Superior Canal Dehiscence and the Risk of Additional Dehiscences: A Retrospective CT Cohort Study.

OBJECTIVE: Determine if superior canal dehiscence (SCD) found on flat-panel CT increases the risk for other defects in the otic capsule. STUDY DESIGN: Retrospective cohort study. SETTING: Tertiary care center. PATIENTS: One hundred ears (50 with SCD and 50 matched controls without SCD). INTERVENTIONS: Flat-panel CT imaging. MAIN OUTCOME MEASURES: (1) Prevalence of other dehiscences in SCD ears, (2) dehiscences in controls, and (3) otic capsule thickness in other reported dehiscence locations (cochlea-carotid, lateral semicircular canal [SCC] and mastoid, facial nerve-lateral SCC, vestibular aqueduct, posterior SCC-jugular bulb, posterior SCC-posterior fossa). Between-group comparisons were considered significant at p < 0.007 after applying the Bonferroni correction for multiple comparisons. RESULTS: Not including the SCD, there was a mean of 0.04 additional dehiscences in the SCD group (n = 2/50, 4%) and 0.04 non-SCD dehiscences in the controls (n = 2/50, 4%, p > 0.007). In the SCD group, there was one dehiscence between the cochlea and carotid artery and one between the posterior SCC and posterior fossa. The control group had one enlarged vestibular aqueduct and one dehiscence between the facial nerve and lateral SCC. As a group, SCD ears had wider vestibular aqueducts (0.68 ± 0.20 vs 0.51 ± 0.30 mm, p < 0.007) and thinner bone between the posterior SCC and posterior fossa (3.12 ± 1.43 vs 4.34 ± 1.67 mm, p < 0.007). The bone between the facial nerve and lateral SCC was thicker in SCD ears (0.77 ± 0.23 vs 0.55 ± 0.27 mm, p < 0.007) and no different for cochlea-carotid, and lateral SCC and mastoid (p > 0.007). CONCLUSIONS: SCD does not increase the likelihood of a second dehiscence in the same otic capsule. SCD patients may have congenitally thinner otic capsule bones compared to controls, particularly near the posterior SCC, where the vestibular aqueduct may be enlarged.

The importance of bone density and anatomical structure in superior semicircular canal dehiscence.

OBJECTIVE: This study investigates the importance of bone density, surface area, and diameter of anatomical structures of the superior semicircular canal (SSC), lateral semicircular canal (LSC), posterior semicircular canal (PSC), utricle, and saccule in patients diagnosed with superior semicircular canal dehiscence (SSCD). MATERIALS AND METHODS: The bone density, surface area, and diameter of SSC, LSC, PSC, utricle, and saccule were measured and compared between the SSCD group and control group. Fifteen ears in the SSCD group and 60 ears in the control group were evaluated. Additionally, within the SSCD group, the dehiscent and healthy sides were evaluated independently. RESULTS: SSC's bone density was significantly lower in the SSCD group compared to the control group (p = 0.008). No significant differences were found in surface area and diameter between the groups (p > 0.05). While most of the anatomical structures showed no significant difference in bone density between dehiscent and healthy ears (p > 0.05), SSC bone density was significantly lower in affected ears (p = 0.000) in SSCD group. CONCLUSION: Based on the data obtained in this study, bone density and anatomical structure may be useful in patients diagnosed with SSCD.

Superior canal dehiscence syndrome: A review.

Superior canal dehiscence syndrome (SCDS) is a vestibular disorder in which the presence of a pathological third window in the labyrinth causes several vestibular and cochlear symptoms. Herein, we review the diagnostic criteria and treatment of SCDS. The cause of SCDS is considered to be congenital or acquired; however, its etiology is not well known. Symptoms: Vertigo and/or oscillopsia induced by loud sounds (Tullio phenomenon) or stimuli that change the middle ear or intracranial pressure (fistula symptoms) with vestibular symptoms and hyperacusis and aural fullness with cochlear symptoms are characteristic clinical complaints of this syndrome. Neurological tests: Vertical-torsional eye movements can be observed when the Tullio phenomenon or fistula symptoms are induced. Conductive hearing loss with both a decrease in the bone conduction threshold at lower frequencies and an increase in the air conduction threshold at lower frequencies may be present on audiometry. Cervical and/or ocular vestibular evoked myogenic potentials are effective in strongly suspecting the presence of a pathologic third window in the labyrinth. Computed tomography (CT) imaging: High-resolution CT findings with multiplanar reconstruction in the plane of the superior semicircular canal consistent with dehiscence indicate SCDS. The Pöschl view along the plane of the superior semicircular canal and the Stenvers view perpendicular to it are recommended as CT imaging conditions. Findings from all three major diagnostic categories (symptoms, neurological tests, and/or CT imaging) are needed to diagnose SCDS. The surgical approaches for SCDS are as follows: the 1) middle cranial fossa approach, 2) transmastoid approach, and 3) round window and oval window reinforcement. Each technique has advantages and disadvantages.

