Sept 2020 The Hearing Journal

Few cochlear implant users require revision cochlear implantation (CI) to correct device failures, with the number of cases ranging from four to 11 percent. As more people with hearing loss adopt cochlear implants as a result of expanded implantation criteria and better insurance coverage for these devices, however, the number of revision CI cases will also increase, an observation that Marc Bennett, MD, an associate professor of otolaryngology at Vanderbilt University Medical Center, made in his work and motivated him to study the outcomes of revision cochlear implantation.

“We have seen increasing numbers of failures over the last couple of years,” Bennett said. “We also want to look and try to distinguish between those patients who actually have an electronic or mechanical failure of the implant versus those with just declining performance over time.”

One way to better understand and identify those who will benefit from revision CI surgery is by characterizing the types of failures that warrant revision surgery and quantifying the improvement associated with each type of failure after the surgery. Dr. Bennett and his colleagues came up with three categories of failures in their research: hard failures, medical or surgical failures, and soft failures. Hard failures, the most common reason for revision surgery in their study, are marked by intermittent or no communication between the speech processor and internal device or failed device integrity testing, while medical or surgical failures involve surgical site infection, incision breakdown, allergic reaction, or migration of electrode array. Soft failures refer to cases with poor post-implant audiologic performance, such as low speech perception scores, or subjective adverse symptoms like headache and facial nerve stimulation. This type of failure is confirmed by the return of function or resolution of adverse symptoms after revision surgery.

Bennett and his colleagues also described a new subcategory of soft failures called presumed soft failures in their study. Presumed soft failures are initially thought to meet the criteria of soft failures, but those with presumed soft failures do not experience improvement in audiologic outcome or adverse symptoms after revision surgery. “This group is unique, and needs to be studied in greater depths to understand why some patients do not improve as much as would expect with revision surgery,” said Bennett.

Those with hard failures, which made up 53.1 percent of the 64 revision CI surgeries included in the study, experienced the greatest improvement following revision surgery, which is defined as 15 percent improvement in speech perception scores and improvement of aversive symptoms, according to the 2005 cochlear implant soft failures consensus statement. The medical or surgical failure group, which accounted for 17.2 percent of all revision surgeries, also saw excellent outcomes, but the soft failure cohort, which consisted of 29.7 percent of all revision surgeries, had the lowest rate of performance improvement.

These results were not surprising to the researchers. When they looked across all the patient's data, they knew those experiencing a mechanical failure with an implant that has stopped functioning well would improve with reimplantation because it was simply a question of getting the electrical connections back in place, Bennett said. “There were those with soft failures that had a normal-appearing implant in the past and a normal integrity test,” he said. “For those patients, we do not understand why the performance is declined, and it is only logical that they would not improve as much as those with broken implants after revision surgery as there is likely some sort of internal damage to the inner ear, the nerves, and neurons in some manner that is causing this decline in performance.”

Bennett said what makes this study unique is their description of and findings regarding presumed soft failures. “We have broken out a group of patients with soft failures that did not respond to reimplantation,” he said. “We need to study this group at length to figure out why they are not improving as much as the normal patient so that we can offer percentages and give patients a realistic predictor of their performance improvement after reimplantation.”

Their findings have implications on how audiologists can help CI users experiencing different types of failures, especially presumed soft failures. “Personally, I think audiologists and ear surgeons need to work together to help continually improve outcomes,” he said. “If we can identify these patients with soft failures who will not improve, we need to figure out other ways to treat them to maximize the performance as opposed to revision surgery.”

Figuring out the best way to improve the outcomes of those suffering from presumed soft failures isn't the only area that requires more investigation when it comes to revision cochlear implantation, however. “I think it is important that we look nationally at the rate of failures across the country,” said Bennett. “The reports of revision surgery very widely, and until we all have a grasp over what these actual numbers are, we are reliant on the implant companies to tell us what their success rates are with their own implants. And it may be time to move towards more objective data and national records to show how durable and reliable each of the implants is.

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