Since the first cochlear implant approved by the US Food and Drug Administration in the early 1980s, great advances have occurred in cochlear implant technology. With these advances, patient selection, preoperative evaluation, and rehabilitation consideration continue to evolve. This article describes the current practice in pediatric candidacy evaluation, reviews the medical and surgical considerations in pediatric cochlear implantation, and explores the expanding criteria for cochlear implantation within the pediatric population.
Pediatric candidacy evaluation
Patient selection is one of the most important determinants of cochlear implant success within the pediatric population. Therefore, comprehensive candidacy evaluation is critical to the patient success. The purpose of the candidacy evaluation is to determine the medical and audiometric suitability of the patient for cochlear implantation. Within the pediatric population, the candidacy evaluation varies slightly by age, but maintains a core of essential components. The pediatric cochlear implantation candidacy evaluation should comprise a battery of testing, including a medical evaluation, imaging evaluation, audiologic evaluation, speech and language evaluation, and patient/family counseling. Table 1 provides a synopsis of the components of the cochlear implantation evaluation.
| Evaluation | Components |
|---|---|
| Medical | History
Physical examination
|
| Imaging | High-resolution computed tomography of temporal bones Magnetic resonance imaging of the internal auditory canal |
| Audiologic | Pure tone audiometry Speech discrimination Hearing aid evaluation Speech perception assessment |
| Speech and language | Assess language development Screen for articulation disorders |
| Physiologic | Auditory brainstem response test Electrically evoked auditory brainstem response test |
| Cognitive and development | Assess for cognitive and developmental delays |
| Patient and family counseling | Establish patient and family expectation Assess family commitment to aural rehabilitation protocol Selection of cochlear implant device Informed consent |
Medical Evaluation
Various medical considerations must be factored when considering cochlear implantation in the pediatric population to facilitate patient selection, create realistic expectations, and design optimal rehabilitation protocol. The cochlear implantation team should be aware of the source of hearing loss. During the medical evaluation, a complete history and physical examination should be performed with the goals of identifying cause of hearing loss and evaluating birth history, family history, and history of otologic disease. In addition, immunization history should be confirmed because appropriate immunization is critical in pediatric cochlear implant candidates.
Sensorineural hearing loss within the pediatric population may be secondary to unknown cause, acquired cause, or hereditary cause. Unknown cause accounts for 15% to 44% of pediatric patients with sensorineural hearing loss ; successful implantation and rehabilitation have been documented in pediatric patients with sensorineural hearing loss of unknown cause.
In most reports approximately 15% to 40% of sensorineural hearing loss in pediatric patients is of acquired cause. Prenatal exposure to certain infections and teratogens has been associated with congenital sensorineural hearing loss. Thus, while obtaining the medical history, history of intrauterine exposure to cytomegalovirus, herpes virus, rubella, syphilis, toxoplasmosis, and varicella should be deciphered. In addition, history of intrauterine exposure to teratogens including alcohol, drug abuse, methyl mercury, and thalidomide should be obtained. During the perinatal period, low birth weight, anoxia, low Apgar score, hyperbilirubinemia, or sepsis have been associated with sensorineural hearing loss. A complete perinatal history should be obtained highlighting these factors as well as history of prematurity, intubation, and neonatal intensive care unit admission because all of these factors may contribute to sensorineural hearing loss. Gentamicin is commonly used in the management of neonatal sepsis. History of aminoglycoside administration, including gentamicin, furosemide and other ototoxin administration, mumps, and meningitis should be noted.
Sensorineural hearing loss has a hereditary cause in most pediatric patients, accounting for approximately 40% to 50% in most reports ; therefore, a complete family history should be obtained, with a focus on relatives with congenital or early-onset hearing loss. Hereditary sensorineural hearing loss may be categorized as nonsyndromic sensorineural hearing loss or syndromic sensorineural hearing loss; nonsyndromic sensorineural hearing loss accounts for most hereditary congenital hearing loss. Mutations within the connexin 26 genes, namely the GJB 2 and GJB 6 genes, are responsible in most cases. Patients with deafness associated with mutations in the connexin 26 genes have been found to be excellent candidates for cochlear implantation because they perform equal to or better than other cochlear implant patients in reading comprehension, nonverbal cognition, speech performance, language perception, speech perception, and speech intelligibility.
