Superior semicircular canal dehiscence postoperative outcomes: a case series of 350 repairs.

BACKGROUND: Superior Semicircular Canal Dehiscence (SSCD) is a dehiscence of the otic capsule which normally lies over the superior semicircular canal. This database constitutes the largest series of SSCD patients to date. OBJECTIVE: To determine what preoperative factors, if any, contribute to postoperative outcomes and evaluate symptom resolution in a large SSCD patient cohort. METHODS: A single-institution, retrospective chart review collected patient demographics, intraoperative findings, and pre-and postoperative symptoms. Fisher's exact t-test was performed for unpaired categorical variables, with a significance level of p < 0.05. RESULTS: 350 SSCD repairs were performed. The median age was 52 years (range: 17-86 years, ± 6.4 years), and the median follow-up duration was 4.6 months (range: 0.03-59.5 months, ± 6.8 months). Preoperative hearing loss was significantly associated with female sex (p = 0.0028). The most reported preoperative symptoms were tinnitus (77.4%), dizziness (74.0%), autophony (66.3%), amplification (63.7%), and disequilibrium (62.6%). Between patients who received unilateral versus bilateral SSCD repair, the greatest postoperative symptomatic resolution was seen in autophony (74.9%, p < 0.001), amplification (77.3%, p = 0.00027), hyperacusis (77.4%, p = 0.023), hearing (62.9%, p = 0.0063), and dizziness (54.6%, p < 0.001) for patients with unilateral SSCD repair. CONCLUSION: Surgical repair via the middle cranial fossa approach can significantly resolve auditory, vestibular, and neurological symptoms of patients with SSCD. Although this is one of the largest single-institution SSCD studies to date, future multi-institutional, prospective studies would be beneficial to validate these results.

Third window lesions of the inner ear: A pictorial review.

PURPOSE: Radiographic review of pathologies that associate with third window syndrome. METHODS: Case series and literature review. RESULTS: Eight unique third window conditions are described and illustrated, including superior, lateral, and posterior semicircular canal dehiscence; carotid-cochlear, facial-cochlear, and internal auditory canal-cochlear dehiscence, labyrinthine erosion from endolymphatic sac tumor, and enlarged vestibular aqueduct. CONCLUSION: The present study highlights the characteristic imaging features and symptoms to differentiate third window pathologies for expedient diagnosis and management planning.

Impact of superior semicircular canal dehiscence on cochlear implant audiologic outcomes.

PURPOSE: Determine whether adult cochlear implant users with radiographic superior semicircular canal dehiscence experience clinically significant differences in audiological outcomes when compared to cochlear implant users with normal temporal bone anatomy. MATERIALS AND METHODS: Retrospective, single institution review. Adult, post-lingual deaf patients implanted between 2010 and 2020. Inclusion criteria included age 18 years or older, available preoperative computed tomography imaging, and preoperative and postoperative AzBio audiological data for at least 6 months of cochlear implant use. Preoperative and postoperative AzBio Sentence Test scores were compared between patients with normal temporal bone anatomy and those with radiographic superior semicircular canal dehiscence or near dehiscence. RESULTS: 110 patients met inclusion criteria. Mean AzBio score for normal temporal bone anatomy group improved from 35.2 % (SD 28.2) preoperatively to 70.3 % (SD 25.7) postoperatively, an improvement of 35.1 % (SD 28.6). Mean AzBio score for near dehiscent temporal bone anatomy group improved from 26.6 % (SD 28.9) preoperatively to 64.5 % (SD 30.6) postoperatively, an improvement of 37.9 % (SD 27.9). Mean AzBio score for dehiscent temporal bone anatomy group improved from 26.3 % (SD 20.4) preoperatively to 65.1 % (SD 27.6) postoperatively, an improvement of 38.7 % (SD 26.9). Utilizing the one-way analysis of variance test, there was no significant difference in audiologic outcomes between the three groups. CONCLUSIONS: Patients with complete or near complete radiographic superior canal dehiscence at the time of cochlear implantation achieve similar improvements in speech perception scores compared to normal anatomy adult cochlear implant users.

Evaluation of clinical predictors of postoperative outcomes in tegmen defect patients with and without concurrent superior semicircular canal dehiscence and cerebrospinal fluid leak.

