Inflammation of the diverticula (small outpouchings) along the wall of the colon, the large intestine.
For diverticulitis to occur, there must be diverticulosis, the presence of diverticula. Diverticulosis can occur anywhere in the colon but it is most typical in the sigmoid colon, the S-shaped segment of the colon the left lower part of the abdomen..
A key factor promoting the formation of diverticulosis is elevated pressure within the colon. The pressure within the colon is raised when a person is constipated and has to push down to pass small, hard bits of stool ("rabbit droppings").