Merck Manual

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Joel A. Baum

, MD, Icahn School of Medicine at Mount Sinai;

Rafael Antonio Ching Companioni

, MD, HCA Florida Gulf Coast Hospital

Reviewed/Revised Nov 2022
Topic Resources

Diverticulitis is inflammation of one or more balloon-like sacs (diverticula). Infection may or may not develop.

  • Diverticulitis usually affects the large intestine (colon).

  • Left lower abdominal pain, tenderness, and fever are the typical symptoms.

  • The diagnosis is based on the results of a computed tomography (CT) scan, and colonoscopy is done after the episode of diverticulitis is over.

  • People with mild diverticulitis symptoms may be treated with rest, whereas those with severe symptoms are hospitalized for treatment with antibiotics given by vein and sometimes surgery.

Diverticula in the large intestine Large Intestine The large intestine consists of the Cecum and ascending (right) colon Transverse colon Descending (left) colon Sigmoid colon (which is connected to the rectum) read more 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. One sac is a diverticulum.

Diverticulitis is more common among people over 40 years old. It can be severe in people of any age, although it is most serious in older people, especially those taking corticosteroids or other medications that suppress the immune system and thus increase the risk of infection, including colon infection. People who have HIV and those undergoing chemotherapy are at increased risk of developing diverticulitis. In people over 50 years old, diverticulitis is most common among women. In people under 50 years old, diverticulitis is most common among men.

Overview of Diverticulosis and Diverticulitis

Causes of Diverticulitis

Diverticulitis occurs in people with diverticulosis Diverticulosis of the Large Intestine Diverticulosis is the presence of one or more balloon-like sacs (diverticula), usually in the large intestine (colon). The cause of diverticulosis is unknown but may be related to diet, a sedentary... read more Diverticulosis of the Large Intestine when a diverticulum develops a small (sometimes microscopic) hole that allows bacteria from the intestines to be released. Some doctors think that a diverticulum can become inflamed even if a hole has not developed. Diverticulitis most commonly affects the sigmoid colon, which is the last part of the large intestine just before the rectum.

Doctors think there may be a connection between diverticulitis and the amount of red meat people eat per week, whether they smoke, and whether they have obesity. The use of nonsteroidal anti-inflammatory drugs (including aspirin), acetaminophen, corticosteroids, and opioids also increases the risk of diverticulosis and diverticulitis.

Diverticulitis is not caused by eating nuts, seeds, corn, or popcorn.

Symptoms of Diverticulitis

Symptoms of diverticulitis typically include pain and/or tenderness (usually in the left lower part of the abdomen), fever, and sometimes nausea and vomiting. Diverticulitis typically does not cause gastrointestinal bleeding Gastrointestinal Bleeding Bleeding may occur anywhere along the digestive (gastrointestinal or GI) tract, from the mouth to the anus. Blood may be easily seen by the naked eye (overt), or blood may be present in amounts... read more Gastrointestinal Bleeding .

Complications of diverticulitis

Complications of diverticulitis include

  • Fistulas

  • Abscess

  • Peritonitis

  • Narrowing (stricture)

A fistula is an abnormal channel connecting one organ with another or with the skin. Intestinal inflammation from diverticulitis can lead to the development of fistulas that connect the large intestine with other organs.

Fistulas usually form when an inflamed diverticulum in the large intestine is touching another organ (such as the bladder). The resulting inflammation along with the bacterial contents of the large intestine slowly penetrate the nearby organ, resulting in a fistula.

Most fistulas form between the sigmoid colon and the bladder. These fistulas are more common among men than women, although women who have had a hysterectomy Treatment The most common type of cancer of the uterus develops in the lining of the uterus (endometrium) and is called endometrial cancer. Endometrial cancer usually affects women after menopause. It... read more Treatment (removal of the uterus) are at increased risk because the large intestine and bladder are no longer separated by the uterus. When fistulas form between the large intestine and bladder, intestinal contents, including normal bacteria, enter the bladder and cause urinary tract infections Overview of Urinary Tract Infections (UTIs) In healthy people, urine in the bladder is sterile—no bacteria or other infectious organisms are present. The tube that carries urine from the bladder out of the body (urethra) contains no bacteria... read more .

Less commonly, a fistula can develop between the large intestine and the small intestine, uterus, vagina, abdominal wall, or even the thigh.

Complications of Diverticulitis

In diverticular disease, a diverticulum may bleed into the intestine. If a diverticulum ruptures, the contents of the intestine, including bacteria and blood, spill into the abdominal cavity, often causing infection. An abnormal channel (fistula) may form between the large intestine and another organ, usually when a diverticulum that touches another organ ruptures.

Complications of Diverticulitis

Other possible complications of diverticulitis include inflammation of nearby organs (such as the uterus, bladder, or other areas of the digestive tract). Repeated bouts of diverticulitis can lead to narrowing (stricture) of the colon because the resulting scarring and muscle thickening can narrow the inside of the large intestine and prevent solid stool from passing through.

