Flexible sigmoidoscopy is a procedure used to see inside the sigmoid colon and rectum. This procedure can detect inflamed tissue, abnormal growths, and ulcers. The procedure is used to look for early signs of cancer and can help doctors diagnose unexplained changes in bowel habits, abdominal pain, bleeding from the anus, and weight loss. The sigmoid colon is the last one-third of the colon. The colon comprises three main parts: the ascending colon, the transverse colon, and the sigmoid colon sometimes called the descending colon. The colon absorbs nutrients and water and forms stool.