OBJECTIVES: Tegmen and superior semicircular canal defects have been well studied, yet the factors contributing to their onset and progression are widely debated. The clinical utility of intraoperative intracranial pressure measurements has yet to be tested. This report aims to use intraoperative opening pressure and concurrent superior semicircular canal dehiscence (SSCD) to analyze factors influencing disease course and clinical outcomes in patients with tegmen dehiscence. METHODS: A retrospective analysis of 61 patients who underwent tegmen defect repair was performed. Multiple variables of interest including body mass index (BMI), presence of SSCD, presence of dural venous sinus stenosis, opening pressure, and acetazolamide therapy use were recorded. The cohort was divided into those with or without concurrent SSCD and those presenting with or without cerebrospinal fluid (CSF) leak for analysis. RESULTS: A linear relationship between opening pressure and BMI (p = 0.009) was noted; however, intraoperative opening pressure was not associated with disease outcome. Concurrent SSCD was present in 25 % of patients, while 62 % presented with CSF leak. The concurrent SSCD group exhibited higher opening pressure, higher likelihood of having dural sinus stenosis, and higher likelihood of being discharged on acetazolamide. The CSF leak group had higher likelihood of obstructive sleep apnea and persistent symptoms. CONCLUSIONS: In patients undergoing tegmen defect repair, concurrent SSCD suggests increased disease severity. The presence of preoperative CSF leak predicts persistent symptoms following repair. BMI is linearly correlated with intracranial pressure in these patients.

Trans-mastoid plugging of superior semicircular canal dehiscence: long-term follow-up.

OBJECTIVE: To evaluate the long-term outcomes of trans-mastoid plugging of superior semicircular canal dehiscence (SSCD), focusing on complicated cases. METHODS: In this cohort study, we included all patients who underwent trans-mastoid plugging of SSCD between 2009 and 2019. We evaluated the symptoms (autophony, sound-/pressure-induced vertigo, disequilibrium, aural fullness and pulsatile tinnitus) before and 1 year after surgery in the medical records. We systematically assessed the current symptoms 6.2 ± 3 years postoperative (range 2.2-12.3 years) using questionnaires sent by post and validated by telephone interviews. We also documented any complications and the need for further procedures. We compared pure tone and speech audiometry before and 1 year after surgery. Finally, the degree of mastoid pneumatisation and mastoid tegmen anatomy were reviewed on preoperative CT scans. RESULTS: We included 24 ears in 23 patients. No complications were recorded, and none required a second procedure for SSCD. Following surgery, oscillopsia and Tullio phenomena resolved in all patients. Hyperacusis, autophony, and aural fullness were also settled in all patients except one. Balance impairment persisted to some degree in 35% of patients. No deterioration over the years was reported regarding the above symptoms. On average, bone conduction pure tone average pre- and 1 year postoperative were 13.7 ± 17 and 20.5 ± 18 dB, respectively (P = 0.002). Air bone gaps were reduced from 12.7 ± 8 to 5.9 ± 6 (P = 0.001). Two patients had a significant sclerotic mastoid, three had a prominent low-lying mastoid tegmen, and two had both. Anatomy had no effect on outcome. CONCLUSION: Trans-mastoid plugging of SSCD is a reliable and effective technique which achieves long-lasting symptom control, even in cases with sclerotic mastoid or low-lying mastoid tegmen.

Association of the superior semicircular canal and tegmen tympani dehiscences and its relationship with the pneumatisation of the temporal bone.

PURPOSE: To analyse the degree of pneumatisation of the temporal bone when there is an association between dehiscence of the superior semicircular canal and dehiscence of the tegmen tympani. MATERIALS AND METHODS: We analysed a retrospective CT study of 124 selected cases. A single inclusion criterion was applied: the presence of a dehiscence of the tegmen tympani. On the other hand, the degree of temporal pneumatisation was assessed by axial and coronal planes, and has been divided into the following grades O, I, II and III, according to the status and relationship of the mastoid, the bony labyrinth, the petrous segment of the carotid canal and sigmoid sinus. RESULTS: Of the 124 cases studied, 35 (28.2%) presented both dehiscences. In 26 of the 35 (47.3%), grade II pneumatisation, 4 (14,8%), grade I, and 5 (11,9%) grade III was observed, with a statistically significant relationship (p < 0.001). On the other hand, we did not find a significant relationship when relating both dehiscences in any age or sex group. However, when relating the degree of pneumatisation to sex, among those with grade III pneumatisation, the proportion of men (52.4%) was significantly higher than that of women (47.6%) (p = 0.017). CONCLUSION: We have detected a statistically significant relationship between the coexistence of grade II pneumatisation and the presence of both dehiscences in the temporal bone.