New classification of superior semicircular canal dehiscence in HRCT.

BACKGROUND AND PURPOSE: The complex anatomy of the temporal bone is difficult to understand and constitutes a challenge in the daily diagnostic routine even for experienced neuroradiologists. In the context of otoneurological (oVEMP) and preoperative diagnostics, the diagnosis of superior semicircular canal dehiscence (SSCD) is of great importance for Ear, Nose, and Throat (ENT) specialists. The gold standard for this diagnosis is a high-resolution CT (HRCT) of the temporal bone. In order to correctly diagnose SSCD, special oblique reconstructions are necessary in addition to standard (axial, coronal, sagittal) reconstructions. We evaluated the frequency of diagnosis and its location in HRCT in correlation with otoneurological examination. From this analysis, we present a new SSCD classification. This classification yields the potential of a differentiated analysis of the patient's clinical symptoms with correlation to the cross-sectional anatomy and may lead to a differentiated therapy approach. STUDY DESIGN AND SETTING: We evaluated 1370 temporal bone scans of patients with residual hearing and verified 343 superior semicircular canal dehiscence (SSCD). We conducted a subgroup analysis of these 343 HRCT scans displaying a SSCD and used them as a basis to create a classification. RESULTS: Three location types of SSCD were identified. These were anterior type 1, superior type 2 and posterior type 3. Type 2 were significantly more frequent in both sexes. SSCD at this location can be overlooked if diagnosis is performed only in the standard axial plane, since it can only be visualized by means of double oblique reconstruction. We present a standardized reconstruction algorithm. CONCLUSION: In total, three types of SSCD with differing incidences can be extrapolated from the locations. Superior type 2 is the most frequent one. Both sexes are affected with roughly equal incidence. The use of standardized double oblique reconstruction algorithm ensures that all three types are diagnosed in the HRCT.

Relationship Between Superior Semicircular Canal Dehiscence Volume with Clinical Symptoms: Case Series.

BACKGROUND: Superior semicircular canal dehiscence (SSCD) is an osseous defect of the arcuate eminence of the petrosal temporal bone. Patients typically present with auditory and vestibular symptoms, such as hearing loss and disequilibrium. Using advanced imaging segmentation techniques, we evaluated whether the volume of SSCD correlated with preoperative symptoms and postoperative outcomes. METHODS: Our laboratory previously described a novel method of quantifying the size of an SSCD via manual segmentation. High-resolution computed tomography images of the temporal bones were imported into a specialized segmentation software. The volume of the dehiscence was outlined on consecutive slices of the coronal and axial planes via a single-pixel-thick paintbrush tool and was then calculated according to the number of nonzero image voxels. RESULTS: This study included 111 patients (70 women and 41 men; mean age, 55.1 years; age range, 24-87 years) with a total of 164 SSCDs. Mean postoperative follow-up time was 5.2 months (range, 0.03-59.5 months). The most common preoperative and postoperative symptoms were tinnitus (n = 85) and dizziness (n = 45), respectively. Surgery resulted in improvement of symptoms in most patients. The average volume of 164 SSCDs was 1.3 mm3. SSCD volume was not significantly associated with either preoperative symptoms or postoperative outcomes. CONCLUSIONS: Advances in imaging techniques have allowed increased visualization of SSCD. Further research will be necessary to evaluate the potential correlation of volume of the dehiscence with clinical variables.

Quantitative three-dimensional image analysis of the superior canal after surgical plugging to treat superior semicircular canal dehiscence.

