Histological classification of epithelial polypoid lesions of the gallbladder.

Thirty epithelial polypoid lesions in 24 surgically resected gallbladders were examined histologically and immunohistochemically and then classified into two types according to the characteristics of the epithelium. One type consisted of proliferation of ordinary gallbladder epithelium without any metaplastic change while the other type was characterized by proliferation of metaplastic epithelium, such as mucous glands, endocrine cells and lysozyme-immunoreactive cells. Moreover, each lesion was subdivided into non-neoplastic epithelial polyp or neoplastic adenoma. We therefore classified the non-neoplastic epithelial polyps into hyperplastic polyps and metaplastic polyps, and the adenomas into ordinary type and metaplastic type. Moreover, we found that atypical glands within metaplastic-type adenoma were not infrequently observed, and that these lesions also presented metaplastic changes. From these results, the possibility of an adenoma-carcinoma sequence was discussed.