Abstract
Introduction
Superior semi-circular canal dehiscence (SSCD) is a known cause of hearing loss. This study quantifies hearing loss in SSCD ears in a frequency-specific fashion.
Methods
A meta-analysis of English language literature pertaining to SSCD was performed, with extraction and evaluation of available human audiometric data. Our own institution’s case series of SSCD patients was also similarly analysed. Hearing loss in SSCD ears was compared to same patient control ears and to age-matched normative audiometric data.
Results
Ears with SSCD had statistically significant worse hearing as compared to both normative data and to own normal ear controls at 2000 Hz and below. The effect appears to diminish with increasing frequency.
Discussion
The presence of statistically significant conductive hearing loss in the low frequencies was confirmed for SSCD ears. SSCD may also predispose ears to high frequency sensorineural hearing loss.
1
Introduction
Superior semi-circular canal dehiscence (SSCD) and its sequelae were first described by Lloyd Minor in 1998 . SSCD has been shown to cause a mostly low frequency hearing loss in some patients, which can be improved by surgical plugging or resurfacing of the canal . It remains unclear why some patients with SSCD have only vestibular symptoms, others only hearing loss, and some both. The low frequency air-bone gap noted in some patients with SSCD is due partly to decreased cochlear impedance secondary to a third mobile window resulting in decreased transmission of low frequency sound to the cochlea and partly due to improvement in the bone line due to complicated factors involved with the transmission of bone conducted sound . Anecdotal evidence suggests that the magnitude of the air-bone gap decreases with frequency and the effects, if any, of SSCD on high frequency hearing in humans are unknown. This paper examines the epidemiology of hearing loss related to SSCD based on a meta-analysis of SSCD cases with audiograms available in the literature as well as analysis of our own case series.
2
Methods
A PubMed search was performed for papers related to SSCD. The search terms used included SSCD, superior semi-circular canal dehiscence, superior semi-circular canal dehiscence syndrome. The search was limited to papers in the English language. Papers containing one or more audiograms that specified the patient’s age, sex and affected ear(s) and included air conduction and bone conduction thresholds from 500 Hz to 4000 Hz were included. The data from the audiograms were digitized in order to facilitate data analysis.
After obtaining institutional review board approval, charts of patients with SSCD from a single surgeon academic neurotology practice (AAM) were reviewed. Patients who carried the diagnosis of SSCD based on documented radiographic evidence of canal dehiscence were selected for inclusion in the study. The patient’s audiometric data were de-identified and digitized in the same manner as the audiometric data obtained from the literature. For patients with multiple audiograms, the most recent audiogram was used. The patients’ age and sex were recorded in addition to their audiometric thresholds.
Age-matched control audiometric data were obtained from the Epidemiology of Hearing Loss Study . These data include pure-tone air-conduction thresholds by frequency (250 Hz to 8,000 Hz), ear, sex and age. The age range covered by the Epidemiology of Hearing Loss Study was 48 to 92 years. The age groups in the control audiometric data were divided by that study’s authors into approximately deciles using the following age ranges: 48–59 years, 60–69 years, 70–79 years, and 80–92 years. Patients with four-frequency (500, 1000, 2000, and 4,000 Hz) pure tone average auditory thresholds greater than 70 dB were excluded from the analysis in order to keep profoundly deaf patients from skewing the results.
The audiometric data for each patient from the literature population and the case series were compared to the relevant age-matched mean pure-tone audiometric thresholds using IBM SPSS Statistics software to perform a paired t-test based on the four-frequency PTA and also at individual thresholds. For patients who had SSCD in both ears, the analysis was performed in two ways: considering only one ear to be the affected ear (right ear), and also with each affected ear as a separate case. Additionally, to assist in graphically depicting the hearing loss, an analysis of averages at each threshold was performed. Only air conduction thresholds were used in the analysis given that the control population audiometric data were published with air conduction thresholds alone.
The minimum age of the control population was 48 years. Thus, for patients in the study population who were younger than 48, modeling assumptions were used to analyse the data. The data were analysed using the audiometric data for patients 48–59 years old from the Epidemiology of Hearing Loss Study as the control data for all patients younger than 48. This meant that all patients younger than 48 were compared to the normative data for the population who was 48–59 years of age. This tends to overestimate the degree of age-related hearing loss and underestimate the degree of hearing loss due to SSCD. To check the validity of these modeling assumptions for the control audiometric data, another analysis was performed using a second method. For this second analysis, a uniform threshold of 20 dB across all frequencies was used to model the control audiometric thresholds for all patients younger than 48 years old. The actual data from the Epidemiology of Hearing Loss Study reveal thresholds of 8.5–26.8 dB for females and 8.8–41.9 dB for males ages 48–59 years.
