Cochlear implantation in children under 12 months of age: surgical outcomes and considerations—a Western Australian perspective

Introduction

The importance of early intervention in paediatric hearing loss, especially pre-lingual loss, is well documented (1-3). The widespread universal newborn hearing screening program (NBHS) has resulted in potential cochlear implantation (CI) candidates being identified as early as 1 month of age. For infants with hearing loss of severe to profound severity, CI offers the best opportunity for hearing rehabilitation, particularly in those with bilateral loss, where bilateral CI provides the opportunity for binaural hearing listening and spoken language development for sound localisation and speech discrimination (4).

CI was initially limited to patients with profound hearing loss due to the potential loss of residual hearing as a result of cochlear trauma during electrode insertion. Over the last decade, the indications for CI have expanded to include younger patients and those with varying degrees of residual hearing due to advances in surgical technique and electrode design (5). Multiple studies have highlighted the benefit of earlier CI for auditory performance, speech comprehension, and spoken language development in prelingually deaf children (6-8).

With the trend towards earlier implantation and expanding candidacy, there has been a surge in the literature reporting promising outcomes in this cohort. To date, most published studies on paediatric CI originate from the United States, with only a single Australian study available—published more than 12 years ago (9). Our study presents the first Western Australian analysis of CI in infants under 12 months, focusing on surgical outcomes and intraoperative feasibility using the round window (RW) approach.

Methods

This was a retrospective, single-centre observational study conducted between 2008 and 2019. This study was reported in accordance with the Strengthening the Reporting of Cohort, Cross-sectional and Case Series in Surgery (STROCSS) 2021 criteria (available at https://www.theajo.com/article/view/10.21037/ajo-24-57/rc). Included in the study were all non-syndromic patients undergoing primary CI surgery before 12 months of age at our institution, Perth Children’s Hospital (formerly Princess Margaret Hospital). Perth Children’s Hospital is a tertiary paediatric hospital that performs the majority of paediatric CI in the state of Western Australia and serves a population of over 2 million people, of which approximately 600,000 are children and is the primary referral centre of the statewide NBHS (10). All CI candidates were discussed at a multi-disciplinary team meeting, which included staff from speech pathology, audiology, clinical nurses and ear, nose and throat (ENT) surgeons, before a consensus to treat is reached. Parents and carers were involved in decision-making throughout the planning process. Children were excluded from the study if they had a known syndromic cause of their hearing loss, which is associated with a higher incidence of cochlear dysplasia.

All patients had a routine preoperative workup test battery which included speech and language assessment, behavioral audiometry, auditory brainstem response testing (ABR), tympanometry, otoacoustic emissions and aided cortical auditory evoked potentials. All patients had a three-dimensional (3D) magnetic resonance imaging (MRI) brain scan with high-resolution T2 sequence of the temporal bone and cochleae. The need for a computed tomography (CT) scan of the temporal bones was considered on a case-by-case basis and was generally reserved for patients with known syndromes or aberrant anatomy on MRI. This protocol is based on a recent study by our group, which highlighted the feed and wrap technique as a viable method for obtaining diagnostic-quality MRI scans of the inner ear structures in infants with hearing loss (11). Prior to surgery, all patients received the pneumococcal and Haemophilus Influenzae B vaccinations, and all patients were free from upper respiratory tract symptoms on the day of surgery.