Diagnosis of Diverticulitis

  • Computed tomography (CT) of the abdomen and pelvis

  • Colonoscopy after episode has ended

If a doctor knows that the person already has diverticulosis Diverticulosis of the Large Intestine Diverticulosis is the presence of one or more balloon-like sacs (diverticula), usually in the large intestine (colon). The cause of diverticulosis is unknown but may be related to diet, a sedentary... read more Diverticulosis of the Large Intestine , a diverticulitis diagnosis may be based almost entirely on the symptoms. However, many other conditions involving the large intestine and other organs in the abdomen and pelvis can cause symptoms similar to diverticulitis, including appendicitis Diagnosis Appendicitis is inflammation and infection of the appendix. Often a blockage inside the appendix causes the appendix to become inflamed and infected. Abdominal pain, nausea, and fever are common... read more , colon cancer Colorectal Cancer Family history and some dietary factors (low fiber, high fat) increase a person’s risk of colorectal cancer. Typical symptoms include bleeding during a bowel movement, fatigue, and weakness... read more Colorectal Cancer or ovarian cancer Diagnosis Ovarian cancer is cancer of the ovaries. It is related to fallopian tube cancer, which develops in the tubes that lead from the ovaries to the uterus, and peritoneal cancer, which is cancer... read more , an abscess Diagnosis An abscess is a pocket of pus, usually caused by a bacterial infection. Most people have constant abdominal pain and a fever. Computed tomography or another imaging test can distinguish an abscess... read more not related to diverticulitis, and noncancerous (benign) growths on the wall of the uterus (uterine fibroids Diagnosis A fibroid is a noncancerous tumor of the uterus that is composed of muscle and fibrous tissue. Uterine fibroids are very common, occurring in approximately 70% of White women and 80% of Black... read more Diagnosis ).

Once inflammation has subsided or the infection has been treated, a doctor may do a colonoscopy Endoscopy Endoscopy is an examination of internal structures using a flexible viewing tube (endoscope). In addition to examinations, doctors can use endoscopy to do biopsies and give treatment. Endoscopes... read more (an examination of the large intestine using a flexible viewing tube) to rule out colon cancer. The colonoscopy may be done if people have complications (such as a perforation or abscess) or if they have risk factors for cancer (such as narrowed stool, bleeding, anemia, weight loss, or a family history of colon cancer). Colonoscopy usually needs to be delayed for 1 to 3 months after treatment because it can damage or rupture an inflamed intestine. Exploratory surgery is rarely needed to confirm the diagnosis.

Treatment of Diverticulitis

  • For mild diverticulitis, rest

  • For severe diverticulitis, no food or fluids by mouth and antibiotics

  • Sometimes surgery

Mild diverticulitis can be treated at home with rest. Diverticulitis symptoms usually lessen rapidly. There are no diet restrictions for people who have mild diverticulitis.

Severe diverticulitis requires different treatment. People who have severe symptoms, such as abdominal pain, body temperature above 101° F (38.3° C), and other evidence of serious infection or complications, are hospitalized. In the hospital, people are given fluids and antibiotics by vein (intravenously), kept on bed rest, and given nothing by mouth until the symptoms subside. People stay in the hospital until their symptoms go away. They can then eat soft foods. Once the episode has ended, people can eat high-fiber foods. To decrease the risk of recurrence, people should avoid using nonsteroidal anti-inflammatory drugs (NSAIDs).

After 1 to 3 months, people have a colonoscopy to evaluate the colon.

For some people, including those who have small abscesses, rest and sometimes antibiotics are all that are needed to treat severe diverticulitis.

Drainage for abscesses

Surgery for diverticulitis

Emergency surgery is necessary for people whose intestine has ruptured or who have peritonitis. Other people who need surgery include those who have severe diverticulitis symptoms that are not relieved by nonsurgical treatment (such as antibiotics) within 3 to 5 days. People who have increasing pain, tenderness, and fever also need surgery.

The surgeon removes the involved section of the intestine. The ends are rejoined immediately in healthy people who do not have a perforation, abscess, or severe intestinal inflammation. Other people need a temporary colostomy.

A colostomy is an opening between the large intestine and the skin surface. About 10 to 12 weeks later (or sometimes longer), after the inflammation has gone away and the person's condition has improved, the cut ends of the intestine are rejoined during a follow-up operation, and the colostomy is closed.

Understanding Colostomy

In a colostomy, the large intestine (colon) is cut. The healthy end of the large intestine, which is before the blockage, is brought to the skin surface through a surgically created opening in the abdominal wall. It is then stitched to the skin of the opening. Stool passes through the opening and into a disposable bag. The colostomy allows the remaining part of the large intestine to rest while the person recovers. After the person recovers from the surgery and the colon heals, the two ends can be reattached so that stool can pass normally.

Understanding Colostomy

Fistula treatment involves removing the section of large intestine where the fistula begins, rejoining the cut ends of the large intestine, and repairing the other affected area (for example, the bladder or small intestine).

Sometimes, after talking with their doctor, people choose to have elective surgery (surgery that is not needed immediately and can be put off for some time) to manage their diverticular disease. Elective surgery is typically considered for people who have had multiple attacks of diverticulitis or for those who have a complication such as narrowing of the colon due to scarring.

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