Pediatric Brain: Normal Variations in Development, Maturation, and Myelination

Abstract

This chapter focuses on neonates, infants, adolescents, and to a lesser degree, teenagers. With the advent of 3T MRI, norms for development and maturation of white matter structures have changed and evolved somewhat. Though it is critical to note the appropriate signal intensities within myelinating and maturing structures in the neonate and within the first 2 years of life, the focus is largely on T2-weight imaging (T2WI) in infants and young children when assessing normal development; fluid-attenuated inversion recovery (FLAIR) is less useful. For example, in neonates, T1-bright signal within the basal ganglia can be a source of consternation and may or may not be abnormal, depending on location, degree, and signal intensity relative to adjacent structures. Additionally, in young children, juveniles, and adolescents, knowledge of normal terminal zones of myelination is necessary to distinguish normal maturation from true pathology. It is also important to mention that CT has been used with decreasing frequency in children (particularly neonates and infants) over the past 10 years, as the lifetime risk of developing malignancy due to the radiation dose increases with decreasing age. Although newer, lower-dose protocols that implement iterative reconstruction have improved the dose profile, it is important to be aware of the cumulative risk of CT over time to children, particularly those with neoplasm or malignancies, who are expected to undergo multiple future CT-based studies. Thus, MRI is increasingly becoming the method of initially diagnosing and following most chronic disorders or neoplasms in children, until positron emission tomography (PET)-MRI becomes routinely available.