Cochlear Implant Surgery

Cochlear implantation has become a routine procedure in the United States and worldwide for the management of severe-to-profound sensorineural hearing loss. It is a remarkable example of success that was made possible through collaboration between engineers, surgeons, scientists and the medical community. As of December 2019, approximately 736,900 cochlear implants have been implanted worldwide. In the United States, roughly 118,100 devices have been implanted in adults and 65,000 in children.[1] The decision to embark upon cochlear implantation is made either by the patient (if adult) or by the parents or caregivers of a child. This procedure is well tolerated and routinely performed on an outpatient basis in both adults and children.

The team concept in cochlear implant evaluation allows for an exchange of information between the surgeon and other members of the implant and rehabilitation process, including audiologists, speech and language therapists, social workers, and psychologists. Typically, the patient is referred to a cochlear implant center, and initial contact is made. The patient may first be seen and identified as an implant candidate by an audiologist. Hence, a patient can enter the evaluation process in a number of different ways. Nonetheless, various issues are taken into consideration, including medical aspects of the patient's history, the audiologic evaluation, radiographic studies, and overall expectations of patient and involvement of family (in pediatric patients) in a rigorous rehabilitative process.

An image depicting cochlear implant surgery can be seen below.

Although the team evaluation concept is explained at greater length in the Indications section, it is notable because it allows for proper selection of patients, the continuous flow of pertinent dialogue, and the promotion of realistic expectations on the part of the patient and the patient's family.

The evaluation process used by the authors at the implant center at the Cleveland Medical Center/University Hospitals of Cleveland and Rainbow Babies and Children's Hospital is summarized below. At the time of the medical evaluation, the patient's general medical history and issues regarding hearing loss are reviewed. A complete neuro-otologic and otolaryngologic examination is performed, and obvious conditions (eg, tympanic membrane perforation, chronic otitis media, congenital anomalies) are noted. The patient's history is reviewed to establish the potential etiology of the hearing loss. Audiologic tests are reviewed and repeated as necessary. Once the patient is deemed to be a potential cochlear implant candidate, the various cochlear implant options are discussed, and audiologic evaluation commences.

Typically, the audiologist measures the patient's hearing with and without hearing aids. Evaluation with pure-tone audiometry and auditory brainstem response (ABR) testing (in the case of children) is often performed. Otoacoustic emission (OAE) testing complements these studies; OAE results often indicate the need for a trial of newer and sometimes stronger hearing aids.

A CT scan is obtained to evaluate the bony anatomy of the cochlea and to establish the presence of a patent (nonossified) cochlear duct. It is also used to identify various anomalies of cochlea-vestibular anatomy (common cavity, incomplete partition defects, enlarged vestibular aqueduct, and cochlear ossification. In some cases, an MRI is used instead of the CT when questions exist regarding the presence of the eight nerve or severe ossification. In children and young adults, speech and language evaluation and educational placement discussions are performed next. Finally, a psychosocial evaluation is completed. Once a patient has been evaluated, a team meeting commences to recommend cochlear implantation advice. If the patient is cleared for cochlear implantation, the patient proceeds with preoperative medical clearance, chooses a cochlear implant device, and proceeds with surgery.

In 1957, Djourno and Eyries made the observation that activation of the auditory nerve with an electrified device provides auditory stimulation in a patient. This observation is considered the seminal observation that paved the way for modern cochlear implantation. In 1963, Doyle and Doyle's early experiments in scala tympani implantation preceded the first House/3M single-channel implant in 1972.[2, 3] Multichannel devices introduced in 1984 have replaced single-channel devices by virtue of improved speech recognition capabilities. As of December 2019, approximately 736,900 cochlear implants have been implanted worldwide. In the United States, roughly 118,100 devices have been implanted in adults and 65,000 in children.[1] Three US Food and Drug Administration (FDA)–approved multichannel devices are routinely used in the United States currently, including the Nucleus 5 cochlear implant system (Cochlear Corporation), the Clarion HiRes 90K (Advanced Bionics Corporation), and the Synchrony device (MED-ELCorporation).

