RESUMEN
A Brunner's cyst, removed from a 54-year-old woman, was studied by light and electron microscopy. The cyst was spherical, measured 1.5 cm in diameter and was located in the duodenal bulb. Histologically, the cyst, confined in the submucosa, consisted of a single layer of epithelial cells and connective tissue. The epithelial cells were composed of an orderly array of tall columnar cells containing basal round nuclei and fine granular cytoplasm. Ultrastructurally, the epithelial cells contained many secretory granules in the cytoplasm. Each secretory granule was membrane-bound and appeared electron-lucid with a dense core. They were small and sparse around the Golgi apparatus but large and numerous in the apical region. Multinucleated cells were intermingled with cells of the epithelial lining.