Patients should be evaluated for signs and symptoms consistent with syndromic forms of sensorineural hearing loss. Patients with various forms of syndromic sensorineural hearing loss have been implanted with successful aural rehabilitation including Usher syndrome, Pendred syndrome, Refsum disease, Jervell Lange-Nielsen syndrome, Waardenburg syndrome, branchio-oto-renal syndrome, and CHARGE syndrome. Of concern amongst this group are patients with syndromes that have characteristic findings that complicate implantation or aural rehabilitation. Both Usher syndrome and Refsum disease include retinitis pigmentosa and progressive blindness; thus, early cochlear implantation should be performed before onset of severe visual deficiency to optimize outcome. The first sign of vestibular dysfunction in patients with Usher syndrome is delayed walking. If it is age appropriate, age at onset of walking should be obtained during the medical interview. Patients with CHARGE syndrome have variable benefit from cochlear implantation secondary to difficulties in aural rehabilitation associated with developmental delay and mental retardation. Although Jervell Lange-Nielsen syndrome is a rare syndrome, patients with congenital sensorineural hearing loss should undergo electrocardiography because of the potential associated prolonged QT interval and propensity of arrhythmia, and cardiac syncope. Patients presenting with a history of a seizure disorder, on anticonvulsants, and with an associated hearing loss should be considered to have Jervell Lange-Nielsen syndrome. Patients with the confirmed diagnosis of Jervell Lange-Nielsen syndrome, preoperative cardiology consultation should be performed, and evaluation of the patient’s immediate family suggested. Because of the significant risk of cardiac event with the administration of general anesthesia, a pacemaker or defibrillator should be considered before cochlear implantation and β-blockers should be administered within the perioperative period. A complete otolaryngology physical examination should be performed with a focus on identifying craniofacial anomalies or physical findings that may elucidate any of the associated syndromes outlined earlier.
In addition, the patient should be screened for chronic otitis media. A history of episodes and frequency of otitis media should be performed. A pressure equalization tube may be required at the time of, before, or after cochlear implantation for management of chronic otitis media with effusion.
A history of immunization is a critical component of the medical cochlear implantation evaluation. The rate of meningitis amongst children with hearing loss has been shown to be higher than in those children without hearing loss. Further, children with cochlear implants are at a higher risk for meningitis than children with hearing loss who have not received cochlear implants. Several risk factors have been associated with these findings, including lack of appropriate immunization. Approximately 90% of cases of meningitis after pediatric cochlear implantation are caused by infections with Streptococcus pneumonia . In October 2003, the United States Centers for Disease Control and Prevention (CDC) published recommendations that all cochlear implant recipients receive age-appropriate vaccination against Streptococcus pneumonia. These recommendations were updated in 2010. Table 2 provides a summary of the current immunization guidelines. All children younger than 24 months should receive the 7-valent pneumococcal conjugate vaccine (PCV7). Children aged 24 months to 59 months who have not previously been vaccinated should undergo a modified vaccination protocol as depicted in Table 2 . All patients older than 5 years should receive the 23-valent pneumococcal polysaccharide vaccine (PPV23). All patients receiving cochlear implantation should be up to date on age-appropriate pneumococcal vaccination at least 2 weeks before cochlear implantation if possible according to the CDC recommendations. Within the medical evaluation, the immunization record should be reviewed to assess compliance with CDC recommendations for pneumococcal vaccination. If discrepancies exist, vaccinations should be administered to maintain compliance with pneumococcal vaccination recommendations.
| Age at First PCV 13 Dose | PCV 13 Primary Series | PCV 13 Booster Dose | PPSV Dose |
|---|---|---|---|
| 2–6 months | 3 doses, 2 months apart | 1 dose at 12–15 months of age | Indicated at ≥24 months of age |
| 7–11 months | 2 doses, 2 months apart | 1 dose at 12–15 months of age | Indicated at ≥24 months of age |
| 12–23 months | 2 doses, 2 months apart | — | Indicated at ≥24 months of age |
| 2–6 years | 2 doses, 2 months apart | — | After PCV 13 series |
| 6–18 years | 1 dose | — | After PCV 13 dose |
| ≥18 years | — | — | Prior to implant |
Imaging Evaluation
Cochleovestibular anomalies are common amongst pediatric cochlear implant candidates because they often correlate with sensorineural hearing loss. Therefore, preoperative evaluation of cochleovestibular anatomy is an important component of the pediatric cochlear implant evaluation. The goals of the preoperative imaging evaluation are to determine whether there are cochleovestibular anomalies that preclude implantation, to evaluate for evidence of luminal obstruction, to identify findings that may complicate the surgery or subsequent patient management, and to determine which ear may be the most appropriate to implant.
In evaluating patients for cochleovestibular anomalies, the patient is assessed for an implantable cavity in proximity to stimulable neural elements with projections that contact the auditory cortex. Up to 35% of pediatric cochlear implant candidates have cochleovestibular anomalies. When present, cochleovestibular anomalies occur bilaterally in 65% of patients and are similar in 93% of patients. The most commonly used classification system for cochleovestibular malformations, by Jackler and colleagues, is presented in Table 3 . Although complete labyrinthine aplasia and cochlear aplasia represent the least commonly encountered deformities, their presence precludes the option of cochlear implantation. Alternative methods of language rehabilitation must be explored within this patient population. During the imaging evaluation, cochlear aplasia must be differentiated from common cavity deformity because the propensity for cochlear implantation differs in these 2 conditions. Patients with common cavity deformity, cochlear hypoplasia, incomplete partition deformity, lateral semicircular canal dysplasia, and enlarged vestibular aqueduct may successfully undergo cochlear implantation. However, knowledge of these deformities preoperatively is critical to success in implantation because the presence of the deformities governs electrode array choice and necessitates alterations in operative technique.
