The Cochlear Implant: Historical Aspects and Key Procedures

Fifty years ago, there were no treatments for deafness and severe loss of hearing until Dr. William House first invented six channel electrodes cochlear implant and implanted in the first patient’s cochlea in 1964. Graeme Clark changed that completely since he first developed the cochlear implant system in 1978 which he referred it as a bionic ear. The cochlear implant has success rapidly and variety of cochlear implants has been developed by Cochlear Division of Nucleus. Now there are 219,000 cochlear implant recipients in worldwide in adults and children. Cochlear implant is an electronic medical device that helps adults and children that is profoundly deaf and severely hard-of-hearing to help them to hear the sounds.

Cochlear implant is two-part device. The first part of the device is an external part that calls BTE (behind the ear) that sits on the ear and the BTE have a microphone, sound processor and transmitter system, and the second part of the device with receiver and electrode system that is surgically implanted under the skin in the head and behind the ear. The implant has electronic circuits that will pick up the environment sounds through BTE processor and send it through electrical current of the damaged ear by simulating the auditory nerve before it reaches to the brain. Although, the cochlear implant surgery is a routine procedure for the otolaryngologists and neurologists. They will perform the surgery together by implanting the device in the head and behind the ear.

Decades ago, the surgery required many hours, a large incision on the scalp and half of the patient’s head would be shaved off. Nowadays, the surgery can perform in a short time with a small incision behind the ear and small chance of having the head shaving or none at all. The implant won’t be noticed because it will be implanted under the skin and the hair will grow over it. Before the surgery, the surgeons will prepare the patient for the surgery with anesthesia and putting in an intravenous antibiotic that is required an hour before the skin incision is made. Once the patient has been heavily sedated with anesthesia, the incision should be clear of hair that may be required for small shaving part behind the edge of the auricle and above the canthomeatal plane line. The head should be turned at 30 to 40-degree posterosuperior to lie flat portion of the skull and mark the incision line on the scalp behind the pinna. The surgeon will use the BTE templates in conjunction with the silicone elastomer implant template to make sure that both will not be interference between the coil and the ear level speech processor. They will also make sure that the speech processor will not rest on the receiver/stimulator by marking them with surgical pen. It should be at least 15 mm between the receiver/stimulator and the incision behind the pinna. After the incision is marked, they will do a drop of methylene blue on a bone by inserting 18-gauge needle through the skin at the center of the implant bed before they can form incision. Moreover, the surgeon will do the incision until the flap is formed. The flap should be kept moist with damp surgical gauze at all the times. The incision must be at least 15 mm to be large enough to fit the receiver/stimulator through the incision. The flap should be inferior and anterior based, but it is very important for the surgeon to be able to secure the implant to the bone.

The next incision will be made down to the avascular plane of the periosteum and temporalis fascia and the flap should be stabilized. During the procedure, the implant position need to be checked with surgical stainless outline template kit before cutting under the periosteum and the lower part of the temporalis fascia muscle. A large palva flap is to be created anteriorly based before lifting a large periosteal pocket for the antenna to go through the temporalis muscle that allow the placement of the extracochlear ball electrode between the skull and the periosteum, however, extracochlear ball electrode must to be avoided by placing in the temporalis muscle. The second incision had been made and they will start the mastoidectomy and the surgeon will need to drill through the well where the blue dot on the bone to create a mastoidectomy cavity allowing to stick out both superiorly and posteriorly in order to help the redundant proximal electrode.

