Posterior Semicircular Canal Dehiscence: CT Prevalence and Clinical Symptoms

Posterior Semicircular Canal Dehiscence with Vestibulo-Ocular Reflex Reduction for the Affected Canal at the Video-Head Impulse Test: Considerations to Pathomechanisms

Posterior semicircular canal dehiscence (PSCD) has been demonstrated to result in a third mobile window mechanism (TMWM) in the inner ear similar to superior semicircular canal dehiscence (SSCD). Typical clinical and instrumental features of TMWM, including low-frequency conductive hearing loss (CHL), autophony, pulsatile tinnitus, sound/pressure-induced vertigo and enhanced vestibular-evoked myogenic potentials, have been widely described in cases with PSCD. Nevertheless, video-head impulse test (vHIT) results have been poorly investigated. Here, we present six patients with PSCD presenting with a clinical scenario consistent with a TMWM and an impaired vestibulo-ocular reflex (VOR) for the affected canal on vHIT. In two cases, an additional dehiscence between the facial nerve and the horizontal semicircular canal (HSC) was detected, leading to a concurrent VOR impairment for the HSC. While in SSCD, a VOR gain reduction could be ascribed to a spontaneous "auto-plugging" process due to a dural prolapse into the canal, the same pathomechanism is difficult to conceive in PSCD due to a different anatomical position, making a dural herniation less likely. Alternative putative pathomechanisms are discussed, including an endolymphatic flow dissipation during head impulses as already hypothesized in SSCD. The association of symptoms/signs consistent with TMWM and a reduced VOR gain for the posterior canal might address the diagnosis toward PSCD.

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.

Prevalence of otic capsule dehiscence in temporal bone computed tomography scan

PURPOSE

To investigate the radiologic prevalence of otic capsule dehiscence in temporal bone computed tomography (CT) scan.

METHODS

This was a cross-sectional study. The temporal bone CT scans of the patients presenting to a tertiary center were evaluated for possible dehiscence in any part of the otic capsule; then, all of the dehiscence were confirmed by a trained academic radiologist. For each type of otic capsule dehiscence, at least three planes were used with a specific type of reconstruction. When a dehiscence was present in at least two consecutive images in all planes, it was considered as a true dehiscence.

RESULTS

Six hundred patients (mean age: 40 ± 18.1 years) were enrolled. The prevalence of superior and posterior semicircular canal dehiscence was 6.0% and 2.7%, respectively. The prevalence of cochlear-facial dehiscence, cochlear-internal auditory canal dehiscence, and cochlear-carotid dehiscence was 6.3%, 0.7%, and 0.7%, respectively. The prevalence of vestibular aqueduct-jugular bulb dehiscence was 6.3% and the prevalence of posterior semicircular canal-jugular bulb dehiscence was 0.2%.

CONCLUSIONS

Considering different types of otic capsule dehiscence described, care should be taken in patients with vestibular and auditory signs and symptoms to diagnose these dehiscences.

Bilateral Superior Semicircular Canal Dehiscence Concurrent With Ehlers-Danlos Syndrome: A Case Report

Superior semicircular canal dehiscence (SSCD) is characterized by temporal bone thinning, which creates an opening between the inner ear and middle cranial fossa. Ehlers-Danlos syndrome, hypermobility type (EDS-HT) is a genetic collagen synthesis disorder, often resulting in bony abnormalities. We present the case of a 39-year-old female with EDS-HT who exhibited the otological symptoms characteristic of bilateral SSCD. High-resolution computed tomography (CT) scans confirmed the diagnosis. The patient elected for middle fossa craniotomy and noted symptomatic improvement. Due to its potential to confer bone fragility, EDS-HT may predispose SSCD development. Further examination of the relationship between these disorders is necessary.

