Diverticulitis


Background

Section of the large bowel (sigmoid colon) showing multiple pouches (diverticula). The diverticula appear on either side of the longitudinal muscle bundle (taenium) which runs horizontally across the specimen in an arc.
Average inner diameters and ranges of different sections of the large intestine.[1]
  • ~200,000 hospital admissions and $2.2 billion in annual US healthcare costs[2]
  • Prevalence of diverticulosis 30% by age 60, >70% by age 85
  • 70% of patients with diverticulosis remain asymptomatic
  • Only 12% of diverticulitis presents as complicated disease (abscess, perforation, fistula, obstruction)[3]
  • 13% of diverticulitis is found in patients <40 yrs of age[4]
    • Younger patients are NOT more likely to have aggressive or complicated disease as previously thought[2]
  • Diverticular disease is almost exclusively left-sided colon (USA) or right-sided (Japan/Asia)[5]

Pathogenesis

  • Erosion of diverticular wall by inspissated fecal material leads to microperforation
    • Most common pathogens are anaerobes, as well as gram-negative rods
  • Emerging data suggest a greater role for the microbiome and genetic predisposition than previously appreciated[6]
  • Diverticular bleeding (painless lower gastrointestinal bleeding) is NOT associated with diverticulitis

Risk Factors

  • Obesity (BMI ≥30 increases risk ~1.8x; higher BMI correlates with younger age of presentation)[7][2]
  • Low-fiber diet, high red meat consumption, sedentary lifestyle[2]
  • Smoking (increases risk of abscess formation and perforation)[8]
  • Medications:
  • Nuts, seeds, and popcorn do NOT increase risk (common myth debunked)[3][2]


Clinical Features

  • LLQ abdominal pain (most common presenting symptom)
    • Asian patients may complain of RLQ or suprapubic pain (right-sided disease)
  • Fever
  • Leukocytosis
  • Elevated CRP (often more sensitive than WBC; CRP >150 mg/L discriminates complicated from uncomplicated disease with 85% sensitivity)[9]
  • Change in bowel habits: diarrhea (30%) or constipation (50%)
  • Nausea/vomiting
  • Anorexia
  • Physical exam: LLQ tenderness, possible palpable mass or fullness, localized peritonitis
    • Diffuse peritonitis or rigidity suggests perforation (Hinchey III-IV) — emergent surgical consult
  • Clinical suspicion alone is only correct in 40–65% of cases — imaging is usually needed to confirm[3]

Immunocompromised Patients

  • Includes transplant recipients, chronic corticosteroid use, active chemotherapy, HIV/AIDS, chronic renal failure, biologic immunosuppression
  • May present with milder symptoms (blunted fever, less tenderness, less leukocytosis) leading to delayed diagnosis and more advanced disease at presentation[3][9][10]
  • Higher risk of failure of non-operative management, higher emergency surgery rate, and significantly higher mortality (20% vs 5% in immunocompetent)[11]
  • Always obtain CT imaging even in mild presentations[3]
  • Always treat with antibiotics (do NOT withhold in this population)[3]
  • Low threshold for surgical consult[3]


Differential Diagnosis

LLQ Pain


Evaluation

Diverticulitis in the left lower quadrant as seen on axial view by a CT scan.
CT demonstrating diverticulitis: edema and thickening of the sigmoid colon wall (arrow) with diverticulum and adjacent fat stranding.

Work-Up

  • Labs
    • CBC
    • Chemistry
    • LFTs
    • Lipase
    • Urinalysis
    • CRP (if available; valuable for risk stratification)[9]
      • CRP >140 mg/L or WBC >15 × 10⁹/L favors antibiotic treatment even in uncomplicated cases[3]
    • Lactate if concern for sepsis or perforation
    • Type and screen if surgical intervention considered
  • Imaging
    • CT with IV and PO contrast (Sn 97%, Sp 100%) — gold standard
      • Pericolic stranding
      • Bowel wall thickening
      • Wall enhancement (inner and outer high attenuation layers)
      • Perforation — extravasation of air/fluid
        • Pericolic extraluminal gas (<5 cm from colon) may still be managed non-operatively with antibiotics[9]
        • Distant free air suggests frank perforation requiring emergent surgical evaluation
      • Abscess in 30% with fluid and/or gas
      • Bladder fistula (consider in patients with pneumaturia or recurrent UTIs)
    • Ultrasound (Sn >90%)[12]
      • Highly operator-dependent
      • Can identify diverticula, bowel wall thickening, inflammation, or abscess formation
      • Reasonable first-line in young patients, pregnancy, or when CT unavailable; step-up to CT if negative or inconclusive[9]
    • MRI (Sn 98%, Sp 70-78%)[13]
      • Difficult to obtain quickly in ED
      • Consider in pregnant patients when US is inconclusive

