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Avoiding Complications of Cochlear Implant Surgery

NOEL L. COHEN AND MICHELLE S. MARRINAN

Complications of cochlear implant surgery may be classified in two categories: device-related and medical-surgical. Device-related complications largely apply to malfunctions and failures of the device or its various components. These may have been caused by faulty design, failure of electronic circuits or components, or external trauma. The trauma may have been caused by a blow to the head, a fall, or exposure to excessive current, as in a powerful electrostatic discharge, lightning strike, or electrocution. Although these are not medical or surgical complications, they require replacement of the device and, therefore, additional surgery. Device failure, regardless of the underlying cause, is by far the most common reason for reimplantations.

Medical complications, on the other hand, are the result of conditions occurring because of the surgery or of the device itself. Surgical complications result directly from the operations itself, are largely avoidable, and may or may not compromise device function and the ability of the recipient to use or benefit from the implant. Surgical complications of multichannel cochlear implants are largely related to the incision and flap, infection, electrode insertion, device migration, and facial nerve injury. These have been steadily diminishing in frequency over time in both adults and children.^1,2,3,4 Table 10–1 lists potential complications and solutions.

The avoidance of surgical complications begins with the thorough evaluation of the patient, continues through careful planning of the operation, and ends with meticulous surgery and postop observation. A major goal of the evaluation process is to eliminate the inappropriate candidate: such candidates include those with useful hearing, active infection in the ear, and absence of a cochlea or eighth nerve. Anesthesia risk must also be considered. High-resolution computed tomographic (CT) scanning and, when indicated, magnetic resonance imaging (MRI) are critical in the evaluation of the temporal bone anatomy and aid in both evaluation of candidacy (e.g., aplasia of the cochlea) and surgical planning (e.g., cochlear dysplasia, aberrant facial nerve). By thoroughly planning the surgery, especially in the potentially difficult case, many complications can be avoided. Meticulous surgical technique is also of major importance in this regard, in avoiding not only intraoperative problems but also postoperative events.^1–7 Finally, careful follow-up is required to identify problems early and avoid true complications.

■ Anesthesia and Preoperative Preparation

The patient is placed on the operating table in the supine position, with the head turned toward the contralateral ear. Facial nerve monitor electrodes are placed adjacent to the orbicularis oris and oculi. Care should be taken that only short-acting paralytic agents are used to ensure that the monitor records any stimulation of the facial nerve. Although some may argue that the facial nerve monitor is not necessary for the experienced surgeon performing a routine cochlear implant operation, it would be difficult in our litigious society to defend the lack of monitoring if something were to go wrong and the patient suffered even a temporary facial palsy. Certainly, even the most accomplished surgeon would be wise to use the monitor in operating on a dysplastic temporal bone or in revising a case when the prior surgery was performed elsewhere.

Planning the incision is critical for several reasons: it is imperative that the implant not abut the behind-the-ear speech processor commonly used. The position of the device is chosen so that it lies on a relatively flat area of the skull with the anterior part above the canthomeatal line. For adults, the long axis is at ± 45 degrees, but for small children it is more vertical. The incision must permit the safe insertion of the implant, and the flap outlined by the incision must have an adequate blood supply to prevent necrosis and breakdown. Because most surgeons have been using smaller incisions with excellent blood supply, flap-related complications have greatly diminished in frequency.1The use of infiltration with dilute (1:100,000 or 1:200,000) epinephrine and the monopolar cautery to make the incision limits blood loss during this phase of the surgery.

Raising the flap must also be done carefully, especially in the small child and the elderly female. The surgeon must dissect gently in the avascular plane deep to the scalp and avoid drying of the flap as well as excessive retraction. When it is necessary to thin the flap of a heavy-set adult, care must be taken not to perforate the scalp or expose the roots of the hair follicles. Using the current short incision, starting at the mastoid tip and ascending behind the postauricular crease to the upper attachment of the auricle and then a short distance posterosuperiorly (Fig. 10–1A,B), we find that barbless fishhooks give sufficient retraction, and we have had no flap problems whatsoever. The Silastic devices (HiRes 90K implant, Advanced Bionics Corporation, Sylmar, California, and Nucleus 24 Contour, Cochlear Americas, Denver, Colorado) require a shorter incision than the ceramic devices (MED-EL Pulsar C100, MED-EL Corporation, Durham, North Carolina) because the posterior portion of the device is inserted into a subperiosteal pocket beneath the scalp.

After retracting the flap posteriorly, we then raise a large anteriorly based Palva flap, exposing the areas for both the mastoidectomy and the well. This is closed over the proximal electrode at the end of the procedure (Fig. 10–2A,B).

The Well or Recess

The location of the well or recess is very important because it determines the location of the device itself. Marking the center of the well with a single drop of methylene blue transcutaneously through the scalp prior to the incision simplifies this (Fig. 10–1A).

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