In recent years, the increase in the number of people with hearing loss has become a major social problem worldwide, and measures to control the problem are being taken in many countries around the world. This review focuses on the pathophysiology of noise-induced hearing loss, particularly outlining the outer hair cell damage caused by acute acoustic hearing loss and cochlear synaptopathy, which is a synaptic disorder of the inner hair cells that has received much attention recently. The author believes that understanding these cochlear pathologies will allow for a more accurate understanding of the patient's complaints in the clinical setting and therefore, more appropriate treatment. Furthermore, understanding the pathophysiology of cochlear synaptopathy could also be expected to allow more accurate treatment of patients with hearing problems, even if their hearing is in the normal range. Recent research has also revealed that the pathophysiology of cochlear synaptopathy is very similar to that of other forms of age-related hearing loss. This not only suggests that noise control is the most important factor in the prevention of age-related hearing loss, but also that the results of research conducted to date on acoustic hearing impairment can be applied to age-related hearing loss as well.

　 We developed a Japanese DTT (Digit Triplet Test) application using binaural multitalker noise (BN-MTN) as background noise for early detection of listening difficulties (LiD) and provision of the opportunity for detailed evaluation and appropriate educational support in children. We enrolled 40 children aged 8 to 12 years old and analyzed the SNR and test time to obtain a 50% correct answer rate. We confirmed sufficient validity of the approach and also that our results were largely consistent with previous reports. This application is considered as being a useful application for the screening of LiD in children, as it is simpler to use and the test time is shorter as compared with previously reported applications.

　 CHARGE syndrome often accompanies sensorineural hearing loss, sometimes necessitating cochlear implantation. However, the effects of cochlear implantation are poor in patients with CHARGE syndrome because of inner ear malformation, cochlear nerve deficiency, and/or developmental delay. In this article, we report three children with CHARGE syndrome who underwent cochlear implantation surgery with intraoperative electrically evoked auditory brainstem response (EABR). All subjects had inner ear malformations, and two of the patients had cochlear nerve hypoplasia, which were identified by computed tomography and high-resolution magnetic resonance imaging. Intraoperative EABR waveforms were detected with a pulse width of 25 and 50 μs in two patients and one patient, respectively. The former two subjects achieved auditory recognition early, although one had a hypoplastic cochlear nerve. In contrast, the latter subject required mapping adjustments with widened pulse widths, which led to the subject achieving auditory recognition almost only a year after surgery for cochlear implantation. These results suggest that the pulse width used in intraoperative EABR precisely predicts the patient's postoperative auditory response. Moreover, preoperative imaging evaluation of the cochlear nerve does not always indicate its function, and intraoperative EABR is indispensable for accurately evaluating the cochlear nerve function in patients with CHARGE syndrome.

　 Electric acoustic stimulation (EAS) has emerged as a feasible treatment for patients with high-frequency hearing loss. In terms of the default mapping procedure for EAS devices, the crossover frequency, defined as the frequency at which postoperative unaided hearing threshold in the implanted ear exceeds a criterion level (e.g., 65 dB HL), refers to the way in which frequencies in the input signal are selected and mapped for acoustic stimulation (AS) and electric stimulation (ES) in the implanted ear. Subsequently, similar to the case for conventional cochlear implants, the threshold levels and maximum comfortable levels are determined for ES. However, we found that patients who did not wear hearing aids preoperatively did not prefer this mapping strategy. Alternatively, such patients did not require AS, instead they combined their natural acoustic hearing with ES. Therefore, we thought that clinical fitting in patients with EAS should be individually tailored. In addition, optimizing maps are likely enhanced by the pre-operative medical interventions as well as postoperative hearing levels.