Severe-to-profound hearing loss, as evidenced by the lack of useful benefit from hearing aids, often determines one's candidacy for cochlear implantation. In children, this is confirmed via auditory testing and failure to develop basic auditory skills. In adults, candidates should receive limited or no benefit from appropriate hearing aids used for 3 months (ie, a score of 50% or less on sentence recognition tests in the best-aided listening situation). Expanded indications include the use of hybrid devices (with preserved hearing in low frequencies) which have more specific audiometric criteria,[4] implantations in pediatric patients less than 12 months of age, and off-label use for unilaterial hearing loss with or without bothersome tinnitus.

Frequency

The incidence of congenital hearing loss varies by study. Niparko reviewed studies from the 1980s and 1990s and noted that one of the most carefully performed epidemiologic studies was that of Van Naarden et al, which noted an overall prevalence rate of serious hearing impairment of 1.1 cases per 1000 children aged 3–10 years.[5]

Age is the strongest predictor of hearing loss among adults aged 20–69 years, with the greatest amount of hearing loss in the 60 to 69 age group.[6] By age 75 years, 360 of 1000 adults have a disabling hearing loss. Approximately 15% of American adults (37.5 million) aged 18 years and older report some trouble hearing. Among adults aged 20–69 years, the overall annual prevalence of hearing loss dropped slightly from 16% (28.0 million) in the 1999–2004 period to 14% (27.7 million) in the 2011–2012 period.[6] Men are almost twice as likely as women to have hearing loss among adults aged 20–69 years.[6] Non-Hispanic white adults are more likely than adults in other racial/ethnic groups to have hearing loss; non-Hispanic black adults have the lowest prevalence of hearing loss among adults aged 20-69 years.[6]

Common etiologies of deafness that lead to consideration of cochlear implantation in pediatric patients include idiopathic, genetic, and acquired causes that result in congenital and delayed-onset hearing loss. Genetic hearing loss can be dominant or recessive. Infectious etiologies, including bacterial and postviral meningitis, can lead to severe hearing loss. Meningitis-related deafness has decreased with the routine use of the Haemophilus influenzae vaccine in children. Adult patients presenting for implantation include those with progressive hearing loss that began in childhood, viral-induced sudden hearing loss, ototoxicity, otosclerosis, Ménière disease, trauma, autoimmune conditions, presbycusis, and bacterial infections.

Typically, patients presenting with severe-to-profound deafness have had a direct or indirect injury to the organ of Corti, leading to degeneration or dysfunction of the hair cell system. Therefore, success of cochlear implantation depends on stimulation of surviving spiral ganglion neurons. The number of surviving neuron populations needed for successful implantation remains unclear. In 1991, Linthicum et al reported successful speech understanding in a patient who demonstrated less than 10% of the normal complement of neurons via a temporal bone study.[7] Therefore, despite the wide range of surviving neurons present in various pathologic causes of deafness (10–70% of the normal 35,000–40,000 cells), most patients are likely potential implant candidates. However, studies do report better post-implantation performance with higher residual spiral ganglion cells.[8] Also, delayed loss of residual hearing in implantation done for hybrid implant procedures is linked with intracochlear fibrosis and interventions aimed at reduction of cochlear trauma and inflammation, i.e., perioperative steroids and hearing preservation approaches, are routinely used successfully.[9]

In the past, children with hearing loss presented to the physician after their parents developed a concern about their child's lack of response to noise and voices. This may have brought the child to the attention of an otolaryngologist promptly (within a few weeks to months), or consultation may have been delayed up to a number of years. With the addition of universal infant screening, babies are identified at birth as having a hearing loss. The loss is confirmed and quantified with ABR and OAE testing and if profound, the patient is referred for cochlear implant evaluation. Children are fitted with hearing aids, and a decision to implant is based on progress or lack of language development and careful counseling of the family. If a child is clearly found to be an implant candidate, an earlier implantation results in superior hearing and speech outcomes.