Operation records were reviewed for mastoid anatomy to assess the degree of difficulty or abnormality within the cohort compared with the literature. All CI surgery was performed by two of the senior authors (S.R. and J.K.) with a standard post-auricular transmastoid surgical approach under general anesthesia. Intravenous cephazolin antibiotic prophylaxis was used on induction. A curvilinear post-auricular incision was made following skin prepping and draping. A musculoperiosteal flap was created to expose the mastoid cortex, external auditory canal and spine of Henle. A cortical mastoidectomy was then performed to identify the mastoid antrum, lateral semicircular canal, and body of the incus. The facial recess was opened after thinning of the posterior canal wall and identification of the mastoid segment of the facial nerve. The facial recess was then widened to identify the RW niche. The RW niche was lowered to identify the RW membrane. The RW membrane was then opened, and the electrode was inserted until the first resistance. If the RW approach was not possible, an anteroinferior cochleostomy insertion was performed, except in cases where anatomical considerations necessitated cochleostomy. A fat or muscle plug is typically used to stabilize the electrode at the RW, and bone wax is used to secure the electrode adjacent to the well. Patients were admitted overnight following surgery, discharged the next morning, and reviewed at 2 weeks postoperatively by the surgical team for wound assessment. The audiology and speech team coordinated CI switch-on (approximately 2 weeks post-operatively), mapping, rehabilitation and periodic assessments of speech and hearing. At the time of this study, our institution provided regular follow-up with paediatric audiologists for a minimum of 3 years following CI. After this time, the patient may continue to be managed by the hospital team or be discharged to community audiology services, depending on the clinical picture. Paediatric speech pathology delivered rehabilitation for 12 months, with routine age-appropriate assessment conducted at one year postoperatively, after which patients were discharged to community services. Ongoing review was arranged if clinically indicated.

Patient files were reviewed for demographics including; gender, age at implantation, aetiology, nature of hearing loss and whether CI was simultaneous, sequential or unilateral. Relevant intraoperative and perioperative decision-making, findings and outcomes were analysed. Intraoperative findings reviewed included the degree of mastoid pneumatisation and RW accessibility to electrode insertion and the subsequent operative approach—RW versus cochleostomy and for any intraoperative complications. Perioperative documentation was reviewed for implant choice, postoperative complications and outcomes of clinical reviews, particularly speech and hearing tests. Data were collected and managed using Microsoft Excel (12). Statistical analysis was primarily descriptive in nature. Continuous variables were summarized using mean, standard deviation (SD), and range, while categorical variables were reported as frequencies and percentages. Given the small sample size and observational design, no inferential statistics were performed.

Missing data were handled by case-wise exclusion from individual analyses; cases with incomplete data for a specific variable were excluded from that portion of the analysis but retained for all other available data points. Data completeness was high across all variables, and missing data were rare. The study was conducted in accordance with the Declaration of Helsinki and its subsequent amendments. The study was approved by the institutional ethics board of Perth Children’s Hospital (approval number 28044). Because of the retrospective nature of the research, the requirement for informed consent was waived.

Results

Study population

Twenty-four patients who underwent a total of 44 CI’s met the study criteria (Figure 1), and 54% of patients were male. Of the 44 CIs, 38 (86%) were performed as bilateral simultaneous implants across 19 patients. Five patients underwent bilateral sequential implantation, of whom only one received both implants before 12 months of age. Among these five patients, one received the first CI at 8 months and the second at 9 months in the contralateral ear. The remaining four patients received their second implant after the age of 1 year; these second implants were not included in the cohort, as they were performed beyond the 12-month age threshold. The mean age at implantation was 8 months (±1.7 SD) and a majority of patients (83%) underwent bilateral simultaneous implantation. There were no cases of unilateral CI in this cohort. Of the 24 patients with 44 implants under 12 months of age, all received the same implant type in each ear. Patient demographics and implant manufacturer utilised are outlined in Table 1.

Figure 1 Study cohort flow diagram. *, not included in cohort due to age over 1 year at time of second implant. CI, cochlear implantation.

An analysis of the underlying causes of hearing loss in this group of children (Table 1) revealed that idiopathic (cause unknown) and genetically confirmed factors were the most prevalent, accounting for 14 out of 24 cases (58.3%). Specifically, genetic testing identified pathogenic or likely pathogenic variants in 7 individuals (29.2% of the cohort), with mutations in the GJB2 gene being the most common (n=6, 25%) followed by SLC26A4 (n=1, 4.2%). The remaining causes, representing 10 cases (41.7%), were linked to well-established antenatal and neonatal complications. These included sequelae of congenital cytomegalovirus (cCMV), sepsis, and meningitis. Additionally, 2 cases (8.3%) were attributed to clinically significant jaundice requiring phototherapy, another 2 cases (8.3%) were associated with craniofacial abnormalities, and 1 case (4.2%) was linked to encephalopathy. A single, further case was classified as ‘other’, involving suspected congenital sensorineural hearing loss (SNHL) related to intrauterine growth restriction.

