MR of the normal neonatal brain: assessment of deep structures

MR imaging is a powerful tool for studying the anatomy of and the developmental changes that occur in the brain. The purpose of this project was to determine which structures can be distinguished on standard spin-echo MR sequences of a normal neonatal brain and with what frequency they can be identified.

The T1- and T2-weighted spin-echo MR images of 12 term neonates, all of whom had normal neonatal courses and were neurologically and developmentally normal at age 12 months, were reviewed retrospectively. All structures that differed in signal intensity from unmyelinated gray matter and unmyelinated white matter were recorded.

In general, myelinated gray matter structures, such as cranial nerve nuclei and other nuclei of the brain stem and deep cerebrum, were the structures best seen on T2-weighted images. Most of these nuclei were seen in 75% to 100% of our subjects on T2-weighted images. They were seen less well on T1-weighted images. Myelinated white matter structures, particularly axonal tracts, were the structures best seen on T1-weighted images. The medial and lateral lemnisci, median longitudinal fasciculus, optic tracts, superior and inferior cerebellar peduncles, and the posterior limbs of the internal capsules were seen in 75% to 100% of our subjects on T1-weighted images. Except for the posterior limbs of the internal capsules, these structures were seen less well on T2-weighted images.

A large number of small structures, such as the nuclei of the brain stem and deep cerebral nuclei, can be routinely identified on standard spin-echo MR imaging sequences. A knowledge of these structures is essential to proper interpretation of imaging studies in neonates and infants.