Diverticulitis, specifically colonic diverticulitis, is a gastrointestinal disease characterized by inflammation of abnormal pouches—diverticula—which can develop in the wall of the large intestine. Symptoms typically include lower abdominal pain of a sudden onset. The onset of symptoms, however, may also occur over a few days. In North America and Europe the abdominal pain is usually on the left lower side, while in Asia it is usually on the right. There may also be nausea; and diarrhea or constipation. Fever or blood in the stool suggests a complication. Repeated attacks may occur.

The causes of diverticulitis are uncertain. Risk factors may include obesity, lack of exercise, smoking, a family history of the disease, and nonsteroidal anti-inflammatory drugs (NSAIDs). The role of a low fiber diet as a risk factor is unclear. Having pouches in the large intestine that are not inflamed is known as diverticulosis. Inflammation occurs in between 10% and 25% at some point in time and is due to a bacterial infection.Diagnosis is typically by CT scan, though blood tests, colonoscopy, or a lower gastrointestinal series may also be supportive. The differential diagnosis includes irritable bowel syndrome.

Preventive measures include altering risk factors such as obesity, inactivity, and smoking. Mesalazine and rifaximin appear useful for preventing attacks in those with diverticulosis. Avoiding nuts and seeds as a preventive measure is no longer recommended since there is no evidence these play a role in initiating inflammation in diverticula. For mild diverticulitis, antibiotics by mouth and a liquid diet is recommended. For severe cases, intravenous antibiotics, hospital admission, and complete bowel rest may be recommended. Probiotics are of unclear use. Complications such as abscess formation, fistula formation, and perforation of the colon may require surgery.

The disease is common in the Western world and uncommon in Africa and Asia. In the Western world about 35% of people have diverticulosis while it affects less than 1% of those in rural Africa, and 4 to 15% of those may go on to develop diverticulitis. The disease becomes more frequent with age, being particularly common in those over the age of 50. It has also become more common in all parts of the world. In 2003 in Europe, it resulted in approximately 13,000 deaths. It is the most frequent anatomic disease of the colon. Costs associated with diverticular disease are around $2.4 billion a year in the United States as of 2013.

Signs and symptoms
Diverticulitis typically presents with left lower quadrant abdominal pain of sudden onset. There may also be fever, nausea, diarrhea or constipation, and blood in the stool.

The causes of diverticulitis are poorly understood, with approximately 40 percent due to genes and 60 percent due to environmental factors. Conditions that increase the risk of developing diverticulitis include arterial hypertension and immunosuppression. Obesity is another risk factor. Low levels of vitamin D are associated with an increased risk of diverticulitis.

It is unclear what role dietary fibre plays in diverticulitis. It is often stated that a diet low in fibre is a risk factor; however, the evidence to support this is unclear. There is no evidence to suggest that the avoidance of nuts and seeds prevents the progression of diverticulosis to an acute case of diverticulitis. It appears in fact that a higher intake of nuts and corn could help to avoid diverticulitis in adult males.

Right-sided diverticula are micro-hernias of the colonic mucosa and submucosa through the colonic muscular layer where blood vessels penetrate it. Left-sided diverticula are pseudodiverticula, since the herniation is not through all the layers of the colon. Diverticulitis is postulated to develop because of changes inside the colon, including high pressures because of abnormally vigorous contractions.

Most cases of simple, uncomplicated diverticulitis respond to conservative therapy with bowel rest.

People may be placed on a low fibre diet. It was previously thought that a low-fibre diet gives the colon adequate time to heal. Evidence tends to run counter to this with a 2011 review finding no evidence for the superiority of low fibre diets in treating diverticular disease and that a high-fibre diet may prevent diverticular disease. A systematic review published in 2012 found no high quality studies, but found that some studies and guidelines favour a high-fibre diet for the treatment of symptomatic disease. While it has been suggested that probiotics may be useful for treatment, the evidence currently neither supports nor refutes this claim.

The use of antibiotics in mild cases of uncomplicated diverticulitis is supported with only “sparse and of low quality” evidence, with no evidence supporting their routine use. In spite of this, antibiotics are recommended by several current guidelines. With CT scan evidence of abscess, fistula, or intestinal rupture with peritonitis, antibiotics are recommended and routinely used.

Indications for surgery are abscess or fistula formation; and intestinal rupture with peritonitis. These, however, rarely occur. Surgery for abscess or fistula is indicated either urgently or electively. The timing of the elective surgery is determined by evaluating factors such as the stage of the disease, the age of the individual, the general medical condition of the individual, the severity and frequency of the attacks, and whether symptoms persist after the first acute episode. In most cases, elective surgery is deemed to be indicated when the risks of the surgery are less than the risks of the complications of the diverticulitis. Elective surgery is not indicated until at least six weeks after recovery from the acute event. Emergency surgery is indicated for intestinal rupture with peritonitis.

The first surgical approach consists of the resection and primary anastomosis. This first stage of surgery is performed on patients if they have a well vascularized, nonedematous and tension-free bowel. The proximal margin should be an area of pliable colon without hypertrophy or inflammation. The distal margin should extend to the upper third of the rectum where the taenia coalesces. Not all of the diverticula-bearing colon must be removed, since diverticula proximal to the descending or sigmoid colon are unlikely to result in further symptoms.

Diverticulitis most often affects the elderly. In Western countries, diverticular disease most commonly involves the sigmoid colon (95 percent of patients). The prevalence of diverticular disease has increased from an estimated 10 percent in the 1920s to between 35 and 50 percent by the late 1960s, and 65 percent of those currently 85 years of age and older can be expected to have some form of diverticular disease of the colon. Less than 5 percent of those aged 40 years and younger may also be affected by diverticular disease.

Left-sided diverticular disease (involving the sigmoid colon) is most common in the West, while right-sided diverticular disease (involving the ascending colon) is more common in Asia and Africa. Among patients with diverticulosis, 4 to 15% may go on to develop diverticulitis.

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