Scanning electron microscopy of aberrant crypt foci in rat colon.

The surface of the colon mucosa of 1,2-dimethylhydrazine-treated F344 rats was examined with the scanning electron microscope. A detailed examination of the mucosal topography revealed foci with one to several aberrant crypts. These were seen as structures elevated from the background mucosa. The shape of the luminal openings of the aberrant crypts varied from elongated or tortuous to circular. However, we found no ultrastructural variations between the different aberrant crypt foci (ACF) or between the ACF and the background mucosa. There was no direct relationship between the size of ACF and the number of aberrant crypts per focus, which may be explained by the mechanism of crypt fission; in two aberrant crypts we discovered the formation of a transverse epithelial septum, dividing the large crypt into two smaller crypts. The gross morphology of the ACF observed by scanning electron microscopy and light microscopy was in principle the same.