Anatomical Variations, Surgical Difficulties, and Complications Associated with Cochlear Implantation in Different Age Groups of the Pediatric Population of Nepal: A Tertiary Level Hospital-Based Study

Abstract

Pediatric cases account for the major proportion of the population for whom cochlear implantation is indicated. This study aims to review the anatomical variations, surgical difficulties, and complications associated with cochlear implantation surgery in different age groups of the pediatric population of Nepal.This study was conducted at Tribhuvan University Teaching Hospital, Nepal. A prospectively set data of cases who underwent cochlear implantation between January 2015 and March 2020 were analyzed for details of surgical procedure, surgical difficulties, and intraoperative and postoperative complications. The anatomical variations encountered during surgery were classified as: developmental anomalies, round window niche variations and acquired abnormalities resulting from inflammation. Intraoperative surgical difficulties were defined based on the operating surgeon’s perspective. Complications following cochlear implantation were classified as surgical and nonsurgical or device-related. We used SPSS version 25 for the analysis of our data. Chi-square test and Fisher’s exact test were used to analyze the statistical association.The most commonly encountered difficulty was the requirement of an extended posterior tympanotomy approach due to poor visualization of round window niche. There was a statistically significant association of difficult insertion of electrodes with round window niche visibility. The common complications encountered were intraoperative facial nerve exposure, bleeding, electrode-related problems, cerebrospinal fluid gusher, and device failure.Cochlear implantation with an experienced surgeon in pediatric population is a relatively safe procedure. There is no association of the difficulties and complications related to surgery with the different age groups.

Introduction

Following the first cochlear implant done by Djourno and Eyriès, cochlear implantation (CI) surgery has thrived in various aspects until today [1]. New innovations are being made in the field and the candidacy for CI is also broadening. As of today, auditory implants either in the cochlea, i.e., cochlear implant, brainstem i.e., auditory brainstem implant or midbrain, i.e., midbrain implant are the only answers to the profound sensorineural hearing loss. In one hand, there is a significant prevalence of sensorineural hearing loss in the pediatric population and a dreaded fear of delayed speech and language development in this group and in the other, a high cost of the device that makes it beyond the reach of economically deprived population. This has led CI surgery a topic of national interest in various nations worldwide.

Nepal, a small land-locked Himalayan country, started its CI programme way back in 2004 at Tribhuvan University Teaching Hospital, Kathmandu, with support from the Cochlear company and a technical team from India. In the following years, with a generous support from implant companies like Cochlear and Med-El, manpowers from the hospital were further trained. Cochlear Implant Nepal Group (CING), a collective endeavor of a team comprising of Otolaryngologists, Audiologists, Speech and Language Pathologists, Pediatricians, Child Psychologists, Radiologists, Anesthesiologists and Nurses came into being in 2013. CING then in collaboration with a German-based organization CoIN, started providing financial aid to some of the implantees. It was until 2017 when Nepal government stepped in and started a partial funding policy to financially aid all the eligible CI candidates. Considering the low economical background, level of education and unawareness amongst a significant number of population and thus a late detection of hearing loss in pre-lingually deaf population, the flexibility of the candidacy in our context extends up to 6 years of age. Although we haven’t been able to comply with the universal neonatal screening, a rigorous campaign on awareness of hearing loss and need for hearing screening in infants at risk and the possibility of hearing restoration with CI, has had a substantial impact in detecting more pediatric cases with sensorineural hearing loss. A major bulk of our implantees belong to the pediatric population. This study thus aims to review the safety, anatomical variations, difficulties, and complications associated with CI surgery in this group of population.

Materials and Methods

This study was conducted in the Department of ENT-HNS at Tribhuvan University Teaching Hospital, Nepal. The study was approved by Institutional Review Committee. A prospectively set data of cases who underwent CI between January 2015 and March 2020 were analyzed for details of surgical procedure, surgical difficulties, and intraoperative and postoperative complications. Cases aged < 15 years of all genders with complete documentation of the above mentioned variables were included in the study. A single, experienced surgeon with formal training in CI was involved in the surgery of all the cases. The surgical approach in all the cases was via trans-mastoid posterior tympanotomy route. An anteriorly based musculoperiosteal Palva flap was used to cover the receiver stimulator. Membranous insertion via round window was the preferable route, however, in cases with poor visualization of RW, cochleostomy was done. A 10 day course of antibiotic (oral amoxicillin/ clavulanic acid) at a dose of 50 mg/kg/day in three divided doses was prescribed following surgery. An alternate day dressing was done for 10 days following surgery. Follow-up duration ranged from 2 weeks to 6 months. Cochlear implants used in our study were manufactured by MeDel and Cochlear company.