2
Methods
A PubMed search was performed for papers related to SSCD. The search terms used included SSCD, superior semi-circular canal dehiscence, superior semi-circular canal dehiscence syndrome. The search was limited to papers in the English language. Papers containing one or more audiograms that specified the patient’s age, sex and affected ear(s) and included air conduction and bone conduction thresholds from 500 Hz to 4000 Hz were included. The data from the audiograms were digitized in order to facilitate data analysis.
After obtaining institutional review board approval, charts of patients with SSCD from a single surgeon academic neurotology practice (AAM) were reviewed. Patients who carried the diagnosis of SSCD based on documented radiographic evidence of canal dehiscence were selected for inclusion in the study. The patient’s audiometric data were de-identified and digitized in the same manner as the audiometric data obtained from the literature. For patients with multiple audiograms, the most recent audiogram was used. The patients’ age and sex were recorded in addition to their audiometric thresholds.
Age-matched control audiometric data were obtained from the Epidemiology of Hearing Loss Study . These data include pure-tone air-conduction thresholds by frequency (250 Hz to 8,000 Hz), ear, sex and age. The age range covered by the Epidemiology of Hearing Loss Study was 48 to 92 years. The age groups in the control audiometric data were divided by that study’s authors into approximately deciles using the following age ranges: 48–59 years, 60–69 years, 70–79 years, and 80–92 years. Patients with four-frequency (500, 1000, 2000, and 4,000 Hz) pure tone average auditory thresholds greater than 70 dB were excluded from the analysis in order to keep profoundly deaf patients from skewing the results.
The audiometric data for each patient from the literature population and the case series were compared to the relevant age-matched mean pure-tone audiometric thresholds using IBM SPSS Statistics software to perform a paired t-test based on the four-frequency PTA and also at individual thresholds. For patients who had SSCD in both ears, the analysis was performed in two ways: considering only one ear to be the affected ear (right ear), and also with each affected ear as a separate case. Additionally, to assist in graphically depicting the hearing loss, an analysis of averages at each threshold was performed. Only air conduction thresholds were used in the analysis given that the control population audiometric data were published with air conduction thresholds alone.
The minimum age of the control population was 48 years. Thus, for patients in the study population who were younger than 48, modeling assumptions were used to analyse the data. The data were analysed using the audiometric data for patients 48–59 years old from the Epidemiology of Hearing Loss Study as the control data for all patients younger than 48. This meant that all patients younger than 48 were compared to the normative data for the population who was 48–59 years of age. This tends to overestimate the degree of age-related hearing loss and underestimate the degree of hearing loss due to SSCD. To check the validity of these modeling assumptions for the control audiometric data, another analysis was performed using a second method. For this second analysis, a uniform threshold of 20 dB across all frequencies was used to model the control audiometric thresholds for all patients younger than 48 years old. The actual data from the Epidemiology of Hearing Loss Study reveal thresholds of 8.5–26.8 dB for females and 8.8–41.9 dB for males ages 48–59 years.
3
Results
The PubMed search provided 152 articles that were published before January 15, 2010, of which 25 articles had one or more complete audiograms for patients with SSCD. A total of 66 patient audiograms were obtained from the literature. The institutional chart review provided 15 additional audiograms for patients with SSCD ( Table 1 ). The combined study population included 81 patients and a total of 104 ears with SSCD. The patient ages ranged from 12 to 87 years with a mean of 47.1 years. Fifty-four percent of the study population was female and 46% was male.
| Patient ID | Age | Affected ear | Sex |
|---|---|---|---|
| 1 | 32 | R | M |
| 2 | 32 | B | M |
| 3 | 38 | R | F |
| 4 | 39 | L | F |
| 5 | 39 | R | F |
| 6 | 42 | B | M |
| 7 | 43 | L | M |
| 8 | 44 | L | F |
| 9 | 44 | B | F |
| 10 | 46 | L | F |
| 11 | 47 | L | F |
| 12 | 48 | B | F |
| 13 | 62 | L | F |
| 14 | 72 | L | F |
| 15 | 87 | R | F |
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