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Innovation in Cochlear Impant Surgery
From: ENT Today, August 2012
by David Bronstein
Twenty years ago, the use of bilateral implants would have headlined any conference on innovations in cochlear implantation. Today, the procedure has become routine for children and adults. Here’s a look at procedures that now represent the cutting edge of cochlear implant (CI) surgery.
There are several candidates for top billing, but one of the more exciting advances involves hybrid implants and techniques that preserve residual hearing, according to Bruce Gantz, MD, professor and head of the department of otolaryngology-head and neck surgery at the University of Iowa Hospitals and Clinics in Iowa City.
“It isn’t all that long ago that implanting a cochlea of a patient with residual hearing would have been unthinkable,” said Dr. Gantz. That’s the case, he noted, because standard-length cochlear implant electrodes that extend more than 20 mm into the scala tympani can obliterate key structures and almost wipe out residual hearing (Acta Otolaryngol. 2004;124:272-280). Although “soft surgery” techniques with the standard-length electrode implants can prevent some of that damage (Otol Neurotol. 2006;27:1083-1088), Dr. Gantz noted, shorter-length hybrid devices offer a dual benefit: They preserve residual hearing in adults and children, while also sparing cells in the organ of Corti, which preliminary studies have shown may respond to future advances in molecular or genetic treatments of the inner ear (Nature. 2006;441:984-987).
—Craig A. Buchman, MD
“I realize the latter benefit is somewhat theoretical,” Dr. Gantz said. “And it’s most relevant to younger patients who have decades of life ahead, where they can eventually benefit from these advances. But our studies also have shown that significant clinical benefits are accruing now—in both young and older patients—who we’ve implanted with the hybrid device.”
A more recent study by Dr. Gantz and colleagues in profoundly deaf children (Otol Neurotol. 2010;31(8):1300-1309) evaluated another short-electrode (10 mm) device, the Nucleus Hybrid S12, which employs 10 active stimulating electrodes versus the six in the Hybrid S device used in the multicenter FDA trial. In the newer study, patients were implanted with the Nucleus S12 in one ear and a standard-length cochlear implant in the other ear. The results showed that both implants provide similar speech perception scores when tested separately, Dr. Gantz noted. “These results suggest that the brain can accommodate for a shorter, less damaging electrode with only 10 electrodes implanted into the base of the cochlea,” he said.
The results, he added, again point to an important benefit with this approach: “Preservation of supporting cells in the organ of Corti could be important for hair-cell regeneration in the future during the lifetime of the children we are implanting today.”
Other advances include a version of the hybrid device that employs a slightly longer electrode (Hybrid L24) than the Hybrid S (16 vs. 10 mm) but also includes more than double the number of electrodes implanted. “The benefit here is that the relatively short electrode still does a good job of preserving residual hearing, but if any low-frequency hearing is ultimately lost, we can use those extra electrodes as a traditional electric processing-only device when necessary,” said Dr. Gantz, who added that an FDA trial of the device is closed, and researchers are now accruing data.
Craig A. Buchman, MD, FACS, chief of the division of otology/neurotology at the University of North Carolina School of Medicine in Chapel Hill and director of the University of North Carolina Ear and Hearing Center and Skull Base Center, said he is eager to see how those data pan out, because “right now, there seems to be a lot of excitement over a procedure that doesn’t have much long-term follow-up behind it,” he told ENT Today. As for the claimed benefit of the hybrid devices preserving structures of the inner ear that could later benefit from advances in genetic and/or molecular therapy, “to me, that’s a little bit like reading between the lines,” Dr. Buchman said. “It’s certainly a reasonable assumption, but at this point it’s more of a theoretical benefit rather than a compelling argument in favor of the devices as a preferred option.”
Dr. Buchman’s preferred approach is known as electroacoustic stimulation (EAS), a procedure in which a longer electrode is placed using soft surgery techniques to preserve key structures of the inner ear. “That way, if a patient loses residual hearing, they don’t need to be re-implanted,” he said.
Dr. Buchman cautioned, however, against putting too much emphasis on the differences between techniques used for preserving residual hearing. “The hybrid devices and EAS are conceptually exactly the same,” he said. “The more important point is that preserving residual hearing—regardless of variations in technique—is here to stay; it totally works, and I am sure Dr. Gantz and I are in complete agreement on that point.”—David Bronstein
Disclosures: Dr. Buchman is an unpaid consultant for Cochlear Ltd. Dr. Gantz is a consultant for Cochlear Ltd. and Advanced Bionics.