The time of birth and a narrow window of a few days before and after birth is a period of our lives when we run a high risk of dying or suffering brain damage. This chapter describes the various brain lesions that occur in that period. Most of these lesions are caused by cerebral hypoxia and ischemia, and are conveniently expressed by the clumsy term "Hypoxic-Ischemic Encephalopathy" (HIE). In term infants, HIE involves primarily the cerebral cortex and deep nuclei; in premature infants, it affects more severely the white matter and is partially to blame for intraventricular hemorrhage (IVH). While most common in the perinatal period, any of these lesions may occur earlier in fetal life. This chapter includes also a brief account of bilirubin encephalopathy, which resembles HIE patterns seen in mature infants.

In addition to global HIE, this chapter describes focal ischemic lesions (cerebral infarcts) that are seen in newborn infants. Many of these occur earlier in fetal life and result in the formation of cavities in the brain (porencephaly, schizencephaly). Some occur in the perinatal period.

Most of HIE pathology develops when cerebral perfusion and oxygenation fall below a critical level, which cannot be defined with precision. Infants with certain types of congenital heart disease (hypoplastic left heart syndrome, transposition of great vessels) who are chronically hypoxic in utero, have diffuse white matter loss, cortical abnormalities, and microcephaly at birth. This suggests that lesser degrees of hypoxia may cause subtle diffuse brain damage, and raises the issue that similar brain damage may develop in other related settings, e.g., placental insufficiency.

The nonspecific terms asphyxia (which literally means absence of pulse) and neonatal encephalopathy describe an irritable or comatose newborn infant with low Apgar scores, apnea, poor feeding, hypotonia, acidosis, and, frequently, seizures. Some infants with this clinical picture have intracranial hemorrhage, CNS infections, hyperbilirubinemia, severe CNS malformations, or metabolic disorders, but most have perinatal HIE. Some of these babies die in the neonatal period; others survive and develop intellectual disability, cerebral palsy, and microcephaly.

The study of perinatal and fetal neuropathology leads to the optimistic conclusion that most of these lesions are potentially preventable, even though a lot remains to be learned about their pathogenesis.

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