Thus, implantation at age 12 months is now considered ideal, and, in some instances, implantation at an earlier age is performed. Adults with progressive loss that ultimately fails to be managed via amplification also may present for implant consideration. Patients are increasingly informed of the various options for cochlear implantation via the Internet and often have specific questions regarding different device options.

For excellent patient education resources, visit eMedicineHealth's Ear, Nose, and Throat Center. Also, see eMedicineHealth's patient education article Hearing Loss.

The main indication for cochlear implantation is severe-to-profound hearing loss that is not adequately treated with standard hearing aids. The clinical conditions that lead to such an indication include various scenarios, as follows:

• Congenital hearing loss and prelingual deafness

• Acquired hearing loss and postlingual deafness

• Severe hearing loss that can be aided and that deteriorates to profound loss in childhood, adolescence, or adulthood (perilingual) and coexists with various degrees of language development

Generally, the candidacy for implantation is considered separately for adults and children. As outlined in the 1995 National Institutes of Health (NIH) consensus statement on cochlear implantation, adult candidacy is noted as being successful in postlingually deaf adults with severe-to-profound hearing loss with no speech perception benefit from hearing aids.[10] In addition, the statement notes that "most marginally successful hearing aid users implanted with a cochlear implant will have improved speech perception performance." Medicare guidelines as of January 2005 allow for cochlear implantation in patients with 50% aided sentence discrimination scores and allow for 60% sentence scores in clinical trials. Clearly, the trend over time is that relaxed guidelines are better, and better cochlear implant performance and outcome have been demonstrated. An evaluation for revised indications for adult CMS population who do not meet current criteria for implantation is underway with results expected in 2019.[11]

Prelingually deafened adults, although potentially suitable for cochlear implantation, must be counseled in regard to realistic expectations, as language and open-set speech discrimination outcomes are less predictable. A strong desire for oral communication is paramount for this group of patients

Children are considered candidates for cochlear implantation at age 12 months, and, because of meningitis-related deafness with progressive cochlear ossification, occasional earlier implantation is necessary. Investigations are ongoing into extending the age of early routine implantation to younger than 12 months. Audiologic criteria include severe-to-profound sensorineural hearing loss bilaterally and poor speech perception under best-aided conditions, with a failure to progress with hearing aids and an educational environment that stresses oral communication. The use of objective testing in this age group includes auditory brainstem response (ABR) testing and otoacoustic emission (OAE) testing in addition to trials of various auditory training programs, which are essential before cochlear implantation. For further discussion, see the Medscape Reference article Indications for Cochlear Implants.

The surgeon performing cochlear implant surgery must be experienced in otologic surgery and, ideally, some aspects of neurotologic surgery. Intimate knowledge of the relevant surgical anatomy of the mastoid cortex, retromastoid region, high riding jugular bulb, and posterior/middle cranial fossa dura is important in properly performing the approach to the facial recess and in properly creating an implant receiver well that provides low-profile placement of the internal device.

In addition, the relationship of the facial nerve, incus, chorda tympani, and the facial recess needs to be properly understood to safely perform the posterior tympanotomy to gain access to the middle ear. Once the facial recess has been opened, knowledge of the round window anatomy as it relates to normal or abnormal middle ear topography is vital. The ability to visualize the round window membrane by removing the bony round window niche is important for creating a proper cochleostomy. Variations in anatomy, ossification of the scala tympani, and various strategies of dealing with cerebrospinal fluid oozers and gushers should be anticipated. The surgeon should be experienced in placement of implants in malformed anatomy and be able to drill out or use split arrays implants in cases of severe ossification.[12, 13]

For more information about the relevant anatomy, see Auditory System Anatomy, Skull Base Anatomy, and Facial Nerve Anatomy.

