Posted on 06 Nov 2009 03:07

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By Amanda Peppercorn
Physician, University of NC, Chapel Hill

What are Diverticulosis and Diverticulitis?

Diverticulosis, defined simply as the presence in the large intestine (colon) of small saccular outpouchings, termed diverticula, is extremely common in “developed” countries and increases dramatically with age (Image 1 below). It affects approximately 5% of the population under 45 years of age and increases to almost 80% in those older than age 85 (1). Diverticula develop most commonly in the descending (“left-sided”) and sigmoid colon, however, there is geographic variability. In Asia and Africa, the ascending (“right-sided”) colon is more commonly involved, but the overall rate is much lower, at approximately 0.2%. Despite the prevalence of diverticulosis, about 70% of all people remain asymptomatic throughout their lifetime; 5-15% develop complications of diverticular bleeding, and 15-25% develop diverticulitis and associated complications.

Diverticulitis refers to inflammation and infection of diverticula (see definitions table). When there is erosion of the diverticular wall due to increased pressure in the gut, irritation from stool or food particles, or obstruction of the diverticular opening, inflammation and death of the intestinal lining can occur and the surrounding tissues are exposed to the overwhelming number of bacteria that are normally contained in stool in the colon. If the inflammation and infection remains localized to the bowel wall, it is referred to as “simple” or uncomplicated diverticulitis. Complicated diverticulitis is defined by the presence of one or more complications. These include:

  • bowel wall perforation with extension of pustular material into the abdominal cavity
  • walled off peri-diverticular abscess formation [Image 2 below]
  • intra-mural sinus tract formation (tunnel-like tract in the wall of the colon) [Image 3 below]
  • fistulous connections between the ruptured diverticula and other organs such as the bladder, vaginal wall, rectum, or skin
  • bowel obstruction due to inflammation and stricture formation
  • pyelephlebitis (infection of the mesenteric vessels that drain the area of diverticulitis)
  • liver abscess, resulting from bacterial infection spreading from the area of diverticulitis into the mesenteric blood vessels which drain into the liver
  • large intestinal rupture with fecal contamination of the peritoneal cavity resulting in chemical and polymicrobial peritonitis

Diverticulosis The presence of diverticula in the large intestine
Diverticulum (pleural: Diverticula) Saccular outpouching of the lining of the large intestine caused by herniation of the mucosal layers through the surrounding muscle layer at a point of intestinal wall weakness in response to intra-intestinal pressure
Diverticulitis Infection and inflammation of the intestinal wall due to erosion of the lining of a diverticulum
Fistula A new connection forged between an infected diverticula and nearby anatomic structures, such as the bladder (colovesicular fistula), the small intestine (colo-intestinal fistula), the skin (colo-cutaneous) and the vagina (colovaginal fistula)
Abscess A walled-off collection of micro-organisms (usually bacteria and fungus) as well as the infection-fighting white blood cells such as neutrophils and macrophages, causing the appearance of pustular material
Peritonitis Infection and inflammation of the abdominal cavity, termed the peritoneum
Pyelephlebitis Infection of blood vessels

What causes diverticulosis and diverticulitis?

Diverticula form when the inner lining (the mucosal and submucosal layers) of the intestinal wall herniates through the outer intestinal muscle layer at a point of muscle weakness, which often occurs at the point where small blood vessels enter.
Colonoscopy picture showing diverticulosis in gut

Image courtesy of Dr. Evan Dellon, M.D.,
University of North Carolina at Chapel Hill, NC

It is thought that increases in intra-intestinal pressure occur during segmentation of the colon in relation to patterns of bowel motility and fiber intake. This pressure is greatest in areas of the bowel with a smaller diameter, such as the sigmoid colon. Ninety five percent of patients have sigmoid diverticula while 35 percent have diverticula involving the sigmoid colon in addition to other areas of the large intestine; only 5 percent of patients have diverticula isolated to proximal regions of the colon. This may also explain why several studies have found an association between diverticulosis and a low fiber diet since fiber is known to keep the stool bulky, enlarge the diameter of the intestine, reduce bowel transit time, and help regulate motility (2). This is also supported by the observation that diverticulosis is less common in vegetarians (3). However, there has been no established correlation between constipation and diverticular formation. While male gender was originally felt to be a risk factor, recent studies suggest equal distribution. Similarly, there has been no correlation between diverticular disease and smoking, or alcohol or caffeine consumption, however there is support for the hypothesis that obesity and lack of vigorous exercise may contribute to the development of diverticulosis for unclear reasons.

