eMedicine Specialties > Otolaryngology and Facial Plastic Surgery > Inner Ear

Superior Canal Dehiscence: Differential Diagnoses & Workup

Author: Wayne T Shaia, MD, Consulting Staff, Department of Otology/Neurotology, Medical College of Virginia
Coauthor(s): Jack M Kartush, MD, Clinical Professor, Department of Otolaryngology, Wayne State University; Director of Otology, Neurotology, and Skull Base Surgery, Providence Hospital; President, Michigan Ear Institute; President, American NeuroMonitoring
Contributor Information and Disclosures

Updated: Sep 2, 2009

Differential Diagnoses

Benign Paroxysmal Positional Vertigo
Inner Ear, Ototoxicity
Inner Ear, Evaluation of Dizziness
Inner Ear, Perilymphatic Fistula
Inner Ear, Labyrinthitis
Middle Ear, Otosclerosis
Inner Ear, Meniere Disease, Medical Treatment
Migraine-Associated Vertigo

Other Problems to Be Considered

Multiple sclerosis
Syphilis

Workup

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).

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. Image 1 displays the typical findings in a patient with SCDS.
  • 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.

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

More on Superior Canal Dehiscence

Overview: Superior Canal Dehiscence
Differential Diagnoses & Workup: Superior Canal Dehiscence
Treatment & Medication: Superior Canal Dehiscence
Follow-up: Superior Canal Dehiscence
Multimedia: Superior Canal Dehiscence
References
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References

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  3. Brantberg K, Verrecchia L. Testing vestibular-evoked myogenic potentials with 90-dB clicks is effective in the diagnosis of superior canal dehiscence syndrome. Audiol Neurootol. Sep 2009;14(1):54-8. [Medline].

  4. White JA, Hughes GB, Ruggieri PN. Vibration-induced nystagmus as an office procedure for the diagnosis of superior semicircular canal dehiscence. Otol Neurotol. Oct 2007;28(7):911-6. [Medline].

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Further Reading

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Keywords

superior canal dehiscence, Hennebert sign, Hennebert's sign, Tullio phenomenon, Tullio's phenomenon, sound-induced vertigo, pressure-induced vertigo, vertigo, dizziness, chronic imbalance, hyperacusis, SCDS, superior canal dehiscence syndrome, vestibular evoked myogenic potentials, VEMPs, hearing loss, dehiscent superior semicircular canal, vestibular symptoms, syphilis, perilymphatic fistula, congenital deafness, Ménière disease, head trauma, Lyme disease, cholesteatomas with labyrinthine fistula, fenestration operations, malpositioned primitive otocyst

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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; Director of Otology, Neurotology, and Skull Base Surgery, Providence Hospital; President, Michigan Ear Institute; President, American NeuroMonitoring
Jack M Kartush, MD 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.

Medical Editor

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.

Pharmacy Editor

Francisco Talavera, PharmD, PhD, Senior Pharmacy Editor, eMedicine
Disclosure: eMedicine Salary Employment

Managing Editor

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: Nothing to disclose.

CME Editor

Christopher L Slack, MD, Otolaryngology-Facial Plastic Surgery, Private Practice, 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 unstricted 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

 
 
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