Rare Disorders of the Vestibular Labyrinth: of Zebras, Chameleons and Wolves in Sheep's Clothing

The differential diagnosis of vertigo syndromes is a challenging issue, as many - and in particular - rare disorders of the vestibular labyrinth can hide behind the very common symptoms of "vertigo" and "dizziness". The following article presents an overview of those rare disorders of the balance organ that are of special interest for the otorhinolaryngologist dealing with vertigo disorders. For a better orientation, these disorders are categorized as acute (AVS), episodic (EVS) and chronic vestibular syndromes (CVS) according to their clinical presentation. The main focus lies on EVS sorted by their duration and the presence/absence of triggering factors (seconds, no triggers: vestibular paroxysmia, Tumarkin attacks; seconds, sound and pressure induced: "third window" syndromes; seconds to minutes, positional: rare variants and differential diagnoses of benign paroxysmal positional vertigo; hours to days, spontaneous: intralabyrinthine schwannomas, endolymphatic sac tumors, autoimmune disorders of the inner ear). Furthermore, rare causes of AVS (inferior vestibular neuritis, otolith organ specific dysfunction, vascular labyrinthine disorders, acute bilateral vestibulopathy) and CVS (chronic bilateral vestibulopathy) are covered. In each case, special emphasis is laid on the decisive diagnostic test for the identification of the rare disease and "red flags" for potentially dangerous disorders (e. g. labyrinthine infarction/hemorrhage). Thus, this chapter may serve as a clinical companion for the otorhinolaryngologist aiding in the efficient diagnosis and treatment of rare disorders of the vestibular labyrinth.

Children with posterior semicircular canal dehiscence: A case series

Posterior semicircular canal dehiscence is a rare condition and can cause a variety of symptoms. We report three cases of children between 5 and 12 years of age with a PSCD. They all presented with different complaints as follows: Tullio phenomenon in the first case, conductive hearing loss in the second and, conductive hearing loss and pulsatile tinnitus in the third. Imaging showed in all cases a PSCD on the right side, caused by a prominent jugular bulb (high riding bulb). We describe the clinical, audiometric and radiological findings, and discuss the management and therapy. A conservative "wait and see" approach is recommended, especially with children, because of the possible complications of surgery and the possibility that the symptoms will lessen with the skull base osseous maturation.

Posterior semicircular canal dehiscence: a diagnostic and surgical conundrum

Third window defects have increasingly been identified as a cause of vertigo. These defects are bony dehiscences that occur in the bony labyrinth, resulting in abnormal pressure gradient in the inner ear fluids leading to sound (Tullio's phenomenon) or pressure (Hennebert's sign) induced vertigo. The superior semicircular canal dehiscence syndrome is a well-described entity in this regard, however defects of the posterior semicircular canal are rare and may have overlapping symptomatology. We describe the history, clinical profile and management of a patient who had importunate symptoms despite being on conservative management for a year and had resolution of vestibular symptoms following surgical management.

Recent surgical options for vestibular vertigo

Vertigo is not a well-defined disease but a symptom that can occur in heterogeneous entities diagnosed and treated mainly by otolaryngologists, neurologists, internal medicine, and primary care physicians. Most vertigo syndromes have a good prognosis and management is predominantly conservative, whereas the need for surgical therapy is rare, but for a subset of patients often the only remaining option. In this paper, we describe and discuss different surgical therapy options for hydropic inner ear diseases, Menière's disease, dehiscence syndromes, perilymph fistulas, and benign paroxysmal positional vertigo. At the end, we shortly introduce the most recent developments in regard to vestibular implants. Surgical therapy is still indicated for vestibular disease in selected patients nowadays when conservative options did not reduce symptoms and patients are still suffering. Success depends on the correct diagnosis and choosing among different procedures the ones going along with an adequate patient selection. With regard to the invasiveness and the possible risks due to surgery, in depth individual counseling is absolutely necessary. Ablative and destructive surgical procedures usually achieve a successful vertigo control, but are associated with a high risk for hearing loss. Therefore, residual hearing has to be included in the decision making process for surgical therapy.

The Efficacy of Magnetic Resonance Imaging for the Diagnosis of Superior Semicircular Canal Dehiscence

OBJECTIVE

This study aimed to evaluate the efficacy of magnetic resonance imaging (MRI) for diagnosing superior semicircular canal dehiscence (SSCD).

