Revision Cochlear Implantation

This article is an edited transcript of the live e-seminar presented in November, 2010. To register to view the recorded course, click here.

Krystine Mullins: Revision cochlear implantation involves the removal or repositioning of a cochlear implant - either for medical reasons or because of device failure. Sometimes it may not need to be removed or replaced with a new device, but repositioned, and this can be for a number of reasons.

In this course, we'll first discuss revision cochlear implantation from the audiologist's perspective, and then Dr. Mark Wiet will discuss the surgical perspective.

Reasons for Revision Cochlear Implantation

Infection

Sometimes the skin flap over the implant can become infected. For example, we had a patient who developed a post-auricular wound infection because of the frame of her eyeglasses. Despite vancomycin treatment for several weeks, there was still one area of wound dehiscence and wound breakdown. In this case, it was recommended that the cochlear implant be removed and the patient will be getting it re-implanted at a later date.

Rejection

Sometimes, the body rejects the implant. This can be due to allergy, and Dr. Wiet will be discussing this in more detail later in this presentation.

Extruded implant receiver

On occasion, the implant becomes extruded and needs to be re-implanted or replaced. We will look at a case study later in the presentation that pertains to an extruded implant.

Incorrect surgical placement of the device

On occasion, and for various reasons, the electrode array may not have been placed in the correct position in the cochlea, resulting in little or no useful performance of the device. Dr. Wiet will be addressing this subject in his presentation.

Damage to the electrode array during insertion

Sometimes, during insertion of the array, one or more electrodes can become damaged, potentially resulting in sub-optimal performance and perhaps necessitating revision surgery.

Electrode migration

Despite good surgical placement of the electrodes, electrodes have been known to migrate out of position, resulting in diminished speech recognition performance for the user. Dr. Wiet will discuss this matter in more detail later in the presentation.

Device Failure

About 2% of cochlear implants fail, necessitating investigation. All failed devices are reported to the FDA and the devices are sent back to the manufacturer for analysis. This helps identify any modifications that are needed to improve internal implant reliability, and if there are modifications that can improve reliability, they're usually implemented in future upgrades from the manufacturer. Device failures are categorized as either hard failures or soft failures.

Hard Failures

When an implant stops working entirely, it is considered a hard failure. The failure is due to either an internal electronic malfunction or to a structural problem. Before re-implantation, a representative from the implant manufacturer conducts a series of integrity tests on the device to confirm that the device has indeed failed. Examples of internal electronic malfunctions include an electrode array that malfunctions or when the electrodes have migrated out of position. An example of a structural problem is electrode sheering as a result of a severe blow to the head, which can immediately halt all sound from the implant.

Soft failures

When the manufacturer's integrity testing of the device fails to confirm that the device has failed, yet there is still suspicion that it has failed, it can be a lengthy process for the implant user and the implant team. Before the device manufacturer's clinical application specialist is contacted to arrange for integrity testing of the device, we check the user's external equipment, troubleshooting with new pieces of the external components to ensure none of the user's external components is defective. We also reprogram their processor to see if doing so might eliminate the problems. If these approaches don't work, the manufacturer's integrity testing assesses the functionality of the internal device, testing the internal receiver -stimulator package, as well as the intra-cochlear electrodes using common ground testing. In addition to common ground testing, stimulation rate is assessed. Sometimes the surgeon or audiologist proposes that a CT scan or x-rays be done to check that the placement of the electrode array is correct. To identify any decrease in speech understanding, speech performance measures are performed and results are compared with the patient's prior results. Such testing can include HINT testing, CNC or pure tone measurements with the cochlear implant only.

Device failure from the user's perspective

Some implant users experiencing device failure hear loud popping sounds or screeching sounds, some hear nothing at all, and for others the sound is intermittent. Sound quality can change. There can be a decrease in speech recognition performance, loss of lock to the internal device, episodes of overly loud stimulation and non-auditory symptoms including pain, shocking sensations, vertigo and facial twitching.

Revision Process

Once device failure has been confirmed, the cochlear implant team, consisting of the surgeon, audiologist, the patient, and on occasion, the device manufacturer's clinical application specialist, decides whether to re-implant the same ear, implant the contralateral ear, or to implant bilateral implants simultaneously. The clinic contacts the insurance company to determine coverage for the surgery and the implant(s). Depending upon what caused the implant process to fail or the device to fail, the manufacturer may help with the cost of the re-implantation.