Contraindications to cochlear implantation may include deafness due to lesions of the eighth cranial nerve or brain stem. In addition, chronic infections of the middle ear and mastoid cavity or tympanic membrane perforation can be contraindications. Cochlear aplasia as demonstrated on CT scans remains an absolute contraindication. Certain medical conditions that preclude cochlear implant surgery (eg, specific hematologic, pulmonary, and cardiac conditions) also may be contraindications. The lack of realistic expectations regarding the benefits of cochlear implantation and/or a lack of strong desire to develop enhanced oral communication skills poses a strong contraindication for implant surgery. The rigorous implant candidacy criteria and process helps to select prospective patients who will yield the greatest benefit from it.

Various institue-specific online and device-specific literature is available and is discussed with the patients and families at the time of initial evaluation and device selection. In addition, advocacy groups such as the American Cochlear Implant Alliance provide further information and resources for further utilization of implantation for hearing loss.

Obtain a detailed otological history including family history of hearing loss. Note the patient's developmental history and immunizations.

Conduct a comprehensive physical including general ENT with focus on otologic exam. Pay specific attention for any infectious, chronic ear component that will influence the decision and sequences of procedures to make the ear safe before implantation.

Preoperative laboratory studies include those germane to any standard otologic procedure. These studies include CBC count, electrolytes, and clotting time studies.

Controversy exists regarding the preoperative laboratory workup with respect to issues particular to patients with severe sensorineural hearing loss.

• If the patient has rapidly progressive hearing loss or other signs or symptoms of autoimmune hearing loss, an immunologic workup is often indicated during the evaluation of the patient. Treatment of autoimmune inner-ear disease should be instituted in patients with bilateral progressive hearing loss in the event that the hearing loss is rapid over weeks. The immunologic workup may include a Western blot analysis for antibodies to the heat shock protein. Failure to achieve serviceable hearing after a course of steroid therapy is often an indication for cochlear implantation.

• If syndromic causes of hearing loss are suggested (eg, Pendred syndrome, Alport syndrome), obtain appropriate complementary serologic tests (eg, thyroid studies, renal studies).

Although genetic testing regarding the molecular basis for a patient's deafness most likely would not change the plans for cochlear implantation, obtaining available blood tests for genetic markers of specific mutations known to cause sensorineural hearing loss, such as the test for connexin 26 mutations, is helpful for counseling reasons.

Traditionally, high-resolution CT scanning of the temporal bone has been the mainstay of the preoperative radiographic workup of cochlear implant candidates.

• This study helps determine the absence of malformations that contraindicate implantation (eg, cochlear aplasia, absence of the auditory nerve). Additional relative contraindications, such as chronic otitis media, are revealed with high-resolution CT.

• CT scanning also reveals abnormalities that alter the standard insertion procedure of the electrode array. These abnormalities include Mondini dysplasia, common cavity, and cochlear ossification. Suspect cochlear ossification in patients with a history of meningitis.

In some centers, high-resolution T2-weighted fast spin echo MRI is complementing and even replacing CT scanning because of its increased ability to reveal cochlear ossification.

In patients older than 40 years, preoperative chest radiography is performed as per protocol in most hospitals. In addition, before leaving the operating room after cochlear implantation, plain film radiography of the cochlea in the anteroposterior plane (transorbital) is useful to confirm correct placement of the electrode array, but, more importantly, chest radiography is used to provide evidence and confirmation of correct initial placement in the event that delayed implant malfunction arises and electrode migration is suspected.

Intra-operative fluoroscopy is not only beneficial to confirm placement but also guides the right trajectory of placement in cases of malformed cochlear anatomy where inadvertent entry into the internal auditory canal (IAC) because of modiolar deficiency is a potential challenge.

