Morphological characterization of the squamocolumnar junction of the esophagus in patients with and without Barrett's epithelium.

Barrett's esophagus is a metaplastic condition in which the normal stratified squamous epithelium of the distal esophagus is replaced by columnar epithelium. Our group has previously characterized a unique surface cell (the "distinctive cell") at the junction of squamous and Barrett's epithelium. This cell is notable for the simultaneous presence on its surface of both squamous and columnar cell features. The aims of our present study were, first, to evaluate prospectively the frequency with which Barrett's patients have the distinctive cell at the squamo-Barrett's junction; second, to further elucidate the characteristics of the distinctive cell; and third, to perform a combined morphological study of the squamo-Barrett's junction using scanning electron microscopy followed by transmission and light microscopy. We divided study patients into two groups: Group I consisted of Barrett's patients and group II of non-Barrett's control patients. Of eight group I Barrett's patients with junctional biopsies, three were noted to have the distinctive cell (37.5%). In contrast, this cell was not observed in any of the group II control patients. Biopsies in control patients as well as Barrett's patients without the distinctive cell revealed abrupt squamogastric or squamo-Barrett's junctions by scanning electron microscopy and light microscopy. In contrast, biopsies from the Barrett's patients with the distinctive cell revealed junctions that were not abrupt and had the distinctive cells overlying normal squamous epithelium. By scanning electron microscopy, the distinctive cells were flattened, polygonal cells with surface microvilli (a columnar cell feature) and were demarcated from one another by shallow depressions, or by intercellular ridges (a squamous cell feature). By transmission electron microscopy, the distinctive cells were cuboidal in shape with abundant apical microvilli and secretory vesicles. We have confirmed that distinctive cells are present in some Barrett's patients. This cell is a morphologic hybrid, sharing features of both squamous and columnar cells, and may be analogous to hybrid cells identified in other locations that undergo metaplasia (eg, the human cervix). Its origin may be the result of transformation of multipotential basal cells of squamous epithelial origin. We hypothesize that the distinctive cells may represent an intermediate stage in the development of Barrett's epithelium.