Dehiscences of the semicircular canals as discrete third window lesions of the inner ear

Optimized Diagnostic Approach to Patients Suspected of Superior Semicircular Canal Dehiscence

OBJECTIVES

Current methods of diagnosing superior semicircular canal dehiscence syndrome (SCDS) include a clinical exam, audiometric testing, temporal bone computer tomography (CT) imaging, and vestibular evoked myogenic potential (VEMP) testing. The main objective of this study was to develop an improved diagnostic approach to SCDS optimized for accuracy, efficiency, and safety that utilizes clinical presentation, audiometric testing, CT imaging, high-frequency cervical VEMP (cVEMP) testing, and patient treatment preference. A secondary aim was to investigate the cost associated with the current versus proposed diagnostic paradigms.

DESIGN

All patients who underwent cVEMP testing since introduction of the 2 kHz cVEMP in our clinical protocol in July 2018 were screened. Patients suspected of SCDS based upon symptoms who also had available audiogram, CT scan, and 2 kHz cVEMP were included (58 ears). Patients were categorized as dehiscent, thin, or not dehiscent based on their CT scan. Symptom prevalence and cVEMP outcomes were analyzed and compared for all groups. The accuracy of the 2 kHz cVEMP was calculated using CT imaging as the standard. Using a combination of patient symptomatology, audiometric, CT and 2 kHz cVEMP data, as well as patient preference, a best clinical practice approach was developed. The cost associated with this approach was calculated and compared with cost of the current SCDS diagnostic workup using Medicare reimbursement rates.

RESULTS

In the overall patient population suspected of SCDS based on clinical presentation, the sensitivity and specificity of 2 kHz cVEMP were 76% and 100%, respectively, while the positive and negative predictive values were 100% and 84.6%, assuming that the CT scan finding was correct. Autophony was the most common symptom in patients who had both superior semicircular canal dehiscence on CT imaging plus abnormal 2 kHz cVEMP (p < 0.001). Combining patient symptomatology, 2 kHz normalized peak to peak cVEMP amplitude, and patient treatment preference to determine, which patients should undergo CT scanning resulted in a potential cost reduction between 45% and 61%.

CONCLUSION

In patients suspected of SCDS based on their clinical presentation, the combination of symptomatology, 2 kHz cVEMP data, and patient preference can be used to determine which patients should undergo CT scanning, resulting in a diagnostic cost reduction and reduced patient radiation exposure.

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.