Cochlear Implant Surgery Treatment & Management

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.