Preoperative radiological work-up included an MRI brain for all patients, while 9 patients (20%) underwent both MRI and CT brain.

Technique and intraoperative findings

Of the 44 implants, 42 (95.5%) were inserted via RW approach and 2 (4.5%) via cochleostomy. Both patients had simultaneous implants and both were 8 months of age at the time of surgery. The two cochleostomy cases involved a RW approach on the contralateral ear.

Operation notes for the 44 implants indicated: adequately pneumatised mastoid bones in 25 implants, ‘difficult’ or partially pneumatised mastoids in eight cases and no note of mastoid appearance in 11 of the implants. Reasons for ‘difficulty’ were articulated in the eight cases—‘small’, ‘marrow-filled’, ‘poor pneumatisation’ and ‘granulation tissue’ were reasons noted. Only one of these ‘difficult’ mastoids required implantation via the cochleostomy approach. One case required an extended RW approach and another case required both chorda tympani nerves to be sacrificed for implantation, also via RW approach. These ‘difficult’ cases were in children ranging from 8 to 11 months of age.

Complications

All 24 children were implanted successfully without significant intraoperative or perioperative complications. There were no facial nerve stimulation or anesthetic complications. One case required an intraoperative CT temporal bone scan due to challenging anatomy which was not identified on preoperative MRI scan.

There were several postoperative complications encountered within this cohort, most of which were minor and managed conservatively. Two patients experienced minor post-operative bleeding in the nasopharynx throughout the hospital stay. Neither case required intervention and resolved following observation, with both patients being discharged home, as planned, the day after surgery. Three patients experienced post-operative wound healing issues. For two of these patients, this issue was minor—limited to inflamed skin under the magnet and minor wound edge break-down, which settled following reduced magnet use temporarily. One of these patients received antibiotics. The third patient required return to theatre for incision and drainage, along with a course of antibiotics. None of these implants required removal. These three patients were 6, 7 and 8 months old, respectively, at the time of implantation; all were bilateral simultaneous implants, and none experienced contralateral wound issues.

Electrode anomalies necessitated single-sided re-implantation in two patients. The cause of the anomalies was unclear as electrode function was adequate on intraoperative testing, and the parents did not report any incidents (such as falls) that would account for the malfunction. The time between implantation and explantation for the two patients was 5 and 22 months, respectively. In both cases, reimplantation occurred at the same operation, and no further issues were reported, with follow-up duration at the time of writing being 4 and 7 years, respectively.

Follow up

All patients were discharged on the day after implantation. The mean time to switch-on following implantation was 15 days (±5.5 SD), with a range of 9 to 28 days. At our institution, at the time of this study, all CI patients who are implanted at under 12 months of age receive follow-up for at least 3 years post-operatively before considering discharge to community services, depending on other factors. Postoperative follow-up duration ranged from 12 months to nearly 8 years, with a mean of 2.7 years (±1.5 SD) after the first implant. Some patients remain under active review, while others were discharged to community care.

Discussion

CI in children under 12 months of age is safe, feasible, and mostly successful via RW approach with low complication rates. The established benefits of early CI have led to a rise in the number of centres implanting before 12 months and to the broadening of criteria for implantation in many healthcare systems (13,14). This has resulted in a shift to implanting children with a broader range of severe hearing loss and to increase bilateral implantation, both simultaneous and sequential. To our knowledge, this is the first Western Australia cohort study to discuss the surgical feasibility of CI in children under 12 months of age, adding to the growing literature on this topic.

In paediatric hearing loss, there is a well-established time-critical period in childhood development in which optimal sound exposure is required to achieve the best speech and language outcomes (15-18). Although the precise timing of this critical window remains unclear, there is evidence to suggest it occurs prior to 12 months of age, with better speech and language skills demonstrated in studies of children implanted before 12 months (19).