| Cochlear Status | Malformation (%) |
|---|---|
| Absent or malformed cochlea | Complete labyrinthine aplasia (1) Cochlear aplasia (2) Cochlear hypoplasia (11.2) Common cavity (19.4) Incomplete partition (42) |
| Normal cochlea | Lateral semicircular canal dysplasia (7.1) Enlarged vestibular aqueduct (17.3) |
During the imaging evaluations, evidence of luminal obstruction is assessed. Luminal obstruction may result from inner ear inflammation, abnormal bone metabolism, or trauma. The most common cause of luminal obstruction within the pediatric population is postmeningitis labyrinthitis ossificans. Luminal obstruction may also result from hematogenous infections including septicemia, mumps, rubella, and viral infections or from suppurative labyrinthitis secondary to otitis media or cholesteatoma. Early-onset Paget disease may cause luminal obstruction. In addition, luminal obstruction may result from temporal bone fractures. The findings of luminal obstruction may interfere with complete insertion of cochlear implant electrode. Thus, identification of luminal obstruction must be determined preoperatively to assist in preoperative planning regarding side of implantation and intraoperative technique for cochleostomy and drill-out.
Findings that may complicate cochlear implant surgery or subsequent patient management are appraised during the imaging evaluation. Amongst pediatric patients with vestibulocochlear anomalies, approximately 15% of patients have an aberrant facial nerve course. An aberrant facial nerve may preclude the traditional facial recess approach for cochleostomy and electrode insertion. Vascular anomalies may complicate cochlear implant surgery as well. Extreme anterior position of the sigmoid sinus may contract exposure to the facial recess. This situation has been reported in approximately 1.6% of patients. High-riding jugular bulbs are present in up to 6% of patients. Jugular diverticuli are exceedingly rare. In addition, the presence of high-riding jugular bulbs or jugular diverticuli overlying the round window niche or promontory may complicate cochlear implantation surgery. Aberrant carotid artery and dehiscent carotid artery may complicate drill-out procedure in patients with ossified cochlea. During the imaging evaluation, mastoid and tympanic pneumatization is evaluated. The imaging is screened for evidence of enlarged vestibular or cochlear aqueduct. Enlargement of either the vestibular aqueduct or the cochlear aqueducts may be associated with an increased risk of cerebrospinal fluid (CSF) gusher. However, this assertion remains controversial.
High-resolution computed tomography (HRCT) of the temporal bones and high-resolution magnetic resonance imaging (MRI) of the otic capsule and internal auditory canal are the most commonly used imaging modalities in the pediatric cochlear implant imaging evaluation. However, the protocol by which these 2 imaging modalities are used remains variable. HRCT of the temporal bones is beneficial in identifying cochlear dysplasia, labyrinthine ossification, position of the facial nerve, aeration of the temporal bone, position of the sigmoid sinus, high-riding jugular bulb, carotid artery dehiscence, jugular diverticuli, size of the vestibular aqueduct, narrowing of the cochlear nerve canal, modiolar deficiency, and lateral semicircular canal dysplasia. There is considerable overlap in the imaging ability of HRCT of the temporal bone and MRI of the internal auditory canal. MRI of the internal auditory canal may be used to identify cochlear dysplasia, labyrinthine ossification, the position of the sigmoid sinus, the size of the vestibular aqueduct, narrowing of the cochlear nerve canal, modiolar deficiency, lateral semicircular canal dysplasia, evaluation of the internal auditory canal neural contents, and the caliber of the cochlear nerve. On comparison of the 2 modalities, MRI has been found to be superior in identifying early ossification of the labyrinth and soft tissue anomalies in the inner ear, the most important of which is presence or absence of the cochlear nerve. HRCT of the temporal bones is superior at identifying the bony labyrinth, including enlarged vestibular aqueduct and caliber of the cochlear nerve canal. No benefit has been shown in using dual-modality (HRCT and MRI) screening in the pediatric population before cochlear implantation. Specificity and negative predictive value for MRI alone and HRCT alone are both high; there is no significant difference between the ability of MRI and HRCT to predict abnormal inner ear anatomy at the time of surgery. For this reason, the choice of primary screening modality in imaging before cochlear implantation is left to the discretion of the cochlear implant team and center. If the patient has any symptoms that may warrant an MRI, this imaging modality should be used preoperatively given the current US Food and Drug Administration (FDA) guidelines precluding MRI in patients with existing cochlear implants.
Audiologic Evaluation
The audiologic evaluation is used to identify current aural performance and to guide aural rehabilitation after cochlear implantation. The main components of the audiologic evaluation include pure tone average assessment, hearing aid evaluation, speech perception testing, and electrophysiologic evaluation.
