Skip to Content

Colonic Diverticulitis


Joel A. Baum

, MD, Icahn School of Medicine at Mount Sinai;

Rafael Antonio Ching Companioni

, MD, Digestive Diseases Center

Last full review/revision Oct 2020| Content last modified Oct 2020

Diverticulitis is inflammation with or without infection of a diverticulum, which can result in phlegmon of the bowel wall, peritonitis, perforation, fistula, or abscess. The primary symptom is abdominal pain. Diagnosis is by CT. Treatment is with bowel rest, sometimes antibiotics, and occasionally surgery.

A colonic diverticulum is a saclike pouch of colonic mucosa and submucosa that protrudes through the muscular layer of the colon; because it does not contain all layers of the bowel, it is considered a pseudodiverticulum (see also Definition of Diverticular Disease). Many people have multiple colonic diverticula (diverticulosis). The incidence of diverticulosis rises with increasing age; it is present in three quarters of people > 80 years. In people > 50 years, acute diverticulitis is most common among women; in those < 50 years, it is most common among men. Patients with HIV and those undergoing chemotherapy are at increased risk of developing acute diverticulitis (1).

Diverticula are usually asymptomatic but sometimes become inflamed (diverticulitis). A 2013 study reported that 4.3% of patients with documented diverticulosis developed diverticulitis over an 11-year follow-up period (2).

Diverticulitis that is managed nonoperatively can recur as either an acute or chronic process. The risk of a recurrent acute episode is up to 39%, although reported rates vary widely (3). A large population-based study found that after an episode of acute diverticulitis the recurrence rate at 1 year was 8% and at 10 years was 22% (4). About half of second episodes of diverticulitis occur within 12 months. In some patients, however, recurrence manifests as chronic, ongoing abdominal pain; this may develop after one or more acute episodes.

General references

  • 1. Francis NK, Sylla P, Abou-Khalil M, et al: EAES and SAGES 2018 consensus conference on acute diverticulitis management: Evidence-based recommendations for clinical practice. Surg Endosc 33(9):2726–2741, 2019.
  • 2. Shahedi K, Fuller G, Bolus R, et al: Long-term risk of acute diverticulitis among patients with incidental diverticulosis found during colonoscopy. Clin Gastroenterol Hepatol 11(12):1609–1613, 2013. doi: 10.1016/j.cgh.2013.06.020
  • 3. Sallinen V, Mali J, Leppäniemi A, Mentula P: Assessment of risk for recurrent diverticulitis: A proposal of risk score for complicated recurrence. Medicine (Baltimore) 94(8):e557, 2015. doi: 10.1097/MD.0000000000000557
  • 4. Bharucha AE, Parthasarathy G, Ditah I, et al: Temporal trends in the incidence and natural history of diverticulitis: A population-based study. Am J Gastroenterol 110(11):1589–1596, 2015. doi: 10.1038/ajg.2015.302

Etiology of Colonic Diverticulitis

The etiology and pathophysiology of diverticulitis is not fully understood and may vary among patients. It has long been thought that diverticulitis occurs when a micro or macro perforation develops in a diverticulum resulting in the release of intestinal bacteria and triggering inflammation. However, emerging data suggest that in some patients, acute diverticulitis is more of an inflammatory than infectious process. Furthermore, cytomegalovirus may be a trigger of that inflammation; active viral replication has been found in affected colon tissue in over two thirds of patients with diverticulitis.

A 2017 study suggested a direct correlation between red meat consumption per week and the incidence of diverticulitis (1, 2). There is no association between consumption of nuts, seeds, corn, or popcorn and development of diverticulitis as was previously thought.

