Rudolf Boeddinghaus

The relationship between the air-bone gap and the size of superior semicircular canal dehiscence.

OBJECTIVE: To examine the relationship between the air-bone gap (ABG) and the size of the superior semicircular canal dehiscence (SSCD) as measured on a computed tomography (CT) scan. STUDY DESIGN: Case series with chart review. SETTING: Tertiary referral center. PATIENTS: Twenty-three patients (28 ears) diagnosed with SSCD. MAIN OUTCOME MEASURES: The size of the dehiscence on CT scans and the ABG on pure-tone audiometry were recorded. RESULTS: The size of the dehiscence ranged from 1.0 to 6.0 mm (mean, 3.5 ± 1.6 mm). Six ears with a dehiscence measuring less than 3.0 mm did not have an ABG (0 dB). The remaining 18 ears showed an average ABG at 500, 1000, and 2000 Hz (AvABG500–2000) ranging from 3.3 to 27.0 dB (mean, 11.6 ± 5.7 dB). The analysis of the relationship between the dehiscence size and AvABG500–2000 revealed a correlation of R 2 = 0.828 (P < 0.001, quadratic fit) and R 2 = 0.780 (P < 0.001, linear fit). Therefore, the larger the dehiscence, the larger the ABG at lower frequencies on pure-tone audiometry. CONCLUSIONS: In SSCD patients, an ABG is consistently shown at the low frequency when the dehiscence is larger than 3 mm. The size of the average ABG correlates with the size of the dehiscence. These findings highlight the effect of the dehiscence size on conductive hearing loss in SSCD and contribute to a better understanding of the symptomatology of patients with SSCD.

The Effects of Superior Semicircular Canal Dehiscence on the Labyrinth: Does Size Matter?

Background: Superior semicircular canal dehiscence (SSCD) is characterized by lack of bony covering of the superior semicircular canal in the inner ear, resulting in a third mobile window with altered functioning of the superior semicircular canal. Vertigo in association with sound and pressure changes often occurs. This study examines the relationship between dehiscence size and frequency of sound-induced vertigo. Method: Retrospective review of 22 patients with SSCD, noting the auditory frequency producing the maximal electronystagmographic response. Results: The study found a correlation between dehiscence size and stimulator frequency of r 2 = 0.856, p < 0.001. The larger the dehiscence, the lower the frequency of stimuli required to provoke a vestibular response. Conclusion: The relationship found between the superior canal dehiscence size and the stimulator frequency has clinical implications in the diagnosis and management of patients with SSCD.

Computed tomography of the temporomandibular joint

We present a pictorial review of the spectrum of temporomandibular joint (TMJ) pathology diagnosed with CT. Although MRI is the modality of choice for most TMJ pathology, CT is useful when MRI is contraindicated or not accessible. With attention to technique and viewing conditions, CT is capable of showing internal disc derangement, arthritis, neoplasms and non‐TMJ regional pathology at a relatively low radiation dose.

Condylar position assessed by magnetic resonance imaging after various bite position registrations

INTRODUCTION In this study, we evaluated the reliability and validity of 3 bite registrations in relation to condylar position in the glenoid fossae using magnetic resonance imaging in a symptom-free population. METHODS Nineteen subjects, 14 men and 5 women (ages, 20-39 years) without temporomandibular disorders were examined. Three bite registrations were taken and evaluated on each subject: centric occlusion, centric relation, and Roth power centric relation. The differences in condyle position among the 3 bite registrations were determined for the left and right condyles: centric occlusion-centric relation, centric occlusion-Roth power centric relation, and centric relation-Roth power centric relation for each plane of space. RESULTS The results indicated that (1) all measurements collected had large standard deviations and ranges with no statistical significance, and (2) of the 19 subjects and 38 condyles assessed, 33 condyles (87%) were concentric in an anteroposterior plane. In the transverse anatomic plane, all condyles were concentric. CONCLUSIONS The clinical concept of positioning the condyles in specific positions in the fossae with various bite registrations as a preventive measure for temporomandibular disorders and as a diagnosis and treatment planning tool is not supported by this study.

Otitic meningitis, superior semicircular canal dehiscence, and encephalocele: a case series.

Background Otitic meningitis in the postantibiotic era is still a serious condition, requiring intensive treatment and prolonged rehabilitation. In view of the significant morbidity and mortality rate, conditions that may increase the likelihood of otitic meningitis developing should be treated promptly. The incidence of meningitis after asymptomatic encephaloceles of the middle cranial fossa varies greatly, and the management differs between elective surgical repair and expectant careful observation. Superior semicircular canal dehiscences (SSCDs) are postulated to have a congenital origin and are associated with a thin or dehiscent tegmen. Several cases of simultaneous SCCD and tegmen defects have been reported, but the findings of otitic meningitis, SCCD, and encephaloceles has, to the best of our knowledge, not been previously explored in the literature. Methods We reviewed a series of 4 patients who all presented with a combination of otitic meningitis, encephaloceles, and SSCD. Results All the 4 patients we reviewed had meningitis secondary to otitis media with computed tomographic scans confirming the presence of SCCD with ipsilateral tegmen tympani defects and associated cephaloceles. All patients were treated with intravenous antibiotics and underwent surgery that ranged from myringotomy and ventilation tube insertions, mastoidectomy, and burr hole drainage for temporal lobe abscess. They were all associated with intensive care unit admission, significant morbidity, and prolonged hospital stays. There were no mortalities. Conclusion We propose that in all SSCD patients, a careful computed tomographic examination of the cranial base should be undertaken to exclude other associated tegmen tympani defects. In cases of SSCD requiring surgery, we support the view that elective surgical repair be recommended where asymptomatic ipsilateral encephaloceles are found, to reduce the risk of otitic meningitis.

Response to: The relationship between the air-bone gap and the size of superior semicircular canal dehiscence, from Dirk Beutner

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. 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. 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, 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, dirk.beutner@uni-koeln.de