A common adenoma of the descending segment of the duodenum should be considered as a general adenoma with a space-occupying lesion in the descending segment of the duodenum. The duodenum is located between the stomach and the jejunum and is a part of the small intestine, divided into four parts: the bulbous, descending, horizontal, and ascending segments, and the whole is in the shape of a “C”, which surrounds the pancreatic head. The duodenal descending bulge means that the duodenal descending segment has occupational changes, and the nature of the bulge can be determined by imaging and pathologic examination. The nature of the bulge in this case should be a common adenomatous tissue. In the case of adenomas in the descending duodenum, elective surgical resection or conservative treatment should be recommended by the clinician in order to avoid obstruction of the occupying site or deterioration of the adenoma.