Diverticulitis begins with the development of a micro-perforation in the pocket (diverticulum) that has formed. Bacteria from the colon then spill into the circular or longitudinal muscle layers of the colon due to this micro-perforation, and the subsequent inflammation causes swelling in the wall of colon and abdominal pain. Occasionally, a free perforation can occur, where frank stool from the colon spills into the abdominal cavity. Free perforation is a surgical emergency and can lead to death if not treated quickly.
There is a higher incidence of constipation in diets that are deficient in fiber. Studies have demonstrated that the higher pressure required to propel stool through the colon creates outward force on the colon muscle wall–especially in the sigmoid colon area. Over time, this pressure leads to the formation of diverticula in the weak areas of the muscle wall. Common complications of diverticulosis include rectal bleeding, which can be severe enough to warrant blood transfusions. More commonly, it leads to acute diverticulitis.
As mentioned above, diverticulitis begins with the micro-perforation of one of these diverticula. The mechanism that leads to this perforation is a partial obstruction of one of the diverticula–usually from stool. If a piece of stool gets stuck in the mouth of the pocket, the mucous secreted by the mucosa (the inner lining) builds and, if the pressure gets high enough, the diverticulum can develop a micro-perforation. In a micro-perforation, some bacteria, but not stool, creates inflammation outside the wall of the colon. This leads to colon wall swelling, abdominal pain, and fevers, as well as other signs of systemic infection. Treatment is geared toward killing the bacteria and giving time for the colon wall to heal.
Diverticulitis medical expert witness specialties include gastroenterology, general surgery, pathology, colon-rectal surgery, immunology, internal medicine, family medicine, and hospitalist medicine.