Cochlear Implant Candidacy
Patients are evaluated by a pediatric otologic surgeon, a pediatric audiologist, and a speech therapist. Testing and evaluation at the Massachusetts General Hospital for Children is also recommended for those with a history of congenital hearing loss and whose parents are interested in pursuing such options. Children are also seen in Ophthalmology to insure that there are no other associated eye problems with the hearing loss. Children also undergo imaging which might include a temporal bone CAT scan or MRI scan of the skull base and of the brain. These imaging modalities are complimentary. For those found to have a connexin 26 mutation, imaging is not necessary as there is generally normal inner ear anatomy and present auditory nerves. Those who do not have a connexin 26 mutation or who have note had genetic testing, imaging certainly is indicated for preoperative planning.
A CT scan is helpful for looking at the bony anatomy to determine the size of the cochlea, abnormal balance orders, or small channel through which the hearing nerve travels. Common inner ear abnormalities that are found include large vestibular aqueduct or a small cochlea such as Mondini malformation. Other than exceptional circumstances where the anatomy is severely affected, these bony abnormalities found on CT scans are not contra-indications for surgery and most children with mild to moderate inner dysplasia can be very success cochlear implant users and achieve significant improvement in sound and speech perception.
For those born with complete or profound hearing loss and no responses on auditory brainstem response (ABR) testing or behavioral testing, or if CT imaging suggests small or absent auditory nerve based on the size of the internal auditory canal or the cochlear nerve canal, a high resolution CT scan performed at the MEEI is important to determine the presence of absence of the auditory nerve itself. That nerve travels from the cochlea (inner ear) to the brain. That nerve should be present to provide the ability of the cochlear implant to electrically stimulate the inner and allow the signals to be sent along the nerve to the rest of the brain. In rare cases an auditory nerve is found to be very deficient or absent on MR imaging. Although this is not an absolute contra-indication to cochlear implant surgery, pooled data on cochlear implant outcomes in children with severely deficient or absent auditory nerves suggest that the overall performance is quite modest compared to those who have a near-normal to normal auditory nerve. These children appear to have some degree of sound awareness, but no true speech perception.