Early myelination patterns in the brainstem auditory nuclei and pathway: MRI evaluation study

The purpose of this study is to investigate the early myelination patterns of brainstem auditory nuclei and pathway on magnetic resonance imaging compared with past histological research. We aimed to identify the time course difference in myelination of the brainstem auditory nuclei and pathway between magnetic resonance imaging and histological research results.

Subjects were 192 infants ranging in age from -4 to 224 corrected postnatal weeks. Images were obtained using a 1.5 T magnetic resonance unit. In four sites (cochlear nucleus, superior olivary nucleus, lateral lemniscus, inferior colliculus) of the brainstem auditory nuclei and pathway on four cross-sections obtained perpendicular to the long axis of the brainstem, signal changes of T1- and T2-weighted magnetic resonance images were analyzed using a region-of-interest methodology according to corrected postnatal age.

The cochlear nucleus and superior olivary nucleus showed myelinated intensity change from -3 to 13 corrected postnatal weeks on T2-weighted images. The lateral lemniscus showed myelinated intensity change from -3 to 8 corrected postnatal weeks on T1-weighted images and from -1 to 13 corrected postnatal weeks on T2-weighted images. The inferior colliculus showed myelinated intensity change from -2 to 39 corrected postnatal weeks on T2-weighted images.

Magnetic resonance imaging revealed the signal intensity change by myelination 11-18 weeks later than those reported in the histological literature. This time lag suggests that apart from histological research, the necessity for the milestones of auditory pathway maturation using MRI is suggested to evaluate the development of brainstem auditory pathway using MRI. This result suggests that myelination does not take place suddenly but happens gradually, so definite myelination, namely the complete change of myelin sheath ingredients, loss of water, and gain of lipids, is needed to be detected by magnetic resonance imaging.