Merck Manual

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Diverticulosis of the Large Intestine


Joel A. Baum

, MD, Icahn School of Medicine at Mount Sinai;

Rafael Antonio Ching Companioni

, MD, Digestive Diseases Center

Last full review/revision Mar 2019| Content last modified Mar 2019
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Diverticulosis is the presence of one or more balloon-like sacs (diverticula), usually in the large intestine (colon).

  • Spasms of the muscular layer of the intestine are thought to cause diverticula.

  • Diverticula usually cause no symptoms, but sometimes they become inflamed or bleed, causing blood in the stool or bleeding from the rectum.

  • Typically, the diagnosis is confirmed by colonoscopy, barium enema, computed tomography (CT) scan, or video capsule endoscopy.

  • A high-fiber diet and stool-bulking agents are given, but sometimes bleeding occurs and requires colonoscopy or even surgery.

What Is Diverticulosis?

In diverticulosis, many balloon-like sacs (diverticula) develop in the large intestine, most commonly in the last part of it (sigmoid colon). Most diverticula vary in diameter from 1/10 inch to more than 1 inch (about ¼ centimeter to more than 2½ centimeters). For unclear reasons, some diverticula become very large—up to 6 inches (about 15 centimeters) in diameter. These are called giant diverticula.

What Is Diverticulosis?

Diverticula in the colon occur when a defect develops in the thick, muscular middle layer of the bowel. The thin inner layers of the bowel bulge out through the defect and create a small sac. Diverticula usually do not cause any problems but they sometimes become inflamed or bleed.

Diverticula may develop anywhere in the large intestine, but they are more common in the sigmoid colon, which is the last part of the large intestine just before the rectum. Diverticula vary in diameter from 1/10 inch to 1 inch (about ¼ to more than 2½ centimeters). They are uncommon before age 40 but become more common rapidly thereafter. Most people over age 80 have many diverticula. Giant diverticula, which are rare, are larger than 1½ inches (about 4 centimeters) in diameter. A person may have only a single giant diverticulum.


Diverticula are thought to be caused by spasms of the muscular layer of the intestine. The cause of these intestinal spasms is unknown but may be related to a diet low in fiber or high in red meat. The resulting pressure that these spasms exert on the intestinal wall causes a part of the wall to bulge at a point of weakness, usually near to where an artery penetrates the muscular layer of the large intestine. An increase in the thickness of the muscular layer is a common finding in the sigmoid colon of people with diverticulosis.

The cause of a giant diverticulum is unclear.


Diverticula themselves are not dangerous. In fact, most people with diverticulosis do not have symptoms. However, people with diverticulosis can sometimes have unexplained painful cramps or bowel movement disturbances.

Complications of diverticulosis

Complications of diverticulosis are more common in people who smoke, are obese, consume a low-fiber diet, or use nonsteroidal anti-inflammatory drugs (NSAIDs).

The most common complications are

Diverticulitis is inflammation and/or infection of a diverticulum, which causes abdominal pain and can result in a collection of pus (abscess) around the inflamed diverticulum. If a hole (perforation) develops in the diverticulum, fluid and bacteria can leak into the abdomen and cause a very serious condition called peritonitis.

A diverticulum can bleed into the intestine. Bleeding is painless but can be heavy and result in blood passing out through the rectum (see Gastrointestinal Bleeding). Most episodes of bleeding stop spontaneously. However, in some people, doctors have to do endoscopy or surgery to stop the bleeding. The bleeding may be serious enough to require a blood transfusion.


  • Colonoscopy, video capsule endoscopy, or computed tomography (CT) scan

Diverticulosis is suspected when symptoms such as unexplained painful cramps, bowel movement disturbances, or painless rectal bleeding, especially in an older person, are present.

The diagnosis of diverticulosis is usually confirmed by examining the large intestine using a flexible viewing tube (colonoscopy) or sometimes a CT scan of the abdomen. If the person has severe abdominal pain, doctors usually prefer CT so as not to rupture the inflamed intestine.

If blood is present in the stool, a colonoscopy is usually the best method with which to identify the source. However, in people who are bleeding a lot, CT angiography or radionuclide scans taken after radioactive red blood cells are injected into a vein (intravenously) may be required to determine the source of bleeding.


  • Changes in diet

  • Treatment of bleeding

The goal of treatment of diverticulosis in people who have symptoms is usually to reduce intestinal spasms, which is best achieved by maintaining a high-fiber diet (which consists of vegetables, fruits, and whole grains) and drinking plenty of fluids. Increased bulk in the large intestine reduces spasms, which in turn decreases the pressure on the walls of the large intestine. If a high-fiber diet alone is not effective, a diet supplemented daily with wheat bran that does not dissolve in water and cannot be digested by the body or a bulking agent, such as psyllium or methylcellulose, may help.

Most bleeding stops without treatment but if it does not, doctors often do colonoscopy to locate and clot (coagulate) the bleeding area with clips, heat, or a laser, or by injecting the area with a drug. Alternatively, doctors may do angiography to stop the bleeding. During this procedure, doctors pass a catheter into the artery that goes to the bleeding diverticulum and then inject material (a process called embolization) or the drug vasopressin to reduce blood flow to the bleeding diverticulum. Rarely, if bleeding recurs often or if the source of the bleeding cannot be determined, doctors may do surgery to remove some or all of the large intestine (a procedure called colectomy).

A giant diverticulum may require surgery because it is likely to become infected and rupture.

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