MATERIALS AND METHODS

The radiological records of patients who were admitted to our clinic with complaints of otologic and neuro-otologic symptoms between October 2014 and December 2015 were retrospectively reviewed. Among these patients, those who underwent both computed tomography and MRI and were reported to have SSCD in the temporal bone on at least one side were included in the study group. MRI records of patients with a confirmed diagnosis were then assessed for the presence of SSCD.

RESULTS

The left and right semicircular canals of 52 patients were evaluated in this study. The sensitivity and specificity of MRI in the diagnosis of SSCD was 89.06% and 90%, respectively. The positive and negative predictive values were 93.44% and 83.72%, respectively.

CONCLUSION

The use of multiplanar reformats and angulation techniques during MRI assessment of patients with neuro-otologic symptoms can improve the diagnostic process for patients with SSCD. This may allow early diagnosis of the disease by using just one imaging method, which would also reduce the costs per patient during the diagnosis period.

CDH23 Related Hearing Loss: A New Genetic Risk Factor for Semicircular Canal Dehiscence?

OBJECTIVE

To investigate the prevalence and relative risk of semicircular canal dehiscence (SCD) in pediatric patients with CDH23 pathogenic variants (Usher syndrome or non-syndromic deafness) compared with age-matched controls.

STUDY DESIGN

Retrospective cohort study.

SETTING

Multi-institutional study.

PATIENTS

Pediatric patients (ages 0-5 years) were compared based on the presence of biallelic pathogenic variants in CDH23 with pediatric controls who underwent computed tomography (CT) temporal bone scan for alternative purposes.

INTERVENTIONS

Retrospective review of diagnostic high resolution CT temporal bone scans and magnetic resonance imaging (MRI) for evaluation of SCD.

MAIN OUTCOME MEASURES

Superior and posterior semicircular canals were evaluated by a neuroradiologist for presence of SCD or abnormal development.

RESULTS

Forty-two CT scans were reviewed for SCD. Eighty-six percent of the CDH23 variant group had abnormalities in at least one canal compared with only 12% in age-matched controls. In the CDH23 variant group there were four patients with superior SCD (57%, RR = 10.0) and three patients with posterior canal abnormalities (43%, RR = 7.5) compared with two, and two patients, respectively, in the control population. Four CDH23 variant children had bilateral abnormalities. One child had thinning or dehiscence in both the superior and posterior canals. Relative risk of SCD in children with CDH23 pathogenic variants is 7.5 (p < 0.001) compared with the pediatric control population.

CONCLUSIONS

Children with a CDH23 pathogenic variants are at significantly increased risk of having SCD and this may be a contributing factor to the vestibular dysfunction in Usher syndrome type 1D patient population.

Semicircular canal dehiscence among idiopathic intracranial hypertension patients

OBJECTIVES/HYPOTHESIS

The cause of superior semicircular canal dehiscence (SSCD) is unknown. Because of a demonstrated association with tegmental defects and obesity, some have suggested idiopathic intracranial hypertension (IIH) could contribute by eroding the bone over the canal and resulting in SSCD. However, an association between IIH and SSCD has not previously been evaluated. Our objective was to evaluate an association between IIH and SSCD.

STUDY DESIGN

Retrospective cohort.

METHODS

A retrospective study was performed of opening pressures for consecutive patients presenting at a lumbar puncture clinic between August 2012 and October 2015. Imaging for patients who also had thin-sectioned computed tomography (CT) imaging was reviewed for the presence of radiographic SSCD. Association between IIH and SSCD was evaluated using the Student t test and multivariate logistic regression.

RESULTS

One hundred twenty-one patients had both a lumbar puncture performed and thin-sectioned CT imaging available, of which 24 patients (19.8%) met the criteria for IIH with an opening pressure >25 cm H₂ O. The remaining 97 patients (80.2%) did not have elevated opening pressures and served as the control cohort. None of the 24 patients with IIH had radiographic SSCD, whereas eight of the 97 patients (8.2%) without IIH had radiographic SSCD. The average opening pressure in patients without radiographic SSCD was 20.2 cm H₂ O compared to 19.3 cm H₂ O in patients with radiographic SSCD (P = .521). In multivariate logistic regression controlling for age, body mass index, gender, and comorbidities (hypertension, diabetes, hyperlipidemia), opening pressure was not a significant predictor of radiographic SSCD.

