Cochlear implants linked to new bone formation, increased hearing loss

Cochlear implants linked to new bone formation, increased hearing loss
Methods for CT assessment. (A) An oblique multiplanar reconstruction through the basal turn of the cochlea was obtained and (B) midmodiolar sections were obtained with radial multiplanar reconstruction through the center of the cochlea (white lines in A). On such midmodiolar images, the presence or absence of new bone formation and the scalar position were assessed at each electrode contact. Angular insertion depth was measured from the lateral border of the horizontal semicircular canal (blue line in A), using a correction factor to the center of the round window (yellow line in A) of 34°. Credit: Radiological Society of North America

The majority of cochlear implant recipients develop new bone formation that adversely affects long-term hearing preservation, according to a study appearing in Radiology.

Cochlear implantation is a well-established means to treat severe hearing loss. The device consists of an external part that sits behind the ear and a second part surgically implanted under the skin that stimulates nerves in the cochlea, a fluid-filled, spiral structure in the inner ear that transmits sound across sensory nerves to the brain. Cochlear implants don't restore normal hearing, but they can help a person recognize words and better understand speech.

While complications from are rare, post-mortem studies have linked them with inflammation, fibrosis and new bone formation. The potential clinical implications of new bone formation make it desirable to visualize and possibly prevent development, but in-vivo—or within the body—detection has not yet been described.

"Such subtle changes are challenging to visualize in vivo, in particular in the vicinity of a metallic implant causing artifacts on computed tomography images," said study co-lead author Floris Heutink, M.D., M.Sc., from the Department of Otorhinolaryngology at Radboud University Medical Center (Radboudumc) in Nijmegen, the Netherlands. "However, through the new availability of an ultra-high-resolution CT scanner, we were encouraged to investigate this."

Cochlear implants linked to new bone formation, increased hearing loss
Schematics of (A) right ear with cochlear implant, midmodiolar cross-section, and close-up of the different compartments within the cochlea and (B) proximal new bone formation (in gray) in the scala tympani (ST) encasing the electrode array (EA), gradually diminishing toward the apex of the cochlea. EM = external magnet, IM = internal magnet, RE = reference electrode, SM = scala media, SP = speech processor, SV = scala vestibuli. Credit: Radiological Society of North America

Dr. Heutink and colleagues used ultra-high spatial resolution CT (UHRCT) to assess new bone formation and its implications in 123 patients with implants.

The researchers were able to detect new bone formation in vivo using UHRCT. Of the 123 patients, 83 (68%) had new bone formation, predominantly located at the base of the cochlea, within four years of implantation. Long-term residual hearing loss was significantly larger in the group with new bone formation.

"As indicated by our study, there is a correlation between new bone formation and long-term residual hearing loss," said study co-author Berit M. Verbist, M.D., Ph.D., from the Departments of Radiology at Radboudumc and Leiden University Medical Center in Leiden, the Netherlands.

New bone formation around the cochlear electrode has a number of negative consequences due to its effects on the device and the structures surrounding it. It can affect the spread of electrical current within the cochlea, leading to complex device fitting, channel interaction and poorer overall hearing outcome. It could also complicate future therapies such as to restore cochlear function.

Cochlear implants linked to new bone formation, increased hearing loss
Midmodiolar ultra-high-spatial-resolution CT scans with corresponding annotations indicating new bone formation (NBF) in red. Note the varying appearance of NBF, ranging from (A) slightly increased attenuation, resembling that of the modiolus, to (D) frank ossification with an attenuation similar to that of the otic capsule surrounding a translocated contact in the scala vestibuli. An intermediate form of NBF appearance is shown in B and C. Moreover, in B, the ossification between the perimodiolar positioned electrode contact and the medial cochlear wall is difficult to discern, resulting in interrater disagreement. Credit: Radiological Society of North America

"Last but not least, new bone formation may complicate reimplantation surgery," Dr. Verbist said.

The researchers noted that improvements in design and have made available for an increasing number of people with severe to profound loss. This increase in patients makes a method for detecting and monitoring new bone formation in vivo more urgent than ever. Still, many remaining questions have to be answered, Dr. Heutink said, before the detection of new bone formation in an individual patient would have therapeutic consequences.

"This technique will be a to gain insight into occurrence, time course and the pathophysiology of this process and maybe used to evaluate still-to-be-developed treatments against new formation," he said.

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More information: Floris Heutink et al, Ultra-High-Resolution CT to Detect Intracochlear New Bone Formation after Cochlear Implantation, Radiology (2021). DOI: 10.1148/radiol.211400
Journal information: Radiology

Citation: Cochlear implants linked to new bone formation, increased hearing loss (2021, December 7) retrieved 17 January 2022 from
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