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.

• ~200,000 hospital admissions and $2.2 billion in annual US healthcare costs
• 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)
• 13% of diverticulitis is found in patients <40 yrs of age
  • Younger patients are NOT more likely to have aggressive or complicated disease as previously thought
• Diverticular disease is almost exclusively left-sided colon (USA) or right-sided (Japan/Asia)

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
• 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)
• Low-fiber diet, high red meat consumption, sedentary lifestyle
• Smoking (increases risk of abscess formation and perforation)
• Medications:
  • NSAIDs (increase mucosal permeability; avoid if possible, aspirin for secondary cardiac prevention is acceptable)
  • Corticosteroids and opioids increase risk of perforation
• Nuts, seeds, and popcorn do NOT increase risk (common myth debunked)

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)
• 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

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
• Higher risk of failure of non-operative management, higher emergency surgery rate, and significantly higher mortality (20% vs 5% in immunocompetent)
• Always obtain CT imaging even in mild presentations
• Always treat with antibiotics (do NOT withhold in this population)
• Low threshold for surgical consult

Differential Diagnosis

LLQ Pain

• Diverticulitis
• Kidney stone
• UTI
• Pyelonephritis
• Ectopic pregnancy
• Infectious colitis
• Inflammatory bowel disease (Crohn's Disease, Ulcerative Colitis)
• Inguinal hernia
• Mesenteric ischemia
• Epiploic appendagitis
• Mittelschmerz
• Ovarian cyst
• Ovarian torsion
• PID
• Psoas abscess
• Testicular torsion
• Appendicitis
• Abdominal aortic aneurysm
• Herpes zoster
• Endometriosis
• Colon cancer
• Irritable bowel syndrome
• Small bowel obstruction

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)
    • CRP >140 mg/L or WBC >15 × 10⁹/L favors antibiotic treatment even in uncomplicated cases
  • 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
      • 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%)
    • 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
  • MRI (Sn 98%, Sp 70-78%)
    • 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
• Always image immunocompromised patients regardless of severity
• Always image patients who fail to improve on therapy

Modified Hinchey Classification

• 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

• Antibiotics should be used selectively and not routinely in acute uncomplicated diverticulitis
• Antibiotics are aimed at treating Gram Negative organisms and Anaerobes (Enterobacteriaceae, Bacteriodes sp., and Enterococci)

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.

When to use antibiotics in uncomplicated diverticulitis:

• 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
• 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
• 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

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

Preferred:

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

Alternatives (penicillin allergy or intolerance):

• Trimethoprim/Sulfamethoxazole one double-strength tablet BID PLUS Metronidazole 500mg PO Q8h x 5 days
• Metronidazole 500mg PO Q8hrs PLUS Ciprofloxacin 500mg PO BID x 5 days (reserve for patients without non-fluoroquinolone options)
• Moxifloxacin 400mg PO QDaily (same fluoroquinolone cautions apply)

Complicated/Inpatient

• Piperacillin/Tazobactam 3.375g IV q6h x 7-10 days

Complicated

• Defined as having a phlegmon, abscess, stricture, obstruction, fistula, or perforation (i.e. Hinchey Stages I-IV; see Evaluation section)
• Antibiotic choice:
  • Ceftriaxone PLUS metronidazole
  • OR piperacillin/tazobactam
• Bowel rest in coordination with antibiotics

Abscess Management

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

Perforation with Peritonitis (Hinchey III-IV)

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

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
• 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)
• Failed outpatient therapy (worsening symptoms or CT findings within 6 weeks of initial episode)
• Large abscess >3-4 cm requiring percutaneous drainage
• Signs of sepsis or hemodynamic instability
• Concern for perforation or peritonitis

Discharge

• Patients may be treated as outpatients if:
  • 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

Follow-Up Counseling

• Refer all newly-diagnosed patients for follow-up colonoscopy in 6 weeks (CT cannot reliably rule out carcinoma)
• 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
  • Exception: immunocompromised patients should be referred for surgical consultation to discuss elective resection after recovery
• Dietary counseling: high-fiber diet or fiber supplementation after resolution; nuts, seeds, and popcorn are safe
• Lifestyle: vigorous physical activity, weight management, smoking cessation
• Medication review: avoid NSAIDs if possible (aspirin for cardiac prevention is acceptable); avoid opioids and corticosteroids when possible

Pearls

• Clinical diagnosis alone is incorrect 35-60% of the time — image liberally on first presentations
• 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
• 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
• Younger patients do NOT necessarily have a worse prognosis (prior dogma now debunked)

See Also

• Hinchey classification for diverticulitis
• Diverticulosis
• Lower gastrointestinal bleeding
• Abscess
• Large bowel obstruction