The exact mechanism for the development of infection and inflammation of diverticula resulting in diverticulitis is not fully understood. The process begins with erosion and damage to the diverticular wall due to food particles or fecaliths (hard pieces of stool) which leads to focal micro-perforation. Conventional wisdom has maintained that small, non-absorbable food particles such as corn, seeds, and nuts may precipitate diverticulitis by becoming lodged within a diverticulum, however this has not been supported in the medical literature and there is considerable practice variability among those who care for patients with diverticulosis with regard to recommending avoidance of these food particles (4).

When the contents of the colon are not properly contained, bacterial infection ensues. In cases of uncomplicated diverticulitis, the inflammation due to micro-perforation can be mild and a small leak can be walled off by the mesenteric fat that surrounds the colon. A small peri-diverticular abscess or phlegmon may form. However, macro-perforation can lead to larger abscesses with extension to distant sites, other organs, and complications of peritonitis or fistula formation as listed above. While the formation of a peri-diverticular abscess is quite common, other complications such as the development of fistulae, peritonitis, pyelephlebitis, and liver abscess are very rare. The distinction between uncomplicated and complicated diverticulitis significantly impacts the clinical presentation and medical management (see below).

Colonoscopy picture showing presence of diverticuli in gut

Image courtesy of Paola Blanco, M.D.,
Beth Israel Deaconess Medical Center, Boston, MA

What are the symptoms of diverticulitis?

The clinical manifestations of diverticulitis are variable. With uncomplicated diverticulitis, the most common symptom is dull left lower quadrant abdominal pain correlating to the anatomic location of the sigmoid colon. The pain can persist for days, with gradual worsening. This may be accompanied by other symptoms such as fever, nausea, vomiting, mild diarrhea, constipation, or urinary symptoms (eg, pain with urination, increased urinary frequency) due to irritation of the bladder, which is positioned adjacent to the colon. A small amount of blood may be present in the stool but large amounts of blood are rarely seen and suggest an alternate diagnosis. When fistulous tracts develop between the perforated diverticulum and nearby structures, air and stool-like material in the urine or vaginal vault may be a clue to the diagnosis as well. With frank perforation and spillage of purulent material from a peri-diverticular abscess, or presence of fecal material from the colon itself in the abdominal cavity, symptoms of peritonitis ensue with severe generalized abdominal pain, often associated with symptoms of septic shock. In the rare case of right-sided diverticulitis, right-sided abdominal pain develops and can be confused with the clinical presentation of appendicitis.

CT Scan of diverticulitis with abscess

Computer tomography scan showing sigmoid diverticulitis
complicated by abscess (right lower quadrant).
Courtesy of Vassili Raptopoulos, M.D., Beth Israel Deaconess
Medical Center, Boston, MA

How is the diagnosis of diverticulitis made?

The diagnosis of diverticulitis is made utilizing symptomatic information from the patient in combination with findings on physical examination and laboratory and radiographic data. On physical examination, the patient may have documented fever and abdominal tenderness and distention. A painful mass in the left lower quadrant is palpable approximately 20% of the time (5). Laboratory data may show an elevated white blood cell count consistent with an infectious and inflammatory process. Urine evaluation may show white blood cells induced by adjacent inflammation; with a colovesicular fistula (colon-bladder connection), stool-type bacteria may grow on urine culture; a finding of several different strains of bacteria differentiate diverticulitis with fistula complication from a simple urinary tract infection, which is usually caused by growth of one type of bacteria.

Image of sigmoid diverticulitis complicated by abscess

Sigmoid diverticulitis complicated by abscess.
Courtesy of Evan Dellon, M.D.,
University of North Carolina at Chapel Hill, NC

