- Email: [email protected]
Response to: The relationship between the air-bone gap and the size of superior semicircular canal dehiscence, from Dirk Beutner
Otolaryngology–Head and Neck Surgery (2010) 142, 634-636
LETTERS TO THE EDITOR The relationship between the air-bone gap and the size of superior semicircular canal dehiscence I read with great interest the article “The relationship between the air-bone gap and the size of superior semicircular canal dehiscence” by Yuen et al.1 They report that the size of the average air-bone gap (ABG) correlates with the size of the superior semicircular canal dehiscence (SSCD). As mentioned by the authors, the weakness of this study is that even thin-section CT scans and reformation in the plane of the superior semicircular canal may overestimate the prevalence of SSCD.2 However, this bias could be avoided if analysis were restricted to surgically explored and confirmed cases. Ten cases underwent surgical confirmation and repair with bone wax for canal occlusion, followed by fascia and bone substitute (hydroxyapatite), without recurrence. As canal occlusion abolishes the dehiscence of the superior semicircular canal, any ABG should be liquidated, according to the authors’ conclusion. Surprisingly, evaluating these confirmed cases, as shown in Table 1 of Yuen et al’s article,1 no relationship between size of the dehiscence and ABG can be found. In three cases, the ABG increased, in one case there was no presurgical ABG, and in five cases, the ABG decreased by an average of only 5 dB. Only one out of these 10 cases, with a 3.3 dB ABG, was surgically liquidated via the middle fossa approach. It would be helpful if the authors provided more detailed data on the bone-conduction thresholds, as well as airconduction thresholds, to allow for assessment of their conclusion and to overcome the limitation of solely reporting ABG. Dirk Beutner, MD Department of Otorhinolaryngology, Head and Neck Surgery University of Cologne Cologne, Germany E-mail, [email protected]
References 1. Yuen HW, Boeddinghaus R, Eikelboom RH, et al. The relationship between the air-bone gap and the size of superior semicircular canal dehiscence. Otolaryngol Head Neck Surg 2009;141:689 –94. 2. Cloutier JF, Belair M, Saliba I. Superior semicircular canal dehiscence: positive predictive value of high-resolution CT scanning. Eur Arch Otorhinolaryngol 2008;265:1455– 60.
doi:10.1016/j.otohns.2010.02.001
Response to: The relationship between the air-bone gap and the size of superior semicircular canal dehiscence, from Dirk Beutner We thank Dr. Beutner for his interest in our article examining the relationship between the air-bone gap (ABG) and size of dehiscence in superior semicircular canal dehiscence (SSCD).1 We agree, and acknowledged in our article, that CT might overestimate the presence of dehiscence using current technology. However, as we pointed out, all of our patients manifested signs and symptoms of SSCD. We would like to reiterate that the diagnosis of SSCD is a clinical one. Nevertheless, even if we restrict the study subjects to only surgically confirmed patients (Table 1 of our article),1 the analysis of the relationship between the size of dehiscence and average ABG (AvABG500 –2000) shows a correlation coefficient of R2 ⫽ 0.841(P ⬍ 0.001) and R2 ⫽ 0.787 (P ⬍ 0.001), respectively, using quadratic and linear regression analysis. We are surprised Dr. Beutner did not find a relationship from our data. In theory, surgical repair and/or canal occlusion abolishes the dehiscence of the superior semicircular canal, and any ABG should disappear after surgery. But we caution against taking an overly simplistic view of the mechanisms of audiological and audiometric manifestations that might be at play in SSCD. It is conceivable that there are other as yet unexplored and unknown causes for the ABG in SSCD. Given the findings of our study, the size of dehiscence is one significant contributing cause. Hence, our study, as well as others,2 showed that most, but not all, patients demonstrate at least partial closure of the ABG. Indeed, some patients show an increased ABG postoperatively. In the same vein, vestibular signs and symptoms should theoretically be abolished in all patients after surgical repair. However, our experience, and that of others,3 showed that this is not the case in clinical practice. Finally, we felt that reporting the average ABG provides a better overall perspective of the effect of size of dehiscence on audiometric parameters. Given that the effects of SSCD on audiometric thresholds involve the low frequencies, it is more useful to examine the ABG between 500 and 2000 Hz. But herein we have included selected bone-conduction and airconduction thresholds of the surgically confirmed cases (Fig 1). It is clear that further studies are needed to fully understand the effects of the dehiscence on audiological and audiometric manifestations in SSCD. We hope our article has provided an impetus. Heng-Wai Yuen, MBBS, MRCSE, MMed(ORL), DOHNS Ear Science Institute Australia Nedlands, Western Australia, Australia Department of Otolaryngology-Head & Neck Surgery Changi General Hospital Republic of Singapore
0194-5998/$36.00 © 2010 American Academy of Otolaryngology–Head and Neck Surgery Foundation. All rights reserved.