Current pediatric guidelines for cochlear implantation stipulate parameters for pure tone audiometry, speech perception, and aided performance required for cochlear implant candidacy. Table 4 details the current FDA guidelines for the most recently approved devices in pediatric cochlear implantation. In general, unaided pure tone audiometry is performed to ensure sensorineural hearing loss with threshold of greater than or equal to 90 dB hearing level (HL). In addition, otoacoustic emissions should be performed. Presence of normal otoacoustic emissions in the presence of sensorineural hearing loss should increase the suspicion for auditory neuropathy/auditory dyssynchrony (AN/AD), the diagnosis of which greatly impacts aural rehabilitation methodology and expected outcomes.
| Device Name | Device Manufacturer | Most Recent Approval | Pediatric Approval | Indications |
|---|---|---|---|---|
Clarion HiResolution TM Bionic Ear System:
| Advanced Bionics Corporation (Advanced Bionics, Sylmar, CA, USA) | 2003 | 12 mo–17 y | Profound, bilateral sensorineural hearing loss (>90 dB HL) Use of appropriately fit hearing aids for at least:
Little or no benefit from appropriately fit hearing aids
|
| Nucleus Freedom implant with Contour AdvanceTM Electrode CI512 and CI513 | Cochlear Corporation (Cochlear Americas, Centennial, CO, USA) | 2009 | 12 mo–17 y | Children 12–24 mo
|
| Med-El Pulsar CI100 | Med-El (MED-EL, Durham, NC, USA) | 2005 | 12 mo–17 y | Bilateral, profound sensorineural hearing loss (>90 dB at 1000 Hz) Little or no benefit from appropriately fit binaural hearing aids
|
Before consideration for cochlear implantation, pediatric candidates usually undergo a trial period with a hearing aid. The length of the hearing aid trial is determined by the implant center based on the characteristics of the candidate, including level of hearing loss, previous hearing aid experience, and other disabilities. Pediatric patients must undergo binaural hearing aid trials for a minimum of 3 to 6 months to document lack of or minimal improvement in auditory development. With children aged 24 months and younger, lack of auditory skills development is assessed by lack of meeting auditory milestones and poor performance on speech perception tests, including the Infant-Toddler Meaningful Auditory Integration Scale, Meaningful Auditory Integration Scale, or Early Speech Perception Test. In children approximately aged 2 years and older, lack of auditory skills development is assessed by open-set word recognition and open-set sentence recognition testing, including the Lexical Neighborhood Test and the Multisyllabic Lexical Neighborhood Test. Additional speech perception tests used in the pediatric cochlear implant candidacy evaluation include the Bamford-Kowal-Bench (BKB) Sentences, Early Speech Perception Test (Low Verbal Version or Standard Version), Glendonald Auditory Screening Procedure, Ling Sound Test, Minimal Pairs, Monosyllable-Trochee-Spondee Test, Northwestern University Children’s Perception of Speech Test, Phonetically Balanced Kindergarten Word List, and Word Intelligibility by Picture Identification.
Electrophysiologic Evaluation
Electrophysiologic testing is of particular importance in evaluating younger pediatric patients (≤24 months of age) and patients with development delay. Electrophysiologic testing serves as an objective measure of audiologic function. The electrophysiologic evaluation may include auditory brainstem response testing or electrically evoked auditory brainstem response testing. Auditory brainstem response testing serves as an objective measure of degree of sensorineural hearing loss in the pediatric cochlear implant evaluation in prelingually deaf and developmentally delayed patients. In addition, auditory brainstem response testing assists in the screening and diagnosis of AN/AD. Patients with AN/AD present with normal otoacoustic emissions and evidence of sensorineural hearing loss on auditory brainstem response testing. Patients with AN/AD have a more variable outcome in cochlear implantation.
Electrically evoked auditory brainstem response testing is most commonly used in pediatric patients less than the age of 24 months, patients with significant developmental delay, patients with observed vestibulocochlear anomalies identified during the imaging evaluation, and patients in whom no residual hearing has been detected on routine audiometry or traditional auditory brainstem response testing. This test confirms electrical stimulability of the auditory system via auditory brainstem response testing in these pediatric patient groups. The presence of stimulability and auditory brainstem response has been correlated with postoperative stimulability after cochlear implantation. Electrically evoked auditory brainstem response testing assists in the selection of the ear for implantation in patients without any residual hearing, in patients with longstanding history of sensorineural hearing loss, and patients with inner ear malformations.
Electrophysiologic testing is of great assistance in evaluating patients with AN/AD. Amongst pediatric patients with AN/AD, approximately 50% show some degree of open-set speech perception abilities. Failure to achieve open-set speech perception after cochlear implantation in pediatric patients is believed to be secondary to cochlear nerve deficiency, lack of electrical-induced neural synchronization, and coexisting developmental delays. Electrically elicited compound action potential testing may be beneficial in assessing which patients with AN/AD perform successfully after cochlear implantation, because robust response has been correlated with improved performance.