Computer tomographic (CT) scanning (with colonic contrast) is the most useful modality for rapid and accrate diagnosis of acute diverticulitis and identification of any associated complications (6). It can also adequately eliminate many other diagnoses that may present similarly to diverticulitis, including appendicitis, constipation, bowel obstruction, inflammatory bowel disease, infectious colitis, and tubo-ovarian abscess or other gynecologic complications in women. A flare of Crohn’s disease, in particular, may be virtually indistinguishable from acute diverticulitis. CT features of acute diverticulitis include increased soft tissue stranding of the pericolic fat due to inflammation, visualization of colonic diverticula, bowel wall thickening, micro-perforation with air in the intestinal wall, and fluid collections that represent abscess formation (see Image 3). CT can also identify fistula formation by visualization of air present in the bladder or vagina, and intestinal rupture with peritonitis by the presence of air in the abdominal cavity outside of the intestinal tract with diffuse inflammatory changes of the mesenteric fat and scattered fluid collections in the peritoneal space. Finally, CT imaging can be repeated over time to document improvement of diverticulitis and associated complications. Prior to CT, barium enema was utilized for radiographic diagnosis (Image 5) but is no longer utilized. Colonoscopy should be avoided when acute diverticulitis is suspected given the risk of perforation.

How is diverticulitis treated?

Uncomplicated diverticulitis is successfully managed with conservative treatment in 70-100% of patients overall and 70-80% of those who require hospitalization (1,7-8). Conservative treatment includes bowel rest (either fasting or small amounts of clear liquids), intravenous hydration, and oral or intravenous antibiotic therapy. A small number of patients who have only a small (<5 cm) peri-diverticular abscess, are minimally symptomatic and who can tolerate oral hydration, merit a trial of outpatient therapy with oral antibiotics, usually for 7-10 days. Elderly patients, those with significant co-morbidities (end-stage liver disease, end-stage renal disease, diabetes) and those with compromised immune systems (AIDS, cancer chemotherapy, organ transplantation, long-term immunosuppressive drugs such as corticosteroids) should always be hospitalized (9).

Like other infections related to the intestinal tract, acute diverticulitis is a polymicrobial infection caused by the various types of bacteria that live in the large intestine, which include Enterobacteriaceae (Escherichia coli, Klebsiella species, Enterobacter and others) viridans streptococci, enterococci, and anaerobic organisms such as Bacteroides and Peptostreptococcus spp. Other, less commonly isolated pathogens, may include Staphylococcus aureus, Pseudomonas aeruginosa, and Candida.

picture of large bowel with multiple diverticula

Large bowel (sigmoid colon) showing multiple diverticula

Oral antibiotic regimens that offer broad antimicrobial coverage include combination quinolone/metronidazole, trimethoprim-sulfamethoxazole/metronidazole, or amoxicillin-clavulanic acid. Successful intravenous antibiotic regimens include beta lactamase inhibitors such as piperacillin-tazobactam, ampicillin-sulbactam, or ticarcillin-clavulanate, single agent carbapenem (imipenem-cilastin, meropenem, ertapenem), or combination treatment with a second or third generation cephalosporin or fluoroquinolone in addition to metronidazole.

For complicated diverticulitis, invasive intervention is almost always required. For large walled-off abscess collections, percutaneous drainage with placement of a drainage catheter can by achieved under fluoroscopic CT guidance. Antibiotics should be modified to treat any particular organism(s) that grow from the abscess material. Indications for emergent surgical exploration and resection include generalized peritonitis from macro-perforation, persistent obstruction, acute clinical deterioration, and failure to respond to conservative therapy. In the acute setting, a two-stage operative approach, such as the Hartmann procedure, is undertaken. This includes resection of the involved area of colon, creation of a colostomy with the proximal bowel loop, and over-sewing the distal colon/rectum into a pouch. Several months after full healing, the colostomy is taken down and the two ends sewn together to restore bowel integrity.

In contrast to acute surgery, elective surgery is often undertaken in the setting of fistula formation or recurrent attacks of diverticulitis, or for complicated diverticulitis that has been brought under control with a prolonged course of antibiotics. In the case of elective surgery, a one-step procedure is usually indicated, with primary resection and anastomosis (surgical re-connection of the two ends of the bowel). Laparoscopic sigmoidectomy is an alternative to laparotomy in cases of mild/moderate disease.

What dietary modifications should be made following acute diverticulitis?

Uncontrolled studies have shown that long-term fiber supplementation may reduce the incidence of recurrence of diverticulitis, however two small controlled trials had conflicting results (10,11). While data is conflicting, patients should generally be advised to consume a diet high in fiber once the acute phase has resolved. No data or consensus guidelines address the widely held belief that corn, seeds, nuts, and small pieces of undigested food particles should be avoided.

What evaluation should occur after resolution of acute diverticulitis?