Etiology references

  • 1. Cao Y, Strate LL, Keeley BR, et al: Meat intake and risk of diverticulitis among men. Gut pii: gutjnl-2016-313082, 2017. doi: 10.1136/gutjnl-2016-313082
  • 2. Strate LL, Keeley BR, Cao Y, et al: Western dietary pattern increases, and prudent dietary pattern decreases, risk of incident diverticulitis in a prospective cohort study. Gastroenterology 152(5):1023–1030.e2, 2017. doi: 10.1053/j.gastro.2016.12.038

Classification of Colonic Diverticulitis

Diverticulitis can be classified as

  • Uncomplicated diverticulitis: The most common (75 to 80%) manifestation of diverticulitis
  • Complicated diverticulitis: Defined by the presence of abscess, fistula, obstruction, or free perforation; several classifications exist (eg, see table Classification of Complicated Diverticulitis)

Complications can develop after perforation of an inflamed diverticulum.

About 15% of patients with complicated diverticulitis have a pericolic or intramesenteric abscess.

Classification of Complicated Diverticulitis


Hinchey Classification

Modified Hinchey Classification


Pericolic abscess or phlegmon

Pericolic abscess


Pelvic, intra-abdominal, or retroperitoneal abscess


Distant abscess that can be drained percutaneously


Complex abscess with fistula


Generalized purulent peritonitis

Generalized purulent peritonitis


Generalized fecal peritonitis

Fecal peritonitis

Adapted from Klarenbeek BR, de Korte N, van der Peet DL, Cuesta MA: Review of current classifications for diverticular disease and a translation into clinical practice. Int J Colorectal Dis 27(2):207–214, 2012. doi: 10.1007/s00384-011-1314-5

Symptoms and Signs of Colonic Diverticulitis

Patients have left lower quadrant abdominal pain and tenderness and often have a palpable sigmoid; pain is occasionally suprapubic. However, Asians with diverticulitis often present with right-sided pain due to right colon involvement. The pain can be accompanied by nausea, vomiting, fever, and sometimes even urinary symptoms as a result of bladder irritation. Peritoneal signs (eg, rebound or guarding) may be present, particularly with abscess or free perforation. Fistula may manifest as pneumaturia, fecaluria (feces in the urine), feculent vaginal discharge, or a cutaneous or myofascial infection of the abdominal wall, perineum, or upper leg. Patients with bowel obstruction have nausea, vomiting, and abdominal distention. Bleeding is uncommon.

Recurrent episodes of acute diverticulitis manifest similar to initial episodes; they are not necessarily more severe.

Diagnosis of Colonic Diverticulitis

  • Abdominal and pelvic CT
  • Colonoscopy after resolution

Clinical suspicion is high in patients with known diverticulosis who present with characteristic abdominal symptoms. However, because other disorders (eg, appendicitis, colon or ovarian cancer, inflammatory bowel disease) may cause similar symptoms, testing is required.

Diverticulitis is evaluated with CT of the abdomen and pelvis with water-soluble contrast given orally and rectally; IV contrast also is given when not contraindicated. However, findings in about 10% of patients cannot distinguish diverticulitis from colon cancer. MRI is an alternative for pregnant and young patients.

Colonoscopy is often recommended 1 to 3 months after resolution of the episode to assess for cancer. However, in the absence of high-risk signs (eg, complicated diverticulitis, uncomplicated diverticulitis with imaging abnormalities or atypical course, family history of colorectal cancer, anemia, weight loss), the likelihood of malignant lesions or advanced adenomas after an episode of uncomplicated acute diverticulitis is low (1).

Diagnosis reference

  • 1. Francis NK, Sylla P, Abou-Khalil M, et al: EAES and SAGES 2018 consensus conference on acute diverticulitis management: Evidence-based recommendations for clinical practice. Surg Endosc 33(9):2726–2741, 2019. doi: 10.1007/s00464-019-06882-z

Treatment of Colonic Diverticulitis

  • Varies with severity
  • Liquid diet for mild disease; nothing by mouth for more severe disease
  • Sometimes antibiotics
  • CT-guided percutaneous drainage of abscess
  • Sometimes surgery

A patient who is not very ill is treated at home with rest and a liquid diet. Symptoms usually subside rapidly.

Patients with more severe symptoms (eg, pain, fever, marked leukocytosis) should be hospitalized, as should patients taking prednisone (who are at higher risk of perforation and general peritonitis). Treatment is bed rest, nothing by mouth, and IV fluids.


