PP502 - Clinical Application of Electrocochleography in Superior Semicircular Canal Dehiscence Syndrome

Abstract:
This case presentation summarizes electrocochleography (EcochG) diagnostic and intraoperative utility in a patient with superior semicircular canal dehiscence syndrome (SSCD). When initially presenting to our clinic, this patient was experiencing daily dizziness described as lightheadedness, unsteadiness, and a floating sensation. Additional symptoms included left-sided aural fullness, facial pressure/numbness, and ear pain. Baseline EcochG testing indicated an elevated SP/AP ratio in the left ear. The patient successfully underwent a left SSCD plugging and resurfacing via middle cranial fossa. Continuous intraoperative EcochG recordings revealed that the SP/AP ratio returned within a normal range post-SSCD repair.

Summary:
EcochG is a test of electrical activity generated by the cochlea and vestibulocochlear nerve (CN VIII). The three components of an EcochG include the cochlear microphonic (CM), summating potential (SP), and action potential (AP). Traditionally, the most common clinical utility of EcochG has been to aid in the diagnosis of Meniere’s disease, as elevated SP/AP ratios may reflect the presence of increased labyrinthine pressure. However, emerging research has suggested that an elevated SP/AP ratio seems to be a consistent finding with other conditions causing displacement of the basilar membrane such as SSCD (Rosowski et al. 2004), which decreases after surgical intervention. A literature review on PubMed using the keywords “electrocochleography and superior semicircular canal dehiscence” yielded only 27 articles suggesting that research regarding this topic is scarce. Using EcochG in patients with SSCD is uncommon but can benefit the diagnosis and intraoperative monitoring during surgical repair.

A 46-year-old female (SM) initially presented to Cleveland Clinic in July 2021 for an evaluation of dizziness. She reported daily dizziness for 3-4 months, which was exacerbated by any head movement and accompanied by a headache. Additional symptoms included numbness in the left side of her head, left ear pressure, left facial pressure, and left ear pain. SM was referred for audiologic and vestibular testing. Audiogram was completed and revealed normal tympanometry and hearing sensitivity within normal limits in both ears. Vestibular testing was completed and suggested possible SSCD in the left ear given positive cervical and ocular vestibular evoked myogenic potential (VEMP) responses in the left ear. SSCD was confirmed in both ears via neuroimaging (CT temporal bone). However, the patient was only symptomatic on the left side. SM was seen for a baseline EcochG in May 2022, which revealed an elevated SP/AP ratio in the left ear and normal SP/AP ratio in the right ear. She underwent surgical repair of her SSCD in the left ear via middle cranial fossa, and a sample of 45 EcochG waveforms was collected post-incision/drilling, during fenestration/packing, and following closure. The SP/AP ratio was maintained throughout the procedure with a shifting in ratio values, as expected. Post-repair indicated a significantly improved averaged ratio compared to baseline.

This clinical poster will highlight best practices in recording EcochG results, both as outpatient and in the operating room. Methodology, including patient setup, electrode montage, protocols, and raw data waveforms will be included and outlined in detail on the poster.

References:
Rosowski, J. J., Songer, J. E., Nakajima, H. H., Brinsko, K. M., & Merchant, S. N. (2004). Clinical, experimental and theoretical investigations of the effect of superior semicircular canal dehiscence on hearing mechanisms. Otology & Neurotology, 25, 323–332.