Whilst there is a growing evidence base for early CI, much still remains unknown or emerging, and long-term follow up data is lacking. It is difficult to aggregate the outcomes of studies that compare CI before and after 12 months of age. This difficulty is partly due to the variety of outcome measures used to assess development, along with generally small study sizes and a lack of longitudinal data, all of which make statistical significance and persistence of benefit difficult to ascertain (20). A recent systematic review analysed 17 studies, comprising 642 children undergoing CI <12 months of age and found that in 10 studies with the availability of a comparison group, similar or superior auditory and language outcomes were consistently reported for earlier implantation compared to CI after 12 months of age (21). Our cohort, despite a small sample size, further adds to the literature and demonstrates that CI under 12 months of age is feasible and safe.

Additional considerations for paediatric CI, apart from age at implantation, include bilateral compared with unilateral CI, and simultaneous compared with sequential implantation. All patients in our cohort received bilateral CI, with a majority of those (83%) receiving bilateral simultaneous implantation. Of those who received a sequential CI, the time between implants ranged from 1–34 months (median 7.2, SD 15.9). The benefits from bilateral CI include; improved speech discrimination in noisy environments, better sound localisation and improved hearing in quiet environments (22-24). There is also strong evidence that for children receiving bilateral CI, there is a benefit derived either from simultaneous implantation or sequential implantation with the interval between implants minimised (25). Superior auditory outcomes have been demonstrated, which relate to the synchronisation of both ears within a critical period (23,25-28). Bilateral stimulation of the central auditory pathways produces a synergistic result, which in the pre-lingual child is integral for optimal hearing (29). Therefore, reducing delays between sequential CI is important in ensuring optimal hearing, although the precise window is unknown (4).

The choice of surgical approach in paediatric CI—specifically, RW insertion versus cochleostomy—remains an area of ongoing discussion. Both techniques aim to optimise electrode placement and hearing outcomes, though their use may vary depending on cochlear anatomy, surgeon preference, and intraoperative findings. In our study, the RW approach was used in 95.5% of cases. These findings are supported by the literature, that most CI, including early paediatric cases, can be successfully performed via the RW approach (30-32). Additionally, the limited use of cochleostomy (4.5%) in our study is in line with recent research that advocates for RW access as the standard surgical approach, reserving cochleostomy for cases where the RW is not accessible or where anatomical challenges arise, as highlighted by Elfanadi et al. (33). Moreover, this approach has been linked to lower rates of intracochlear trauma, better hearing preservation and reduced electrode-to-modiolus distance compared to cochleostomy (34). Interestingly, a small number of implants in our cohort required an extended RW approach or sacrifice of the chorda tympani nerve. This underscores the complexity and variability of paediatric CI and highlights the importance of preoperative imaging and meticulous surgical planning to anticipate anatomical challenges.

Peri-operative complications in paediatric CI, though relatively rare, can have significant implications given the delicate anatomy and long-term impact on auditory development. There were no significant intraoperative or perioperative complications in our cohort. For this particular age group, possible peri-operative risks of early CI include blood loss, surgical access, unexpected anatomy, anaesthetic risks and electrode failure or movement (35). Blood loss is a serious consideration in infants under 12 months of age, given the small total circulating blood volume and the hypovolemic effects with loss of less than 10% volume loss in combination with a rich supply around the operating area located in the bone marrow and emissary veins (36). There were no issues with significant intraoperative blood loss in our cohort, and the two cases of postoperative ooze were of minimal volume, self-ceasing and likely related to minor ooze into the Eustachian tube rather than ongoing bleeding from the surgical site.