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 semicircular canal dehiscence in relation with the superior petrosal sinus: our experience, surgical management and systematic review of literature.

PURPOSE: Most of Superior Semicircular Canal Dehiscence (SSCD) are located in the apical region of the SSC. However, in a small number of cases, it may be situated in the medial wall, causing the SSC to contact with the superior petrosal sinus (SPS). The aim of this study is to describe four patients with SSCD involving the superior petrosal sinus (SSCD-SPS) and to perform a review of the literature. METHODS: Observational retrospective study of patients diagnosed of SSCD-SPS in a tertiary referral center. A systematic review was made, identifying 7 articles in the literature. Clinical presentation, complementary test (pure-tone audiometry, PTA; vestibular evoked myogenic potential, VEMP; computed tomography, CT), therapeutic management and outcomes were reported. RESULTS: Four new cases of SSCD-SPS are reported, in three of them a transmastoid plugging was performed. 54 patients with SSCD-SPS (57 dehiscences) were reported in the literature. The most frequent symptoms were aural pressure (57.41%) and vertigo provoked by pressure/Valsalva (55.55%). Conductive hearing loss was the most common finding in PTA (47.37%). Abnormally low thresholds were observed in 59.46% of reported VEMP. Transmastoid approach was used in ten cases, middle fossa approach in four, round window reinforcement in one, and occlusion of the SPS using coils in two. CONCLUSIONS: Within SSCD, we have encountered a rare subtype characterized by its medial wall location in close proximity to the SPS. This subgroup needs special consideration as it has shown its own distinct characteristics. Regarding therapeutic management, we advocate a transmastoid approach.

Comparison of Superior Semicircular Canal Bone Thickness and Patterns in Unilateral and Bilateral Cleft Patients and Normal Controls: A CBCT Study.

Superior Semicircular Canal Dehiscence (SSCD) is a recently-defined developmental defect may be associated with several craniofacial anomalies such as Cleft Lip/Palate (CLP). The present study aimed to compare subjects with unilateral and bilateral CLP and normal controls in terms of Superior Semicircular Canal (SSC) bone thickness and pattern.A total of 238 Cone Beam Computed Tomography (CBCT) images were collected from 52 unilateral Cleft Lip and Palate (UCLP) subjects (104 temporal bones) and 38 Bilateral Cleft Lip and Palate (BCLP) (76 temporal bones) subjects and 148 healthy controls (296 temporal bones). The SSC bone thickness was measured twice and validated by a maxillofacial radiologist. The samples were then classified into five categories based on bone thickness: papyraceous or thin, normal, thick, pneumatized, and dehiscence. After all, the UCLP, BCLP, and normal control groups were compared concerning the SSC pattern and thickness.The results revealed no significant difference among the three groups regarding the SSC pattern and thickness based on gender. The SSC patterns (P value = .001) and SSC thickness (0.01) were strongly correlated to the cleft type. The thinnest bone thickness and the highest incidence of SSCD were observed among the subjects with BCLP.The results showed a significant association between the SSC patterns and SSC thickness and the study groups.

Dehiscence or thinning of bone overlying the superior semicircular canal in idiopathic intracranial hypertension.

STUDY DESIGN: Retrospective cohort. OBJECTIVES: The objective of the study is to evaluate a relationship between idiopathic intracranial hypertension (IIH) and superior semicircular canal dehiscence (SSCD) of bone overlying the superior semicircular canal (SSC). MATERIALS AND METHODS: A total of 57 (114 ears) individuals, 20 of whom were controls and 37 of whom were IIH, were included in the study. Individuals were evaluated with 0.8 mm slice thickness computed tomography (CT) images for SSC bony roof thickness and SSCD. Thickness of the bony roof over the SSC was graded from Grade 1 to Grade 4. Grade 3 was defined as pre-dehiscence and Grade 4 as dehiscence. RESULTS: Bony roof thickness was 1.25 mm in the control group and 0.76 mm in the IIH group. When bony roof thickness was compared between the groups, it was found to be significantly thinner in the IIH group (p = 0.012). In the IIH group, while dehiscence was detected in 25 of 74 ears, no dehiscence was detected in 49 ears. In the control group, while dehiscence was detected in 5 ears, no dehiscence was detected in 35 ears. The difference is statistically significant (p = 0.015). The correlation between bony roof thickness and cerebrospinal fluid (CSF) pressure in the IIH group was not statistically significant (p = 0.343; rho = 0.110). The correlation between bony roof thickness and age in the IIH group was not statistically significant (p = 0.082; rho = - 0.164). CONCLUSION: Increased CSF pressure in patients with IIH may cause chronic, progressive, and irreversible damage to the bone of the SSC and, according to our study, the rate of SSCD was found to be high in IIH patients.

