Superior Canal Dehiscence Workup

  • Author: Wayne T Shaia, MD; Chief Editor: Arlen D Meyers, MD, MBA   more...
 
Updated: Sep 30, 2011
 

Laboratory Studies

No specific laboratory studies confirm the diagnosis of superior canal dehiscence syndrome (SCDS). Laboratory tests may be obtained to rule out other pathological causes of vertigo (ie, multiple sclerosis, syphilis).

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Imaging Studies

Imaging studies are critical in the diagnosis of SCDS. A high-resolution computed tomography (HRCT) scan of the temporal bones without contrast is required to make a definitive diagnosis. Views that are oblique to the temporal bone must be obtained with a HRCT scan in order to properly see the superior semicircular canal. The image below displays the typical findings in a patient with SCDS.

Coronal high-resolution computed tomography scan (Coronal high-resolution computed tomography scan (1-mm sections) that demonstrates the presence of the superior semicircular canal (figure A, black arrow). As the scan is followed posteriorly (figures B, C, D), the bony dehiscence over the superior canal (black arrow) becomes more apparent.

Magnetic resonance imaging (MRI) cannot be used to confirm the diagnosis of SCDS; however, it may be of benefit in ruling out a retrocochlear process.

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Other Tests

Audiometric testing

Comprehensive audiometric evaluation is indicated in any patient with vestibular symptoms. In a patient with SCDS, key factors may be revealed. One key is the presence of normal symmetrical hearing, which helps eliminate a retrocochlear process as a cause of vertigo.

Patients with SCDS may have conductive hearing loss. The air-bone gaps are typically greatest at frequencies below 1 kHz.

The conductive hearing loss is believed to be due to the third mobile window of the superior semicircular canal dehiscence, resulting in elevation of thresholds of air-conduction sounds and a reduction of thresholds for bone-conduction sounds.

Acoustic reflex testing is preserved in a patient with SCDS as a cause of conductive hearing loss, as opposed to a loss of the reflex with other conductive or mixed hearing loss conditions such as otosclerosis.

Electronystagmography testing

Routine electronystagmography (ENG) testing reveals no objective or pathognomonic signs of SCDS. All patients with suspicion of the disorder should undergo ENG to further eliminate other potential causes.

Video-oculography can be valuable in recording the vertical and torsional eye movements specific to SCDS.

Caloric test results are usually unaffected in patients with SCDS; however, when the dehiscence is large (>0.5 mm), reduced caloric test results may be demonstrated on the affected side.

Vestibular evoked myogenic potentials

Vestibular evoked myogenic potentials (VEMPs) have recently been suggested to help with the diagnosis of SCDS. The inferior vestibular nerve innervates the saccule, which has some sound sensitivity. The inferior vestibular nerve has its main input to the lateral vestibular nucleus (Deiter nucleus), where the 2 main postural tracts originate. The medial vestibulospinal tract is responsible for postural control of the neck, whereas the lateral vestibulospinal tract is dedicated to the lower trunk and limbs.

For the most part, sound-evoked VEMPs are considered completely unilateral. This test is performed by placing electrodes on the sternocleidomastoid neck muscle. Patients hold their head up unsupported, using only their anterior neck muscles. Patients are instructed to tense the muscle during acoustic stimulation and to relax after the stimulation stops. Loud clicks or tone bursts (95-100 dB nHL) are repeatedly presented to each ear.[3] If the neck muscles are activated at this level, a VEMP is produced.

In patients with SCDS, a response at very low thresholds (< 65 dB) can be noted to produce a VEMP on the affected side. This is thought to occur secondary to the hypercompliance of the vestibular system on the affected sided secondary to the third-window effect. A low-threshold VEMP raises the suspicion of SCDS

Vibration-induced nystagmus

Most recently, patients with known SCDS underwent a series of cranial vibratory tests. A 100 Hz oscillator was placed against the cranium at different places for 10-15 seconds. Nystagmus was digitally recorded by infrared video oculography. All patients demonstrated distinct torsional vibration-induced nystagmus that was especially prominent with suboccipital vibration. Vibration of the suboccipital region and the demonstration of torsional nystagmus is an emerging technique for the diagnosis of SCDS.[4]

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Contributor Information and Disclosures
Author

Wayne T Shaia, MD  Consulting Staff, Department of Otology/Neurotology, Medical College of Virginia

Disclosure: Nothing to disclose.