Following successful conservative treatment for a first attack of diverticulitis, 30-40% of patients will remain asymptomatic, 30-40% will have subsequent symptoms such as abdominal cramps without frank diverticulitis, and approximately 33% will proceed to a second attack of diverticulitis (5). For patients with compromised immune systems or significant comorbidities, elective sigmoid resection is recommended after a primary attack of diverticulitis whereas most other patients are advised to undergo surgical resection only after a second attack (9). Younger patients (defined broadly as those younger than 40- 50 years of age) have traditionally received recommendations to have elective resection following a first episode of diverticulitis, however this remains controversial. For all patients, colonoscopy is recommended following full resolution of diverticulitis to assess for colon cancer and to determine the extent of diverticulosis, which may impact prognosis and surgical management.


Diverticulitis is a common problem in developed nations and increases substantially with age. The diagnosis should be considered in those patients who develop progressive left lower quadrant pain and fever, and in whom a contrast-enhanced CT shows consistent findings. The treatment depends on the severity of disease and the presence of associated complications. Many patients can be treated with bowel rest and antibiotics but a substantial portion require abscess drainage via percutaneous catheter or surgical resection to treat complications. Elective sigmoid resection is recommended in most patients following a recurrence of diverticulitis. All patients who have an attack of diverticulitis should subsequently follow a high-fiber diet to prevent further complications and should undergo colonoscopy to assess for colonic neoplasm and degree of diverticular disease.

Barium enema image of sigmoid diverticulitis and intra-mural sinus tract

Barium enema showing sigmoid diverticulitis with intra-mural sinus tract.


1) Ferzoco LB, Paptopoulos V, Silen W. Acute diverticulitis. NEJM 1998; 338: 1521-1526

2) Aldoori WH, Giovannucci EL, Rimm EB et al. A prospective study of diet and the risk of symptomatic diverticular disease in men. Am J Clin Nutr 1994; 60: 757.

3) Nair P, Mayberry JF. Vegetarianism, dietary fibre and gastrointestinal disease. Dig Dis 1994; 12: 177.

4) Schechter S, Mulvey J, Eisenstate TE. Management of uncomplicated acute diverticulitis: results of a survey. Di Colon Rectum 1999; 42: 470.

5) Parks TG. Natural history of diverticular disease of the colon. Clin Gastroenterol 1975; 4:53.

6) Rao PM, Rhea JT, Novelline RA et al. Helical CT with only colonic contrast material for diagnosing diverticulitis: Prospective evaluation of 150 patients. Am J Roentgenol 1998; 170: 1445.

7) Detry R, Jamez J, Kartheuser A et al. Acute localized diverticulitis: Optimum management requires accurate staging. Int J Colorectal Dis 1992; 7: 38.

8) Young-Fadok TM, Roberts PL, Spencer MP, Wolff BG. Colonic diverticular disease. Curr Probl Surg 2000; 37: 457.

9) Wong WD, Wexner SD, Lowry A et al. Practice parameters for the treatment of sigmoid diverticulitis: Supporting documentation. The Standards Taskforce. The American Society of Colon and Rectal Surgeons. Dis Colon Rectum. 2000; 43: 290-297.

10) Painter NS. Diverticular disease of the colon. The first of the Western diseases shown to be due to deficiency of dietary fibre. S Afr Med J. 1982; 61: 1016.

11) Ornstein MH, Littlewood ER, Baird IM et al. Are fibre supplements really necessary in diverticular disease of the colon? A controlled clinical trial. Br Med J. 1981; 282: 1353.


1) American Society of Colon and Rectal Surgeons (www.fascrs.org): this is the official website of the main organization of intestinal surgeons in the United States.

2) The American College of Gastroenterology (www.acg.gi.org): this is the official website of the main organization of gastroenterologists in the United States and offers background information and weblinks to all disease related to the intestinal tract

3) Infectious Disease Society of America (www.idsociety.org): this is the official website of guidelines on management of intra-abdominal infections and recommendations for antibiotic treatment

4) The DAVE Project – Gastroenterology – Atlas (http://dave1.mgh.harvard.edu/): this website features several images of the intestinal tract and different pathology visualized on endoscopy and colonoscopy

About the Author:

Dr. Amanda Peppercorn is an infectious disease specialist at the University of North Carolina. She focuses on patients with defects in the immune system, such as HIV/AIDS and bone marrow and solid organ transplantation, as well as issues related to hepatitis B and hepatitis C co-infection with HIV. Her medical training was at Harvard Medical School and at the Massachusetts General Hospital.

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