Three-dimensional imaging for the localization of related anatomical structures during surgery on the internal auditory canal.

BACKGROUND: The Fisch infra-temporal fossa approach (Fisch's method), first proposed in 1970, is commonly used during internal auditory canal (IAC) surgery with an approach that advances through the middle cranial fossa. This study was designed to address the technical difficulties encountered in recognizing and localizing the arcuate eminence with respect to the superior semicircular canal (SSC). METHODS: Forty men and 40 women (18-57 years of age) without space-occupying lesions in the petrous part of the temporal bone were selected for the study. In total, 160 samples were obtained from both sides of the temporal bone. The temporal bone in these 160 samples was scanned using computed tomography, and a three-dimensional coordinate system was established to measure the three-dimensional coordinate values of structures adjacent to the arcuate eminence, the SSC, and the IAC. RESULTS: The results showed that the shape of the arcuate eminence is highly variable. Approximately 23.12% of samples had no obvious arcuate eminence, which prevented the use of Fisch's method to localize the SSC. The arcuate eminence was difficult to identify in 37 samples. CONCLUSIONS: Analysis samples showed that the SSC was located in a fan ring centered at the midpoint of the upper edge of the petrous portion of the temporal bone. The arcuate eminence did not correspond directly with the SSC, as the former was located posterolateral to the latter in 85.83% of samples. The angle between the SSC and the IAC ranged from 0° to 60° degrees, as reported previously by Fisch. However, the angle typically ranged from 10-30° in our study.

Elevated ocular VEMP responses in the absence of a superior semicircular canal dehiscence.

BACKGROUND: Vestibular evoked myogenic potentials (VEMPs) have an accepted role in the diagnosis of the superior semicircular canal dehiscence (SSCD) syndrome. The current impression is that ocular VEMPs (oVEMPs) are more sensitive than cervical VEMPs (cVEMPs) for detecting a SSCD and that oVEMP testing in response to air conducted sound provides an excellent screening test without risk of radiation exposure from computerized tomography (CT). AIMS/OBJECTIVES: To report on patients with elevated oVEMP amplitudes but without evidence for a SSCD on multiplanar CT imaging. MATERIAL AND METHODS: Retrospective chart review of all patients referred for vestibular function testing to our department. Patients with oVEMP peak-to-peak amplitudes ≥17 µν without evidence for a SSCD on imaging were evaluated. RESULTS: 26 patients had oVEMP peak-to-peak amplitudes ≥17 µν with no evidence of a SSCD on imaging. The most common diagnosis was Meniere's disease in those identified. CONCLUSION AND SIGNIFICANCE: oVEMPs can provide false positive results for diagnosis of a SSCD and an elevated oVEMP amplitude in itself is insufficient for diagnosis of a SSCD.

MRI contribution for the detection of endolymphatic hydrops in patients with superior canal dehiscence syndrome.

PURPOSE: Patients with superior semicircular canal dehiscence syndrome, which can only be treated by surgery, present cochleo-vestibular symptoms related to a third-mobile window but also endolymphatic hydrops. Since cVEMP and oVEMP are disturbed by the presence of the dehiscence, the aim of the study is to assess the value of MRI for the diagnosis of endolymphatic hydrops in patients with superior semicircular canal dehiscence syndrome in comparison with cVEMP and oVEMP. METHODS: In this retrospective cohort study we enrolled 33 ears in 24 patients with superior semicircular dehiscence syndrome who underwent a 4-h delayed intravenous Gd-enhanced 3D-FLAIR MRI and pure tone audiometry, cVEMP and oVEMP. For each patient MRI images were evaluated by two radiologists who used a compartmental endolymphatic hydrops grading system in comparison with cVEMP and oVEMP. RESULTS: Endolymphatic hydrops was found on MRI in 9 out of 33 SCDS ears (27.3%). We found no significant correlation between the presence of endolymphatic hydrops on MRI and cVEMP and oVEMP (p = 0.36 and p = 0.7, respectively). However, there was a significant correlation between the presence of endolymphatic hydrops on MRI and the degree of sensorineural hearing loss, Air Conduction-Pure Tone Average level (p = 0.012) and Bone Conduction-Pure Tone Average level (p = 0.09), respectively. CONCLUSION: We demonstrated that EH might be observed in 27.3% of superior semicircular dehiscence syndrome ears. The role of inner ear MRI is important to detect endolymphatic hydrops, since cVEMP and oVEMP are disturbed by the presence of the dehiscence, because these patients could benefit from a medical treatment. LEVEL OF EVIDENCE: Level 3.

