A straight groove in the middle of the stool may be caused by rectal polyps, hemorrhoids, intestinal tumors and other reasons. 1. Rectal polyps: Rectal polyps are proliferative and protruding tissues present on the surface of the rectal mucosa. As the polyps protrude into the intestinal lumen, they may cause a groove in the middle of the stool in the process of formation, and may also be accompanied by the symptom of blood in the stool. 2. Hemorrhoids: Hemorrhoids are caused by varicose veins at the lower end of the rectum or the anal canal, resulting in a swelling at the lower end of the rectum or outside the anus, of which internal hemorrhoids may lead to the symptom of grooves in the middle of the stool, and the patient may also suffer from painful bowel movements and bleeding. 3. Intestinal tumor: if the patient has a tumor in the rectum, due to the occupying mass protruding from the intestinal cavity, it can lead to a groove in the middle of the stool, and the patient may also suffer from anemia, emaciation, abdominal pain and other symptoms. If there is a groove in the middle of the stool, it is recommended to go to the regular hospital in time to find out the cause and get timely treatment.