Inverted cystic tubulovillous adenoma involving Brunner's glands of duodenum.

Benign neoplasia of the duodenum are very rare. Moreover, duodenal tubulovillous adenomas are more uncommon lesions. The microscopic structure of tubulovillous adenoma has frond-like projection of mucosa with branching papillary structure and generally upward growth into the lumen. We describe a 72-year-old man who showed aduodenal tubulovillous adenoma with unusual inverted cystic growth pattern. Interestingly, this tubulovillous adenomatous lesion was interrupted by gastric metaplasia in the deep portion of the cyst and was closely surrounded by Brunner's glands. Although histogenesis of gastric metaplasia of duodenum is not fully understood, Brunner's glands has been suggested as a precursor for gastric metaplasia. Therefore, these findings argued that this adenoma arises from Brunner's glands through gastric metaplasia. This is the first case of inverted cystic tubulovillous adenoma involving Brunner's glands of duodenum with gastric metaplasia.