In the context of this article, any medically available treatments for sudden or progressive sensorineural hearing loss are assumed to have been exhausted. In addition, standard modes of amplification are assumed to have been deemed by the patient and clinician to provide unsatisfactory levels of hearing and speech discrimination.

The implant evaluation and workup can seem time consuming and cumbersome to some patients. Accurately assessing candidacy from an audiologic, medical, and emotional standpoint is necessary. In addition, with the various cochlear implant options available, the patient often spends much time and thought on choosing the most appropriate implant.

In addition to the otoneurologic examination, pediatric and adult patients are cleared through their primary medical physician for suitability for general anesthesia.

Determine the side of the cochlear implant. Cochlear implant manufacturers no longer make side-specific implants (eg, early generation Clarion); however, a frank preoperative discussion between the surgeon and recipient should include a suggestion and agreement of the ear to be implanted.

Implanting the better-hearing ear, in many cases of bilateral severe-to-profound deafness, allows for a greater population of surviving spiral ganglion cells to receive electrical stimulation and, hence, potentially results in a better outcome. However, some patients, especially those who have progressive bilateral sensorineural hearing loss and are experiencing asymmetric deafness bilaterally, are still reluctant to implant their best-hearing (although poor-hearing) ear out of fear of cochlear implant failure and loss of sound awareness input before stimulation of the device. Therefore, these patients want to maintain that ear although it does not allow useful speech discrimination. In such patients, the poorer-hearing ear may be implanted.

For the hearing preservation approach, perioperative steroids are started the day before the implant procedure and continued for a week post implantation. Some surgeons do use another course of steroids at the time of implant activation.

Immunization using the standard pneumococcal regimen is mandatory before implantation to reduce the likelihood of meningitis.[14]

On the day of surgery, the operative ear is marked in the preoperative holding area. A patient who still uses a hearing aid is allowed to take the hearing aid into the operating room, and it is removed after anesthesia is induced. The hearing aid is returned to the patient postoperatively. In certain circumstances, a sign language interpreter accompanies the patient into the holding area and operating room to assist with anesthesia induction. Nurses can facilitate patient comfort by communicating on a small writing board. Upon entering the operating room, the operating surgeon and the nursing team again confirm the correct side of surgery. Intravenous prophylactic antibiotics are routinely given and the facial nerve monitor is applied.

Step 1 - Flap marking and incision design

Postauricular incision is seen in the image below.

Once the patient is properly anesthetized, the postauricular crease is infiltrated with 1% lidocaine with 1/100,000 epinephrine. At the authors' center, minimal to no hair is shaved. In order to establish where the cochlear implant receiver will lie, an imaginary line is drawn through the lateral canthus of the eye through the external canal and posteriorly into the retromastoid region. Then, the surgeon visualizes a nearly perpendicular line that travels along the postauricular area tangential to the line at which the helix touches the retroauricular region. The posterior-superior quadrant marked out by the angle created by these intersecting lines is the region in which the implant receiver well should be drilled. Because all 3 commercially available FDA-approved multichannel cochlear implant devices have a behind-the-ear (BTE) processor, room for a BTE device should be taken into account; hence, a mock-up of a BTE may be helpful.

The incision that is now standard in the authors' center, as well as in many others, is a line along the postauricular crease, with little or no extension superior to the hair-bearing area. After making an incision and carrying it down to the level of the temporalis fascia superiorly and to the level of the mastoid periosteum, develop anterior and posterior supraperiosteal flaps. Anteriorly raise an anteriorly based periosteal flap, including temporalis fascia, until the spine of Henle is identified. Using a mock-up of the implant receiver, mark the position along the mastoid region for the cochlear implant and leave room for a BTE processor. Mark this spot with methylene blue before the incision or with a marking pen directly on bone after the periosteal flap is raised.

Attention then is turned to the mastoidectomy.

Step 2 - Mastoidectomy and posterior tympanotomy

Mastoidectomy is seen in the image below.

