive and bilateral otosclerosis on CT scan was commonly found in patients with a family history of otosclerosis. Genetic factors would play a crucial role in extensive otosclerosis, and may explain the homogenous association observed between clinical symptoms, poor hearing thresholds, and radiological expression, with multifocal and endosteal extended disease. Conclusion HRCT can detect various forms of otosclerosis, with high sensitivity and specificity. We distinguished isolated fenestral otosclerosis from extensive forms, which involved multiple foci such as pericochlea and cochlear endosteum. In our series, patients with extensive otosclerosis showed poorer preoperative and postoperative AC and BC thresholds. Further, their chance to improve their BC thresholds postoperatively is significantly reduced, compared with patients with an isolated form of otosclerosis. Thus, CT scan may provide relevant information regarding the prognosis for hearing in the operated ear. Concerning the nonoperated ear, hearing thresholds are also related to CT scan findings but the initial audiometric status remains a better predictive parameter. In our study, most patients with initial normal or 357 near-normal hearing in the opposite ear showed stable hearing abilities 3 years later. Evolution of the hearing thresholds in the nonoperated ear is a matter of concern for many patients; long-term prospective studies are needed to allow provision of appropriate counseling. Acknowledgments The authors thank Kuzma Strelnikov for his contribution to statistical analyses, Chris James and Sara Alshehri for their helpful comments. Declaration of interest: The authors report no conflicts of interest. 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[13] Shin YJ, Calvas P, Deguine O, Charlet JP, Cognard C, Fraysse B. Correlations between computed tomography findings and family history in otosclerotic patients. Otol Neurotol 2001;22:461–4. Copyright of Acta Oto-Laryngologica is the property of Taylor & Francis Ltd and its content may not be copied or emailed to multiple sites or posted to a listserv without the copyright holder's express written permission. However, users may print, download, or email articles for individual use.