Anatomical study between the correlation of the arcuate eminence and the superior semicircular canal.

OBJECTIVE: To study the anatomical correlation between the arcuate eminence and the superior semicircular canal. MATERIAL AND METHODS: A study of the height of the arcuate eminence was carried out in 295 temporal bones. In addition, 30 temporals with different heights of the arcuate eminence (10 flat, 10 prominent and 10 very prominent) were randomly selected and radiological tests were performed by computed tomography (Pöschl projection) and subsequent dissection by milling until the apex of the superior semicircular canal was found, establishing, with both methods, the anatomical relationship with the arcuate eminence. RESULTS: The arcuate eminence was classified as: smooth, when there was no relief (1.7%); flat, measured less than 1 mm (20.3%), prominent, measured between 1 and 2 mm, in (62%), and very prominent, measured above 2 mm (12.6%). The tomographic study (CT) and its subsequent dissection by bone milling showed a direct relationship between the arcuate eminence and the semicircular canal only when it was flat, while the rest of the types corresponded to the presence of pneumatized peri-labyrinthine cells and/or cancellous bone without a direct anatomical relationship with the apex of the superior semicircular canal. CONCLUSION: The correlation between the arcuate eminence and the superior semicircular canal is direct only when it is flat (1 mm), being related to peri-labyrinthine cells and/or cancellous bone when the arcuate eminence is prominent or very prominent.

The evaluation of superior semicircular canal bone thickness and radiological patterns in relation to age and gender.

PURPOSE: The present study aims to evaluate the superior semicircular canal (SSC) bone thickness and radiological patterns in relation to age and gender in a Turkish population using cone beam computed tomography (CBCT). METHODS: A total of 450 temporal bones were evaluated in the study by two examiners. The radiological patterns of SSC were categorized as follows: dehiscent, papyraceous, normal, thick and pneumatised patterns. The bone thickness of SSCs were measured. RESULTS: The mean bone thickness of the SSC for females was 1.079 ± 0.8 mm. For males, the mean bone thickness was 0.952 ± 0.6 mm. There was no significant difference between males and females for the mean bone thickness of the SSC. (p > 0.05) The normal pattern was found in 258 temporal bones (57.3%). Seventy-two cases (16%) were defined as "papyraceous pattern"; 23 cases (5.1%) were defined as "thick pattern" and 42 cases (9.3%) were defined as "pneumatised pattern". SSC dehiscence was determined in 55 cases (12.2%). There was no significant difference between radiological patterns for age groups and gender (p > 0.05). CONCLUSION: There was no significant relationship between SSC bone thickness with age and gender. The radiological patterns of SSC were not associated with age and gender. Radiologists evaluating the head and neck region for various reasons should be aware of these structures and report not only the SSC dehiscence but also the papyraceous pattern.

Quality of life outcomes after transmastoid plugging of superior semicircular canal dehiscence.

PURPOSE: This study was performed to evaluate the effectiveness and impact on quality of life in patients undergoing plugging of superior semicircular canal dehiscence using the transmastoid approach. MATERIALS AND METHODS: Retrospective chart review with prospective outcomes assessment, using validated quantitative scoring systems, was performed on 10 patients (23-76 years) who underwent transmastoid plugging of superior semicircular canal dehiscence between February 2014 and February 2018 at a tertiary referral center. Pre-operative and post-operative autophony and vertigo were measured by The Autophony Index and the Dizziness Handicap Index. Overall quality of life following intervention was measured by the Glasgow Benefit Inventory. Subjective improvement, audiological changes, and subjective quality of life changes were also recorded. RESULTS: A significant reduction in the total Dizziness Handicap Index was seen following transmastoid repair of superior semicircular canal dehiscence (p = 0.0078). This was also evident when subgroup analysis of the Dizziness Handicap Index was performed, as physical (p = 0.0273), emotional (p = 0.0078), and functional subgroups were all significantly reduced (p = 0.0117). Autophony was also significantly reduced following intervention (p = 0.0312). Overall quality of life was seen to be improved following surgery as measured by the Glasgow Benefit Inventory (p = 0.0345). CONCLUSION: Our data suggest that transmastoid plugging of a dehiscence in the superior semicircular canal is a safe and effective means of improving autophony, dizziness and overall quality of life in these patients. We believe that these results should be taken into consideration in discussions regarding surgical approach for patients who are contemplating this procedure.