Using a large (6-mm) cutting burr, suction irrigation, and a high-powered microscope, perform a mastoidectomy with care taken to avoid the standard saucerization and skeletonization of the sinodural angle, tegmen mastoideum, and sigmoid sinus. Leaving bone over these areas is important to allow retention of the implant array leads. Thin the bony posterior canal and open the antrum and identify the horizontal semicircular canal. Using a 3-mm cutting burr, thin the canal wall further and identify the incus. With a 2-mm diamond burr, skeletonize the facial nerve in its descending portion, identify the chorda tympani, and begin the posterior tympanotomy.

Open the facial recess widely with the 2-mm diamond burr and copious suction irrigation, with care taken to leave bone over the facial nerve. As the recess is opened, identify the stapedial tendon and stapes suprastructure. Then, identify the round window niche inferiorly. If visualizing the round window is difficult, remove bone anteriorly and medially to the facial nerve with the diamond burr and rotate (airplane) the patient's bed toward the surgeon to allow for visualization of the round window. In some circumstances of poor round-window visualization, an extended facial recess approach, which requires sacrifice of the chorda tympani at its inferior-most region, may be helpful. Again, take care to avoid any injury to the tympanic membrane, which is just lateral to the chorda tympani. Thoroughly irrigate the wound, and identify and confirm clear visualization and accessibility of the round window membrane. Then, turn attention to the site of the receiver well.

Step 3 - Cochlear implant receiver well drill out with tie-down holes

The image below depicts the creation of tie-down holes with drilling of the well.

Once the mastoidectomy has been completed, place a surgical mock-up of the implant and identify the position for the drilling of the well, usually posterior and superior to the mastoidectomy site. In children, the skull typically is not thick enough to reliably achieve a depth that allows full cochlear implant placement; therefore, a dural island may be created. Using a marking pen, outline the mock-up and drill out the well to skeletonize the bone down to the level of the dura.

Using a diamond burr, remove the bone around the perimeter of the well to expose dura and allow mobility of the dural island of bone. Once the surgical mock-up of the receiver can be fully recessed into the bony well, create dural tie-down holes. Using a brain retractor to protect dura and a small cutting burr, create 4 tie-down holes. Place nonabsorbing 2-0 sutures through the tie-down holes, and hold the sutures aside with mosquito clamps.[15] Thoroughly irrigate the wound. Manage bleeding with cautery. Then, turn attention toward the facial recess.

Step 4 - Cochleostomy

The image below depicts cochleostomy.

The recommendations for cochleostomy size given by a number of different cochlear implant manufactures vary. Regardless of the type of implant, the author uses a small cochleostomy, which is performed 1 mm inferior and posterior to the stapes suprastructure on the cochlear promontory. This is performed with a 1-mm diamond burr. Once the basilar turn is visualized, any bone from ossification can be drilled out and further removed with stapes picks. Take care to use irrigation and suction to avoid thermal injury to the facial nerve. The rotating shaft of the drill is always kept away from the facial nerve. Facial nerve monitoring is routinely used and is helpful in circumstances in which variations of normal facial nerve anatomy are present. In addition, from a patient and surgeon's comfort perspective and for medicolegal reasons, using the facial nerve monitor in routine cases is wise.

Step 5 - Implant tie down and electrode insertion

The insertion of electrodes is seen in the image below.

Once the cochleostomy has been achieved satisfactorily, the wound is irrigated again. Bring the cochlear implant into the field only after ensuring that no further cauterization with electrocautery is necessary. Then, secure the cochlear implant within the well and tie it down. If the Clarion device is used, an inserter tool then can facilitate the insertion of the implant. Use a temporalis fascia graft to pack the cochleostomy site. Using the Nucleus 24 Freedom device, the cochlear implant array is held with toothless forceps and introduced partially into the scala tympani. At this point, the off-stylet introduction technique is performed, and the stylet is removed.