Speech and Language Evaluation
The speech and language evaluation should be performed in all pediatric patients before cochlear implantation. This strategy allows for the determination as to whether factors in addition to hearing impairment are contributing to hindrance in auditory development. Numerous children with developmental, cognitive, and language delay have been implanted with successful aural rehabilitation after modified aural rehabilitation protocols to optimized speech perception and production. Children with cognitive and developmental delays have been found to develop speech perception skills at a slower rate compared with children without. Despite this finding, cochlear implantation in patients with cognitive and developmental delay has been shown to improve quality of life, increase listening and communication skills, enhance self-sufficiency, and enhance their ability to interact with others.
During the speech and language evaluation, the pediatric patients are screened for developmental language and articulation disorders. In addition, a description of the patient’s communication status with respect to normative data by age is performed. This strategy assists in the development of appropriate goals and expectations of cochlear implantation and in the design of rehabilitation program for use postoperatively.
Patient and Family Counseling
After completion of the medical, imaging, audiologic, physiologic, speech and language, and cognitive and development evaluation, patient and family counseling is performed. The goal of the patient and family counseling is to summarize the findings of the cochlear implant evaluation and provide the family with recommendations from the cochlear implant team. At this time, expectations for cochlear implantation outcome are established. Explanation and assurance of understanding regarding the components and extent of postoperative aural rehabilitation are explained to the family. The level of commitment of the patient and family to the requirements of aural rehabilitation is assessed. Any questions asked by the family are answered. The family should be provided with literature regarding the available devices for implantation, and with the assistance of the cochlear implantation team, a decision regarding desired device for implantation are made. The patient’s family is provided with a detailed description of the cochlear implantation procedure, informed consent is obtained, and the procedure and all options to the procedure are discussed.
Surgical considerations
Various surgical considerations must be factored when performing cochlear implantation within the pediatric population. The cochlear implant surgeon must be aware of the potential need for alterations in the cochlear implantation procedure to accommodate cochleovestibular anomalies within the pediatric population and the considerations in electrode array choice to optimize postoperative aural rehabilitation. The surgeon should be abreast of techniques for simultaneous, bilateral cochlear implantation in children. In addition, the cochlear implant surgeon should be aware of complications that may accompany cochlear implantation in the pediatric population to minimize associated morbidity. The surgical section presented here is an overview of important considerations in pediatric cochlear implantation.
The Traditional Pediatric Cochlear Implantation Procedure
The traditional approach for cochlear implantation in the pediatric population uses the transmastoid, facial recess approach similar to that used in the adult population. Because the cochlear and the facial recess are adult size at birth, there is no additional risk related to cochleostomy and electrode insertion. The main components of the traditional pediatric implant procedure include incision and receiver placement design, simple mastoidectomy with facial recess, drill-out for receiver placement, securing of the receiver, cochleostomy, electrode placement, device telemetry, and closure. Mild variations are performed based on surgeon preference, but there are general principles that govern each stage:
- •
The procedure is performed with the patient under general anesthesia.
- •
Minimal or no shaving is performed in the postauricular region to facilitate exposure.
- •
The incision is designed and marked with a marking pen.
- •
A superior extension may be incorporated to facilitate implant receiver placement.
- •
The placement of the receiver is designed 2 cm posterior to the postauricular incision and superior to the imaginary line extending from the lateral canthus and superior aspect of the external auditory canal.
- •
The proposed position of the receiver is marked.
- •
Facial nerve monitoring is used through the duration of the procedure.
- •
The patient is prepared and draped in the normal sterile fashion.
- •
The skin incision is infiltrated in 1:100,000 epinephrine (or 2% lidocaine 1:100,000 epinephrine) in older children or 1:200,000 epinephrine in younger children.
- •
The skin incision is created as designed and skin flaps are elevated to the level of the posterior external auditory canal.
- •
Periosteal incisions are created and the Palva flap is elevated.
- •
Fascia for occlusion of the cochleostomy may be obtained from the most posterior portion of the Palva flap.
- •
The periosteum is then elevated posteriorly and superiorly for placement of the electrode receiver.
- •
The angulation of the receiver has evolved over time without impact on patient satisfaction, cosmesis, or clinical and functional outcomes. A recent survey revealed that the average placement of cochlear implant receiver is currently 56.8° relative to the skull base.
- •
The implant template may be used to facilitate assessing adequacy of periosteal elevation and to mark positioning of receiver.
- •
The cortex may be drilled out to facilitate stability of the receiver, prevent cutaneous complication (including implant exposure), and to improve cosmetic appearance via a lower profile.
- •
The bone in the periphery of the drill-out may be completed to the level of the dura, creating a central island of bone if necessary to facilitate deeper inset of the receiver.
- •
Simple mastoidectomy is performed with identification of the facial nerve and thinning of the posterior canal wall, facilitating exposure and light penetrance into the facial recess.
- •
The facial recess should be funnel shaped, not a tunnel, to allow thorough visualization of and access to the posterior mesotympanic structures.
- •
Maximum exposure is of utmost importance to allow proper cochleostomy placement and this can be accomplished by skeletonizing the facial nerve and the chorda tympani nerve without injury to the nerves and removing the bone anterior to the facial nerve over the stapedius muscle.
- •
The round window niche is visualized and drilled for complete visualization of the round window membrane.
