Cochlear Implant

Abstract

For patients who present with bilateral severe-to-profound sensorineural hearing loss who have little-to-no benefit from conventional hearing aids, cochlear implants can restore hearing by directly stimulating the cochlear nerve. A standard mastoidectomy and facial recess approach is performed to visualize the round window niche and membrane. The round window membrane is opened, and the cochlear implant electrode is carefully inserted into the scala tympani. After several weeks, the patient returns for implant activation with a dedicated team of audiologists.

Case Overview

Focused History of the Patient

In this case, a 65-year-old patient presented with bilateral, progressive sensorineural hearing loss. He had used hearing aids for many years but in recent years began losing the benefit he initially received. He underwent an audiometric workup specifically for cochlear implant and was deemed a candidate bilaterally. He was right-handed and selected this side to be implanted first.

He denied a history of meningitis, vertigo, significant noise exposure, head trauma, or the use of ototoxic medications such as chemotherapy. He did have a history of ear infections but denied any otologic surgery.

Physical Exam

The patient’s physical exam was unremarkable. He used hearing aids in order to communicate but still had significant difficulty with speech understanding. There were no craniofacial abnormalities. His face was symmetrical at rest, and facial function and sensation were normal bilaterally. The external ear was normal in appearance, as were the tympanic membrane and middle ear spacea bilaterally.

Adjunctive Studies

The patient had a history of ear infections as a child and adolescent, so a computed tomography (CT) scan was obtained. This demonstrated a well aerated mastoid cavity and facial recess. The cochlea and vestibule had normal morphology. Magnetic resonance imaging (MRI) showed normal cochlear and facial nerves bilaterally.

Natural History

The prognosis for hearing loss varies depending on the underlying etiology. For patients with congenital forms of hearing loss, it may progress in gradual or stepwise fashion. Similarly, patients with presbycusis typically experience hearing loss in the high frequency range, which makes understanding speech more difficult. Ultimately, these patients should be monitored on an annual or biannual basis, or undergo audiometric testing should they experience a noticeable change in their hearing.¹

Options for Treatment

For patients with mild hearing loss, treatment may involve observation or the early institution of hearing aids if they have difficulty in situations that are frequent in their day to day life (meetings, group conversation, etc.). As hearing loss progresses, recommendations are based on not only hearing thresholds but also speech understanding both in quiet environments as well as in situations with background noise.

Rationale for Treatment in this Case

In this case, the patient no longer received benefit from conventional hearing aids. While the specific indications from the Federal Drug Administration continue to evolve and are beyond the scope of this particular case, the following factors should be considered in adult patients:

1. Severe or profound hearing loss with a pure-tone average of 70 dB hearing level.
2. Use of appropriately-fitted hearing aids or a trial with amplification.
3. Aided scores on open-set sentence tests of less than 60%.
4. No evidence of central auditory lesions or lack of an auditory nerve.
5. No evidence of contraindications for surgery.

Step-by-Step Technique

Please note that these are general steps for surgery, and that significant variation exists in how this is accomplished.

Anesthesia

General endotracheal anesthesia is required. No long-active paralytic agents should be used during induction or during the case as facial nerve monitoring is performed.

Patient Positioning

The patient remains supine on the operating room table. Depending on the surgeon preference a gel-ring may be used to stabilize the head, or it can be laid flat on the table. The bed should be rotated 180 degrees from the anesthesiologist, with the bed controlled by the anesthesia team at the request of the surgeon throughout the case.

Facial Nerve Monitoring

As with many other otologic procedures, facial nerve monitoring is recommended during cochlear implant surgery.

Prepping the Patient

Specific ways of prepping the patient vary by surgeon preference. The hair is typically shaved behind the mastoid so that the area can be prepped and the drapes may stick without having hair into the field. However, if securing the implant is not feasible via a standard periosteal pocket, the incision may need to be extended superiorly, and this should be considered when draping the surgical field. A standard Betadine prep may be used, and Ioban can be used to hold the ear forward during the surgery.

Procedure Details

A postauricular incision is planned, typically extending 1.5–2.0 cm behind the postauricular sulcus along the temporal line.

