Reversible electrocochleographic abnormalities in superior canal dehiscence.
OBJECTIVE
Electrocochleography (ECoG) is often used in the evaluation of episodic vertigo, and abnormal findings are commonly thought to be due to endolymphatic hydrops. We have observed that a number of patients with abnormal ECoG were ultimately found to have superior semicircular canal dehiscence (SSCD). Therefore, we examined the electrocochleographic findings in a series of patients with documented SSCD.


METHODS
Retrospective case series.


METHODS
Academic medical center.


METHODS
Seven adult patients with unilateral SSCD and 4 patients with bilateral SSCD who underwent tympanic ECoG as part of a diagnostic or preoperative evaluation that also included vestibular-evoked myogenic potentials (VEMPs).


METHODS
Patients underwent audiometric testing, ECoG, VEMP, and high-resolution temporal bone computed tomography reformatted to optimally view the superior semicircular canal. Five patients underwent superior canal obliteration. Postoperative VEMP and ECoG were performed in 4 of these patients. Intraoperative continuous ECoG was performed in 1 patient.


METHODS
Summating potential to action potential (SP/AP) ratio on ECoG.


RESULTS
Fourteen of 15 ears confirmed to have SSCD on computed tomographic imaging were found to have an elevated SP/AP ratio (defined as >0.40). In one patient with bilateral SSCD, the ear with the radiographically less severe dehiscence had an SP/AP ratio of 0.40, at the upper limit of normal, and a normal VEMP threshold. In all 4 patients who underwent obliteration of the dehiscent canal, and for whom postoperative test results were available, the SP/AP ratio normalized in the operated ear. In the 1 patient who underwent intraoperative ECoG, the SP/AP ratio normalized immediately after canal occlusion.


CONCLUSIONS
An elevated SP/AP ratio seems to be a consistent finding in SSCD syndrome and, like the other abnormal audiometric and electrophysiologic findings associated with the syndrome, normalizes after surgical correction. Elevation of the SP/AP ratio has historically been associated with endolymphatic hydrops. The present findings expand the differential diagnosis of an abnormal ECoG and may shed light on the origin of an elevated summating potential.
Arts
H Alexander
HA
Department of Otolaryngology-Head and Neck Surgery, University of Michigan School of Medicine, Ann Arbor, Michigan 48109-0312, USA. aarts@umich.edu
Adams
Meredith E
ME
Telian
Steven A
SA
El-Kashlan
Hussam
H
Kileny
Paul R
PR
D000328:Adult; D000388:Air; D001299:Audiometry; D001300:Audiometry, Evoked Response / Q000379:methods; D003051:Cochlea / Q000502:physiology* / Q000601:surgery*; D004424:Ear Canal / Q000002:abnormalities* / Q000000981:diagnostic imaging / Q000601:surgery*; D004568:Electrodiagnosis / Q000379:methods; D004594:Electrophysiology / Q000379:methods; D005260:Female; D007839:Functional Laterality; D006801:Humans; D008297:Male; D008875:Middle Aged; D012016:Reference Values; D012189:Retrospective Studies; D013529:Surgical Wound Dehiscence / Q000000981:diagnostic imaging; D014057:Tomography, X-Ray Computed; D014432:Tympanic Membrane / Q000502:physiology