Analysis of non-posterior canal benign paroxysmal positional vertigo in patients treated using the particle repositioning chair: A large, single-institution series.

PURPOSE: Benign paroxysmal positional vertigo (BPPV) involving the horizontal and superior semicircular canals is difficult to study due to variability in diagnosis. We aim to compare disease, treatment, and outcome characteristics between patients with BPPV of non-posterior semicircular canals (NP-BPPV) and BPPV involving the posterior canal only (P-BPPV) using the particle repositioning chair as a diagnostic and therapeutic tool. METHODS: Retrospective review of patients diagnosed with and treated for BPPV at a high volume otology institution using the particle repositioning chair. RESULTS: A total of 610 patients with BPPV were identified, 19.0% of whom had NP-BPPV. Patients with NP-BPPV were more likely to have bilateral BPPV (52.6% vs. 27.6%, p < 0.0005) and Meniere's disease (12.1% vs. 5.9%, p = 0.02) and were more likely to have caloric weakness (40.3% vs. 24.3%, p = 0.01). Patients with NP-BPPV required more treatments for BPPV (average 3.4 vs. 2.4, p = 0.01) but did not have a significantly different rate of resolution, rate of recurrence, or time to resolution or recurrence than patients with posterior canal BPPV. CONCLUSIONS: Comparison of NP-BPPV and P-BPPV is presented with reliable diagnosis by the particle repositioning chair. NP-BPPV affects 19% of patients with BPPV, and these patients are more likely to have bilateral BPPV and to require more treatment visits but have similar outcomes to those with P-BPPV. NP-BPPV is common and should be part of the differential diagnosis for patients presenting with positional vertigo.

Hearing eyeball and/or eyelid movements on the side of a unilateral superior semicircular canal dehiscence.

Hearing of eyeball movements has been reported in superior semicircular canal dehiscence (SSCD), but not hearing of eyelid movements. Our main objective was to report the hearing of eyeball and/or eyelid movements in unilateral SSCD. Our secondary objective was to access its specificity to SSCD and discuss the underlying mechanism. Six patients with SSCD who could hear their eyeball and/or eyelid movements were retrospectively reviewed. With the aim of comparisons, eight patients with an enlarged vestibular aqueduct (EVA), who share the same mechanism of an abnormal third window, were questioned on their ability to hear their eyeball and/or eyelid movements. Three patients with SSCD could hear both their eyeball and eyelid movements as a soft low-pitch friction sound. Two patients with SSCD could hear only their eyelid movements, one of whom after the surgery of a traumatic chronic subdural hematoma. The latter remarked that every gently tapping on the skin covering the burr-hole was heard in his dehiscent ear as the sound produced when banging on a drum, in keeping with a direct transmission of the sound to the inner ear via the cerebrospinal fluid. One patient with SSCD, who could hear only his eyeball movements, had other disabling symptoms deserving operation through a middle fossa approach with an immediate relief of his symptoms. None of the eight patients with EVA could hear his/her eyeball or eyelid movements. Hearing of eyeball and/or eyelid movements is highly suggestive of a SSCD and do not seem to occur in EVA. In case of radiological SSCD, clinicians should search for hearing of eyeball and/or eyelid movements providing arguments for a symptomatic dehiscence. The underlying mechanism is discussed particularly the role of a cerebrospinal fluid transmission.

Development of ossification in the vertical semicircular canals: tomographic study.

PURPOSE: To describe the ontogeny of vertical semicircular canals using computed tomography. MATERIALS AND METHODS: We have studied 39 human fetuses aged between 17 and 38 weeks of development through multi-helicoidal CT. RESULTS: The first signs of ossification in the semicircular canals, superior and posterior, are from 19 weeks of development, through two primary ossification centers in each canal, which will take part in the formation of the outer cover oriented towards the middle and posterior brain fossae, respectively. In this process it must be added the intervention of the common branch. Internal bone covers are formed by ossification of the fossa subarcuata in the superior semicircular canal, and from the compact center of the labyrinthine capsule into the posterior canal. The tomographic study has allowed us to demonstrate how ossification follows a variable rate, establishing a period between 21 and 26 weeks where there are completely closed canals with others still open to the brain fossae. CONCLUSIONS: The tomographic study of the semicircular canals has enabled us to establish a critical period in its ossification that could explain the etiology of the congenital-type dehiscence.