Superior semicircular canal dehiscence syndrome: a new aetiology

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.

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.

Superior petrosal sinus causing superior canal dehiscence syndrome

Objective:

To determine signs and symptoms for superior canal dehiscence syndrome caused by the superior petrosal sinus.

Methods:

A review of the English-language literature on PubMed and Embase databases was conducted, in addition to a multi-centre case series report.

Results:

The most common symptoms of 17 patients with superior petrosal sinus related superior canal dehiscence syndrome were: hearing loss (53 per cent), aural fullness (47 per cent), pulsatile tinnitus (41 per cent) and pressure-induced vertigo (41 per cent). The diagnosis was made by demonstration of the characteristic bony groove of the superior petrosal sinus and the ‘cookie bite’ out of the superior semicircular canal on computed tomography imaging.

Conclusion:

Pulsatile tinnitus, hearing loss, aural fullness and pressure-induced vertigo are the most common symptoms in superior petrosal sinus related superior canal dehiscence syndrome. Compared to superior canal dehiscence syndrome caused by the more common apical location of the dehiscence, pulsatile tinnitus and exercise-induced vertigo are more frequent, while sound-induced vertigo and autophony are less frequent. There is, however, considerable overlap between the two subtypes. The distinction cannot as yet be made on clinical signs and symptoms alone, and requires careful analysis of computed tomography imaging.

Radiological prevalence of superior and posterior semicircular canal dehiscence in children

OBJECTIVE

Establishing the prevalence of semicircular canal dehiscence in a pediatric population using temporal bone CT imaging.

STUDY DESIGN

Retrospective analysis of all temporal bone CT scans during a 5-year period (2007-2012).

METHODS

CT scan images were reformatted in the plane of the canals and assessed by two independent reviewers with a third to resolve disagreement. Detailed chart review was performed for those found to have dehiscence. Superior and posterior canals were classified as "dehiscent", "possibly dehiscent", "thin" or "normal" for each case.

RESULTS

649 temporal bones were assessed from 334 children (under 18 years of age). The prevalence rate of superior canal dehiscence (SCD) was 1.7% (3.3% of individuals). Posterior canal dehiscence (PCD) was present in 1.2% (2.1% of individuals). There were no cases of bilateral SCD, and one case of bilateral PCD. Age under 3 years was associated with a higher prevalence of thinning but not dehiscence. Congenital inner ear malformation was not related to a higher probability of dehiscence. The superior petrosal sinus was associated with the SCD in three cases (27.3%). Retrospective chart review highlighted possible vestibular symptoms in 3/11 patients with SCD (27.3%).

CONCLUSIONS

This forms the largest pediatric study of canal dehiscence to date. This study's prevalence rate is significantly lower than previous reports. The identified association with overlying venous structures may reflect the etiological process involved. The occurrence in children supports the hypothesis of a congenital predisposition for development of canal dehiscence syndrome.

Large bilateral internal auditory meatus associated with bilateral superior semicircular canal dehiscence

Superior semicircular canal dehiscence and an abnormally wide internal auditory meatus are clinical entities characterized by vestibular and cochlear symptoms. These symptoms are induced by hypersensitivity of labyrinthine receptors secondary to a bone defect of the otic capsule. We report the case of a 41-year-old man with congenital right-sided hearing loss who presented with bilateral superior semicircular canal dehiscence that was associated with wide, bulbous internal auditory meatus and a loss of the bony wall separating the lateral end of the meatus from the cochlea. The patient was experiencing vestibular and cochlear symptoms in the right ear and disabling tinnitus in the left ear. However, he refused all treatment and was lost to follow-up.

Anatomical feature of the middle cranial fossa in fetal periods: possible etiology of superior canal dehiscence syndrome

CONCLUSION

Different from adults, the superior semicircular canal (SSC) protrudes into the cranium during the fetal period. This might cause adhesion of the membranous labyrinth to dura as the bony labyrinth develops much later than the membranous labyrinth. This adhesion interferes with ossification and leads to a bony defect in the SSC.

OBJECTIVES

The purpose of this study was to investigate a possible etiology of superior canal dehiscence syndrome (SCDS) from a view point of ontogeny.

METHODS

Forty-two adult cadavers and 4 fetal cadavers were used for macroscopic observation of the middle cranial fossa (MCF). In addition, six fetuses underwent computed tomography (CT) examinations. The volume data of the CT obtained from four adults were also used for comparison. Using these CT data, we investigated the anatomic relationship between the MCF and SSC.

RESULTS

The SSC and the cochlea in fetuses protruded into the cranium in macroscopic anatomy and CT examination. On the other hand, the SSC of all adults was completely or mostly buried in the temporal bone.

CT imaging of superior semicircular canal dehiscence: added value of reformatted images

CONCLUSION

Superior semicircular canal dehiscence (SSCD) syndrome may present with various symptoms. CT scans previously interpreted as normal may show SSCD, especially if special reconstructions tailored for superior canal evaluation are added.

OBJECTIVES

The purpose of this study was to investigate prevalence of SSCD, its length and its correlation with symptoms in patients who had previously undergone temporal bone CT examination that was reported normal and to demonstrate the importance of reformatted images in the diagnosis of SSCD.

METHODS

We retrospectively reviewed 108 patients who had undergone temporal bone CT examination for various symptoms and were reported as normal. High-resolution temporal bone CT imaging was performed with 1 mm slice thickness in the transverse plane. Each of the superior semicircular canals was evaluated in the plane of Pöschl and Stenver reformatted images together with axial images.

RESULTS

Ninety-three patients were included in the study. Nineteen patients with semicircular canal dehiscence were detected. The mean age of the study group was 45 years. Radiologic evidence of SSCD occurred in 23 of 186 temporal bones with a radiologic prevalence of 12%. The most common symptoms in dehiscent patients were vertigo, hearing loss and tinnitus. Defect lengths varied between 1 mm and 6.5 mm.

[Two particular cases of superior semicircular canal dehiscence related to a procidence of the superior petrous sinus]

We report two cases of superior semicircular canal dehiscence related to a dehiscence of the superior petrous sinus that creates a localized notch of the most superior part of the superior semicircular canal. This vascular dehiscence was suspected at CT and was confirmed by MR imaging with identification of the superior petrous sinus in touch with the intralabyrinthine fluid at this level. This not well-known etiology of the superior semicircular canal dehiscence syndrome has to be searched and described by radiologists, allowing an optimal surgical approach.