Diverticula in ulcerative colitis. Endoscopic view of diverticula in the sigmoid colon (large intestine) of a patient with ulcerative colitis. Ulcerative colitis is an autoimmune disease causing chronic inflammation of the colon and rectum of the large intestine. It can cause ulceration, pain, discomfort, malabsorption leading to malnutrition, and bleeding leading to anaemia. Diverticula are abnormal protruding pouches formed in the wall of the gastrointestinal system. Severe cases may require surgery to remove part of the colon.