Audiologic assessment is completed. To ensure that there are no other medical contraindications patients usually have another CT scan, primary care clearance, and cardiology clearance if needed. We also make sure to counsel the patient so that they demonstrate continued high levels of motivation and appropriate expectations. Post-surgical programming would proceed as it did following the initial cochlear implant surgery except that now we can compare pre- and post reimplantation speech performance measures. As for follow-up appointments, we often do not need as many appointments because patients sometimes adjust more quickly to the second implant because they know what to expect.

Speech recognition results after implant revision surgery

Patients typically perform just as well with their implants after revision has occurred as they performed initially before their first device failed. However, there's no guarantee that speech recognition will improve with re-implantation, and it may, in fact, become worse. Results vary from patient to patient, so we ensure that patients have realistic expectations for re-implantation just as they did for their first implant.

Case study #1: Device failure

The first case study is a 65-year-old man who experienced device failure after 13 years of successful implant use in his right ear. He received his implant in 1995. In July 2008, the patient was fitted with a new speech processor and he felt he wasn't hearing as well as he had heard with his older processor. He reported that the sound quality of the implant was a little too high-pitched, and speech clarity was poorer.

We did some testing and noted that his average NBN thresholds were about 45 dB HL, which is not as good as we would have expected with a cochlear implant. Usually with the particular implant device that he had, we find thresholds in the 25 dB HL range. In September of 2008 we made programming changes and he said that there was some improvement but it still wasn't as good as his previous processor, so we sent the processor in for repair to the manufacturer.

In December 2008, the patient reported that he was wearing the device for about a minute and then it would cut out on him. We gave him a loaner processor, but he came back with the processor and clinic loaners reporting that they were not helping at all. We called the manufacturer's clinical application specialist who came out on December 24th to do an integrity test.

Device integrity testing revealed that the internal device was working but a few of the electrodes were bad. The specialist reprogrammed a loaner body worn cochlear implant processor. It seemed to help but about an hour after the patient left the office, the patient reported that he heard a loud screeching sound and then the device stopped working altogether.

On January 2nd, 2009 we had another appointment with the manufacturer's representative. We were unable to connect with any processers. A few days later the representative returned and did another integrity test, and it showed the internal device was not functioning at all. The patient met with the rest of the cochlear implant team to discuss options and next steps.

The patient decided to pursue bilateral simultaneous implants. He obtained a CT scan, X-ray, and medical clearance from the cardiologist all on the same day so we were able to get the process started promptly. The next day he came back for his cochlear implant evaluation and we sent a letter to the insurance company for approval. We worked with otologic management services, which is part of Cochlear Americas and helps get insurance approval. Each cochlear implant manufacturer (Advanced Bionics, Med-El, and Cochlear Americas) has its own otologic management service.

We counseled him on revision surgery and he demonstrated understanding of everything, so we went ahead with the surgery on the 21st of January. In February he came back for his initial stimulation with both of the implants but he was initially frustrated because he wasn't able to understand speech. However, he returned a week later and said that the sound quality was improving tremendously.

About one month after his initial stimulation the NBN thresholds averaged 17 dB HL in each ear. HINT testing (using CD) was completed at 45 dB HL with each implant individually. The score was 20% with the right implant, 13% with the left implant and 14% bilaterally. Three months after initial stimulation we repeated the HINT testing (using CD) at 45 dB HL. The right side, which was the side with the revision surgery, had essentially unchanged results, with 16% correct. The left ear improved from 13% at the initial testing to 57%, and the bilateral score went from 14% to 61%. The patient was happy with these results, and felt he was doing a lot better in real life situations than what these results were indicating.

Case Study #2: Extruded implant

This is an example of an extruded implant in a 61-year-old man. During his initial cochlear implantation evaluation in October of 2009, using the HINT test at 45 dB HL (on CD) with appropriate hearing aids, his scores were 6% in his right ear, 0% in his left ear, and 0% binaurally. He received his first implant in December 2009 in the left ear and initial stimulation took place in January 2010. With the cochlear implant only the HINT score was 16%. At one month after initial stimulation performance improved to 58% correct. This was a big improvement after only one month. Shortly thereafter, his wife called to report that his internal device was showing through the skin. The patient said he bumped his head about two weeks earlier and he felt that he might have gotten an infection. The patient cuts trees for a living, and it was suspected that he may have had a contaminated liner in his helmet, which was filled with sawdust and bacteria. This may have caused the infection.

