Spontaneous hemorrhage in the cerebral cortex of immature rats.

We report the presence of spontaneous hemorrhages in the brain of normal neonatal rats. The quantitative evaluation showed that the hemorrhaging was most frequent in 4- to 5-day-old rats. Nearly all the lesions were found in the cerebral cortex of the lateral part of the forebrain hemisphere, particularly in the middle cortical layers. Their average incidence amounted to 6.71 +/- 2.95 per six 5-microns sections from 5-day-old rats. The lesions were nearly absent in the newborn and 7-day-old animals. We suggest that vascular wall immaturity and some extravascular factors, like developmental increase of blood pressure, may account for the perinatal hemorrhaging.