Mild dilatation of the horizontal segment of the duodenum is caused by congenital factors such as congenital adhesions or acquired factors such as compression by benign or malignant tumors. 1.Congenital factors: (1) Congenital megaduodenum can lead to mild dilatation of the horizontal segment of the duodenum. (2) Congenital adhesions make the distal part of the horizontal duodenum twisted and obstructed, making the horizontal segment of the duodenum mildly dilated. (3) Inadequate rotation of the small intestine or colon causes the cecum to press in front of the horizontal duodenum, resulting in mild dilatation of the horizontal duodenum in the non-compacted portion of the duodenum. 2. Acquired factors: (1) benign or malignant tumors compressing the distal part of the horizontal segment and causing obstruction, resulting in mild dilatation of the horizontal segment of the duodenum (2) Gallstones, parasites and other foreign bodies cause obstruction at the distal end of the horizontal segment, resulting in mild dilatation of the horizontal segment of the duodenum. (3) Enlarged mesenteric lymph nodes caused by gastric cancer or pancreatic cancer, or lymph node tuberculosis distributed along the mesenteric blood vessels, causing obstruction at the distal end of the horizontal segment, resulting in mild dilatation of the horizontal segment of the duodenum. If the examination result shows mild dilatation of the horizontal segment of duodenum, please follow the doctor’s instruction for treatment in time.