Cerebrocortical microdysgenesis in neurologically normal subjects: a histopathologic study.

Previous studies showed that few foci of cerebro-cortical microdysgenesis (molecular layer neuronal ectopias and focal laminar dysplasia) are present in up to 26% of variably processed normal brains; they are more common in the right inferior frontal region. Brains of male developmental dyslexics processed in serial histologic sections showed 30 to 140 foci of these types of anomalies, predominantly in left perisylvian cortex. Here, we present the results of a detailed analysis of ten normal brains also processed in serial sections. The ages ranged from 3.5 to 87 years, all male. Three brains showed abnormalities similar in type to those of the dyslexic, but in far smaller numbers and in different locations: two showed a single cingulate focus--one right, one left; the third brain showed two right supratemporal foci. We conclude that the present form of developmental anomaly is rare in normal brains, and that the findings in the dyslexic brains may be significant.