The anatomical variations encountered during surgery were classified as follows:

• Developmental anomalies of the external ear, middle ear cleft, and inner ear

• RWN variations based on its visibility via posterior tympanotomy [2]

  1. Type A: Not visible
  2. Type B: Partially visible
  3. Type C: Completely visible

• Acquired abnormalities resulting from inflammation, e.g., granulations, mucosal edema, labyrinthine ossification, etc.

Intraoperative surgical difficulties were defined based on the operating surgeon’s perspective. Any difficulties rendering the surgeon to extend the surgical time, e.g., CSF gusher, excessive bleeding, requirement of extended tympanotomy due to poor visualization of RWN, difficulty in inserting electrodes, difficulty in achieving a proper telemetry response, extended time for drilling, etc. were considered for evaluation.

Complications following CI were classified as surgical and nonsurgical or device-related. Surgical complications were further classified into intraoperative, early postoperative (≤ 1 week following surgery), and late postoperative (> 1 week following surgery). Device-related complications were further classified as soft failure and hard failure.

We used SPSS version 25 for the analysis of our data. Chi-square test and Fisher’s exact test were used to analyze the statistical association between different groups. A p value of < 0.05 was considered statistically significant.

Results

Record data of 105 cases were reviewed, of which 88 cases met the inclusion criteria. Seventy-two cases were below six years with a male preponderance. Sixteen cases were above 6 years and had post-lingual deafness. This group, however, had more females compared to males. The age and gender distribution has been shown in Table 1.

Table 1.

Age and gender distribution

Age groups	Gender
	Male	Female
≤ 3 years	26	11
$>$ 3– ≤ 6 years	20	15
> 6 years	6	10

A range of developmental anomalies of the inner ear was encountered, namely: enlarged cochlear aqueduct (two cases), Mondini’s malformation (two cases), broad operculum of RWN (two cases) and cystic apical cochlea (one case). All cases were below six years except for the case with cystic apical cochlea, who was above 6 years. Type C RWN (fully visible via posterior tympanotomy) was the commonest variant (48 cases) found in all the age groups followed by Type B (partially visible via posterior tympanotomy) (21 cases) and Type A (not visible via posterior tympanotomy) (19 cases). Inflammatory mucosal changes in middle ear cleft such as granulation and oedematous mucosa were found in five cases. All the cases were below 6 years. Table 2 demonstrates the anatomical variations in different age groups.

Table 2.

Anatomical variations of the middle and inner ear in the different age groups

Anatomical variations	Age group in years	No of patients
Developmental anomalies
Enlarged cochlear aqueduct	≤ 3	1
	> 3– ≤ 6	1
Mondini’s malformation	≤ 3	1
	> 3– ≤ 6	1
Broad operculum of RW	≤ 3	2
Cystic apical cochlea	> 6	1
RWN variations based on visibility via tympanotomy
Type A	≤ 3	7
	> 3– ≤ 6	6
	> 6	6
Type B	≤ 3	11
	> 3– ≤ 6	8
	> 6	2
Type C	≤ 3	19
	> 3– ≤ 6	21
	> 6	8
Inflammatory changes
Granulation tissue with oedematous mucosa	≤ 3	1
	> 3– ≤ 6	4

