Developmental neuropathology of the second half of gestation.

In this review we focus primarily on the events taking place in the second half of gestation. At second trimester end, human brain weight gain accelerates rapidly. Germinal matrix attains maximal absolute volume, only to ablate 50% over two gestational weeks. At 10 weeks of gestation interhemispheric, choroidal, and transverse fissures exist. Germinal matrix hemorrhages peak during its devolution and some of these rupture into the lateral ventricle. By 28 weeks homologous primary sulci are present, having appeared in both hemispheres at slightly different gestational ages. Secondary sulcation, during the third trimester, is hemispherically unique. Despite emphasis on neuronal vulnerability, prevalence of lesions in white matter exceeds that of gray matter and, within white matter, diffuse white matter astrocytosis prevalence exceeds that of focal necroses. Gray matter hypotensive lesions most commonly occur in the upper brainstem and thalami followed by convexity borderzone lesions causing sclerotic microgyria. White matter hypoplasia with normal gray matter volume is sometimes associated with hypomyelination.