Surgical plugging to treat superior semicircular canal dehiscence (SCD) has been proven to impede the effect of the third mobile window, abating cochleovestibular symptoms. Knowledge of superior semicircular canal (SC)-plugging status has been proposed to serve as a guide for adjuvant treatment. Here, we investigated disturbances in the inner ear fluid space following SC plugging using a novel three-dimensional (3D) reconstruction-based method. This approach used a semi-automatic segmentation algorithm and a direct volume rendering method derived from conventional magnetic resonance images. The variable extents of filling defects at the sites of SC plugging and the positional relation of the defect to the ampulla and common crus were identified. The success group exhibited markedly reduced volumes following surgery, whereas the failure group displayed no changes in volume. These results indicate that the success or failure of SC plugging was related to 3D volume changes in the labyrinth fluid signal. Collectively, this study presents individualized SC-plugging statuses using a novel 3D reconstruction-based method and it facilitates future work regarding easy-to-measure 3D volume changes. This current technology also aids in the exploration of pathologic changes in various targets of interest.

Video-head impulse test in superior canal dehiscence.

BACKGROUND: Superior Canal Dehiscence is classically diagnosed with typical abnormalities on Vestibular Evoked Myogenic Potentials (VEMPs) and Computed Tomography (CT) scans. AIM: This paper discusses the utility of the video Head Impulse Test (vHIT) in SCD. METHODS: Data from 11 ears (8 patients) with SCD were retrospectively reviewed. Results from vHIT, VEMPs and CT and when possible, MRI scans were correlated. An audit of 300 vHIT from patients undergoing routine testing for any neurotological complaint was also conducted to look at the incidence of isolated abnormal superior canal function. RESULTS: 82% of patients (9 ears) with SCD showed abnormal vHIT (reduced gain and catch-up saccades) isolated to the affected superior semicircular canal. CONCLUSION: Correlation of the CT and VEMPs are important in forming a diagnosis of SCD. However, if isolated superior canal vHIT abnormalities are demonstrated, it is suggestive of SCD and such patients should be referred for further investigations.

Influence of Semicircular Canal Dehiscence on Cochlear Implant Outcome.

INTRODUCTION: Semicircular canal dehiscence (SCD) is defined as a defect of the bone overlying the semicircular canal. It has a relatively high prevalence of 3% in the general population, which makes it likely that a certain number of patients receiving a cochlear implant (CI) would have it. However, little is known about the influence of SCD on the CI outcome. Therefore, the aim of this study was to determine the influence of SCD on CI outcome with regard to short- and long-term word perception and hearing preservation. METHODS: This study was a retrospective analysis of postoperative word perception ability in the electric-only condition after 6, 12, and ≥18 months and of hearing preservation 4 weeks after surgery in CI recipients with and without SCD. All patients received a preoperative 1.5- or 3-tesla magnetic resonance imaging. RESULTS: Fifty-five patients were included. Forty-eight patients (87%) had no SCD, and 7 patients (13%) had SCD. Mean postoperative word perception scores were 66% in the non-SCD group versus 50% in the SCD group (p = 0.17) after 6 months, 74 versus 64% (p = 0.28) after 12 months, and 77 versus 73% (p = 0.62) after 18 or more months. The mean postoperative hearing loss in patients with functional residual hearing before surgery (n = 34) was 22 dB in the non-SCD group versus 31 dB in the SCD group (p = 0.15). CONCLUSIONS: CI outcome is comparable between recipients without and with SCD. Specifically, hearing preservation rate and word perception ability in the electric-only condition seem not affected by SCD. The rate of progress of word perception ability in the first 12 months after cochlear implantation is not influenced by SCD.

The Sensitivity of the cVEMP Test in Detecting A Superior Semicircular Canal Dehiscence and the Influence of a Coexisting Incudal Lysis: A Case Report.

In this case report, the air-conducted cervical vestibular evoked myogenic potentials (AC cVEMP) test was only sensitive for the left superior semicircular canal dehiscence (SCD), even though the contralateral SCD was of equal length (2.5 mm). Furthermore, a lysis of the processus lenticularis incudis caused a real conductive hearing loss in the left ear. A diminished left AC cVEMP was thus expected, but the opposite was shown (increased corrected amplitude, lowered detection threshold). The patient only experienced hearing loss, so middle ear surgery was performed to repair the lysis. The postoperative AC cVEMP showed a further "uncovering" of the SCD with increased corrected amplitude on the left but no vestibular symptoms. The significance of an SCD should be interpreted with caution, even when the AC cVEMP and the imaging are significant. Furthermore, AC cVEMPs should not be considered as evidence for the absence or presence of conductive hearing loss.