Difficulties rendering the surgeon to extend the surgical time or deviate from the standard technique, i.e., posterior tympanotomy approach and membranous insertion of the electrodes via RW were considered for the evaluation. The most commonly encountered difficulty was the requirement of an extended posterior tympanotomy approach due to poor visualization of RWN (Type A and Type B), i.e., in 69 cases. Of them, membranous insertion of the electrodes was done in 56 cases with ten cases requiring extended RW approach. Cochleostomy had to be done in 13 cases. Difficult and incomplete insertion of electrodes was the next common difficulty encountered in 9 cases. In one case, incompletely inserted last 6 electrodes were detected in postoperative X-ray with the Stenver’s view and had to be reoperated for reinsertion of the electrodes. The rest eight cases had incomplete insertion of the last electrode only. When the association of difficult insertion of electrodes with RWN visibility was analyzed with Fisher’s exact test, a statistical significance was yielded with p value = 0.02. This states, cases with poor visibility of RWN will have a difficult insertion of electrodes. In seven cases, impedance abnormality (short circuit/ open circuit) was encountered. Five cases had inflammatory changes such as granulation and mucosal edema in the middle ear cleft resulting in excessive mucosal oozing of blood. CSF gusher was seen in two cases who had enlarged cochlear aqueduct. Both cases were managed by giving hypotensive anesthesia and intraoperative mannitol, followed by acetazolamide for 3 days following surgery. In both cases surgery was uneventful. Similarly, in two cases below three years, a broad RW operculum was found which was difficult to drill out for complete exposure of RWM. Although the difficulties encountered were more prevalent in the age group of > 3– ≤ 6 years followed by ≤ 3 years, a statistically significant association couldn’t be yielded. The surgical difficulties in the different age groups and the related statistical associations have been shown in Table 3 and Table 4.

Table 3.

Difficulties encountered during CI surgery in the various age groups

Difficulties	Age group in years	No. of cases
Excessive mucosal bleeding from inflammatory changes	≤ 3	1
	> 3– ≤ 6	4
Requirement of extended tympanotomy due to poor visualization of RWN	≤ 3	30
	> 3– ≤ 6	29
	> 6	10
Requirement of extended RW approach or chochleostomy due to poor visualization of RWN	≤ 3	3(5)
	> 3– ≤ 6	4(5)
	> 6	6
Difficulty in drilling of broad operculum of RW	≤ 3	2
CSF gusher	≤ 3	1
	> 3– ≤ 6	1
Difficult and incomplete insertion of electrodes	≤ 3	1
	> 3– ≤ 6	6
	> 6	2
Technical difficulties (Impedance abnormalities)	≤ 3	2
	> 3– ≤ 6	4
	> 6	1

^*Numerical in the bracket depicts the number of cases requiring extended round window approach

Table 4.

Statistical association of surgical difficulties in different age groups and visibility of RWN in cases with difficult and incomplete insertion of the electrodes

Age group in years	Surgical difficulties		Chi-square test
	Yes	No
≤ 3	21	16	P value: 0.977
> 3– ≤ 6	19	16
> 6	9	7

Visibility of RWN via tympanotomy	Difficulty in insertion of electrodes		Fisher’s exact test
	Yes	No
Fully visible	2	46	P value: 0.020
Partially or completely invisible	8	32

The complications related to the surgery were predominantly intraoperative with the exposure of the facial nerve in its vertical portion being the most common. Of the ten cases, four were from > 3– ≤ 6 years age group and 6 were below three years. In majority cases, the exposure was due to an attempt to extend the tympanotomy window for proper visualization of RWN. Despite of the majority cases with the exposed vertical portion of the facial nerve having poor visibility of RWN (Type A and B), a statistically significant association could not be yielded (p value > 0.05). Two cases had CSF gusher which has already been mentioned. In one case of a 6 years-old child, scala vestibuli was accidentally opened. Another case of a 10-years-old child had accidental traumatic injury to the annulus during posterior tympanotomy. The complications in the different age groups and the related statistical associations have been shown in Table 5 and Table 6.

Table 5.

Complications associated with CI in the different age groups

Complications	Age group in years	No. of cases
Intra-operative
Exposed vertical portion of facial nerve	≤ 3	6
	> 3– ≤ 6	4
CSF gusher	≤ 3	1
	> 3– ≤ 6	1
Accidental opening of scala vestibuli	> 3– ≤ 6	1
Traumatic injury to annulus	> 6	1
Early post-operative
Facial nerve palsy(Grade II)	≤ 3	1
	> 3– ≤ 6	1
Late post-operative (device related)
Soft failure	≤ 3	3
Hard failure	> 3– ≤ 6	1

Table 6.

