In the current study, we provided evidence on the suitability of the CDL estimation method as proposed by Grover et al. [26] in pediatric patients. Remarkably, the otolaryngology attending physician provided similar results when compared to the radiologist. However, otolaryngology residents seem to warrant further training and experience to utilize this method for CDL measurement.

Notably, we observed significant differences in measurements performed by otolaryngology and radiology attendings compared to otolaryngology residents. Even among both residents, the measurements were significantly different, further highlighting their need for more training to achieve reproducible results. On the contrary, the long-standing experience of both attendings may be explained by their insignificant difference in CDL results for both inner ear sides of pediatric patients. Thus, the respective measurements might also be accurately performed by an otolaryngologist with finished training without additional quality control via radiology, which could contribute to reduced costs and time of preoperative cochlear implantation planning.

The relatively variable cochlear sizes between individuals require accurate ‘A value’ measurements before CI surgery [20], as the most size adequate implant should be chosen. This way, structural inner ear damage may be prevented, as it may lead to long-term fibrosis and decreased implant function over time. As a result of precise planning via ‘A value’ measurements and further calculations before CI insertion, an improved hearing function should be achieved. This is especially important as the precise intracochlear array positioning ideally covers the functionally deaf parts of the tonotopically organized cochlea without the risk of an intrascalar CI tip dislocation. Most studies with ‘A value’ measurements have been performed on adult patient radiological data. However, it is assumed that the length of the human cochlea is determined by the time of birth, changing skull dimensions and overall growth may have some impact not only on actual inner ear micro-dimensions but also on the overall use of ‘A values’ by professionals due to the rare indication in this patient group. Due to the relatively low number of prelingually deafened patients, the measurement of CDL and ‘A values’ in this patient group is often impossible. Primarily in tertial referral hospitals, it is important to train the staff for these measurements for both adult and pediatric patients. Without this training, it is expected to receive a relatively high interobserver variability in ‘A values’, which can result in poor CI planning.

One crucial factor is that in Bosnia and Herzegovina (and possibly other less developed countries), the implantation of only one CI device insertion in pediatric patients is covered by the general health insurance. Therefore, this highlights the need for even more precise preoperative planning, particularly regarding the electrode length.

The calculated CDL range in this study fits well with the data of previous groups, which confirms a high variability of the cochlear length between individuals [6]. To the best of our knowledge, an interobserver variability study on CDL measurements has never been performed on a pediatric patient population.

The study by Iyaniwura et al. confirmed the variability of CDL measurements obtained from CT scans of cadavers with an average absolute difference of 0.77 ± 0.42 mm [22]. This study revealed a significant difference in ‘A value’ measurements between trained otolaryngology or radiologist specialists. However, this difference was not confirmed in our results. To the best of our knowledge, our study was the first to assess the interobserver variability of CDL calculation between attending otolaryngologists and radiologists and two differently experienced otolaryngology training doctors. The evident differences in measurements between attendings and residents provide valuable viewpoints concerning CDL calculations for pediatric patients. Next to attending radiologists, attending otolaryngology doctors may be suitable for those measurements by providing a low interobserver variability. Regarding the differences in measured results between otolaryngology residents, it might be advisable to emphasize the evaluation of radiological imaging during the otolaryngology residency training schedule. This could ultimately lead to more stable results, better cost-effectiveness, and faster preoperative preparation in pediatric cochlear implantation.

Although this study provided the first insights into CDL measurements between different otolaryngology residents of different training levels, this study also has limitations. First, we included a relatively small cohort of pediatric patients; therefore, multivariate analysis is not applicable. Second, data on interrater reliability and interclass correlation coefficients could not be collected. However, given the fact that significant differences were observed, this study could pave the ground for future work to extend these observations and potentially replicate the results. Indeed, we provided evidence that the proposed method of CDL calculation may be suitable not only for radiologists, but also for experienced otolaryngologists. This may certainly reduce the time and costs of CI planning in pediatric patients.