Structural abnormalities and dysfunction of the auditory cortex in infants with nonsyndromic cleft lip and/or palate

Abstract

BACKGROUND: Hearing loss as a common co-morbidity in children with cleft lip and/or palate has been well documented. Most previous studies have focused on peripheral hearing impairments, or the middle ear disease prevalent in this group. More recently, cortical malformation and auditory processing dysfunction in individuals with cleft lip/palate have been reported. Objective: The purposes of our research were: (1) To investigate and compare the anatomical structure and function of the auditory cortex in infants with nonsyndromic cleft lip and/or palate (NSCLP) and normal controls; (2) To initiate further studies that determine the auditory processing abilities of children with NSCLP. METHODS: 27 infants aged from 6 to 24 months (mean age=15.4 months, SD=5.9 months), with NSCLP and normal peripheral hearing function, participated the study. 27 non-cleft children matched for age and sex were included as normal controls. Brain images acquired from magnetic resonance imaging (MRI) were evaluated using a specially designed software package. The volume of brain structures related to the central auditory nervous system (CANS), including the brain stem, thalamus, auditory cortex (superior temporal gyrus, STG), and average thickness of STG, were calculated and analyzed. Mismatch negativity (MMN), an evoked potential indicating auditory discrimination abilities which is mainly generated in the auditory cortex, was used to estimate the function of the auditory cortex. RESULTS: Compared with the normal infants, the NSCLP group had smaller volume in the cerebrum and brain stem (controlled for body height and cerebral volume, respectively), but no overall significant group difference was found in our study. However, infants with NSCLP were found to have smaller volume in the left thalamus and auditory cortex, and reduced average thickness in the auditory cortex (controlled by left cerebral volume) and a significant between groups difference was obtained. Another conspicuous finding was that the average difference in thickness of the auditory cortex between the two groups was more distinct with increasing age, from a very slight difference in subjects at 6 months to nearly 12% difference at 24 months of age. The results of MMN recording showed considerable inter-subject and intra-individual variability, with better results being acquired using the mean peak amplitude multiplied by duration as an index, and distinct differences were found between groups. The infants with NSCLP were found to have reduced MMN amplitude and duration compared to normal children, indicating potential impairment of the auditory discrimination abilities in this group. CONCLUSION: Our study revealed that infants with NSCLP could have auditory impairment at the cortical level, in view of their having anatomical structural abnormalities and cortical auditory dysfunction, even when normal peripheral hearing function was noted. Compared with non-NSCLP children, the development of the CANS and the maturation of the auditory cortex in cleft infants might be inhibited by developmental factors. These findings may lead to new directions for research and treatment of NSCLP, and suggest that central auditory processing abilities in patients with NSCLP should be routinely monitored and individuals with processing disorders provided with appropriate habilitation.