Differentiating Fistula and SSCD via Pressure Testing

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Answer

In the pressure (fistula) testing, superior semicircular canal dehiscence syndrome (SSCD) generates nystagmus in the plane of vertical canals that is synchronized with the pressure change. That is, the nystagmus has torsional and vertical components. Depending on the direction of cupular deflection, the response can be excitatory or inhibitory. Typically, positive pressure generates excitatory responses resulting in torsional nystagmus with fast phases directed toward the pressurized ear and vertical nystagmus with fast phases beating downward. Negative pressure usually generates inhibitory responses resulting in torsional nystagmus with fast phases directed away from the pressurized ear and vertical nystagmus with fast phases beating upward.

Perilymphatic fistulas typically generate horizontal nystagmus that is synchronized with the pressure change. However, absence of nystagmus in the pressure test does not rule out presence of perilymph fistulas.

Kamran Barin, Ph.D. is the Director of Balance Disorders Clinic at the Ohio State University Medical Center and Assistant Professor, Department of Otolaryngology, Department of Speech and Hearing Sciences, and Biomedical Engineering Program. He received his Master's and Doctorate degrees in Electrical/Biomedical Engineering from The Ohio State University. He has taught national and international courses and seminars in different areas of vestibular assessment and rehabilitation. He has served on NIH and NASA panels and was an appointed member of the Equilibrium Subcommittee of the American Neurotology Society. He works as a consultant to GN Otometrics and provides courses and other educational material to the company.