- •
Copious irrigation and attention to drill shaft position are used to minimize the risk of heat transmission and trauma to the facial nerve.
- •
The cochleostomy is then performed.
- •
The positioning of the cochleostomy varies by institution and by surgeon preference. However, placement of the cochleostomy inferior or anteroinferior to the round window membrane has been found to facilitate atraumatic insertion of cochlear implant electrodes within the central scala tympani.
- •
The size of electrode varies slightly by device. The smallest cochleostomy should be performed for safe and easy advancement of the cochlear implant electrode without resistance.
- •
Using a 1-mm diamond burr, the cochlea is drilled to expose endosteum.
- •
Using a Barbara needle, straight pick, or McGee oval window rasp, with care not to displace bone fragments into the cochlea, the cochleostomy is widened.
- •
In addition, suctioning over the cochleostomy should not be performed to decrease risk of trauma.
- •
Many surgeons choose to use the round window for insertion depending on the electrode being used and the anatomic visualization of the round window.
- •
Round window insertion is facilitated by removal of the superior and posterior bony overhanging round window niche.
- •
The device is next placed into position.
- •
The receiver is secured. Various techniques are used for securing the device without significant impact on outcome.
- •
Once the device is secured, the electrode is atraumatically advanced through to cochleostomy with a goal of complete insertion.
- •
The cochleostomy is packed with fascia, muscle, periosteum or fat to prevent perilymph fistula and to seal the cochlea to prevent bacterial penetration into the cochlea in the event of otitis media.
- •
At this time, neural response telemetry may be performed. Intraoperative neural response telemetry has been shown to provide valuable information regarding electrical output, the response of the auditory system to electrical stimulation, and preliminary device programming data.
- •
On completion of the neural response telemetry, the periosteum is closed and the incision is closed.
- •
Intraoperative radiograph of the skull may be taken to confirm electrode positioning.
- •
The patient is awakened from general anesthesia and transferred to the postanesthesia recovery unit.
- •
Patients may be monitored overnight; however, cochlear implantation in the pediatric population may safely be performed on an outpatient basis without increased incidence of morbidity or complications.
Cochlear Implantation in Pediatric Patients with Vestibulocochlear Anomalies
Approximately one-third of pediatric patients undergoing cochlear implantation have some degree of vestibulocochlear abnormality. However, these patients have successfully undergone a cochlear implantation procedure. Knowledge of the presence of the malformation and minor alterations of the cochlear implantation procedure facilitates successful implantation and aural rehabilitation.
Incomplete partitioning
Incomplete partitioning is the most commonly encountered vestibulocochlear anomaly. With incomplete partitioning, the cochlea completes 1 to 1.5 turns instead of the 2.5 associated with normal cochlear development around the modiolus. The 1.5 turns typically comprise the basal turn with the apparent confluence of the middle and apical turn. In patients with true Mondini-type cochleas (incomplete partitioning) regular full electrodes can be used successfully and the cochlear implantation procedure may be performed as described earlier. The main concern within these patients is partial insertion of the electrode because of the lack of 2.5 complete turns to the cochlea. Despite this concern, patients with incomplete partitioning and cochlear hypoplasia have undergone successful aural rehabilitation and function well after cochlear implantation. The main issue in these patients is optimizing the number of electrodes implanted and the functionality of these electrodes.
Common cavity deformity
Common cavity deformity is the second most common vestibulocochlear anomaly in the pediatric population. Common cavity deformity represents a confluence of the cochlea and vestibule into a common rudimentary cavity lacking internal architecture. Neural components within the common cavity have been histologically shown to lie within the periphery of the common cavity. Ideal electrode placement in the common cavity therefore requires placement of the electrode along the periphery of the common cavity with a circumferential vector of stimulation. For these reasons, straight-banded, circumferentially stimulating electrode array may be of benefit in patients with common cavity deformity. With common cavity deformity, a transmastoid antral approach most often can be used without need for facial recess to perform cochleostomy. An attempt should be made to avoid positioning the cochleostomy directly opposite the internal auditory canal. The electrode is inserted along the lateral wall to prevent kinking and bending. Intraoperative fluoroscopy has been shown to facilitate successful implantation in patients with common cavity deformity. Newer portable intraoperative computed tomography scanners can also be used.
Intraoperative fluoroscopy
Intraoperative fluoroscopy has been proposed for cochlear implantation in pediatric patients with vestibulocochlear anomalies. Intraoperative fluoroscopy allows real-time assessment of cochlear implant electrode positioning during insertion. Intraoperative fluoroscopy has been found to be safe for patients and pose minimal risk to operative staff. Radiation exposure to the patient should not exceed 200 rad for the duration of the procedure. Most contemporary fluoroscopy units produce radiation doses less than 10 rad per minute. The average exposure during cochlear implantation is for less than 3 minutes’ total fluoroscopy time. In cochlear implantation with intraoperative fluoroscopy, the C-arm is positioned and target image acquisition confirmed after induction of general anesthesia, before initiation of the procedure. The C-arm is placed with the beam director beneath the operative table in an anti-Stenvers view. The beam is narrowed, centered, and magnified to facilitate visualization of the cochlea. The implantation procedure then proceeds as described earlier.