Letters to the Editor Rudolf Boeddinghaus, MBChB, FCRad(SA), FRANZCR, FRCR Perth Radiological Clinic Subiaco Western Australia, Australia Robert H. Eikelboom, MApplSc, PhD Marcus D. Atlas, MBBS, FRACS Ear Science Institute Australia Ear Science Centre School of Surgery University of Western Australia Department of Otolaryngology-Head & Neck Surgery Sir Charles Gairdner Hospital
635 Nedlands Western Australia, Australia E-mail, [email protected]
References 1. Yuen HW, Boeddinghaus R, Eikelboom RH, et al. The relationship between the air-bone gap and the size of superior semicircular canal dehiscence. Otolaryngol Head Neck Surg 2009;141:689 –94. 2. Limb CJ, Carey JP, Srireddy S, et al. Auditory function in patients with surgically treated superior semicircular canal dehiscence. Otol Neurotol 2006;27:969 – 80. 3. Crane BT, Minor LB, Carey JP. Superior canal dehiscence plugging reduces dizziness handicap. Laryngoscope 2008;118:1809 –13.
doi:10.1016/j.otohns.2010.02.002
636
Otolaryngology–Head and Neck Surgery, Vol 142, No 4, April 2010
Figure 1 Preoperative and postoperative audiograms of patients with surgically confirmed and repaired superior semicircular canal dehiscence. Œ, air conduction on the right; e, air conduction on the left; [, bone conduction on the right, masked; ], bone conduction on the left, masked.
LETTERS TO THE EDITOR The relationship between the air-bone gap and the size of superior semicircular canal dehiscence I read with great interest the article “The relationship between the air-bone gap and the size of superior semicircular canal dehiscence” by Yuen et al.1 They report that the size of the average air-bone gap (ABG) correlates with the size of the superior semicircular canal dehiscence (SSCD). As mentioned by the authors, the weakness of this study is that even thin-section CT scans and reformation in the plane of the superior semicircular canal may overestimate the prevalence of SSCD.2 However, this bias could be avoided if analysis were restricted to surgically explored and confirmed cases. Ten cases underwent surgical confirmation and repair with bone wax for canal occlusion, followed by fascia and bone substitute (hydroxyapatite), without recurrence. As canal occlusion abolishes the dehiscence of the superior semicircular canal, any ABG should be liquidated, according to the authors’ conclusion. Surprisingly, evaluating these confirmed cases, as shown in Table 1 of Yuen et al’s article,1 no relationship between size of the dehiscence and ABG can be found. In three cases, the ABG increased, in one case there was no presurgical ABG, and in five cases, the ABG decreased by an average of only 5 dB. Only one out of these 10 cases, with a 3.3 dB ABG, was surgically liquidated via the middle fossa approach. It would be helpful if the authors provided more detailed data on the bone-conduction thresholds, as well as airconduction thresholds, to allow for assessment of their conclusion and to overcome the limitation of solely reporting ABG. Dirk Beutner, MD Department of Otorhinolaryngology, Head and Neck Surgery University of Cologne Cologne, Germany E-mail, [email protected]
References 1. Yuen HW, Boeddinghaus R, Eikelboom RH, et al. The relationship between the air-bone gap and the size of superior semicircular canal dehiscence. Otolaryngol Head Neck Surg 2009;141:689 –94. 2. Cloutier JF, Belair M, Saliba I. Superior semicircular canal dehiscence: positive predictive value of high-resolution CT scanning. Eur Arch Otorhinolaryngol 2008;265:1455– 60.
