cells, the cells that support neurons throughout the nervous system. These factors are especially likely to interact in premature infants, resulting in a sequence of events that leads to the development of white matter lesions. The initial hypoxia (decreased oxygen flow) or ischemia (decreased blood flow) can occur for a number of reasons. Fetal blood vessels are thin-walled structures, and it is likely that the vessels providing nutrients to the periventricular region cannot maintain a sufficient blood flow during episodes of decreased oxygenation during development. Additionally, hypotension resulting from fetal distress or cesarean section births can lead to decreased blood and oxygen flow to the developing brain. These hypoxic-ischemic incidents can cause damage to the blood brain barrier (BBB), a system of endothelial cells and glial cells that regulates the flow of nutrients to the brain. A damaged BBB can contribute to even greater levels of hypoxia. Alternatively, damage to the BBB can occur due to maternal infection during fetal development, fetal infections, or infection of the newly delivered infant. Because their cardiovascular and immune systems are not fully developed, premature infants are especially at risk for these initial insults. Damage caused to the BBB by hypoxic-ischemic injury or infection sets off a sequence of responses called the inflammatory response. Immediately after an injury, the nervous system generates "pro-inflammatory" cytokines, which are molecules used to coordinate a response to the insult. These cytokines are toxic to the developing brain, and their activity in an effort to respond to specific areas of damaged tissue is believed to cause "bystander damage" to nearby areas that were not affected by the original insult. Further damage is believed to be caused by free radicals, compounds produced during ischemic episodes. The processes affecting neurons also cause damage to glial cells, leaving nearby neurons with little or no support system. It is thought that other factors might lead to PVL, and researchers are studying other potential pathways. A 2007 article by Miller, et al., provides evidence that white-matter injury is not a condition limited to premature infants: full-term infants with congenital heart diseases also exhibit a "strikingly high incidence of white-matter injury." In a study described by Miller, of 41 full-term newborns with congenital heart disease, 13 infants (32%) exhibited white matter injury. Diagnosis As previously noted, there are often few signs of white matter injury in newborns. Occasionally, physicians can make the initial observations of