In March, the patient was seen by the surgeon to have the sawdust and bacteria removed from the incision site, and the revision surgery was discussed at that time in case the infection wasn't responsive to treatment. In fact revision surgery was done later in March. In April he returned for follow up and everything was completely healed. There were no signs of extrusion. We tested again three weeks after the initial stimulation. We did the HINT testing on CD, which was completed at 45 dB HL. Results showed 23% correct using the implant alone. Testing again two months after initial stimulation showed results improved to 54% correct. This case study demonstrates that even after revision cochlear implantation, the patient achieved similar performance as he had achieved prior to the revision surgery.

At this time, I'll turn it over to Dr. Wiet to discuss the surgical considerations for revision cochlear implantation.

Cochlear Implant Revision - Surgical Perspective

R. Mark Wiet: Depending upon which review you read, the incidence of cochlear implant revision operations is about 3 - 8% of all cochlear implants. Prior to revision, patients need thorough otologic and audiologic evaluations, including speech performance measures and reprogramming of the initial device, replacement of the external components, imaging of the temporal bone which includes plain films and CT scans of the temporal bone, and integrity analysis by the cochlear implant manufacturer. Hard failure is the most common indication for revision surgery, accounting for 40 - 80% of all revision operations (Zeitler, Budenz & Roland, 2009).

In addition to hard and soft failures, infections and extrusions, there can also be improper initial placement of the device. There can also be wound or flap complications and occasionally people need an actual upgrade of the implant technology. For example, ten years ago single channel device users were upgrading to multichannel devices.

Zeitler and colleagues (2009) report head trauma as being the cause for hard failure revision surgery in as many as 41% of the cases. In cases of hard failure, often times revision cochlear implantation can take place expeditiously.

Hard failures of devices can include cracked casings, electrode failures, capacitor failures, transistor failure, coil damage, and leaks in the casing.

Soft failures

As Krystine indicated, soft failures are defined as a suspected device failure or decrement of function without a detectable defect on integrity testing. In 15% to 40% of revisions, soft failure is suspected (Chung et al., 2010). These patients notice a gradual decrease in performance scores and also may have non-auditory complaints like facial nerve stimulation, vertigo, tinnitus and intermittent functioning of the cochlear implant.

Soft Failure Consensus 2005

In 2005 a group of 18 implant specialists met to address the issue of soft failures and to develop some type of consensus for evaluating soft failures (Balkany et al., 2005). These people were directly involved in the development, manufacturing and clinical application of cochlear implants and represented the fields of otolaryngology, audiology and bioengineering. They investigated the literature, gathered clinical data, and drew on their experience to develop a joint statement on the management of soft failures. They wanted to provide professionals working in all areas of cochlear implantation with terminology, definition, diagnosis, and management of suspected cochlear implant malfunctions widely referred to as soft failures. Their consensus statement was published in the journal Otology & Neurotology (Balkany et al., 2005).

Soft failures are uncommon. With soft failures, device malfunction is suspected but cannot be proven using currently available in-vivo methods. Re-implantation with subsequent alleviation of the symptoms strongly supports the diagnosis of a soft failure but cannot conclusively confirm device malfunction. The 2005 consensus provided us with a process for evaluating soft failures. The process is broken down into symptoms, the medical evaluation, audiologic evaluation and the internal device assessment itself, which is the manufacturer's role.

From a medical standpoint it is the physician's responsibility to confirm the electrode position, consider lines of infection, consider a differential diagnosis for reasons for failure that might be medical in nature and also to consider the cochlea itself. The 2005 Consensus Statement also provides a checklist for evaluating these patients, and it is subdivided into 2 sections: adults/older children, and young children. In adults we consider the auditory and non-auditory symptoms, as well as performance and mapping issues. We also take a critical look at the hardware, and we do an objective assessment of the implant itself.

