Electrocochleography summating potential seen on auditory brainstem response in a case of superior semicircular canal dehiscence

Abstract

Background:Superior canal dehiscence syndrome (SCDS) is a condition in which an abnormal communication between the superior semicircular canal and the middle cranial fossa causes patients to hear internal noises transmitted loudly to their affected ear as well as to experience vertigo with pressure changes or loud sounds. Patients with SCDS can have an elevated ratio of summating potential (SP) to action potential (AP) as measured by electrocochleography (ECochG). Changes in this ratio have been observed during surgical intervention to correct this abnormal communication.Case Description:We present a case of SCDS along with history, physical examination, vestibular function testing, and computed tomography imaging. Due to the disabling symptoms, the patient elected to undergo surgery for plugging of the superior semicircular canal by middle cranial fossa approach. Simultaneous intraoperative ECochG and auditory brainstem response (ABR) were performed. Changes in SP/AP ratio, SP amplitude, and ABR wave I latency were observed during surgery, with a large ECochG SP amplitude generating a new wave, identifiable on the ABR and preceding the traditional wave I. The patient's symptoms resolved after surgery, and no long-term detriment to hearing was observed.Conclusions:This case demonstrates the intraoperative changes in ECochG during surgery for repair of a SCDS. The substantial intraoperative changes in the summating potential can create a novel wave on intraoperative ABR.

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“…ECochG may also be applied for intraoperative monitoring during SCD surgery. After successful closure of the dehiscence, the pathognomonic electrophysiological findings - such as SP/AP ratio, VEMP amplitudes and thresholds – normalize, thus indicating successful closure of the dehiscence and recovery of inner ear fluid dynamics 12 175 176 .…”

“…Die ECochG lässt sich auch zum intraoperativen Monitoring einsetzen. Nach erfolgreichem Verschluss einer SCD normalisieren sich die auffälligen neurophysiologischen Befunde, wie der SP/AP-Quotient 175 176 und die VEMPs 12 .…”

“…Die ECochG lässt sich auch zum intraoperativen Monitoring einsetzen. Nach erfolgreichem Verschluss einer SCD normalisieren sich die auffälligen neurophysiologischen Befunde, wie der SP/AP-Quotient[175,176] und die VEMPs[12].3.2.2.3 BildgebungAls Goldstandard gilt hier das hochauflösende Schläfenbein-CT (high resolution computed tomography, HRCT) mit Schichtdicken von ≤ 0,625 mm und Rekonstruktion in der Pöschl-Ebene (senkrecht zur Längsachse des Felsenbeins, d. h. in der Ebene des oberen Bogenganges) und der Stenvers-Ebene (senkrecht zur Pöschl-Ebene)[130]. Inzwischen wird die digitale Volumentomographie (DVT)/Cone beam Tomografie (CBT) als mindestens gleichwertig zum HRCT in der SCD-Diagnostik angesehen: die Strahlendosis ist im Vergleich zum HRCT geringer, die Auflösung besser und die Kosten niedriger[177,178].Stark T2-gewichtete MRT-Aufnahmen (z. B.…”