Antibiotics were traditionally recommended for all cases of acute diverticulitis whether or not they were complicated. However, recent data suggest that antibiotics may not improve outcome in uncomplicated diverticulitis, therefore, selected patients with acute uncomplicated diverticulitis can be managed conservatively. (See also the American Gastroenterological Association's 2015 guidelines on management of acute diverticulitis.). Antibiotic therapy should be reserved for patients with acute but complicated diverticulitis, immunosuppression, or significant comorbidities.

If antibiotics are used, they should cover gram-negative rods and anaerobic bacteria.

Oral antibiotic regimens that can be given to outpatients for whom treatment is elected include 7 to 10 days of

  • Metronidazole (500 mg every 8 hours) plus a fluoroquinolone (eg, ciprofloxacin 500 mg every 12 hours)
  • Metronidazole (500 mg every 8 hours) plus a cephalexin (500 mg every 6 or 8 or 12 hours)
  • Metronidazole (500 mg every 8 hours) plus trimethoprim/sulfamethoxazole (800/160 mg every 12 hours)
  • Amoxicillin (875 mg every 12 hours) plus clavulanate (125 mg every 12 hours)
  • Moxifloxacin (400 mg once/day for patients unable to take penicillins or metronidazole)

IV antibiotic regimens for hospitalized patients are selected based on many factors, including the severity of illness, risk of adverse outcome (eg, due to other illnesses, older age, immunosuppression), and likelihood of resistant organisms. Many regimens exist.

There are no well-defined standards relating abscess size to the need for surgery or interventional (ultrasound- or CT-guided) drainage. However, small pericolic abscesses (less than 2 to 3 cm in diameter) often resolve with broad-spectrum antibiotics and bowel rest alone.

If response is satisfactory, the patient remains hospitalized until symptoms are relieved and a soft diet is resumed. After the episode resolves, patients should consume a high-fiber diet and avoid routine analgesic use of nonsteroidal anti-inflammatory drugs (NSAIDs) or aspirin to prevent recurrence.

Percutaneous drainage or endoscopic ultrasound-guided drainage

CT-guided percutaneous or endoscopic ultrasound-guided drainage is becoming the standard of care for larger abscesses (over 3 cm in diameter), for abscesses that do not resolve with antibiotics, and/or for clinical deterioration. However, abscesses that are multiloculated, inaccessible, or not improving with drainage require surgical intervention.


Surgery is required immediately for patients with free perforation or general peritonitis. Other indications for surgery include severe symptoms that do not respond to nonsurgical treatment within 3 to 5 days and increasing pain, tenderness, and fever. About 15 to 20% of people admitted with acute diverticulitis require surgery during that admission (1).

For uncomplicated diverticulitis, surgical resection was previously recommended based on the number of recurrences. Currently, the American Society of Colon and Rectal Surgeons (ASCRS) and other practice guidelines recommend a case-by-case evaluation rather than mandatory elective segmental colectomy after a second episode (2, 3, 4, 5; see also the Japan Gastroenterological Association's guidelines for colonic diverticular bleeding and colonic diverticulitis and the American Society of Colon and Rectal Surgeons' guidelines for the treatment of left-sided colonic diverticulitis). Patients for whom recurrent attacks pose a higher risk of death or complications are typically considered candidates for surgery.

For complicated diverticulitis, elective segmental colectomy is recommended after one episode. For those whose symptoms resolved with antibiotics and/or percutaneous drainage, the surgery can be done electively at a later time, when a single rather than multi-stage procedure can be used.

The involved section of the colon is resected. The ends can be reanastomosed immediately in healthy patients without perforation, abscess, or significant inflammation. Other patients have a temporary colostomy with anastomosis carried out in a subsequent operation after inflammation resolves and their general condition improves.