Intraoperative fluoroscopy has been shown to facilitate cochlear implant placement in patients with vestibulocochlear anomalies. It allows for real-time visualization of the electrode during the insertion process and the insertional stop point is delineated, which can minimize kinking and bending of the electrode and prevent internal auditory canal insertions. It has also been described for use in cases in which the intracochlear behavior of the electrode array cannot be predicted, in use with new electrode designs, and in patients with intraluminal obstruction of the cochlea (ie, labyrinthitis ossificans).
Cochlear Implantation in Pediatric Patients with Ossified Cochleae
Since the introduction of the 7-valent pneumococcal conjugate vaccine and the Haemophilus influenza type B vaccine, the incidence of postmeningitic sensorineural hearing loss has declined. However, in cases of pediatric meningitis, 5% of patients present with profound sensorineural hearing loss. Early bilateral cochlear implantation, before complete cochlear obstruction from labyrinthitis ossificans, has been associated with improved outcomes in terms of completeness of insertion, speech intelligibility, and sound localization. Cochlear ossification associated with postmeningitic deafness in the pediatric population requires additional surgical consideration to drill out the area of obstruction, allowing for implant electrode advancement.
Ossification in postmeningitic patients can be classified in 3 categories:
- 1.
obliteration of the round window niche
- 2.
obstruction limited to the inferior segment
- 3.
upper segment obstruction.
Slight variations in operative technique are associated with implantation in each of these scenarios.
Obliteration of the round window niche
With obliteration of the round window niche from a fibrous tissue obliteration to dense calcific bony occlusion, drill-out must be performed within the region of the round window niche for exposure of the scala tympani. No evidence of the round window niche can be identified in the most severe cases. With obliteration of the round window niche, drill-out should be performed approximately 1.5 mm inferior to the pyramidal process, allowing for exposure to the region of the round window. If not visible, the niche can be identified by encountering less dense and more lightly colored bone within this region. Following this bone anteriorly reveals the scala tympani, allowing for cochleostomy performance and electrode insertion.
Obstruction limited to the inferior segment
In most cases, limited obstruction of the basal turn of the cochlea is identified. The character of the obstruction may vary from a fibrous tissue band to dense calcified bony plate. The length of obstruction within the inferior segment greatly impacts the surgical approach to implantation. Involvement limited to the inferior 8 to 10 mm of the basal turn may be subjugated by drilling out over the round window niche as described earlier with extension along the basal turn of the cochlea. The open lumen may be encountered beyond the drill-out by tunneling through with a fine pick, delicate drill, or hand-held laser. Once luminal patency is observed, cochlear implant electrode may be inserted.
Upper segment obstruction
In the final scenario of involvement within the ascending segment of the cochlea, the initial drill-out is performed as described earlier. Once the inferior 8 to 10 mm of the cochlea are opened, various options for implantation have been described. Partial insertion may be performed. With ossified cochleae and partial insertions, the use of double-array electrodes via a basal and middle turn cochleostomy has been found to result in more usable electrode contacts than single-stranded arrays. The use of a depth gauge or test electrode may be useful in determining which electrode to insert. In general, if the test electrode cannot be inserted beyond the proximal basal segment into the pars ascendens and superior, a double array is considered. A double array necessitates creation of an additional, second cochleostomy in the second turn of the cochlea. To prepare for the second cochleostomy, the incus, incus bar, and stapes superstructure are removed to maximize access anterior to the oval window. Using a 1-mm diamond burr and copious irrigation, this superior cochleostomy is created immediately anterior to the oval window, adjacent to the annular ligament of the stapes footplate. The cochleariform process serves as the superior limit of dissection and a landmark for facial nerve location. Drilling below the cochleariform process parallel to the tensor tympani muscle is critical to avoid damage to the facial nerve. One array is placed in the basal turn tunnel (described earlier) and the other array is inserted either retrograde or anterograde through the superior cochleostomy, based on patient anatomy and manufacturer recommendations. (Cochlear [Cochlear Americas, Centennial, CO, USA] prefers anterograde and MED-EL [MED-EL, Durham, NC, USA] encourages retrograde.) If no lumen is found in the upper cochlea, an apical tunnel can be created through the new bone using a rasp or 0.5-mm to 1-mm diamond bur. This tunnel should be directed toward the tensor tympani, away from the probable location of neural elements. The second array can then be placed in this superior tunnel. In general, the electrodes should not overlap and forceful insertion or overinsertion, leading to kinking or tip roll-over, should be avoided. Each cochleostomy should be effectively packed with periosteum or fascia to firmly secure the electrode position.
