Cochlear implantation (CI) is well established and performed for children with prelingual deafness and severe-profound sensorineural hearing loss as well as progressive hearing loss (1, 2). With a prevalence of hearing impairment in childhood and adolescence of 1–4% and a prevalence of profound hearing loss of 0.1% in Germany and 1.7 in 1,000 children born with bilateral deafness in the United States of America, this is an important issue that requires a lot of medical and financial resources (3, 4). Bilateral CI can restore binaural hearing, which then allows for better speech discrimination in silence and noise, as well as better sound localization, explained by mechanisms such as squelch effect, head shadow effect, and summation effect (5–7). In children with bilateral hearing impairment early bilateral CI is important for their speech development as it relies on their hearing ability (6, 8, 9). The first bilateral CI was performed in 1996 followed by the first bilaterally implanted child in 1998, being now a standard treatment for patients with bilateral severe to profound sensorineural hearing loss (6, 10). Several studies comparing bilateral with unilateral CI exist which indicate an additional benefit for the second CI especially in sound localization and speech development (6, 8, 11–14). While there is no doubt for bilateral CI in bilateral deaf patients, there still exist controversies in sequential versus simultaneous CI. Simultaneous CI has become the standard procedure in most countries as early implantation and shorter inter-implant intervals are considered to improve speech recognition and hearing performance (2, 15–18). Despite that, the cost-effectiveness presents another argument for simultaneous implantation (19, 20). In contrast to the existing recommendation for simultaneous CI in bilaterally deaf children, some centers still prefer to perform sequential implantation due to lower estimated perioperative morbidity. Major argument performing sequential CI is a possible total bilateral vestibular loss and the possible loss of residual hearing mostly important for non-users as well as additional anesthetic and surgical risks (8, 11).

The present study is a retrospective review of the surgical outcomes of CI over a six-year period. The aim of our study was to examine the differences between simultaneous bilateral CI and sequential bilateral CI. In particular, the two surgical modalities were contrasted for cumulative duration of surgery and anesthesia as well as the perioperative morbidity and mortality. Furthermore, we collected information on the length of hospital stay, as CI surgery in children usually is an inpatient procedure in Germany.

We performed a retrospective analysis of children with bilateral hearing loss or profound hearing impairment receiving a CI between 2019 and 2024. The study was performed in the Department of Otorhinolaryngology, Head and Neck surgery, at the Implant Center of the University Hospital Freiburg. Patients aged under 10 years at the time of either simultaneous or second CI were included regardless of the cause of hearing impairment. CI surgery was performed in our department of six different surgeons, patients implanted in another clinic or with missing implantation data were excluded. We included both patients for whom we recommended direct bilateral CI at the first presentation and patients who were initially adequately fitted with hearing aids but were meeting the indication criteria for CI later at a second or third presentation due to progressive hearing loss. Records were retrospectively analyzed for age at implantation, duration of surgery and anesthesia, anesthesia risk, perioperative morbidity and mortality as well as pre-existing illnesses and syndromes. These were compared between the simultaneous and the sequential implantation cohorts. The decision for simultaneous or sequential implantation was made either primarily by the parents after discussion and counseling with the surgeons in the case of CI indication for both ears or by the surgeons who evaluated the indication criteria based on residual hearing.

The statistical analysis was performed using Prism 7-software (GraphPad Software, Inc., La Jolla, CA, United States). We used the nonparametric Mann–Whitney test for statistical analysis. For calculating the results significance level of p < 0.05 was used in all statistical analyses. Approval was obtained from the hospital ethics committee in accordance with the Declaration of Helsinki (Washington, 2002) (ethics committee approval number: 406/19 amendment number: 230282).

The performance of CI in bilaterally deaf children or children with severe-profound sensorineural hearing loss at a young age is essential for enhancing speech recognition and production (8, 13). Bilateral implantation has proven to enhance speech performance and sound localization. This procedure may be executed in either a simultaneous or sequential manner. In our study 132 patients were included and retrospectively evaluated. Among the 92 patients being implanted simultaneously the age was younger than in the sequential cohort with a mean of approximately 20 months, and the youngest child was implanted at the age of 6 months. This phenomenon can be explained by the earlier implantation of children in the simultaneous cohort caused by the elevated prevalence of deafness in the sample. In contrast, the sequential cohort comprises a substantial number of children who present with AHL and progression of the second ear over time.

