A cochlear implant is a sophisticated electronic medical device designed to bypass damaged parts of the inner ear, specifically the non-functional hair cells in the cochlea. This device converts sound waves into electrical signals, which are then sent directly to the auditory nerve, allowing the brain to perceive sound. While these implants are intended to be a permanent solution for profound hearing loss, the internal components can be surgically removed in a procedure known as explantation. This decision is based on specific medical or technical necessity.
Primary Reasons for Cochlear Implant Explantation
The most frequent reason for removing a cochlear implant is a device malfunction, categorized as either a hard or soft failure. A hard failure involves a complete lack of communication between components, resulting in no sound perception. Soft failures are more subtle, involving a decline in performance, decreased speech understanding, or uncomfortable symptoms like pain, vertigo, or facial nerve stimulation.
Medical complications at the implant site also necessitate explantation, accounting for a significant portion of all removals. These complications often involve the soft tissue flap behind the ear, such as severe or chronic infections, wound breakdown, or necrosis of the skin flap. Other medical issues include hematoma formation, the development of cholesteatoma, or a rare allergic reaction to materials within the device.
Less common reasons for removal include severe head trauma that causes the internal receiver-stimulator package to shift or the electrode array to become displaced. Explantation is also pursued due to patient or parental choice, sometimes stemming from dissatisfaction with the auditory outcome or the individual embracing a different cultural identity. Finally, removal may be performed to upgrade an older model to a newer device.
The Surgical Procedure for Removal
The explantation procedure is performed under general anesthesia by an experienced otolaryngologist and often follows a modified version of the original implantation surgery. The surgeon typically uses the existing scar line behind the ear to create a new incision, allowing access to the internal device. This approach helps minimize the creation of new scar tissue and facilitates the dissection of the skin flap.
Once the receiver-stimulator package is exposed, the surgeon carefully detaches it from the surrounding bone and tissue. The most delicate step involves the extraction of the electrode array, which is carefully threaded out of the cochlea through the cochleostomy, the small opening created during the initial surgery. This removal must be done with extreme caution to prevent further trauma to the inner ear structures.
After removing the array and the internal device, the surgeon must address the exposed mastoid bone cavity and the cochleostomy. The mastoid bone is often sealed using bone wax or a small piece of muscle or cartilage to prevent cerebrospinal fluid leakage and minimize the risk of infection. Reconstructive techniques are then used to close the skin flap, ensuring a smooth contour behind the ear, especially if immediate reimplantation with a new device is not planned.
Recovery and Long-Term Auditory Outcomes
Recovery from the explantation surgery follows a timeline similar to the initial implantation, with the incision site requiring about two weeks to heal. Patients commonly experience mild to moderate pain around the surgical site for several days, which is manageable with oral pain medication. Temporary symptoms like swelling, bruising, or a sensation of dizziness are also expected in the immediate post-operative period.
Following the removal of the device, the patient’s hearing reverts to their pre-implant baseline, which is profound deafness. This occurs because the original implantation process causes irreversible structural changes to the inner ear, including the destruction of the hair cells. The explantation itself does not restore any natural hearing ability lost before the initial surgery.
The long-term outcome often involves a revision surgery, where a new cochlear implant is placed, either immediately or in a staged procedure after the surgical site has fully healed. Reimplantation is a common and successful pathway, and the performance of the replacement device is excellent. However, a challenge during reimplantation is the potential for new bone growth (osteoneogenesis) within the cochlea, which can make the reinsertion of a new electrode array more technically challenging.