CONCLUSIONS

The results of this retrospective pilot study do not suggest an association between IIH and SSCD.

LEVEL OF EVIDENCE

3b. Laryngoscope, 128:1196-1199, 2018.

Influence of Sex and Age on Posterior Semicircular Canal Thickness

OBJECTIVE

The aim of this study is to determine whether sex and age influence posterior semicircular canal (PSC) thickness.

METHODS

This observational study was conducted in 3 tertiary hospitals. The minimal distance between the PSC and the posterior cranial fossa (PSC thickness) was estimated by thin-section multidetector row computed axial tomography (CAT) scan of the temporal bones. Nonselected consecutive patients of all ages (607 temporal bones) were considered.

RESULTS

A significant effect was only detected for sex (F = 5.418, p = 0.020); PSC thickness showed a higher mean value in women (mean difference ± SE: 0.224 ± 0.096 mm). A significant and negative r value was detected for males aged >45 years (-0.173, p = 0.026); in that group of patients, PSC thickness decreased as age increased (0.018 ± 0.008 mm/year). For females aged ≤45 years, a significant and positive r value was found (0.198, p = 0.022); in that group, PSC thickness increased as age increased (0.020 ± 0.008 mm/year).

CONCLUSIONS

PSC thickness did not significantly evolve with age in young males (≤45 years) but it decreased from age 45 years onwards. On the other hand, PCS thickness increased with age in women until the age of 45 years and it did not significantly change in older females.

Superior semicircular canal dehiscence syndrome

Superior semicircular canal dehiscence (SSCD) syndrome is an increasingly recognized cause of vestibular and/or auditory symptoms in both adults and children. These symptoms are believed to result from the presence of a pathological mobile "third window" into the labyrinth due to deficiency in the osseous shell, leading to inadvertent hydroacoustic transmissions through the cochlea and labyrinth. The most common bony defect of the superior canal is found over the arcuate eminence, with rare cases involving the posteromedial limb of the superior canal associated with the superior petrosal sinus. Operative intervention is indicated for intractable or debilitating symptoms that persist despite conservative management and vestibular sedation. Surgical repair can be accomplished by reconstruction or plugging of the bony defect or reinforcement of the round window through a variety of operative approaches. The authors review the etiology, pathophysiology, presentation, diagnosis, surgical options, and outcomes in the treatment of this entity, with a focus on potential pitfalls that may be encountered during clinical management.

Otologic disorders causing dizziness, including surgery for vestibular disorders

This chapter will focus on vertigo/dizziness due to inner-ear malformations, labyrinthine fistula, otosclerosis, infectious processes, and autoimmune inner-ear disorders. Inner-ear malformation due to dehiscence of the superior semicircular canal is the most recently described inner-ear malformation. Vertigo/dizziness is typically induced by sound and pressure stimuli and can be associated with auditory symptoms (conductive or mixed hearing loss). Labyrinthine fistula, except after surgery for otosclerosis, in the context of trauma or chronic otitis media with cholesteatoma, still remains a challenging disorder due to multiple uncertainties regarding diagnostic and management strategies. Otosclerosis typically manifests with auditory symptoms and conductive or mixed hearing loss on audiometry. Vertigo/dizziness is rare in nonoperated otosclerosis and should draw clinical attention to an inner-ear malformation. Computed tomography scan confirms otosclerosis in most cases and should rule out an inner-ear malformation, avoiding needless middle-ear surgical exploration. Labyrinth involvement after an infectious process is unilateral when it complicates a middle-ear infection but can be bilateral after meningitis. Labyrinth involvement due to an inflammatory disease is a challenging issue, particularly when restricted to the inner ear. The diagnosis relies on the bilateral and rapid aggravation of audiovestibular symptoms that will not respond to conventional therapy but to immunosuppressive drugs.