Statistical association of complications in different age groups and accidental facial nerve exposure in cases with different types of RWN

Age group in years	Complications (surgical and non-surgical)		Fisher’s exact test
	Yes	No
≤ 3	10	27	P value: 0.226
> 3– ≤ 6	7	28
> 6	1	15

Visibility of RWN via tympanotomy	Facial nerve exposure		Fisher’s exact test
	Yes	No
Fully visible	3	45	P value: 0.098
Partially or completely invisible	7	33

Discussion

Cochlear implantation for a developing country like Nepal, is yet a new surgical field. In this study, we evaluated the surgical difficulties and complications encountered in pediatric cases who had undergone cochlear implantation so far in Nepal.

The majority of cases (72) in this study were operated for pre-lingual deafness. The age group ranged from 12 months to 6 years with most of the cases being ≤ 3 years. Only a small proportion of our cases (16) were post-lingually deaf. Their age ranged from 6.5 to 14 years. Overall, M:F amongst the candidates was 1.4:1. Several countries have a nuanced discrepancy among the practice guidelines [3]. However, there is a consensus on the fact that CI in pre-lingual deaf children should be done preferably before 3 years of age which is the “sensitive period”. The brain in this period is plastic and can develop new neuronal networks on auditory stimulation [4]. In the developed nations, where newborn hearing screening programs have been implemented, early diagnosis of hearing loss and thus a timely intervention is possible. Various studies have shown a clear benefit of CI at an early age [5, 6]. But in our part of the world, many factors such as economic constraints, level of education, unawareness, and poor access to health facilities play a major role in the flexibility of the candidacy. Although early intervention holds a good promise over late, there are, however, significant benefits of CI even in post-lingual deaf children implanted after 5 years of age as shown by the study of Gaurav et al. [7]

In this study, a range of anatomical variations was encountered. The majority of these variations had an impact on difficulties and complications related to the surgery. Two cases with enlarged cochlear aqueduct (ECA) had CSF gusher during the surgery. We defined ECA as the cochlear aqueduct having a diameter of > 1 mm in the medial portion in CT scan [8]. Both cases had cochleostomy to be done due to poor visualization of RWN. However, cases with other inner ear anomalies, i.e., Mondini dysplasia and cystic apical cochlea, had an uneventful course. The prevalence of inner ear anomalies in cases with congenital hearing loss has been estimated to vary from 2 to 28.4% [9]. CSF gusher is one of the dreaded complications in this group of population. The incidence of CSF gusher ranges from 1 to 5% during cochlear implantation. However, in cases with inner ear anomalies it may increase to 30% [10]. Moreover, it is commonly encountered in pediatric population, mostly during cochleostomy [11]. A wide communication between sub-arachnoid space and inner ear is thought to result this pathology. A well-documented evidence of CSF gusher in cases with enlarged cochlear aqueduct is shown by the study of Bianchin et al. [12]. On the contrary, CSF gusher in cases with enlarged vestibular aqueduct (EVA) was very low. Mondini dysplasia and cystic apical cochlea fall in incomplete partition (IP) II category. Mondini’s malformation, as defined by Carlo Mondini, is a triad of defective apical part of the modiolus, EVA and slightly enlarged vestibule [13]. It is not uncommon to encounter CSF gusher in these cases as shown in the study by Hongjian et al. [14]. Of 197 cases of Mondini dysplasia amongst 442 cases with inner ear anomalies, 116 developed CSF gusher during surgery. However, in our study, of the two cases encountered, none developed any complications. The management of gusher involves a creation of a tight seal in the leakage site, which in our study was achieved with temporalis muscle. A tight seal can be achieved in various ways as discussed by Eftekharian et al. in their study such as creation of a small cochleostomy, sealing with temporalis fascia, periosteum, fibrin glue, etc.[11]. We also used mannitol intraoperatively and acetazolamide postoperatively for 3 days. Loundoun et al. in their study have advocated the use of hyperosmolar agents in reducing CSF gusher intraoperatively [15].

