Anatomical and clinical aspects and outcomes of bilateral cochlear implantation in cochlear hypoplasia type IV - a case report

Cochlear hypoplasia is a congenital inner ear malformation (IEM) characterized by a reduced external cochlear dimension, usually accompanied by an abnormal internal architecture. Type IV cochlear hypoplasia is a cochlea with hypoplastic middle and apical turns. It may occur along with dislocation of the facial nerve, associated with semicircular abnormalities, less clearly marked promontory, or stapedial fixation. Such patients can present a broad spectrum of audiological test results, from sensorineural or mixed mild or profound hearing loss. The above anatomical changes may be responsible for intraoperative difficulties during cochlear implantation. In the studied case, a 6-month-old patient was diagnosed with an inner ear malformation - cochlear hypoplasia type IV on both sides. Computed tomography with multiplanar and 3D reconstruction was performed to analyze the middle and inner ear anatomy in detail. Both types of imaging reconstruction helped decide which cochlear implant electrode to choose. Perimodiolar-positioned cochlear implant electrode was found to be the most suitable choice. The patient underwent sequential bilateral cochlear implantation with expected incomplete electrode array insertion on both sides. First repeatable auditory responses were observed two months after the second implant activation. Good parental cooperation with therapists and adequately defined developmental goals in the presented patient allowed the multidisciplinary team to take advantage of the child's intellectual abilities and choose the suitable communication method; however, the patient's auditory responses were obtained slowly. The final auditory results cannot be predicted in inner ear malformations due to abnormal anatomical structure and, thus, heterogeneous innervation within the deformed cochlea. The programming of the sound processor must be individual in each case, based on the child's behavior observation and, if possible, objective test results. Patients with cochlear malformations usually require higher stimulation intensities to obtain sound sensations than patients with a typical cochlear structure.