Imaging Review of the Temporal Bone: Part II. Traumatic, Postoperative, and Noninflammatory Nonneoplastic Conditions

The first part of this review of the temporal bone discussed anatomy of the temporal bone as well as inflammatory and neoplastic processes in the temporal bone region (1). This second part will first discuss trauma to the temporal bone and posttraumatic complications. The indications for common surgical procedures performed in the temporal bone and their postoperative imaging appearance are then presented. Finally, a few noninflammatory nonneoplastic entities involving the temporal bone are reviewed. They are relatively uncommon diagnoses compared with infectious or inflammatory diseases. However, because patients present with symptoms that are either common (hearing loss) or distinctive (sensorineural hearing loss in a child), they are important for the radiologist to be aware of and recognize.

Comparison of digital volume tomography and high-resolution computed tomography in detecting superior semicircular canal dehiscence--a temporal bone study

CONCLUSION

In detecting a thin bony coverage of a superior semicircular canal (SSC), digital volume tomography (DVT) scans in Poeschl projection seem to be superior to high-resolution computed tomography (CT) scans. Still, a definite diagnosis of SSC dehiscence (SSCD) is not possible with any radiologic imaging technique.

OBJECTIVE

To compare CT and DVT to find out whether DVT is equal, better or worse in showing a thin bony layer on top of an SCC.

METHODS

In 11 human temporal bone specimens, the SSC was microscopically blue-lined leaving a thin bony coverage on top of it. All specimens were assessed with both high-resolution CT and DVT. After reconstructing the images in Stenvers and Poeschl projections, all images were evaluated by five independent examiners experienced in radiologic imaging of the temporal bone using a four-point ordinal scale, from 1 (distinct dehiscence) to 4 (distinct coverage).

RESULTS

The mean score for all CT scans was 2.58 compared with 3.22 for DVT scans (p = 0.000). Poeschl projection showed a mean score of 3.25 compared with 2.55 for Stenvers projection (p = 0.000). The best imaging modality was found to be DVT scans in Poeschl projections, with a mean score of 3.60.

Quantification of hearing loss in patients with posterior semicircular canal dehiscence

CONCLUSION

Patients with posterior semicircular canal dehiscence (PSCD) have low frequency conductive hearing loss similar to patients with superior semicircular canal dehiscence (SSCD) secondary to a pathologic third window.

OBJECTIVES

PSCD can result in conductive hearing loss, but the magnitude of this hearing loss remains to be quantified. Patients with SSCD have been shown to have low frequency conductive hearing loss. The underlying pathophysiology of hearing loss from PSCD and SSCD is similar and related to a pathologic third window.

METHOD

A PubMed search was completed for a meta-analysis of patients with PSCD. Articles with quality audiograms were obtained. Air conduction thresholds for ears with posterior semicircular canal dehiscence were compared to the opposite ear as well as normal control data.

RESULTS

Eight articles with 21 patients with PSCD and quality audiograms were included. Two patients had bilateral PSCD and one of those was excluded because hearing thresholds were at the limit of the audiometer. Patients with posterior semicircular canal dehiscence have statistically significant lower air conduction thresholds in frequencies at and below 2000 Hz.

On the biological plausibility of Wind Turbine Syndrome

An emerging environmental health issue relates to potential ill-effects of wind turbine noise. There have been numerous suggestions that the low-frequency acoustic components in wind turbine signals can cause symptoms associated with vestibular system disorders, namely vertigo, nausea, and nystagmus. This constellation of symptoms has been labeled as Wind Turbine Syndrome, and has been identified in case studies of individuals living close to wind farms. This review discusses whether it is biologically plausible for the turbine noise to stimulate the vestibular parts of the inner ear and, by extension, cause Wind Turbine Syndrome. We consider the sound levels that can activate the semicircular canals or otolith end organs in normal subjects, as well as in those with preexisting conditions known to lower vestibular threshold to sound stimulation.