In younger children it can be much more difficult to determine whether a revision operation is needed. Factors that we consider are inner ear development at the time of surgery, central auditory pathway issues, and cognitive abilities. During post-implant follow-up we need a way to concisely define clinical improvement.

Soft failures were reviewed by the New York Eye and Ear group recently, which found that about 50% of their patients who had soft failure had a history of meningitis, asthma, or some type of congenital inner ear malformation (Chung et al., 2010).

Facial nerve stimulation

Facial nerve stimulation is considered a soft failure. According to Zeitler and colleagues (2009), deactivation of five or more electrodes may suggest an impending device failure. These devices can be reprogrammed or have selective deactivation of electrodes. If that does not solve the facial nerve stimulation problem, these patients are candidates for revision cochlear implantation either with a replacement (same model) or with a newer device with broader programming options. You can also replace an outer wall, straight electrode array design with a newer perimodiolar design which may reduce the chance of facial nerve stimulation.

Imaging

Most centers will obtain images following revision surgery with plain films of the skull base. Other centers will obtain images of the placement of the implants. A CT scan of the temporal bone is usually done if there's some post-operative tissue-related malfunction. In a typical post-operative x ray of a patient with a cochlear implant in place, you can see the receiver stimulator in place, and you can see the electrode array coiling into the patient's cochlea.

Improper placement of the cochlear implant

When we study images of some implanted ears, it becomes obvious why the patient did not obtain benefit from the device. We sometimes see images of implants located mainly within the middle ear space. This can occur because of cochlear ossification secondary to meningitis. Even in a normal cochlea you can have incomplete insertion. We have seen images where the cochlear implant is evident in the basal turn of the cochlea, but in successive slices that expose the middle and apical turns of the cochlea, there is no evidence of the cochlear implant. There are multiple structures in the tiny place where we insert cochlear implants. The carotid canal is one of them. The internal carotid is a branch of the common carotid artery. It comes up toward the ear and makes its first turn or genu in the middle ear space, and heads towards the cavernous sinus. This portion of the carotid is called the horizontal segment and it lies in the carotid canal. We have seen images where the cochlear implant runs right next to the first genu of the patient's carotid, heading toward the carotid canal.

We have also seen the implant lying in the Eustachian tube. It is also possible to place the cochlear implant in the fallopian canal (labyrinthine) which is the canal through which the facial nerve travels from the lateral aspect of the patient's internal auditory canal and through three segments (labyrinthine, horizontal and vertical) of the facial nerve. We have seen images where a patient had a cochlear implant in the labyrinthine segment of his facial nerve canal. None of these improper implant placements will result in any auditory benefits for the users.

Ensuring proper implant placement

How do we avoid improper placement? As in any operation, we use landmarks. In surgery we go from known structures to unknown structures. In some ears however, the usual landmarks are not available, due to congenital malformations, ossification, history of infection or otosclerosis.

To avoid improper initial placement, we identify the round window then open the cochleostomy. One surgical approach is a mastoidectomy - facial recess approach. One typical landmark is the posterior wall of the external auditory canal. That's where the chorda tympani runs. Basically we look for two segments of the facial nerve, the horizontal segment and the vertical segment, as well as the horizontal canal. Within the facial recess the first thing you want to do is identify the oval window. You will see the long process of the incus and then the super structure of the patient's stapes. One to two millimeters below the patient's oval window will be the round window. The round window is typically a niche so there will be an overhang of bone just lateral to the round window.

If you take away that tiny overhang of bone, you will have a good view of the round window itself, and of course, that's the perfect landmark for the scala tympani and designing the cochleostomy. It is placed inferior to the round window. Some surgeons like to place their cochlear implant directly through the round window.

Extrusion

Another indication for revision cochlear implantation is extrusion as Krystine previously mentioned. Occasionally devices extrude. I will usually start these patients on antibiotics whether or not there's evidence of infection, and I will keep them on antibiotics until we have a revision operation. The question of whether we're going to be able to salvage the device is going to be answered by the infectious agent. As we all know there are resistant bacteria out there that can prolong the infection or make things much more difficult for us. We will monitor the response of the patient to the antibiotic treatment.