Postoperative complications, both minor and major, following CI in children under 12 months of age are an important consideration, with several studies reporting varying rates in this vulnerable population. Loundon et al. (37) report the lowest major complication rate of 2–8%, however it is worth noting that they did not include re-implantation due to spontaneous device failure in this number. In our cohort, the major complication rate was 6.8% (including wound infection and explantation due to spontaneous device failure), while minor complications, such as wound pain and minor bleeding, occurred in 9% of cases. Two patients in which skin irritation was evident at the magnet site required conservative and medical management only, respectively. The ages were 6 and 7 months at the time of implantation, and though both patients healed well without further complications, the outcomes prompted the initiation of a minimum age of 6 months for CI at our institution for future cases to ensure the skin underlying the magnet is of adequate strength. The thin and delicate nature of the posterior auricular scalp flap necessitates atraumatic handling of the flap and the thinner skin in very young children has raised concerns about whether flap infection and necrosis are more common in younger children. Flap complications are among the more common issues of CI, and although still rare (4.5%), the potentially higher rate among children under 1 year is a serious consideration in surgical planning (38,39). As CI technology progresses, the potential issues surrounding flap irritation or breakdown may resolve and a lower age limit related to this concern may no longer be applicable. A third patient (implanted at 8 months) developed a post-auricular abscess one month postoperatively which resolved following antibiotics and drainage, without further issue.

The anatomy of the temporal bone of very young children warrants particular surgical considerations regarding technique and surgical approach. Intraoperative access difficulties and higher rates of complications in the under 12-month age group have been noted in the literature (14,36,40). The high marrow content of mastoids in infants is one factor sighted as a risk in early paediatric CI, which reduces with increasing age (14). It has been postulated that usual surgical landmarks may be obscured in poorly pneumatised mastoid bones, placing structures such as the facial nerve at increased risk of damage and increasing the risk of significant bleeding. Within our cohort, no issues were identified as sufficiently significant to prevent the completion of implantation, cause a clinically relevant complication or result in an inferior outcome for the patient. Partial pneumatisation was found in a number of the mastoids of patients in our cohort, although these weren’t associated with complications around landmark identification or blood loss and did not necessarily preclude RW insertion.

Facial paralysis is reported to be of higher risk in younger children as the facial nerve may sit more laterally and superficially compared to older children or adults (41). There were no facial nerve complications in our cohort and the use of facial nerve monitoring is standard practice at our institution. Evidence suggests that with careful identification and monitoring of the facial nerve, complication rates in children under 12 months of age need not exceed that of older children (36).

The increased frequency of laterally and inferiorly located stapedial tendon in children under 12 months of age is also noted in the literature, which may impede facial recess access and make for more challenging electrode advancement, though again, this was not noted to be a hindrance within our cohort (42). The facial nerve is known to be at increased risk of damage during CI in children born prematurely as the facial recess may cease to grow after birth, placing the patient at higher risk of damage from drilling at a more acute angle than is usually required (42). Consideration of the corrected age of children who were born prematurely is a routine part of the surgical planning process at our institution, aided by a radiological review of anatomy preoperatively.

The shallow skull thickness of very young children and the propensity for falls has led to queries around the protrusion of CI and whether drilling the skull down and implanting on dura, along with ligature fixation of the implant, may reduce protrusion and dislodgement (36,43). At our institution, it is not common practice to site the CI on dura or secure the device, and no complications have occurred regarding mobile or dislodged implants. The two patients who required explantation due to electrode anomalies showed no radiological evidence of the anomaly being related to a mobile receiver. One of these patients, demonstrated uncertain audiological responses at follow up which prompted further work up and a dedicated CT temporal bone scan. This CT scan was suspicious for electrode lead break at the apical/basal cochlea turn. This patient had pre-operative imaging which suspected cochlear dysplasia involving the middle and apical turns on this side and a small left cochlear nerve canal. For the second patient, despite adequate imaging and investigation, no cause for electrode failure could be identified and there were no known patient factors to explain this outcome. All explant/re-implant surgeries were performed simultaneously and without further complication. Revision CI surgery is common among paediatric CI recipients, where hard device failure is the most common reason for undertaking revision surgery. Our re-implantation rate of 8% is below the proposed literature rates of reimplantation in children, ranging from 10–13% (44,45).

