MR Imaging of Perinatal Brain Injury

In the last two decades, major advances have been made in the clinical care of premature and term infants, including in the management of sepsis and respiratory compromise that can contribute to neurological disabilities in survivors. The incidence of classic cystic periventricular leukomalacia (PVL) has declined and a more diffuse and non-cystic pattern of cerebral white matter injury is more predominant. Although multiple pathologies occur in premature infants, the principal variety accounting for the predominance of neurodevelopmental disability is PVL. This disability in very low birth weight infants (VLBW) (< 1500 grams) includes cognitive/behavioral deficits in 25-50% and cerebral palsy in 5-10%. Neuroimaging studies of VLBW survivors suggest that the cerebral palsy is related to the focal necrotic lesions of PVL, whereas the cognitive/behavioral deficits correlate with more diffuse cerebral white matter injury. PVL is defined as damaged immature cerebral white matter with periventricular focal necrosis ("focal" component) in association with diffuse reactive gliosis and microglial activation in the surrounding white matter ("diffuse" component). Of note, PVL occurs in the late preterm infant and the term infant, particularly in cases of congenital heart disease. The pathogenesis of perinatal white matter injury is currently thought to be related to a complex interaction between maternal/fetal infection, cytokines and hypoxia-ischemia which results in both the generation of reactive oxygen specific agents (oxidative stress), apoptotic oligodendrocyte cell death, and axonal injury. In long-term survivors with PVL, neuroimaging studies often demonstrate reduced cerebral white matter volume, impaired myelination, ventriculomegaly and reduced volume in the cerebral cortex, thalamus/basal ganglia and cerebellum. In many of these long-term studies, the preterm children studies had normal cranial ultrasound. Cranial ultrasound, however, is not adequate for assessing non-cystic focal or diffuse white matter injury. To date, there are no longitudinal MR studies of preterm or congenital heart disease infants which correlate advanced neonatal MR imaging techniques with long-term neurodevelopmental outcome or advanced MR techniques performed in the childhood period.