Meckel's diverticulum is one of the most common congenital abnormalities. It occurs when the connection between the intestine and the umbilical cord doesn't completely close off during fetal development. This results in a small outpouching of the small intestine, know as a Meckel's diverticulum. In most cases, Meckel's diverticula do not cause any problems. In a small number of patients however, these diverticula can become infected (diverticulitis) cause an obstruction of the intestine, or cause bleeding from the intestine. The most common symptom of Meckel's diverticulitis is painless bleeding from the rectum. The stools may contain fresh blood or may look black and tarry. Diverticulitis, or infection, of a Meckel's diverticulum is often mistaken for appendicitis.