Prediction of Cochlear Implant Outcomes Possible by Assessing Auditory Nerve Condition

A study has found that the condition of the auditory nerve in patients with severe hearing loss can predict the outcomes of cochlear implant surgery.

This research was published in the recent issue of the official journal of the American Otological Society, Otology & Neurotology. Professor Hongjoo Park’s team from the Department of Otorhinolaryngology at Seoul Asan Medical Center conducted a long-term follow-up of over 7 years on auditory function development after cochlear implant surgery in 42 pediatric patients with inner ear malformations. The subjects were diagnosed with severe hearing loss due to Mondini dysplasia (incomplete development of the cochlea) and had received cochlear implants between 1994 and 2013.

Goseong Auditory Canal CT Scan Image

Analysis of the patients’ ear computed tomography (CT) scans revealed that four ears had a narrow bony cochlear nerve canal (the passageway for the auditory nerve bundle). These patients showed poorer auditory function and less favorable cochlear implant outcomes compared to those with normal canal widths.

In the Word Recognition Score (WRS) test, which measures how well patients can distinguish spoken words, patients with a narrow bony cochlear nerve canal had an average accuracy of 58%, whereas those with normal canal widths averaged 79% accuracy.

Similar to the bony cochlear nerve canal width, the maximum diameter of the auditory nerve was also closely correlated with auditory function after cochlear implantation. Patients with a thicker auditory nerve on magnetic resonance imaging (MRI) demonstrated higher speech discrimination accuracy than those without.

Meanwhile, in a control group of 86 pediatric patients with normal inner ears but hearing impairment who received cochlear implants, the average speech discrimination accuracy was found to be 77%. This led the research team to confirm that even with inner ear malformations, if the auditory nerve is well preserved, the improvement in auditory ability is comparable to that of implant recipients with normal inner ears.

Professor Hongjoo Park of the Department of Otorhinolaryngology at Seoul Asan Medical Center stated, “Our previous research showed that adult patients with severe hearing loss, to the extent that hearing aids are ineffective, experienced progressive auditory nerve degeneration and poor cochlear implant outcomes if auditory rehabilitation was neglected for a long time.” He added, “This study confirms that in children as well, the condition of the auditory nerve can predict cochlear implant outcomes, which will help many hearing-impaired patients make informed decisions about surgery.” He continued, “Recently, pediatric hearing loss is being diagnosed early through newborn screening, and cochlear implantation leads to nearly normal auditory and language development. Therefore, if diagnosed with hearing loss, it is important to consult a specialist and initiate appropriate treatment early.”

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