Testing the Diagnostic Value of Electrical Ear Canal Stimulation in Cochlear Implant Candidates by Functional Magnetic Resonance Imaging

Abstract

Prior to cochlear implant (CI) surgery in children, the integrity of the auditory pathway is sometimes assessed by electrical ear canal stimulation (ECS). However, the evaluation of reactions as auditory is subjective. To test the prognostic value of ECS, functional magnetic resonance imaging (fMRI) was performed during ECS vicariously in 18 adult CI candidates. Activation of the primary auditory cortex was detected in 9 of 16 cases when auditory sensations during ECS occurred, and tended to be more bilaterally distributed in CI candidates than in normal-hearing controls. ECS sensations only tended to correlate with fMRI activations. However, solely frequency discrimination during electrical stimulation predicted CI outcome, but neither other auditory sensations nor fMRI activations did so satisfactorily, which limits the diagnostic value of these measures. Instead, preoperative residual hearing (nonamplified and amplified) was a robust predictor for CI benefit.

Evaluation of temporal difference limen in preoperative non-invasive ear canal audiometry as a predictive factor for speech perception after cochlear implantation

“…This is in line with earlier results. 5 , 7 A possible limitation in the current study is the use of open-set bisyllabic word recognition test in quiet as a marker for speech perception and CI outcome in general. Other audiological tests, such as nonsense syllable, word, phrase or sentence tests, might de more appropriate in judging speech perception after cochlear implantation, but the open-set bisyllabic word recognition test is currently the only validated speech perception test in Finnish language, and thus used in this retrospective chart analysis.…”

“…6 While this method is noninvasive and can be used with children, its predictive value has thus far been insufficiently documented. In EECS measurements of CI candidates Neumann et al 7 found postoperative speech recognition to correlate with frequency differentation but not with other measured variables [sensations, threshold level, temporal difference limen (TDL), dynamic range]. Takanami et al 8 used EECS successfully in awake child patients with inner ear anomaly to demonstrate electroneural hearing before cochlear implantation.…”