Coauthor(s)

Jack M Kartush  MD, Clinical Professor, Department of Otolaryngology, Wayne State University School of Medicine; Director of Otology Neurotology and Skull Base Surgery, Providence Hospital; President, Michigan Ear Institute; President, American NeuroMonitoring

Jack M Kartush is a member of the following medical societies: American Academy of Otolaryngology-Head and Neck Surgery, American Neurotology Society, and American Otological Society

Disclosure: Nothing to disclose.

Angela Shu-Yuen Peng, MD  Resident Physician, Department of Otolaryngology/Head and Neck Surgery, Virginia Commonwealth University Medical Center

Angela Shu-Yuen Peng, MD is a member of the following medical societies: American Academy of Otolaryngology-Head and Neck Surgery, American Medical Association, and Virginia Society of Otolaryngology-Head and Neck Surgery

Disclosure: Nothing to disclose.

Specialty Editor Board

Robert A Battista, MD, FACS  Assistant Professor of Otolaryngology, Northwestern University Medical School; Physician, Ear Institute of Chicago, LLC

Robert A Battista, MD, FACS is a member of the following medical societies: American Academy of Otolaryngology-Head and Neck Surgery, American College of Surgeons, American Neurotology Society, and Illinois State Medical Society

Disclosure: Nothing to disclose.

Francisco Talavera, PharmD, PhD  Adjunct Assistant Professor, University of Nebraska Medical Center College of Pharmacy; Editor-in-Chief, Medscape Drug Reference

Disclosure: Medscape Salary Employment

Gerard J Gianoli, MD  Clinical Associate Professor, Department of Otolaryngology-Head and Neck Surgery, Tulane University School of Medicine; Vice President, The Ear and Balance Institute; Chief Executive Officer, Ponchartrain Surgery Center

Gerard J Gianoli, MD is a member of the following medical societies: American Academy of Otolaryngology-Head and Neck Surgery, American College of Surgeons, American Neurotology Society, American Otological Society, Society of University Otolaryngologists-Head and Neck Surgeons, and Triological Society

Disclosure: Vesticon, Inc. None Board membership

Christopher L Slack, MD  Private Practice in Otolaryngology and Facial Plastic Surgery, Associated Coastal ENT; Medical Director, Treasure Coast Sleep Disorders

Christopher L Slack, MD is a member of the following medical societies: Alpha Omega Alpha, American Academy of Facial Plastic and Reconstructive Surgery, American Academy of Otolaryngology-Head and Neck Surgery, and American Medical Association

Disclosure: Nothing to disclose.

Chief Editor

Arlen D Meyers, MD, MBA  Professor, Department of Otolaryngology-Head and Neck Surgery, University of Colorado School of Medicine

Arlen D Meyers, MD, MBA is a member of the following medical societies: American Academy of Facial Plastic and Reconstructive Surgery, American Academy of Otolaryngology-Head and Neck Surgery, and American Head and Neck Society

Disclosure: Covidien Corp Consulting fee Consulting; US Tobacco Corporation Unrestricted gift Unknown; Axis Three Corporation Ownership interest Consulting; Omni Biosciences Ownership interest Consulting; Sentegra Ownership interest Board membership; Syndicom Ownership interest Consulting; Oxlo Consulting; Medvoy Ownership interest Management position; Cerescan Imaging Honoraria Consulting; GYRUS ACMI Honoraria Consulting

References

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Coronal high-resolution computed tomography scan (1-mm sections) that demonstrates the presence of the superior semicircular canal (figure A, black arrow). As the scan is followed posteriorly (figures B, C, D), the bony dehiscence over the superior canal (black arrow) becomes more apparent.
 
 
 
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