An unusual heterotopia of pyloric glands of the stomach with inverted downgrowth.

A rarely reported, large heterotopia of gastric glands in the submucosal layer of the stomach is observed in a 79 year old Japanese man with early gastric cancer. Histologically, it consists of marked hyperplasia of benign foveolar-type epithelia and tubular glands which instead of growing upwards grow downwards into the submucosa. Immunohistochemically, many gastrin-positive G cells are observed within it, indicating the existence of independent pyloric-type glands from the surrounding mucosa with intestinal metaplasia. Muscle actin-positive fascicles, derived from the muscularis mucosae, are demonstrated to branch into it and to encapsulate it. This result suggests that the present lesion may not represent a truly submucosal ectopic location, but an inverted downgrowth of the mucosa into the submucosa, thus resembling an inverted polyp of the colon. An awareness of this unique lesion is important in order that it not be mistaken for a submucosal extension of the primary adenocarcinoma.