An incision is made through the skin and subcutaneous tissue and then elevated anteriorly and posteriorly within this plane. This is done so that the periosteal incision can be staggered away from the skin incision so that in the event of any superficial wound breakdown, the receiver stimulator does not become exposed. A periosteal incision is made along the temporal line and bisecting the mastoid tip, and the periosteum elevated anteriorly. If the surgeon plans to use a subperiosteal pocket, minimal elevation of the posterior and superior flaps should be performed. A small amount of fascia and muscle can also be harvested at this time to be used to stabilize the implant at the round window and in the facial recess.

Next, the lambdoid suture line is identified and the periosteum superior to this is elevated. This is taken posteriorly and then superiorly until resistance from the temporoparietal suture line is encountered. Within these confines, a subperiosteal pocket is created. It should be sized accordingly in order to accommodate the silicone “sizer” for the receiver-stimulator of the cochlear implant. It can either be removed at this time or left in place until the implant is brought onto the field. A three-dimensional mastoidectomy is performed. For some surgeons, if a straight electrode is used, then bone pate may be collected to use for stabilization after insertion. Otherwise, the limits of the mastoidectomy may be narrower than for other chronic ear cases; the tegmen and sigmoid sinus do not necessarily need to be exposed. The posterior bony ear canal should be thinned adequately, however, to allow for exposure and access through a facial recess approach. When the antrum is entered, the short process of the incus and the lateral semicircular canal should be in view. Opening the facial recess can proceed by several methods. Some surgeons prefer to identify the facial nerve distal to the second genu to ensure that it is in an appropriate position and to increase confidence during facial recess exposure. Others may identify facial recess air cells and open from “inside-out” ensuring that a bony covering is left over the facial nerve at all times. Both are appropriate approaches. The chorda tympani nerve should be identified and preserved. When the facial recess is opened, the implant may be opened and should be soaked in an antibiotic solution. With the facial recess opened, the round window and its niche are identified. If this is difficult, one can recall a relationship of 1.5–2 mm between the oval and round windows. When identified, the drill speed should be set no greater than 10,000 revolutions per minute, and the niche drilled superiorly to expose the round window membrane. If encountered, the false membrane should be removed. When exposed, a piece of Gelfoam with dexamethasone solution is placed over the round window membrane. The field should be copiously irrigated with antibiotic solution, and the surgeon should either change gloves or ensure that they are cleaned. The implant is brought onto the field and placed in the subperiosteal pocket. The surgeon removes the Gelfoam from the round window membrane. The membrane can be opened with a variety of instruments (straight pick, beaver blade). Some electrodes require directionality to be oriented towards the modiolus, and then the electrode is inserted slowly into the scala tympani, over the course of at least one minute. If resistance is encountered, the surgeon pauses before attempting to advance further. When full insertion is achieved, the electrode is stabilized and then supported around the round window with the previously harvested fascia and/or muscle. The remaining electrode is coiled within the mastoid cavity and is typically protected with a large piece of Gelfoam.

Closure

• The periosteal layer is closed in interrupted fashion with 3-0 Vicryl suture.
• The deep subcuticular layer is closed in interrupted fashion with 4-0 Monocryl suture.
• The skin is dressed with Mastisol/benzoin and Steri-Strips.
• The ear canal should be examined to ensure that the posterior ear canal and tympanic membrane were not violated or disturbed during the surgery.

Dressing

A mastoid dressing or Glasscock dressing may be used.

Postoperative Restrictions

• No heavy lifting or straining for at least 10 days (greater than 10 lbs).
• Avoid sneezing or coughing, but do so with the mouth open if necessary.
• If narcotic medication is prescribed, a stool softener should be used.
• Remove the dressing on the first postoperative day.
• Antibiotics are given for five days.
• Some dizziness may be expected after surgery.

Equipment

• Drill system.
• Basic microscopic ear tray.
• Cochlear implant insertion tray (specific to the company of the selected implant).

Disclosure

Author C. Scott Brown also works as editor of the Otolaryngology section of the Journal of Medical Insight.

Statement of Consent

The patient referred to in this video article has given their informed consent to be filmed and is aware that information and images will be published online.