In addition, also 16 children with bilateral deafness underwent sequential implantation. Our data demonstrates an inter-implant interval of 26.16 months between surgeries. While another study describes a mean inter-implant interval of 58 months (range 3–143 months), Uecker et al. (12, 21) showed an exemplary average of 10 months between the surgeries differing from other studies with an interval of around 19 months. The increased inter-implant interval observed in the present study is partly due to the manifestation of hearing loss in the second ear over time, resulting in a longer latency to reach the established inclusion criteria. Another reason for delayed implantation of the second ear is related to the fact that families may not be aware of the need for bilateral implantation, which should be evaluated regularly during follow-up. Given the documented inferior outcomes observed in speech performance in cases involving delayed implantation of the second ear in children with bilateral profound hearing loss, it is imperative to minimize the delay in such cases (15). Concomitantly, it is necessary to consider the heightened surgical risk associated with performing surgical procedures on very young infants (22). Lately, studies have shown that CI in infants under the age of 12 months is safe with appropriate anesthesia and postoperative management in centers with advanced pediatric experience (22–24). In our study cohort, no significant differences in anesthesiological or perioperative complications were observed between younger children (12 months old or younger) and older children (over 12 months old). In addition, the youngest child in our study underwent simultaneous CI at the age of 6 months without experiencing any anesthesiological or perioperative complications. Our study shows a significant reduction of surgical duration for simultaneous CI compared to the cumulative time needed for sequential surgery. The findings of our study are consistent with previous literature (21, 25). Furthermore, the findings of this study demonstrate that the cumulative anesthesia time for simultaneous CI is shorter than for sequential CI. This is an important consideration for children with predominant illnesses. However, it should be noted that operating one ear after the other does exhibit a shorter duration of anesthesia for one ear. This approach may be considered for children with elevated anesthesiological risks, such as those with lung disorders. Comparing the anesthesiological risk there is no difference between the two surgery modalities with both cohorts showing roughly 10% minor complications such as bradycardia, bronchial reaction or prolonged extubating in our study. Regarding minor surgical complications such as fever, vertigo, pain exacerbation and hematoma also no statistical difference was demonstrated. This is concordant with the data of a previous study also comparing bilateral CI (14, 21, 26). Nevertheless, there is also evidence indicating elevated risks of perioperative complications for simultaneous CI, which can be reduced by an assumed learning curve of surgeons in the recent years (16, 27). In summary, the present study indicates that simultaneous bilateral CI in childhood does not result in a higher incidence of complications when compared with the sequential implantation approach. Consistent with Uecker et al. (21), in our data the simultaneous implantation required a significantly reduced hospitalization time. The increase in hospital stays up to twice the duration for sequential CI (a total of 10 days for sequential CI and 5 days for simultaneous CI) also compromises cost-effectiveness, resulting in higher costs for the sequential procedure. Nevertheless, the total increase in hospitalization time reflects the current treatment modalities according to the German CI guidelines. In addition to the reduced length of hospital stay, cost efficiency may be achieved through the economical use of surgical time and materials with one simultaneous surgery versus two required surgeries. Indirect costs due to parents being absent from work or the need to organize childcare for other children are also reduced with the simultaneous approach (21).

In our study cohort, only two sequentially implanted patients experienced postoperative vertigo, which is a rare risk of CI. Of the two patients who underwent sequential CI, one patient who was 47 months old, experienced vertigo the day after surgery, while the other experienced vertigo 7 days postoperatively, requiring inpatient treatment. This is one of the main arguments of the critics of simultaneous surgery and must be taken into account when deciding on the surgical modality (8, 11).

The aforementioned arguments illustrate the advantages of concurrent CI, thereby prompting the inquiry into the continued necessity of sequential CI. As previously stated, sequential CI remains a viable option for patients with predominant illnesses, such as those requiring a shorter duration of anesthesia or blood-clotting disorders. Additionally, it may be considered for patients with special malformations or syndromes for whom the benefit of a CI is uncertain. Especially in latter, this is a valuable option for parents who are still skeptical about undergoing surgery. In summary, the two procedures should be thoroughly discussed interdisciplinary by the healthcare team and the families. Despite the study’s notable strength in including the largest number of patients to date who are comparing the simultaneous and sequential CI, the number of cases is insufficient for conducting further statistical evaluation or subgroup analysis. This limitation is particularly problematic when it comes to considering the influence of the patient’s age or prevailing risk factors. A further limitation is posed by the retrospective design, which precludes comprehension of the decision-making process undertaken by parents and the healthcare team. This may result in the occurrence of selection bias. Moreover, the duration of surgery and anesthesia vary, a discrepancy that can be partially attributed to the varying experience of the participating surgeons and anesthesiologists.

Although vertigo is rare in children with CI, it has been mentioned as a critical factor in the discussion of simultaneous implantation in several studies (8, 11). In our study, only two children experienced postoperative vertigo, both of which resolved completely. However, and this must be considered a limitation of this study, adequate functional diagnostic tests were not available due to the retrospective nature of this study. Therefore, vestibular dysfunction in CI children should be prospectively investigated in future studies.

Bilateral simultaneous CI is a sufficient and safe surgical procedure for bilaterally deaf children or children with bilateral severe-profound sensorineural hearing loss. The outlining benefits are the shortened duration of surgery and anesthesia as well as the shorter hospitalization resulting in lower healthcare costs. However, the absence of significant differences in perioperative morbidity, mortality, and anesthesia risks must be considered and make the sequential CI a considerable treatment alternative. Our data illustrate the advantages of simultaneous CI in case of bilateral CI indication as the preferable option, while emphasizing the necessity of a thorough preoperative evaluation. Sequential CI is still offering an individualized treatment approach that considers existing comorbidities and individual patient and parental factors.