Effectiveness of skull X-RAY to determine cochlear implant insertion depth

Abstract

BackgroundCochlear implant (CI) insertion depth can affect residual hearing preservation, tonotopic range coverage, and Mapping. Therefore, determining insertion depth has the potential to maximize CI performance. A post-op skull X-RAY is commonly used to assess insertion depth, however its effectiveness has not been well established. Our primary objective was to assess the accuracy of post-op skull X-RAYs to determine insertion depth, compared to CT as the gold standard. Secondary objectives were to compare experience level of raters and different skull X-RAY views.MethodsThirteen patients with Advanced Bionic HiRes 90 K implants, and post-operative temporal bone CT scans were selected from the CI database at Sunnybrook Health Sciences Centre. Medical students, otology fellows, and CI surgeons evaluated insertion depths on post-op skull X-RAYs, while neuroradiologists evaluated CT scans. Descriptive statistics, regression analysis, and paired t-tests were used to compare the two types of imaging.ResultsX-RAYs and CTs provided an equivalent mean insertion depth of 337 degrees (p = 0.93), a mean difference of − 0.9 degrees and a standard deviation of paired differences of 43 degrees. Although means were similar across rater groups, CI surgeons (45 degrees) had the lowest standard deviation of paired differences. Comparing X-RAY views, Caldwell (29 degrees) had less variation than Towne (59 degrees) for standard deviation of paired differences.ConclusionsSkull X-RAYs provide accurate and reliable measurements for CI insertion depth. The Caldwell view alone may be sufficient for evaluations of insertion depth, and experience has a minor impact on the variability of estimates.Electronic supplementary materialThe online version of this article (10.1186/s40463-018-0304-9) contains supplementary material, which is available to authorized users.

Frequency of electrode migration after cochlear implantation in the early postoperative period. What are associated risk factors?

“…A conventional CT may be more precise than plain radiographs, but multiple studies have shown that plain radiographs perform equally well in determining insertion depth and extracochlear electrodes, avoiding exposure to high-dose ionising radiation. [14][15][16] In our study, we endeavoured to address the inherent imprecision of plain radiographs by taking a higher threshold of 2 or more electrodes lateral to the approximate position of the round window to define extracochlear electrodes. With this definition, the prevalence of migration in our study cohort concurs with a previous report using CT to define EM.…”

“…Cone beam computed tomography (CT) scan is often considered gold standard for determining EM, however, this modality is not routinely available, 13 and not at our centre during this period. A conventional CT may be more precise than plain radiographs, but multiple studies have shown that plain radiographs perform equally well in determining insertion depth and extracochlear electrodes, avoiding exposure to high‐dose ionising radiation 14–16 . In our study, we endeavoured to address the inherent imprecision of plain radiographs by taking a higher threshold of 2 or more electrodes lateral to the approximate position of the round window to define extracochlear electrodes.…”

Cochlear Implantation in Infants: Why and How

“…Intraoperative audiometric monitoring can often be performed while the surgeon is closing the surgical site to avoid prolonging the duration of anesthetic. Finally, an anterior-posterior skull X-ray can be performed to confirm appropriate positioning of the electrode within the cochlea, verifying the insertion depth and absence of kinking or tip rollover ( Fernandes et al., 2018 ); other X-ray views such as lateral or Stenver’s ( Shaul et al., 2020 ) could be performed depending on surgeon preference.…”

Reliability of Measuring Insertion Depth in Cochlear Implanted Infants and Children Using Cochlear View Radiography

“…The accuracy of estimating electrode location using computer tomography (CT) images has been demonstrated in studies comparing measurements made radiographically to those determined on histologic review 24 , 25 . Studies comparing aDOI measurements obtained from CTs have also shown comparable accuracy to those obtained using conventional radiography 26 , 27 . Measurements of aDOI using radiographs have shown good reliability in vitro as well as in adult CI listeners 7,23,26 .…”

“…24,25 Studies comparing aDOI measurements obtained from CTs have also shown comparable accuracy to those obtained using conventional radiography. 26,27 Measurements of aDOI using radiographs have shown good reliability in vitro as well as in adult CI listeners. 7,23,26 This has not been demonstrated in infants and young children, who may be more challenging to position for a cochlear view.…”