7     Complications and Revision Surgery in Cochlear Implantation

The complication rate in cochlear implant surgery as reported in the literature is 4 to 15%.1–6 Most of these studies distinguish between major and minor complications, as first described by Cohen et al.⁷ The complications that necessitate revision surgery (the major complications) have a mean incidence of around 4 to 5%,^3,5 but the range is between 2.3 and 13.3%.^8,9

7.1 Major Complications

Major complications are complications requiring explantation of the device, surgical re-exploration, facial paresis or paralysis, or other serious complications with continuous discomfort or dys-function.7

7.2 Minor Complications

It is suggested that minor complications should cause little distress to the patient.4,10

7.3 Device Failure Complications

Device failures range from 0.8 to 26.7%1,11 but depend on the scale of the implant center, the time of follow-up, and the brands and types of implants used. In the decade up to the time of writing (2015) the overall device failure rate has improved.¹² Failure modes are most commonly related to trauma, electronic dysfunction, or CSF leakage. After device failure, explantation and re-implantation is a safe and acceptable treatment option.

Definition

The device exhibits characteristics outside the manufacturer’s specification, resulting in a loss of clinical benefit or failure to attain benefit.^13,14

Other definitions concerning device function are:

• Functioning device: The device has no evidence of any device-related malfunction or no deficiency can be observed from the available test results.

• Characteristics decrement: A device has measured characteristics outside the manufacturer’s specification, but still of ben- efit to the patient.

• Performance decrement: Unexplained but documented decrement in performance or a device that causes nonauditory sensations necessitating explantation.

• Loss to follow-up: Those implanted patients who have been lost to clinical surveillance.

In a consensus paper, specialists and cochlear implant companies have agreed on the uniform reporting of these failures.^13,14 With this uniform reporting, the cumulative survival rate (CSR) per implant type can be calculated. The CSR can be split into rates for adults and children, if needed.¹²

Device failure can also be split into “hard” device failures and “soft” device failures.¹⁵

7.3.1 Hard Device Failure

Although the failure rates have decreased over the years with newer implants, the most common reason for re-implantation is hard device failure.3

7.3.2 Soft Device Failure

The proposed work-up of a soft failure includes of four items of evaluation16:

1. Symptoms: take careful history and write down an exact description of the symptoms (auditory and nonauditory).

2. Medical evaluation: evaluate history, physical examination, and imaging to assess electrode position; evaluate central nervous system pathology; and rule out intracochlear ossification or infection.

3. Audiologic evaluation: assess speech performance and mapping to evaluate a drop in performance, a failure to achieve expected benefit, or a change in sensitivity to stimulation.

4. Device assessment: evaluate the function of the hardware using device integrity testing, programming, and troubleshooting.

Soft device failure is an uncommon occurrence. Before this diagnosis is established, two steps must have been taken: First, a thorough evaluation of the function of the implant by the manufacturer and the implant team in cooperation with the patient has to be performed (steps as described above). Second, the suspected implant should be removed, examined, and the technical failure should be identified. Often a soft device failure is a working diagnosis and initially a conservative approach must be taken to attempt to solve the problem. If there is a proven malfunction of the device, it is considered a hard failure.

7.4 Pediatric vs. Adult Complication Rate

The overall revision rate in cochlear implant surgery is estimated to be 5 to 8%,1,3 but when comparing the pediatric and adult revision rates a difference is apparent. Adult revisions are estimated to be less than 5%,¹⁵ whereas some pediatric studies show a 13% revision rate.¹⁷ The reason for this difference could be the vulnerability of children to infection as well as to trauma. This is often associated with a hard device failure. Another suggested reason for failure could be the more complex surgical anatomy in young children, especially in congenital malformation cases or in relation to their cause of deafness (meningitis, local infection).³ Although often seen, this difference in re-implantation rate between children and adults was not found in all centers.³

7.5 Bilateral vs. Unilateral Implant Complication Rates

Although there are not many reports on this aspect, the overall impression is that patients who received a cochlear implant bilaterally do not have twice the risk of a complication.3 Nevertheless, vestibular effects and bilateral chorda tympani injury could be a concern.¹⁸

7.6 Therapeutic Options for Several Complications

7.6.1 Flap Infection/Subcutaneous Hematoma or Seroma

Most cochlear implant centers use perioperative antibiotics. In the postoperative period antibiotic treatment can be prolonged, especially when an infection is suspected (redness, swelling, and pain over the implant). When a hematoma or seroma is present, infection prevention should be aggressive.3 Care must be taken when a Pseudomonas aeruginosa or a methicillin-resistant Staphylococcus aureus (MRSA) infection is suspected and readmission should be considered for administration of intravenous antibiotics.¹⁹ This may seem rather radical, but an infection around the implant can eventually cause extrusion, or an unmanageable infection resulting in explantation.¹⁹ In cases with suspicion of a low-grade infection, nuclear scanning can be helpful.¹⁹ The formation of a bacterial biofilm around the implant has also been described²⁰ and can only be treated with explantation.