When to Image

  • Stable patient with history of prior CT-confirmed diverticulitis presenting with identical symptoms does not require repeat imaging
  • First-time episode or current episode different from previous requires diagnostic imaging[3]
  • Always image immunocompromised patients regardless of severity[3]
  • Always image patients who fail to improve on therapy[3]


Modified Hinchey Classification[14]

  • 0 Mild clinical diverticulitis
  • Ia Confined pericolic inflammation or phlegmon
  • Ib Pericolic or mesocolic abscess
  • II Pelvic, distant intraabdominal, or retroperitoneal abscess
  • III Generalized purulent peritonitis
  • IV Generalized fecal peritonitis


Management

Uncomplicated (Modified Hinchey Class 0)

Current evidence suggests that antibiotics may not be necessary in immunocompetent patients with mild, uncomplicated diverticulitis (no systemic signs) given sufficient bowel rest and close follow-up. A meta-analysis of 9 studies (2,505 patients) showed no difference in recovery time, readmission, progression to complications, or need for surgery with vs without antibiotics.[3][17][18]

When to use antibiotics in uncomplicated diverticulitis:[3]

  • Immunocompromised patients (always)
  • Significant comorbidities or frailty
  • Refractory symptoms or vomiting
  • CRP >140 mg/L or WBC >15 × 10⁹/L
  • CT showing fluid collection or longer segment of inflammation, even without abscess
  • Patient preference or inability to ensure reliable follow-up

If antibiotics are given:

  • Shorter courses (4-7 days) are preferred over historic 10-14 day courses[3][17]
  • Liquid diet and bowel rest (low fiber foods) are most important

Antibiotic Regimen

  • First, consider whether antibiotics are needed:
  • In immunocompetent patients with mild uncomplicated diverticulitis (no systemic signs, able to tolerate PO, reliable follow-up), a trial of supportive care alone (bowel rest, hydration, pain control) without antibiotics is reasonable[3][19]
  • Antibiotics ARE indicated if: immunocompromised, significant comorbidities/frailty, CRP >140 mg/L, WBC >15 × 10⁹/L, refractory symptoms, vomiting, or CT showing fluid collection or longer segment of inflammation[3]

If antibiotics are prescribed (4-7 day course preferred):[3]

Preferred:

  • Amoxicillin/Clavulanate 875/125mg PO Q8hrs x 5 days (or Augmentin XR 2 tablets BID [each tablet 1gm amoxicillin 62.5mg clavulanate])[20][21]
    • Equally effective as fluoroquinolone + metronidazole with lower C. difficile risk (especially in patients ≥65 years)[21]
    • Avoids FDA black box fluoroquinolone risks (tendinopathy, neuropathy, aortic dissection, CNS effects)[22]

Alternatives (penicillin allergy or intolerance):

Complicated/Inpatient

Complicated

Abscess Management

  • Small abscess (<4-5 cm): Initial trial of antibiotics alone (without percutaneous drainage) is reasonable[9]
  • Large abscess (>3-4 cm) or failure to improve: Percutaneous CT- or US-guided drainage plus antibiotics[25]
  • If percutaneous drainage is not feasible, initial antibiotic therapy alone may be attempted if clinical condition permits[9]

Perforation with Peritonitis (Hinchey III-IV)

  • Emergent surgical consult
  • Hemodynamically unstable or critically ill: Hartmann procedure recommended[9]
  • Stable patients without significant comorbidities: primary resection with anastomosis ± diverting stoma may be considered[9]
  • Damage control surgery with staged laparotomy may be appropriate in select unstable patients[9]

Pericolic Extraluminal Gas

  • Gas located <5 cm from the affected segment on CT (without abscess or distant free air)
  • Non-operative management with antibiotics is reasonable in clinically stable patients[9]
  • Monitor closely for clinical deterioration


Disposition

Admit

  • All complicated diverticulitis (Hinchey I-IV)
  • Intractable nausea/vomiting
  • Comorbid disease
  • High WBC, high fever, elderly
  • Immunocompromised patients (low threshold — consider admission for all)[3][9]
  • Failed outpatient therapy (worsening symptoms or CT findings within 6 weeks of initial episode)
  • Large abscess >3-4 cm requiring percutaneous drainage[25]
  • Signs of sepsis or hemodynamic instability
  • Concern for perforation or peritonitis


