Researchers and clinicians interested in brain development.Congenital sensorineural hearing loss (CSHL) is a common disease in newborns, with an incidence rate of 0.1 ~ 0.3 %¹. Underdeveloped corpus callosum (CC) caused by CSHL, however, has been rarely reported. Being the largest inter-hemispheric commissure of the human brain, CC contains nerve fibers crossing through and connecting most brain regions of the two hemispheres, including bilateral auditory cortices². At present, cochlear implantation stays the best treatment for CSHL, so the purpose of this study is to investigate the effect of CSHL on CC and find the best time point for treatment and intervention, using a novel CC thickness analysis method.Twenty nine deaf children (age 6~45 m, mean 22.56 ± 12.61 m, 10 female, 19 male) were included in this study. The hearing screening results of the auditory brain stem response (ABR) test of all deaf children were larger than 90 dnBL. Eighteen children (age 4~48 m, mean 27.62 ± 11.97 m, 4 female, 14 male) with normal hearing served as the control group. There was no statistically significant difference for age and gender between the two groups. Informed consent was obtained from the parent of every infant and all the checks were agreed by the ethics committee of Tianjin first central hospital. All children were scanned on a Siemens 3T scanner (Trio Tim, Siemens Healthcare) with a 32-channel head coil. For sedation, all children were given oral administration of 10% chloral hydrate (0.6 ml/kg) prior to MRI examination. The MPRAGE sequence was employed for CC thickness analysis with the following parameters: TR/TE/TI = 1900 ms / 2.53 ms / 900 ms, flip angle = 9º, FOV = 250 × 250 mm², voxel size = 0.98 × 0.98 × 1 mm³, 176 slices. The intensity of images was corrected by N3 method after converting the DICOM files to NIFTI format; all images were reoriented according to MNI space. The method of CC thickness measurement was followed as described by Weiwei Men, et al³. In this study, both deaf and control groups were subdivided into two subgroups: 4~24 m and 25~48 m. The two-sample T test was used to compare the difference of the registered CC thickness between deaf and control groups. An area of significant difference was observed. The mean CC thickness of this area was calculated for every infant, and fitting plots were given for both groups. We finally conducted intra- and inter-group comparisons among the mean CC thickness of each subgroup with the same T test.Before 24 month old, there are no difference in CC thickness between deaf and control groups, see Fig. 1. Between 25~48 month old, the CC thickness of deaf group is significant thinner than that of control group, see Fig. 2. Overall, the anterior splenium of deaf group develops slower than that of control group, especially after 24 month old, see Fig. 3 and 4.The results of this study indicate that CSHL will affect the development of CC anterior splenium, where nerve fibers cross through and connect with bilateral auditory cortices2, especially after 24 month old. The auditory cortices of deaf group have not been stimulated sufficiently, which can lead to delay of brain development. The method of CC thickness analysis is more prominent than other analysis method due to better registration in CC space and rubus, allowing the display of significant difference among CC of the subgroups.Our study suggests that 12~24 month old is the best time period for CSHL treatment and intervention.