DETECTION BY SCANNING ELECTRON-MICROSCOPY OF A DISTINCTIVE ESOPHAGEAL SURFACE CELL AT THE JUNCTION OF SQUAMOUS AND BARRETTS EPITHELIUM

Metaplastic columnar epithelium replaces the normal squamous epithelium in Barrett's esophagus. We characterized the surface epithelial cells of the junction between squamous and Barrett's epithelium using scanning electron microscopy and light microscopy. In four biopsy specimens from the squamous-Barrett's junction in three patients, we found a distinctive cell type having features intermediate between those of squamous and columnar epithelium. Its distinguishing characteristic is the presence on its surface of two disparate structures not normally present on the same cell in the gastrointestinal tract: microvilli (a scanning electron microscopy feature of glandular epithelium) and intercellular ridges (a scanning electron microscopy feature of squamous mucosa). The surface characteristics of this newly recognized cell were strikingly similar to those of cells found in the transformation zone of the uterine cervix, an area in which squamous epithelium physiologically replaces columnar epithelium. We also examined 28 biopsies of the gastroesophageal junction area from 14 patients with and without a history of heartburn but with no evidence of Barrett's esophagus. None of these biopsies showed the distinctive cell. We hypothesize that this distinctive cell represents an intermediate step in either the development or the healing of Barrett's epithelium, during which surface characteristics of two different cell types, columnar and squamous, coexist on the same cell.