DISTRIBUTION OF HETEROTOPIC NEURONS IN NORMAL HEMISPHERIC WHITE-MATTER - A MORPHOMETRIC ANALYSIS

One of the frequent abnormalities described in the context of surgical ly resected temporal lobe (TL) specimens is the presence of heterotopi c neurons within white matter (WM). We have attempted to morphometrica lly define the distribution of these heterotopic neurons in normal sub jects, comparing the incidence of heterotopic neurons in TL WM with th at in occipital (OL) and frontal lobe (FL) sections. Using a combinati on of routine and special stains combined with immunohistochemical con firmation 20 adult autopsy cases were examined. WM from TL, FL, and OL sections was outlined and the area was measured by image analysis. Us ing defined criteria, heterotopic neurons within these areas were coun ted. Results confirm our hypothesis that normal adult TL WM contains a significantly higher population of residual/heterotopic neurons than OL and FL WM groups. It is felt that these neurons represent interstit ial remnants of the subplate which have Failed to undergo programmed c ell death. The significance of these findings with regard to assessmen t of similar findings in temporal lobectomy specimens is addressed. A second intriguing association of this TL WM heterotopia concerns its p ossible relationship to the more frequent occurrence of ''malformative neoplasms'' with neuronal elements (such as ganglioglioma and dysembr yoplastic neuroepithelial tumor) in the temporal lobe.