If resistance is met, consider reinspecting the basilar turn of the cochlea for ossification and/or open the cochleostomy further prior to removal of the stylet. If the Clarion device is used, carefully reload the insertion tool and, in both cases, avoid forcing a cochlear implant when resistance is met. Be careful not to injure or inadvertently bend the electrode array at this time. Partial insertion is sometimes necessary. Then, secure the cochlear implant within the well, and tuck the silastic receiver portion of the device under a temporalis or pericranial flap. Secure the electrode lead within the mastoidectomy defect.

Gel foam may be used to secure the lead within the drilled-out trough in between the well and the mastoidectomy site and may be used to help secure lead 1 of the Nucleus 24 device, which is tucked under the temporalis fascia. With most commercially available multichannel cochlear implant devices, make plans for impedance testing and neural-response telemetry (NRT) before closure.

Step 6 - Telemetry, closure, and radiograph

A water-tight periosteal closure is seen in the image below.

Place the skin flap back over the cochlear implant device. Using an intraoperative sterile telemetry device, perform impedance testing for implant integrity. For MED-EL, Clarion, and Nucleus systems, impedance testing and NRT is routinely performed. After confirming the integrity of the electrodes, initiate closure. Typically, the periosteal flap is closed over the mastoidectomy site and the cochlear implant with absorbable sutures. Return and close the skin flap with subcutaneous interrupted sutures and a running subcutaneous-subcuticular absorbable suture. Place Steri-Strips with a tincture of benzoin; also place a mastoid dressing. Anteroposterior plain films can be obtained at this point to document intracochlear placement of the electrode array.

Awaken and extubate the patient; then, return the patient to the recovery room. Prior to discharging the patient from same-day surgery, the audiology team meets with the family, provides cochlear implant documents, and makes plans for initial stimulation and mapping, which takes place 3-5 weeks postoperatively.

Patients are typically returned to the recovery room with orders for antinausea medication. Most patients have minimal nausea and vertigo because routine intraoperative administration of dexamethasone (Decadron) has a prophylactic effect on postoperative nausea. Most patients have minimal dizziness or gait issues and are able to be discharged an hour and a half following surgery.

Send patients home with their mastoid dressing intact and 7 days of an oral antibiotic and pain medication. Provide follow-up care in 2-3 days to remove the mastoid dressing. Many patients now simply remove their mastoid dressing at home on postoperative day 2 and are instructed to inspect the wound for bleeding or hematoma. Schedule a second visit at 2 weeks postoperative, and schedule plans for device stimulation 3-5 weeks following the initial surgery.

The risks of cochlear implantation mimic those of mastoidectomy. These include postoperative infection, facial paralysis, cerebrospinal fluid (CSF) leakage, and meningitis. Manage these risks via standard techniques. In 2002, the risk of meningitis was approximately 1 in 1000 cases and likely related to either the size of the cochleostomy or the design of the Clarion device with implant positioner. Clarion withdrew the positioner, and analyses of non—positioner-related cases of meningitis revealed that the risk of meningitis in these patients was similar to that of a nonimplanted deaf patient. To minimize the risk of meningitis, the Centers for Disease Control and Prevention (CDC) has recommended all patients have up-to-date immunizations to Streptococcus and Haemophilus.

The risk of meningitis in a patient who has received an implant with a positioner persists for at least 2 years postimplantation, so a high index of suspicion is indicated for these patients, as well as verification of proper immunization.[14] Patients should be aware that any residual hearing in the operated ear is lost after implantation. Complications specific to cochlear implantation include flap dehiscence, seroma formation, implant migration, facial nerve stimulation, perilymphatic or CSF gusher, and device failure. The FDA maintains a Web site (MAUDE) dedicated to tracking individual implant complications. As this database develops, the consumer can more easily gain access to useful real-time information that pertains to individual manufacturer or device quality.[16]

Flap complications can be avoided by using an incision that does not compromise the blood supply to the postauricular region, such as the one outlined in the Intraoperative details section. Seroma formation may be avoided by use of a mastoid compressive dressing for at least 2 days. If a seroma develops, it can be evacuated using an 18-gauge or larger needle using sterile technique. A mastoid dressing should be reapplied for 2 days. Initially raising a supraperiosteal flap and then raising a subperiosteal and pericranial flap based in opposite directions results in complete coverage of the internal receiver with fascia, which creates a secure closure that minimizes postoperative complications.