Discharge

  • Patients may be treated as outpatients if:[26]
    • Can tolerate PO
    • No significant comorbidities
    • Not immunocompromised
    • Able to obtain outpatient antibiotics (if prescribed)
    • Have adequate pain control
    • Have uncomplicated disease on CT (Hinchey 0)
    • Reliable follow-up within 2-3 days
  • Outpatient re-evaluation should occur within 7 days; return sooner if worsening[9]

Follow-Up Counseling

  • Refer all newly-diagnosed patients for follow-up colonoscopy in 6 weeks (CT cannot reliably rule out carcinoma)[3][15]
  • Elective surgery should NOT be recommended based on number of episodes alone; decisions should be individualized based on severity, quality of life, patient preferences, and comorbidities[3][9]
    • Exception: immunocompromised patients should be referred for surgical consultation to discuss elective resection after recovery[9]
  • Dietary counseling: high-fiber diet or fiber supplementation after resolution; nuts, seeds, and popcorn are safe[15]
  • Lifestyle: vigorous physical activity, weight management, smoking cessation[3]
  • Medication review: avoid NSAIDs if possible (aspirin for cardiac prevention is acceptable); avoid opioids and corticosteroids when possible[3][8]


Pearls

  • Clinical diagnosis alone is incorrect 35-60% of the time — image liberally on first presentations[3]
  • Immunocompromised patients may look well but have advanced disease — always image, always treat with antibiotics, low threshold for admission and surgical consult
  • Nuts, seeds, and popcorn are safe — correct the common patient misconception
  • Avoid NSAIDs for pain control in diverticular disease patients; use acetaminophen instead
  • CRP (when available) can help risk-stratify: CRP >150 mg/L suggests complicated disease[9]
  • Antibiotics are NOT needed in all uncomplicated diverticulitis — bowel rest and follow-up may be sufficient in immunocompetent patients without systemic signs
  • The risk of complicated disease is highest with the first episode, not with recurrences[3]
  • Younger patients do NOT necessarily have a worse prognosis (prior dogma now debunked)[2]


