A pocket of infection (abscess) that forms in the abdominal cavity. The inflammation or infection may spread to the membrane that covers the inside of the abdominal wall. This infection, called peritonitis, may spread to other parts of the body (sepsis).
Free perforation. In rare cases, a hole in a diverticulum may allow stool to enter the abdominal cavity, causing peritonitis.
An abnormal opening (fistula) that forms between the large intestine and organs near it. In diverticulitis, a fistula may form between two parts of the large intestine or between the large intestine and the bladder, vagina, or urethra.