Extra‐ampullary duodenal adenoma: a clinicopathological study

Extra-ampullary duodenal adenoma (EADA) is a rare condition with poorly described clinicopathological details. In this study, we aimed to characterize EADA clinicopathologically.We performed a retrospective review of 44 serial cases of EADA. Each EADA was categorized as either gastric-type (n = 5) or intestinal-type (n = 39). All gastric-type adenomas were located in the first portion of the duodenum and exhibited a pedunculated shape. Gastric-type adenomas were classified into two subtypes: pyloric gland and foveolar. The former consisted of mucin 6 (MUC6)-positive glands covered with MUC5AC-positive cells, whereas nearly all the latter consisted of MUC5AC-positive cells. When EADAs were categorized into high and low grades, approximately 40% (16 of 44) were high-grade. The high-grade adenomas were significantly larger than the low-grade adenomas (19.4 ± 8.6 mm versus 11.8 ± 5.1 mm, P = 0.021), and all adenomas greater than 20 mm in largest diameter were categorized as high-grade adenomas. Among 16 individuals who underwent total colonoscopy before or after duodenal mucosal resection, nine had a colorectal neoplasm, and all nine duodenal lesions were of the intestinal phenotype.We clarified the clinicopathological characteristics of gastric- and intestinal-type EADAs. EADAs greater than 20 mm at the largest diameter were consistently high-grade, and are thought to have the potential to progress to adenocarcinoma. These findings should be helpful for the clinical management of EADA.