doi:10.1016/j.otohns.2010.02.001
Response to: The relationship between the air-bone gap and the size of superior semicircular canal dehiscence, from Dirk Beutner We thank Dr. Beutner for his interest in our article examining the relationship between the air-bone gap (ABG) and size of dehiscence in superior semicircular canal dehiscence (SSCD).1 We agree, and acknowledged in our article, that CT might overestimate the presence of dehiscence using current technology. However, as we pointed out, all of our patients manifested signs and symptoms of SSCD. We would like to reiterate that the diagnosis of SSCD is a clinical one. Nevertheless, even if we restrict the study subjects to only surgically confirmed patients (Table 1 of our article),1 the analysis of the relationship between the size of dehiscence and average ABG (AvABG500 –2000) shows a correlation coefficient of R2 ⫽ 0.841(P ⬍ 0.001) and R2 ⫽ 0.787 (P ⬍ 0.001), respectively, using quadratic and linear regression analysis. We are surprised Dr. Beutner did not find a relationship from our data. In theory, surgical repair and/or canal occlusion abolishes the dehiscence of the superior semicircular canal, and any ABG should disappear after surgery. But we caution against taking an overly simplistic view of the mechanisms of audiological and audiometric manifestations that might be at play in SSCD. It is conceivable that there are other as yet unexplored and unknown causes for the ABG in SSCD. Given the findings of our study, the size of dehiscence is one significant contributing cause. Hence, our study, as well as others,2 showed that most, but not all, patients demonstrate at least partial closure of the ABG. Indeed, some patients show an increased ABG postoperatively. In the same vein, vestibular signs and symptoms should theoretically be abolished in all patients after surgical repair. However, our experience, and that of others,3 showed that this is not the case in clinical practice. Finally, we felt that reporting the average ABG provides a better overall perspective of the effect of size of dehiscence on audiometric parameters. Given that the effects of SSCD on audiometric thresholds involve the low frequencies, it is more useful to examine the ABG between 500 and 2000 Hz. But herein we have included selected bone-conduction and airconduction thresholds of the surgically confirmed cases (Fig 1). It is clear that further studies are needed to fully understand the effects of the dehiscence on audiological and audiometric manifestations in SSCD. We hope our article has provided an impetus. Heng-Wai Yuen, MBBS, MRCSE, MMed(ORL), DOHNS Ear Science Institute Australia Nedlands, Western Australia, Australia Department of Otolaryngology-Head & Neck Surgery Changi General Hospital Republic of Singapore
0194-5998/$36.00 © 2010 American Academy of Otolaryngology–Head and Neck Surgery Foundation. All rights reserved.
Letters to the Editor Rudolf Boeddinghaus, MBChB, FCRad(SA), FRANZCR, FRCR Perth Radiological Clinic Subiaco Western Australia, Australia Robert H. Eikelboom, MApplSc, PhD Marcus D. Atlas, MBBS, FRACS Ear Science Institute Australia Ear Science Centre School of Surgery University of Western Australia Department of Otolaryngology-Head & Neck Surgery Sir Charles Gairdner Hospital
635 Nedlands Western Australia, Australia E-mail, [email protected]
References 1. Yuen HW, Boeddinghaus R, Eikelboom RH, et al. The relationship between the air-bone gap and the size of superior semicircular canal dehiscence. Otolaryngol Head Neck Surg 2009;141:689 –94. 2. Limb CJ, Carey JP, Srireddy S, et al. Auditory function in patients with surgically treated superior semicircular canal dehiscence. Otol Neurotol 2006;27:969 – 80. 3. Crane BT, Minor LB, Carey JP. Superior canal dehiscence plugging reduces dizziness handicap. Laryngoscope 2008;118:1809 –13.
doi:10.1016/j.otohns.2010.02.002
636
Otolaryngology–Head and Neck Surgery, Vol 142, No 4, April 2010
Figure 1 Preoperative and postoperative audiograms of patients with surgically confirmed and repaired superior semicircular canal dehiscence. Œ, air conduction on the right; e, air conduction on the left; [, bone conduction on the right, masked; ], bone conduction on the left, masked.