Pediatric patients with incomplete insertion with at least 10 electrodes have been shown to obtain open-set speech recognition. If the ossification is limited to the scala tympani, the cochleostomy may be extended superiorly 1 to 2 mm, allowing for insertion of the electrode within the scala vestibule. If both the scala tympani and scala vestibule are involved beyond the inferior segment, a perimodiolar trough may be drilled out. This technique requires a radical mastoidectomy. The tympanic membrane (TM), malleus, and incus are removed, and the external auditory canal is obliterated. The carotid artery is skeletonized. The inferior segment is drilled out as described earlier, and the drill-out is continued to create an open trough around the modiolus. The electrode is then placed through the inferior segment tunnel into the trough and secured in place with fascia and tissue glue.
Complications in Pediatric Cochlear Implantation
Cochlear implantation within the pediatric population is safe and effective. Although major complications are rare, the cochlear implant surgeon should be well versed of the potential associated complications and potential means for their prevention. The rate of complications in pediatric cochlear implantation is on average approximately 10%. Most complications reported represent minor complications, with major complications accounting for only 20% to 30% of all complications on average. The presence of inner ear malformation has been correlated with an increased rate of complication in pediatric cochlear implantation. Complications after cochlear implantation may be classified as early (within the first 2 weeks of implantation) and late (greater than 2 weeks after cochlear implantation).
Infection
Amongst the early complications of cochlear implantation, infection is the most commonly reported, presenting as wound infections or otitis media. Infection comprises approximately half of all complications, early and late, after cochlear implantation. For this reason, perioperative antibiotics are commonly administered, including a brief postoperative course of oral antibiotics after discharge. Additional early complications of hematoma and seroma, which occur in approximately 2% of patients, may contribute to the development of postoperative wound infection. For this reason, care should be taken to ensure a completely dry field before closure of incision. In addition compressive dressing is applied postoperatively to prevent the accumulation of blood or serous fluid. When large seromas and hematomas occur, evacuation should be performed; whereas small stable collections may be monitored closely.
Facial nerve paresis
Despite the fact that facial nerve sheath exposure is commonly reported in pediatric cochlear implantation, facial nerve paresis is an uncommon complication of cochlear implantation surgery. In up to 9% of patients, facial nerve sheath and nerve exposure has been reported. Intraoperative facial nerve monitoring should be used in all cochlear implant procedures to minimize injury. In addition, during posterior tympanotomy and cochleostomy, copious irrigation should be used and care should be taken to prevent inadvertent contact of the drill shaft with the facial nerve. Injury to the chorda tympani nerve is a more common. Rates of chorda tympani injury have been reported in up to 20% of pediatric patients. With the increase in bilateral cochlear implantation, care should be taken to maintain the integrity of the chorda tympani nerve while opening the facial recess.
CSF fistulas
CSF fistulas may present early or late after cochlear implantation in the pediatric population. CSF fistulas have been reported to present in up to 1% of pediatric patients after cochlear implantation. Secondary meningitis has been reported in only a small percentage of pediatric patients after cochlear implantation. CSF fistulas may be prevented by securely packing the cochleostomy around the electrode after implantation with fascia or muscle to prevent leakage.
Device failures
In addition, device failures may present early or late after cochlear implantation. Device failure has been reported to occur at a rate of up to 2%. There are no methods available to prevent late device failures; however, early device failures may be circumvented. Intraoperative telemetry may be helpful in ensuring the function of the cochlear implant device at the time of implantation, decreasing the risk of early failure.
Cholesteatomas
Cholesteatomas have been reported after cochlear implantation as late complications. Iatrogenic, undiagnosed TM perforation or preexisting chronic ear disease may be the inciting factors in cholesteatoma formation. TM perforation and cholesteatoma place the patient at risk for electrode exposure. Multiple surgical options exist for the management of TM perforation, chronic ear disease, or cholesteatoma in the setting of planned cochlear implantation. Ideally, risk factors for the development of cholesteatoma or chronic otitis media (such as chronic, purulent otorrhea, large TM perforation, or significant TM retraction pockets) are identified at the initial cochlear implantation evaluation. Surgical strategy should be individualized and incorporate a range of factors, including the extent of middle ear disease and mastoid disease, the size of the TM perforation or retraction pocket, and the presence of ongoing or active infection.
Evidence exists to support both single-stage and multistage procedures to address chronic ear disease and cholesteatoma before cochlear implantation. Multistage procedures require postponement or delay of implantation until creation of a safe, dry ear is confirmed, whereas single-stage procedures can be combined with and performed at the same time as cochlear implantation. In cases of TM perforations or small retraction pockets, cartilage tympanoplasty techniques can be used to prevent the development of secondary, acquired cholesteatoma. If cholesteatoma is found, a radical mastoidectomy with removal of all squamous epithelium and closure of the external auditory canal (ie, creation of a blind sac) is an option. This procedure can be single-stage or multistage and attempts to create a safe cavity for the cochlear implantation device by removing all potentially infected tissue and squamous epithelium. Although rates of cholesteatoma recurrence are low with this technique, the inability to visually monitor the surgical cavity (because of closure of the canal) is a frequently cited drawback of this approach.
Stay updated, free articles. Join our Telegram channel
Full access? Get Clinical Tree
