The implantation of a cochlear implant requires general anesthesia and the use of antibiotics, such as cephalosporin, during the operation.  Hair is shaved from around the ear and a 10 cm incision is made above and posterior to the ear. The two most common scalp flap designs are “C” shaped or “J” shaped. The flap of tissue is then retracted and two pockets are then created.  One pocket is made in the mastoid bone to house the implant package and the other is for the ground electrode.  Afterwards, bone is removed to expose the cochlea and a cochleostomy is performed and the electrode array is inserted.  Care has to be taken that the cochleostomy is performed too low or the electrode will not be placed in the correct position. Hyaluronic acid or dilute glycerin is used as a lubricate for the electrode array.  The array is carefully pushed in, moving only 1-2 mm at a time. 

The implant package has to be secured in place.  This is accomplished by making tie-down holes are drilled into the bone above and below the implant and then suturing the implant to the bone using a braided  polyester material such as Ticron™ or Tevdeck ™.

Before closing the flap, surgeons test the implant to ensure the device is working and the electrode array is in the right place.  The tests performed include electrode impedance measurements, acoustic reflexes, measurement of voltages produces by electrical stimulation, and auditory brain stem responses.  After these tests are performed and results are satisfactory, the wound is sutured and dry, sterile dressing is applied.

The entire procedure takes approximately 2 to 3 hours.  A patient will typically be released from the hospital the same day or the day after the procedure.  It takes 3 to 5 weeks for the incision to heal and swelling to go down.  At this point in time, recipients return to the hospital for their initial hook-up appointment.  This means that recipients are not using their implants to hear from the time they receive them to the date of their initial hook-up appointments because the device has yet to be programmed. 

Complications:

            In general, cochlear implants have a very low complication rate.  Cochlear Corporation, the manufacturer of the Nucleus devices, reports an overall complication rate of less than 1%.  Advanced Bionics Corporation, the makers of Clarion devices, indicate comparable complication rates.  However, the most common complications (according to Cochlear) are problems with the scalp flap.  Other surgical complications, which are for the most part rare, include Meningitis, Otitis Media, facial nerve paralysis, tinnitus, vertigo, and device migration.  Complications due to the device include device failure and facial nerve stimulation.

(1)    Scalp Flap Problems – can include infection, necrosis and thickness. Infections require immediate treatment with antibiotics. If the scalp flap is too thick, it does not allow good transmission of the radio frequency signals necessary to transmit information from the external components to the internal components.  In this case, thick flaps have to be carefully thinned by a surgeon.

(2)   Otitis Media – is an infection of the middle ear, which can be either bacterial or viral.  The mastoidectomy may make it easier for bacterial or viruses to spread into the middle ear.  Otitis Media in cochlear implant patients, usually children, is treated the same way as in any other patient: administration of antibiotics and sometimes pain reliever.

(3)   Meningitis – is the inflammation of the layers of tissue surrounding the brain and spinal cord.  This is a rare postoperative complication but has the potential to be serious. Cerebrospinal fluid (CSF) may leak and cause problems with the implant.  To avoid this type of complication, a leak has to be identified early and treated.  Packing the cochlea with tissue after the cochleostomy and draining the CSF may avoid leakage.

(4)   Facial nerve paralysis – may result because during implantation, drilling is done only millimeters from the facial nerve.  Electromyographic monitoring of the facial during the surgery can help reduce the possibility of paralysis.  Should the nerve become immediately paralyzed, it should be treated with decompression and steroids.

(5)   Tinnitus – is the perception of sound when no external noise is present.  This type of complication is often reported by patients immediately after implantation but rarely after stimulation. Adults also report tinnitus more often than children. Tinnitus may be the result of further damage to existing hair cells.

(6)   Vertigo – or dizziness may be caused by labyrinthitis, inflammation of the part of the ear responsible for balance, and is a larger issue for the elderly who have more difficulty compensating.

(7)   Device migration – is a rare complication.  If the implant package is not secured it may create shear forces that can break the electrode.  It is also possible for the electrode to be misplaced.  If only a few electrodes move, it will probably not effect the performance of the device. If many electrodes migrate, it will require another operation to reinsert the array.

(8)   Device failure – can result from manufacturing defects or from trauma.  Delayed device failure occurs in about 1.5% of implants and need to be replaced. The causes for implant replacement include receiver/stimulator malfunction, the shorting out of electrodes, the breakdown of insulation or the cracking of a ceramic case. Tests during the operation procedure can avoid implanting a defective device. 

(9)    Facial nerve stimulation – occurs when stimulation to the electrode is conducted through bone and also stimulates the facial nerve.  This type of complication is fixed by changing the programming of a device to not send pulses to the electrode causing the facial nerve stimulation

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