Treatment references

  • 1. Wieghard N, Geltzeiler CB, Tsikitis VL: Trends in the surgical management of diverticulitis. Ann Gastroenterol 28(1):25–30, 2015.
  • 2. Feingold D, Steele SR, Lee S, et al: Practice parameters for the treatment of sigmoid diverticulitis. Dis Colon Rectum 57:284–294, 2014. doi: 10.1097/DCR.0000000000000075
  • 3. Regenbogen SE, Hardiman KM, Hendren S, Morris AM: Surgery for diverticulitis in the 21st century: A systematic review. JAMA Surg 149(3):292–303, 2014. doi: 10.1001/jamasurg.2013.5477
  • 4. Comparato G, Di Mario F: Recurrent diverticulitis. J Clin Gastroenterol 42(10):1130–1134, 2008. doi: 10.1097/MCG.0b013e3181886ee4
  • 5. Young-Fadok TM: Diverticulitis. N Engl J Med 379(17):1635–1642, 2018. doi: 10.1056/NEJMcp1800468

Key Points

  • Diverticulitis is inflammation and/or infection of a diverticulum.
  • Inflammation remains localized in about 75% of patients; the remainder develop abscesses, peritonitis, bowel obstruction, or fistulas.
  • Diagnose using abdominal and pelvic CT with oral, rectal, and IV contrast; do colonoscopy 1 to 3 months after the episode to look for cancer.
  • Management depends on severity but typically includes conservative management, often antibiotics, and sometimes percutaneous or endoscopic ultrasound-guided drainage or surgical resection.

More Information

The following are English-language resources that may be useful. Please note that THE MANUAL is not responsible for the content of these resources.

  • American Gastroenterological Association: Guidelines on management of acute diverticulitis
  • Japan Gastroenterological Association: Guidelines for colonic diverticular bleeding and colonic diverticulitis
  • American Society of Colon and Rectal Surgeons: Guidelines for the treatment of left-sided colonic diverticulitis

Segmental Colitis Associated With Diverticulosis (SCAD)

Segmental colitis associated with diverticular disease refers to chronic colonic inflammation affecting the interdiverticular mucosa. Diagnosis is by endoscopy. Treatment is symptomatic.

(See also Colonic Diverticulosis.)

Segmental colitis associated with diverticulosis (SCAD) and chronic recurrent diverticulitis are terms used to describe chronic colonic inflammation attributed to diverticulosis. SCAD usually affects the interdiverticular mucosa and is usually present on the left side sparing the rectum and ascending colon.

The cause of SCAD is unknown and may be multifactorial. Mucosal prolapse, fecal stasis, localized ischemia, alterations in the gut microbiota, and/or chronic inflammation may play a role. It is unclear how much the relationship between the diverticulosis and colitis is causal, is due to a common underlying factor, or is coincidental: the histologic characteristics contain features similar to those seen in inflammatory bowel disease, infectious colitis, and ischemic colitis. The prevalence of SCAD in people with diverticulosis is very low (1%). SCAD usually affects males > 60 years of age.

Symptoms of SCAD include hematochezia, abdominal pain, and diarrhea.

The diagnosis of SCAD is suggested when endoscopy reveals erythematous, friable, and granular mucosa with either a diffuse or patchy distribution involving the interdiverticular mucosa.

Treatment of SCAD is symptomatic. Initial treatment with the oral antibiotics ciprofloxacin and metronidazole is recommended. In patients who do not improve with antibiotics, oral preparations of 5-aminosalicylic acid (5-ASA) can be used. Corticosteroids (eg, prednisone) are used for refractory cases, but, to date, high-quality randomized clinical trials have not been done. Surgery (segmental colectomy) is an option for patients with corticosteroid-refractory or corticosteroid-dependent SCAD.

Drugs Mentioned In This Article

Drug Name Select Trade
ciprofloxacin CILOXAN, CIPRO
Metronidazole FLAGYL
trimethoprim No US brand name
Moxifloxacin AVELOX
Amoxicillin AMOXIL
prednisone RAYOS
cephalexin KEFLEX

Copyright © 2022 Merck & Co., Inc., known as MSD outside of the US, Kenilworth, New Jersey, USA. All rights reserved. Merck Manual Disclaimer