7.6.2 Receiver-Stimulator or Electrode Extrusion (Fig. 7.1)

Occasionally, the receiver-stimulator extrudes through the skin even years after the surgery. Various factors can be of influence in the occurrence of extrusion. To avoid extrusion, particular attention should be paid to the skin incision, flap development, choice of sutures, fixation of the receiver-stimulator, position of the receiver-stimulator, and sometimes the choice of side for implantation. These points are explained step by step in Chapter 5 (p. 67–69). The surgical history, social history, and general medical condition are important factors to be aware of prior to surgery. These may affect wound healing, when local blood supply is compromised due to previous ear surgery, diabetes mellitus, or smoking, or may affect the risk of infection according to the dermatologic or infectious history.⁵ Most array extrusions can be dealt with locally but it is still advisable to perform the surgery under general anesthesia, as the patient should not move during delicate handling of the electrode. Cutting, damaging, or sudden extraction of the electrode array should be avoided throughout the procedure. Furthermore, the repositioning of the electrode is often a matter of creating a covering flap, which normally exceeds the bounds of local anesthesia.

7.6.3 Facial Nerve Stimulation

Postoperative facial nerve stimulation is a more common complication in otosclerosis and osteogenesis imperfecta.21 Precurved electrodes have their contact endings facing the modiolus and this could reduce the problem. If the problem remains, then reprogramming the electrodes can be of help. Usually, the electrodes in the superior part of the cochlea stimulate the facial nerve just superiorly (see Chapter 3 on radiology). These electrodes can then be switched off one by one and the side effect should subside (for additional information see Chapter 13 on oto-sclerosis and implantation). In some very severe cases it can be challenging to program the implant so that no facial nerve stimulation occurs; even re-implantation has been suggested for this.^15,22

7.6.4 Facial Nerve Injury

In the surgical approach using the posterior tympanotomy, the facial nerve can be well identified and injury can easily be avoided. Facial nerve monitoring will also be of great help but it does not replace proper knowledge of the anatomy and accurate training in performing a posterior tympanotomy. In malformations, the chance of an anomalous facial nerve increases (see Chapter 15). Accurate imaging and interpretation are necessary for proper surgical planning. In these cases, in which the course of the facial nerve is uncertain or interfering with a normal approach, one might think of a subtotal petrosectomy. A subtotal petrosectomy (see Chapter 10) provides a wide access and visibility and diminishes the chance of iatrogenic injury and postoperative infection. In this way, a subtotal petrosectomy protects the facial nerve if it is dehiscent in the course of the electrode.

If a slight facial nerve injury does occur, a high dose of prednisone will diminish swelling and further damage, but it might still take weeks before recovery of the facial nerve function. If there is a severe injury or total interruption of the facial nerve, direct anastomosis or a graft should be considered. It is important to remember that the best results are seen with a facial nerve graft performed within the first months after the injury. After 6 to 12 months the results are much worse.²³

7.6.5 Electrode Placement

Sometimes the electrode insertion, although gentle, forceless, and well directed, does not follow smoothly when inserting the last few millimeters of the electrode array. Malpositioning or kinking of the electrode can be the result; the electrode can end up in the wrong position, that is, within the hypotympanum, in an otospongiotic double ring (see Chapter 13, Case 13.6), in the semicircular canal (as shown in Fig. 7.2), or even in the carotid artery (see Case 7.3). Examples of this are shown here and at the end of this chapter. Audiologic testing (see Chapter 4), radiography, or CT scan during surgery may be used in difficult cases or when malpositioning is suspected. Further diagnostic assessment postoperatively may also be needed. A displaced electrode can be readjusted immediately or at a later stage.

7.6.6 CSF Gusher/CSF leakage

A CSF gusher, which is CSF coming from the internal auditory canal through an opening in the cochlea into the tympanic cavity, should be anticipated during preoperative imaging. Cases most often associated with a gusher are an incomplete partition type 1, a common cavity, or an enlarged cochlear aperture as in incomplete partition type 3. A gusher can usually be controlled by waiting for the flow to subside (10–15 minutes) and firmly packing the cochleostomy with soft tissue such as fascia, periosteum, or muscle. A CSF leak could also occur during cochlear implantation, in association with (previous) cholesteatoma, fractures, tumors, or other pathology. To avoid meningitis as a direct or late complication of a CSF leak, the best approach, next to the proper sealing of the leak, would be a subtotal petrosectomy (see Chapter 10 on subtotal petrosectomy). A lumbar CSF drain increases the risk of meningitis and is not needed in combination with a subtotal petrosectomy.

7.6.7 Revision Surgery/Re-implantation

In most re-implantation cases the hearing typically remains the same, but worsening of the hearing is possible. Revision surgery can be harmful to the patient or to the implant and has to conform with the expectations of the patient and/or the guardian(s). It is wise to be conservative regarding expectations postoperatively as in revision surgery the outcome is unpredictable, and preoperative counseling of the expectations should be managed accordingly.3

Case 7.1 Extrusion of the Electrode Array (Left Ear) (Fig. 7.1.1–Fig. 7.1.4)

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