If there's extrusion of the receiver-stimulator device, we're going to do a revision of the scalp flap and initiate antibiotics. If we cannot cover the receiver-stimulator it may need to be removed, or just moved to a different location on the skull, either inferior to the previous location or more superiorly. If there's infection and extrusion, occasionally we will consider removing the cochlear implant. If that's the case, we leave the cochlear implant electrode array within the cochlea and cut it at the level of the facial recess. The receiver-stimulator portion and the more proximal portion of the electrode array are removed. The wound is closed and allowed to heal, and the device re-implantation is delayed.

Avoiding cochlear implant extrusion

Most surgeons today use a stair-step type of incision to the skull which can help prevent cochlear implant extrusion. The more common incision is a post-auricular incision with a limb up above the auricle. I typically will make the limb about
2 - 2 1/2 cm above the auricle and bring it down in the post auricular area, about 1.5 cm from the post auricular crease. Once the skin flap is elevated, I identify the temporalis fascia and the temporalis muscle. I create a pocket heading posteriorly toward the back of the patient's skull until I identify the back of the patient's temporalis muscle. I then make the next incision deeper through the temoralis muscle superiorly and bring it down through the pericranium below. Once the implant is in place and this incision is closed, the skin is folded back across and the subsequent skin incision is closed. This is a stair step type approach to the skull base, so it heals in layers. That works pretty well at preventing cochlear implant extrusion.

Another recommended technique is to use implant tie downs. You can place them through tie down holes that you create within the skull at the time of the operation. If the skull is thin, you can place titanium screws on either side and tie a nylon suture across there. Some surgeons create small pockets in the area. Instead of an elevating the post-auricular subperiosteal pocket widely, some surgeons will create a small pocket in this area so they can slide the cochlear implant into it and then the periosteum will hold it in place.

Electrode extrusion

The cause of electrode extrusions is usually unknown, possibly occurring with skull growth or possibly from forces from the cochlear implant itself (Rivas, Marlowe, Chinnici, Niparko & Francis, 2008). Perhaps, in the case of a straight electrode, it could push against the lateral wall of the cochlea and possibly push itself out of the cochlea. Electrode extrusion is more common in cases of ossification. Occasionally we have to drill out portions of the cochlea to place a cochlear implant in patients with history of meningitis and ossification.

If there is electrode extrusion, 50% of the time the electrode can be replaced with a full insertion. One of the more important points to make here with revision surgery is that premature removal of the electrode can lead to loss of the cochleostomy tract. Therefore, at the time of the revision operation the best practice is to cut the electrode at the level of the facial recess, and then remove the remaining portion of the electrode that's attached to the receiver stimulator as I mentioned earlier. Next, prepare the patient's wound for the new implant, get the new implant ready and then insert the new implant electrode immediately following removal of the old electrode.

The problem that you can run in to is that there can be a loss of the cochleostomy tract; or, soft tissue within the first part of the cochleostomy can collapse and make it difficult for the surgeon to re-implant the new electrode. As I mentioned before in cases of serious infection, the receiver stimulator can be removed and the distal end of the electrode array left within the cochlea, cut at the facial recess. The wound is closed, the patient is placed on antibiotics whether oral or intravenous and once the wound is healed the patient can return to the operating room for the new cochlear implant. The old electrode can be left in place for months while the patient recovers on antibiotics.

Allergic reactions

Silicone allergy has been reported. This should be suspected whenever there is a case of delayed device extrusion along with negative cultures or non-responsiveness to antibiotics. Silicone allergy testing is available and implants can be custom designed for candidates with silicone allergies.

Revisions for the Purpose of Technology Upgrade

It is important to note in terms of counseling patients that technological upgrade may not mean an improved performance, and some believe this might be due to reduced plasticity of the user's nervous system or inability to adjust completely to a new device.

Additional Surgical Considerations

Monopolar cautery is a common instrument for hemostasis throughout any operation, but the problem with cochlear implants is that the electrical current can damage the cochlear implant device directly. It also can transmit through the cochlear implant to the cochlea and damage residual neurons. Monopolar current cautery should not be used during the revision cochlear implant operation, (nor during bilateral cochlear implant surgery or in surgery of the head and neck in a patient with a cochlear implant). Alternatives to monopolar cautery include bipolar cautery, and the ultrasonic harmonic scalpel.