Promptly treat minor infections with oral and topical antibiotics. Intravenous antibiotics and, if necessary, flap revision can save an otherwise extruding device secondary to major infection.[17] Implant migration can be avoided by securing the device deep within the bony well with secure tie-down sutures. Electrode migration is minimized by packing the cochleostomy with tissue such as temporalis fascia or muscle. Facial stimulation usually can be managed by deactivating certain offending electrodes.

A CSF/perilymph gusher via the round window is common in patients with cochlear anomalies such as enlarged vestibular aqueduct syndrome, common cavity, and wide internal auditory canal syndrome. These complications are best managed by packing the round window with fascia after implant insertion. Dizziness after cochlear implantation surgery is typically short lived and usually resolves with observation. When device failure is believed to have occurred, perform telemetry and consider consultation with the manufacturer before explantation and reimplantation.

The overall prognosis for hearing improvement and improved quality of life in the properly selected patient is excellent. Patient selection is addressed in Indications.

Cochlear ossification results from inflammation of the inner ear, often following deafness secondary to meningitis. Most instances of ossification do not preclude cochlear implantation because total ossification is rare. In one series, bony growth was confined to the basal-most portion of the cochlea and was easily traversed with minimal drilling. Electrode insertion was complete in 14 of 15 patients in the series.

Most cases of ossification in the authors' center are found to be limited to the basilar turn and are easily drilled open, allowing for full insertion of a standard device. However, in 5 cases of severe widespread meningitis-related ossification, the split-array technique was performed with the Nucleus split array device, with satisfactory results.

Gantz et al have described more aggressive approaches to total ossification; these approaches use a circumferential cochlear trough for implant insertion.[18] Cochlear malformations, such as common cavity deformity and Mondini malformations with incomplete partitions, are also amenable to full or near-full implantation. In cases involving common cavity, the author prefers to use the nucleus straight array device so that the electrodes can stimulate the perimeter of the common cavity where the nerve endings reside.

The future of cochlear implantation is exciting and is now upon us. Bilateral cochlear implantation has demonstrated significant benefits for patients in a number of areas, which include hearing in noise, speech perception outcomes, and sound directionality.[19] Audiologists, otolaryngologists, and pediatricians have known for years that the standard of care for children is binaural hearing (2 hearing aids) habilitation for hearing aid–serviceable hearing disorders. Now, the norm is rapidly becoming parents and clinicians who offer binaural cochlear implantation to maximize hearing and speech outcomes in both children and adults. The concept of implanting patients with residual hearing in the low frequencies has led to the development of short implants, which contact the basal or high frequency portion of the cochlea while leaving the low frequency (apex) undisturbed.[20] This hybrid implantation technique for hearing preservation has recently been reviewed.[4]

In the future, patients can expect faster and better coding strategies, which result in better speech perception. In addition, the improvement in chip design and battery design will likely pave the way for totally implantable cochlear implants as microphones become integrated to middle- or external-ear structures. Nanotechnology is rapidly providing hope for smaller, more robust, electrode array designs with a virtually endless number of electrode contact sites. These advances will likely continue to lead to a lowering of candidacy thresholds and improved performance and will result in expanding the criteria for future implantation.

Patients are typically followed up in two weeks to assess the incision and are cleared for implant activation.

Not routinely required. In case of specific etiologies (e.g., Pendred syndrome) specific services can be consulted (e.g., endocrinology).

Advise against strenuous activity until the first post-operative appointment.