See Also


References

  1. ↑ Nguyen H, Loustaunau C, Facista A, Ramsey L, Hassounah N, Taylor H, et al. (July 2010). "Deficient Pms2, ERCC1, Ku86, CcOI in field defects during progression to colon cancer". Journal of Visualized Experiments (41). doi:10.3791/1931. PMC 3149991. PMID 20689513.
  2. ↑ 2.0 2.1 2.2 2.3 2.4 2.5 Carr S, Velasco AL. Colon Diverticulitis. [Updated 2024 Jul 25]. In: StatPearls. Treasure Island (FL): StatPearls Publishing; 2025.
  3. ↑ 3.00 3.01 3.02 3.03 3.04 3.05 3.06 3.07 3.08 3.09 3.10 3.11 3.12 3.13 3.14 3.15 3.16 3.17 3.18 3.19 3.20 3.21 3.22 3.23 3.24 3.25 Peery AF, Shaukat A, Strate LL. AGA Clinical Practice Update on Medical Management of Colonic Diverticulitis: Expert Review. Gastroenterology. 2021;160(3):906-911.e1. doi:10.1053/j.gastro.2020.09.059
  4. ↑ Schneider EB, et al. Emergency department presentation, admission, and surgical intervention for colonic diverticulitis in the United States. American Journal of Surgery. April 29, 2015.
  5. ↑ Peterson MA, Wu AW. Disorders of the large intestine. In: Walls RM, Hockberger RS, Gausche-Hill M, et al., eds. Rosen's Emergency Medicine: Concepts and Clinical Practice. 9th ed. Philadelphia, PA: Elsevier Saunders; 2018:(Ch) 85:1150–1165.
  6. ↑ Diverticulitis: A Review of Current and Emerging Practice-Changing Evidence. Clin Colon Rectal Surg. 2024;37(6). doi:10.1055/s-0044-1791284
  7. ↑ Strate LL, Liu YL, Aldoori WH, Syngal S, Giovannucci EL. Obesity increases the risks of diverticulitis and diverticular bleeding. Gastroenterology. 2009;136(1):115-122.e1.
  8. ↑ 8.0 8.1 8.2 8.3 Chetwood JD, et al. Diverticular disease: update on pathophysiology, classification and management. Frontline Gastroenterol. 2024;15(1):56-63. doi:10.1136/flgastro-2023-102467
  9. ↑ 9.00 9.01 9.02 9.03 9.04 9.05 9.06 9.07 9.08 9.09 9.10 9.11 9.12 9.13 9.14 9.15 Sartelli M, Weber DG, Kluger Y, et al. 2020 update of the WSES guidelines for the management of acute colonic diverticulitis in the emergency setting. World J Emerg Surg. 2020;15(1):32. doi:10.1186/s13017-020-00313-4
  10. ↑ Sangster GP, et al. Acute diverticulitis in immunocompromised patients: evidence from WIRES-T. Tech Coloproctol. 2023;27(8):667-676. doi:10.1007/s10151-023-02758-6
  11. ↑ Biondo S, et al. Diverticulitis in immunosuppressed patients: A fatal outcome requiring a new approach? Can J Surg. 2016;59(4):254-259. doi:10.1503/cjs.014915
  12. ↑ Dirks K, Calabrese E, Dietrich CF, et al. EFSUMB Position Paper: Recommendations for Gastrointestinal Ultrasound (GIUS) in Acute Appendicitis and Diverticulitis. Ultraschall Med. 2019;40(2):163-175. doi:10.1055/a-0824-6952
  13. ↑ Andeweg CS, Wegdam JA, Groenewoud J, van der Wilt GJ, van Goor H, Bleichrodt RP. Toward an evidence-based step-up approach in diagnosing diverticulitis. Scand J Gastroenterol. 2014;49(7):775-784. doi:10.3109/00365521.2014.908475
  14. ↑ Wasvary H, Turfah F, Kadro O, et al. Same hospitalization resection for acute diverticulitis. Am Surg. 1999;65:632–635.
  15. ↑ 15.0 15.1 15.2 Stollman N, Smalley W, and Hirano I. American Gastroenterological Association Institute guideline on the management of acute diverticulitis. Gastroenterology. 2015; 149(7):1944-1949.
  16. ↑ Tursi, A. et al. Diverticular disease: A therapeutic overview. World J Gastrointest Pharmacol Ther. Feb 6, 2010; 1(1): 27–35
  17. ↑ 17.0 17.1 Chabok A. Randomized clinical trial of antibiotics in acute uncomplicated diverticulitis. Br J Surg. 2012 Apr;99(4):532-9. doi: 10.1002/bjs.8688
  18. ↑ Jaung R, Nisbet S, Gosselink MP, et al. Antibiotics Do Not Reduce Length of Hospital Stay for Uncomplicated Diverticulitis in a Pragmatic Double-Blind Randomized Trial. Clin Gastroenterol Hepatol. 2020;S1542-3565(20)30426-2. doi: 10.1016/j.cgh.2020.03.049. PMID: 32240832
  19. ↑ Qaseem A, et al. Diagnosis and Management of Acute Left-Sided Colonic Diverticulitis: A Clinical Guideline From the American College of Physicians. Ann Intern Med. 2022;175(3):399-415.
  20. ↑ Balasubramanian I et al. Out-Patient Management of Mild or Uncomplicated Diverticulitis: A Systematic Review. Dig Surg. 2017;34(2):151-160.
  21. ↑ 21.0 21.1 Gaber CE, Kinlaw AC, Edwards JK, et al. Comparative Effectiveness and Harms of Antibiotics for Outpatient Diverticulitis: Two Nationwide Cohort Studies. Ann Intern Med. 2021;174(6):737-746. doi:10.7326/M20-6315
  22. ↑ 22.0 22.1 FDA Drug Safety Communication: FDA updates warnings for oral and injectable fluoroquinolone antibiotics due to disabling side effects. July 26, 2016.
  23. ↑ Wilkins T et al. Diagnosis and Management of Acute Diverticulitis. Am Fam Physician. 2013 May 1;87(9):612-620.
  24. ↑ Carns et al. Clinical impacts of utilizing ceftriaxone and metronidazole versus piperacillin/tazobactam in patients diagnosed with complicated diverticulitis. Am J Surg. 2025 Mar:241:116195. doi: 10.1016/j.amjsurg.2025.116195.
  25. ↑ 25.0 25.1 Siewert B et al. Impact of CT-guided drainage in the treatment of diverticular abscesses: size matters. AJR Am J Roentgenol. 2006 Mar;186(3):680-6.
  26. ↑ Friend K, Mills AM. Annals of EM. 2011.
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