Outcomes of Revision Cochlear Implantation

There have been several hundred revision cochlear implants in the United States and throughout the world. In general revision implantation is well tolerated and shows stable or improved outcomes. There have been many reviews on this topic. Most show that mean thresholds and speech performance scores are either the same or improved (Parisier, Chute, Popp & Suh, 2001; Fayad, Baino & Parisier, 2004). Rivas and colleagues (2008) showed that 2/3 of patients with revisions in their practice (n = 48) had achieved or exceeded peak performance levels, 80% of soft failure patients had resolution of their symptoms with reimplantation, and all patients with facial nerve stimulation had resolution of symptoms upon reimplantation.

Case Study #3: Electrode Array in Internal Auditory Canal

Lastly, I'd like to share with you a case study of a patient that I had seen during my fellowship. He had undergone a cochlear implant in his right ear at another institution when he was six years old and presented to us six years later when he was 12 years old.

After receiving his right cochlear implant, he developed chronic suppurative otitis media and had to undergo five operations to treat the infection. He eventually developed a right facial nerve paralysis three years after the insertion of the right cochlear implant. He was admitted to a hospital and started on intravenous vancomycin which eventually cleared the infection. Later at school it was discovered his cochlear implant was not functioning. At that point he was referred to us at the University of Michigan for cochlear implant evaluation.

Upon evaluation, it was noted that he was actually hearing better with his left hearing aid than he was with his right cochlear implant. The audiologic evaluation revealed a non-functioning right cochlear implant, and that the patient was mainly functioning by lip reading with limited benefit from left ear hearing aid. He met the criteria for left cochlear implantation. Physical examination at the time revealed a right House-Brackmann facial weakness of two out of six, which means there was a slight weakness on the right side of his face. There was moisture and debris in his right external auditory canal and a right tympanic membrane perforation.

CT scans revealed that the right cochlear implant was in his internal auditory canal. The scans also showed a sclerotic mastoid which is typical of a patient with a history of chronic otitis media. The cochlear implant electrode was coming through the cochlear aperature into the internal auditory canal. These results explained the facial paralysis as well as why he was receiving no benefit from the cochlear implant.

This patient underwent a right cochlear implant explantation. Post-explantation facial nerve function was the same as it was before the operation. The right external auditory canal was closed, and the patient had a mastoidectomy and was put on antibiotics for the infection. Later he underwent sequential cochlear implantation on the left ear. He did well with the left implant.

The right implant was examined after explantation and it definitely appeared abnormal. There was some residual debris attached to the implant that we thought might represent a biofilm, a housing structure that bacteria can build. Biofilm has subsequently been reported on cochlear implants in patients with a history of infection.

Concluding Remarks

In conclusion, the decision making for revision cochlear implantation is not always clear-cut. In general, outcomes are usually equal to or better than prior performance, but individual results vary. It is important that patients are counseled that revision cochlear implantation does not guarantee an improved outcome.

References

Balkany, T.J., Hodges, A.V., Buchman, C.A., Luxford, W.M., Pillsbury, C.H., Roland, P.S., et al. (2005). Cochlear implant soft failure consensus development conference statement. Otology & Neurotology, 26, 815-818.

Chung, D., Kim, A.H., Parisier, S., Linstrom, C., Alexiades, G., Hoffman, R. & Kohan, D. (2010). Revision cochlear implant surgery in patients with suspected soft failures. Otology and Neurotology, 31(8), 1194-1198.

Fayad, J.N., Baino, T., & Parisier, S.C. (2004). Revision cochlear implant surgery: Causes and outcome. Otolaryngology Head Neck Surg. 131(4),429-432.

Parisier, S.C., Chute, P.M., Popp, A.L., & Suh, G.D. (2001). Outcome analysis of cochlear implant reimplantation in children. Laryngoscope, 111(1), 26 - 32.

Rivas, A., Marlowe, A.L., Chinnici, J.E., Niparko, J.K., & Francis, H.W. (2008). Revision cochlear implantation surgery in adults: Indications and results. Otology & Neurotology, 29,639-648.

Zeitler, D. M., Budenz, C. L., & Roland, J. T. Jr. (2009). Revision cochlear implantation. Otolaryngology - Head & Neck Surgery, 15(5), 334 - 338.