range corresponds to the severity of PVL, which can also be quite variable. More white matter damage leads to more severe cerebral palsy; different subtypes are identified and diagnosed by a neurologist. Despite the varying grades of PVL and cerebral palsy, affected infants typically begin to exhibit signs of cerebral palsy in a predictable manner. Typically, some abnormal neurological signs (such as those previously mentioned) are visible by the third trimester of pregnancy (28 to 40 weeks after conception), and definitive signs of cerebral palsy are visible by six to nine months of age. Epilepsy Another common but severe outcome of PVL patients is the development of epilepsy. The link between the two is not entirely clear; however, it appears that both genetic and early environmental factors are involved. One study estimated that 47% of children with PVL also have epilepsy, with 78% of those patients having a form of epilepsy not easily managed by medication. Many of these affected patients exhibit some seizures, as well as spastic diplegia or more severe forms of cerebral palsy, before a diagnosis of epilepsy is made. Frequency Unfortunately, there are very few population-based studies on the frequency of PVL. As previously described, the highest frequency of PVL is seen in premature, very low birth weight infants. These infants are typically seen in the NICU in a hospital, with approximately 4-20% of patients in the NICU being affected by PVL. On a large autopsy material without selecting the most frequently detected PVL in male children with birth weight was 1500-2500 g., dying at 6–8 days of life. Diffuse brain damage with softening (diffus leucomalacia, DFL) are found more frequently in children weighing less than 1500 g. However, PVL is not a DFL. Research Animal research Animal models are frequently used to develop improved treatments for and a more complete understanding of PVL. A rat model that has white matter lesions and experiences seizures has been developed, as well as other rodents used in the study of PVL. These animal models can be used to examine the potential efficacy of new medications in the prevention and treatment of PVL. Clinical research Current clinical research ranges from studies aimed at understanding the progression and pathology of PVL to developing protocols for the prevention of PVL development. Many studies examine the trends in outcomes of individuals with PVL: a recent study by Hamrick, et al., considered the