Ultrastructural features of the colonic epithelium in familial polyposis coli

Colectomy specimens from 6 cases of familial polyposis coli (FPC) were examined. Macroscopically normal mucosa between polyps was taken at intervals along the ascending, transverse and descending colons and studied at EM level. All three regions show the same cell populations varying only in their ratio and height of the epithelium. The same cell types seen in the normal crypt epithelium are present in the mucosa from FPC. As in the normal, 'intermediate' cells are present in FPC but they are less conspicuous than in the mucosa adjacent to colonic carcinoma. However, there are ultrastructural features which distinguish the "normal" mucosa in FPC from the true normal: (a) the presence of "clear columnar" cells; (b) increased vesiculation in the absorptive cells; (c) large number of lysosomes; and (d) the presence of small electron-dense bodies. The ultrastructure of the "clear columnar" cells suggests their being incompletely differentiated cells, thus raising the possibility that their presence in the upper crypt and surface epithelium may represent an early stage in the process of polyp and cancer formation.