Diverticulitis is inflammation in one or more diverticula (a diverticulum is an outpouching of the wall of part of the gastro-intestinal tract). It can happen anywhere along the gastro-intestinal tract, but is more common in the colon (90% in the sigmoid colon).
True diverticula are congenital and are made up of all the layers of the intestinal wall. Pseudodiverticula or mucosal diverticula are far more common and consist of the mucosal layer herniating through the muscle layer of the intestinal wall to form a pouch. This almost always happens at areas where tiny arterioles feed the mucosa, as these are areas of relative weakness. A colonic pouch can become filled with faecal content and form a faecalith, which almost always becomes infected. This causes diverticulitis.
Diverticula are reasonably common -- 20-50% of all people in Western societies will have a few diverticula on autopsy. The incidence is lower in Asian countries, and a proposed reason for this is that the higher amount of fiber in the Asian diet leads to less problems with constipation and high intra-luminal pressure, and therefore less pressure damage to the intestinal walls.
Diverticulitis can cause bleeding per rectum. There are three patterns (as described by Prof. Chapuis to me this afternoon) -
1. massive bleeding (requiring urgent surgery)
2. repeated start/stop bleeding
3. bleeding which resolves spontaneously.
Complications of diverticulitis include abscess formation, phlegmon formation, peritonitis and fistula formation.
In the management of acute diverticulitis (peritonitis or massive bleeding), barium enemas and endoscopy is frowned against because adding more pressure into the colon may well cause further trauma or exacerbation of an existing perforation. Surgical treatment of diverticulitis usually involves a resection of the part of offending bowel (a hemicolectomy) - with either reanastomosis of the ends of bowel or a colostomy and a Hartmann's procedure with the aim of reanastomosis later.