Although not a focus of this study, there is a body of literature around bilateral simultaneous CI, and whether the prolonged operating time (approximately 4-hour operation) poses particular neurological risks associated with anaesthetic agents and general physiological stress due to the duration, in which the debate is ongoing (46). The literature is conflicting on this with one study by Ueker, reported no difference in complications comparing 22 patients undergoing sequential CI versus 32 patients undergoing bilateral CI (47). However, a recent systematic review looking at 643 children who underwent CI under 12 months of age, noted that the study with the highest complication rate (6.6%) was predominantly bilateral CI rather than unilateral (21). Duration of surgery may not be an independent risk factor for early CI but rather age of the patient and paediatric expertise in the operative setting, and further randomised controlled trials are needed (48).

The short and medium-term risks associated with delayed implantation are well documented, while the long-term risks are yet to be understood, due to the lack of longitudinal studies, as previously noted (28,49,50). The precise optimal age for CI has yet to be determined but is likely to vary between patients (14,20). At the time of this study, children were followed up in the audiology/speech pathology department for 3 years before being discharge to community serviced. The current protocol has changed at our institution, with all children now followed up every 12 months until the age of 16 years to better monitor device integrity, speech and language outcomes, and audiological performance during critical developmental stages, particularly adolescence. This change reflects growing evidence that late device failures, evolving communication needs, and psychosocial factors emerge beyond early childhood, requiring ongoing multidisciplinary support to optimise long-term outcomes.

Overall, the findings of our study align with recent trends in paediatric CI, including the preference for bilateral simultaneous implantation, the importance of early intervention, and the safety and efficacy of the RW approach. The minor complications observed are consistent with other studies, and the study’s follow-up duration provides valuable insights into medium-term outcomes.

This study has several key limitations that must be considered. One major limitation is the incomplete long-term audiological and speech-language follow-up, as only a subset of patients had detailed evaluations beyond 12 months due to the transfer to community-based centres for therapy. Additionally, the small sample size limits the statistical power and generalizability of the results. The retrospective design introduces potential biases in data collection and patient management, while the absence of a control group further limits conclusions on the effectiveness of the surgical approaches. Future studies with extended follow-up and standardized speech-language testing across all participants would provide a more complete picture of the long-term functional outcomes of early CI.

Conclusions

This Western Australian cohort study indicates that CI under 12 months of age is both feasible and safe, and addresses key surgical considerations in this age group. The findings suggest a risk profile comparable to that in older children, while potentially avoiding the speech, language, and auditory delays associated with later implantation.

Acknowledgments

Our abstract was accepted for oral presentation at the ASOHNS 74th Annual Scientific Meeting, Perth, Australia, which took place between the 8th and 10th of March, 2024.

Footnote

Reporting Checklist: The authors have completed the STROCSS reporting checklist. Available at https://www.theajo.com/article/view/10.21037/10.21037/ajo-24-57/rc

Data Sharing Statement: Available at https://www.theajo.com/article/view/10.21037/ajo-24-57/dss

Peer Review File: Available at https://www.theajo.com/article/view/10.21037/ajo-24-57/prf

Funding: None.

Conflicts of Interest: All authors have completed the ICMJE uniform disclosure form (available at https://www.theajo.com/article/view/10.21037/ajo-24-57/coif). J.K. serves as an unpaid editorial board member of Australian Journal of Otolaryngology from January 2019 to December 2027. The other authors have no conflicts of interest to declare.

Ethical Statement: The authors are accountable for all aspects of the work in ensuring that questions related to the accuracy or integrity of any part of the work are appropriately investigated and resolved. The study was conducted in accordance with the Declaration of Helsinki and its subsequent amendments. The study was approved by the institutional ethics board of Perth Children’s Hospital (approval number 28044). Because of the retrospective nature of the research, the requirement for informed consent was waived.

Open Access Statement: This is an Open Access article distributed in accordance with the Creative Commons Attribution-NonCommercial-NoDerivs 4.0 International License (CC BY-NC-ND 4.0), which permits the non-commercial replication and distribution of the article with the strict proviso that no changes or edits are made and the original work is properly cited (including links to both the formal publication through the relevant DOI and the license). See: https://creativecommons.org/licenses/by-nc-nd/4.0/.

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