The visibility of the round window had a significant bearing in the surgical difficulties and complications. We could yield a statistically significant association between poor visibility of the RWN and difficult and incomplete insertion of the electrodes. In cases who had intraoperative FN exposure, cases with poor visibility of the RWN outnumbered those with good visibility, however, a statistical association could not be achieved. Poor visibility of RWN is one of the common difficulties that surgeons face. With the more posterior and inferior location of RWN, its visibility via standard posterior tympanotomy also decreases [16]. Results from studies by Kashio et al. and Sarafaz et al. have shown Type C RWN being the most common, however, Type A and Type B RWN are not uncommon [2, 17]. Requirement of cochleostomy is often warranted in cases with poor visibility of RW as seen in the studies by Panda et al. and Leong et al. [18, 19]. As the tympanotomy window has to be extended in cases with poor visibility of the RWN, the risk of exposing the FN also increases. In our study, we didn’t use facial nerve monitor during surgery. FN palsy of Grade 2 was the only early postoperative complication we encountered. As the nerve sheath was intact in both cases, they recovered completely in the subsequent weeks with oral steroids. Although having a low incidence, FN palsy is one of the frequently reported minor complications. In one of the largest case series of 4400 paediatric patients undergoing CI by Daneshi et al., intraoperative FN injury was seen in three cases (0.07%). All cases were managed by cable graft and didn’t fare well on follow-up [20]. Similarly, in another study by Tarkan et al., of 475 paediatric cases, two had FN exposure during posterior tympanotomy. Both cases developed transient FN palsy, which later improved with oral steroids [21].

Technical difficulties related to electrodes such as impedance abnormalities although didn’t have a significant impact in the surgical outcome, a lengthened operative time increased the duration of anesthetic exposure to the children in this study. Impedance abnormalities can be broadly classified into short circuit (SC), i.e., having an impedance value of ~ 1 kilohm or less, and open circuit (OC), i.e. having an impedance value of > 20–30 kilohms. A retrospective review on impedance data by Goehring et al. showed the incidence of impedance abnormalities in atleast 1 electrode intra-operatively to be 12%, with majority of the abnormalities being OC [22]. In another review by Terry et al. on complications related to CI surgery, various studies were shown to have electrode issues such as electrode failure, electrode migration, nonauditory stimulation, etc. Based on their review, electrode failure ranged from 6.8 to 9% in various studies [23]. A generalized rather than an isolated malfunction of electrodes causes poor audiological outcomes and may often require reimplantation. In our study, impedance abnormalities were confined to only 1–2 electrodes, so none of them had to be explanted.

Iatrogenic injury to the annulus and accidental opening of scala vestibuli were the fewest of all the complications. Injury to the annulus and tympanic membrane was well managed intraoperatively with conchal cartilage reconstruction along with temporalis fascia graft. The case with accidentally opened scala vestibuli had difficult and incomplete insertion of the last electrode. The postoperative course, however, was uneventful. Although not a surgical complication, device failure in four cases is worth mentioning. Device failure can be broadly classified as “soft failure” and “hard failure”. In soft failure, the patient may show progressively deteriorating performance or complain of aversive symptoms, e.g., shocking or popping, however, device malfunction cannot be detected by in vivo methods [24]. On the other hand, devices with hard failure show malfunction in in vivo testing [25]. Of our four cases, one had history of head trauma and thus causing the device malfunction. The rest of the three cases had soft failure and were diagnosed following a decrease in their performance. All the cases with device failure had Sonata TI 100 with standard electrode of MedEl company. The overall rate of CI device failure is estimated to be 4%–15% [26]. A retrospective review by Blanchard et al. showed a device failure rate of 5.7% with majority being hard failure (78%) [25]. Similarly, Ikeya et al. in their study had device failure in 4 out of 151 children. Two of them had a history of head trauma [27]. Complications such as wound infection, flap necrosis, extrusion or migration of the device, biofilm formation, etc. were not encountered in our series.

In this study, we didn’t analyze the functional outcome measures as majority of our patients are still under follow-up and intensive speech and language therapy. One of the commonest early postoperative morbidities is vertigo or dizziness. As a considerable size of our samples was pre-lingually deaf, this could have been missed on our evaluation.

Conclusion

CI with an experienced surgeon in pediatric population is a relatively safe procedure. Intraoperative bleeding, electrode-related problems, CSF gusher, and device failure were the commonest complications we encountered. FN palsy, although seen in two cases, had a good recovery. It is an unarguable fact that with the increase in the number of surgeries, the rate of detection of new complications will also increase. A study with a larger sample size and a longer duration of follow-up will have a lot to add up in the field of CI surgery.

Funding

None.

Compliance with Ethical Standards

Conflict of Interest

They author declare that they have no conflict of interest.