The surgeon will use the drill with a circular drill bed to create a hole using the recess template that is shaped almost oval but more of round shape to allow the surgeon to be able rotate the receiver/stimulator. It will be required to achieve optimal placement then to drill a channel connecting the well and the cavity so that the proximal intracochlear electrode array can go through the facial recess. It is preferred that the receiver/stimulator is not to be extended over the edge or the mastoid cavity. After the mastoidectomy and well is completed and they will decide which longitudinal axis for the receiver/stimulator before creating a tie-down holes above and below the anterior portion of these receiver/stimulator so that way the implant can be securely tied down. They will use 2 mm diamond burr to drill the holes. After the short process of the incus and carefully open the facial recess and the horizontal canal should be visible clearly without having the facial nerve to be exposed. It is very important to know where the nerves are during the procedures. The chorda tympani nerve can be very easily damaged if the doctors are not being careful. It is located on the left on the anterior surface of the facial nerve in the posterior middle ear including the stapedius tendon, promontory and round window niche should be clearly visualized. The round window niche should be 2 mm inferior posterior to the oval window and staples. The round window membrane may be obscured by the overhang of the lateral margin of the niche. When the scala tympani by drilling anteroinferior to the around window niche while performing the cochleostomy. The surgeon will drill anteriorly on the promontory and it will goes through the scala media or vestibuli. If they drilled too far and they will miss the cochlea which could cause hypotympanic aircell leading to incorrect electrode placement. It need to be drilled with 1 or 1.4 mm diamond burr through the bone until 1 mm spot of endosteum is exposed. They will need to be very carefully not to be exposed to bone dust or blood from entering the cochleostomy when opening the endosteum to make sure that it is used stapes footplate instrument to open. The cochleostomy will need to be at last 1 mm diameter to be able put the electrode array through and to be sure that the electrodes do not catch on any bony ridge. When opening the package to remove the device and it is needing to be checked for any damages before implanting the device into a patient’s head. The surgeon will need to hold the receiver/stimulator in the non-dominant hand and remove the protective tub from the electrode array. They will need to guide the tip of the electrode array toward the cochleostomy using with their surgical instruments to stroke the array into the scala tympani without using the forces. It is very important that the electrode array is secured at two points to avoid the risk of migration or breaking the seal between the electrode array and the tissue packing at the cochleostomy. Therefore, the electrode array should be secured in close proximity exit from the cochleostomy and the pedestal of the receiver/stimulator to be placed in the well and rotate it to the right angel.

The implant need to be secured with single mattress suture with non-absorbable material and move the knot to the edge of the implant. The suture shall not be over the magnet in case the magnet will need to be removed in later date. The antenna portion needs to be tied down or place under a pericramnial/temporalis pocket and the extracochlear ball electrode to be placed in periosteal pocket under the temporalis muscle. The electrode in the cochleostomy should be covered with autograft completely with strips of fascia or pericranium. They need to check to make sure there is no gaps and is completely sealed to avoid perilymph leak. If there is any signs of leak or gaps is not sealed tightly, they will need extra tissue to have it sealed completely. During the surgery, they will use intraoperative measurement through telemetry to make sure the electrode array to see if it is working correctly. The surgeon will also put intraoperative spacer between external transmitting coil and implant to keep it apart for the tests. The transmitting range for the implant need to be at between 2 to 10 mm. When the surgeons are prepared to close the incision site, the implant will need to be contact with the patient and will use the bipolar electrosurgical instruments if the cautery electrodes are kept at more than 1 cm from extracochlear electrode. They are not allowing to use the monopolar cautery for the implant for tests. While the patient is still heavily sedated with anesthesia and is cleaned up, they will take a single transorbital x-ray to make sure that the electrode placement is in the right place. Facial recess will be packed with soft tissue and suture the palva flap over the proximal portion of the intracochlear electrode then close the wound with each layer. Sometime the drainage will be needed but most of the time they will apply a large mastoid dressing around the incision site. However, the patient should be closely monitored for all of the procedures after the surgery. They will need to be watch out for reactions from general anesthesia, blood drainage through the pressure dressing and any side effects relating with the surgery. The pressure dressing should be kept on for a day before the doctor can take a look on the wound. The doctor will replace a new dressing on the incision site and it need to be leave on for five days from becoming infected. At the tenth days of healing process the stitches will be removed. The patient will have to wait for few weeks until the suture is fully healed before they could turn on the devices.

There are 7 billion of people in worldwide and only 466 million people including children and adults who is severely hard-of-hearing or profoundly deaf. Most recent number shows that there are 219,000 deaf or hard of hearing people who received cochlear implant. The statistic shows that since 1997 to 2015, there were only 57 patients with cochlear implant malfunctioned and 534 patients has reimplantation because of internal device failure, scalp flap complication, optimization of electrode placement or unexplained cause. The cochlear implant surgery has the lower rate of complication and is very safe. The cochlear implant gives a lot of benefit to those who has lost their hearing. Most of the children at the age of 0-3 have the higher rate of success of developing hearing and speech with cochlear implant by 80 to 90 percent as a normal group of hearing children. Children at later age or adults will have the improvement with hearing after three months after the devices has been activated. Every cochlear implant recipients can continue to improve their hearing and speech abilities throughout the years. Graeme Clark has changed the world for the deaf person and he developed the cochlear implant system to give a chance for the deaf person to hear sounds that surrounds them and for them to be able to adapt in hearing world.