Diagnosis and Treatment of Diverticulitis

Diagnostic Approach

Contrast-enhanced CT of the abdomen and pelvis with intravenous contrast is the mandatory first-line diagnostic test for suspected acute diverticulitis, achieving 98-99% sensitivity and 99-100% specificity. 1 Clinical examination alone misdiagnoses 34-68% of cases because the classic triad of left lower quadrant pain, fever, and leukocytosis occurs in only 25% of patients. 1

When to Image

Obtain CT imaging immediately for any patient presenting with left lower quadrant pain plus fever, inability to tolerate oral intake, severe or worsening pain, signs of peritonitis (guarding, rebound tenderness, rigidity), or systemic symptoms. 1
Image all elderly patients (>65 years) regardless of symptom severity due to high rates of atypical presentations and alternative diagnoses including colon cancer. 1
Defer imaging only in patients with known diverticulosis presenting with mild, intermittent pain, no fever, no peritoneal signs, and ability to tolerate oral intake—but obtain CT if symptoms persist beyond 2-3 days. 1, 2

Laboratory Assessment

Obtain complete blood count, C-reactive protein, basic metabolic panel, and urinalysis in all patients with suspected diverticulitis. 1, 3
CRP >140 mg/L predicts complicated disease with 87.5% sensitivity and 91.1% specificity. 1
White blood cell count >15 × 10⁹/L or rising leukocytosis indicates high-risk disease requiring antibiotics. 1, 4

Classification: Uncomplicated vs. Complicated

Uncomplicated diverticulitis is localized colonic inflammation without abscess, perforation, fistula, obstruction, or bleeding—confirmed by CT. 1, 4 This represents approximately 85-88% of cases. 1, 5

Complicated diverticulitis involves any abscess, perforation with free air, fistula formation, bowel obstruction, or generalized peritonitis. 1, 4 This accounts for 12% of presentations. 1

Treatment of Uncomplicated Diverticulitis

First-Line Management: Observation Without Antibiotics

For immunocompetent patients with CT-confirmed uncomplicated diverticulitis, observation with supportive care alone—without routine antibiotics—is the recommended first-line approach. 1, 4 The DIABOLO trial (528 patients) demonstrated that antibiotics do not accelerate recovery, prevent complications, or reduce recurrence in this population. 1, 4

Supportive Care Protocol

Clear liquid diet for 2-3 days during the acute phase, then advance as tolerated. 4, 5
Adequate oral hydration. 4
Acetaminophen 1 gram three times daily for pain control (avoid NSAIDs). 4, 5
Bowel rest while symptoms persist. 4

Eligibility Criteria for Outpatient Management (All Must Be Met)

CT-confirmed uncomplicated disease (no abscess, perforation, fistula, obstruction). 1, 4
Ability to tolerate oral fluids and medications. 1, 4
Temperature <100.4°F (38°C). 1, 4
Pain controlled with acetaminophen alone (pain score <4/10). 1, 4
No significant comorbidities or frailty (cirrhosis, chronic kidney disease, heart failure, poorly controlled diabetes). 1, 4
Immunocompetent status. 1, 4
Adequate home/social support with reliable follow-up within 7 days. 1, 4

Outpatient management yields 35-83% cost savings per episode compared with hospitalization, with only 4.3% requiring subsequent admission. 1, 4

When to Add Antibiotics: High-Risk Features

Reserve antibiotics for patients with ANY of the following high-risk features:

Clinical Indicators

Persistent fever >100.4°F or chills despite supportive care. 1, 4
Refractory symptoms, vomiting, or inability to maintain oral hydration. 1, 4
Symptom duration >5 days before presentation. 1, 4

Laboratory Markers

C-reactive protein >140 mg/L. 1, 4
White blood cell count >15 × 10⁹/L or rising leukocytosis. 1, 4

CT Findings

Fluid collection or abscess. 1, 4
Extensive segment of colonic inflammation. 1, 4
Pericolic extraluminal air. 1, 4

Patient Factors

Immunocompromised status (chemotherapy, high-dose steroids >20 mg prednisone daily, organ transplant). 1, 4, 5
Age >80 years. 1, 4, 5
Pregnancy. 1, 4, 5
ASA physical status III-IV. 1, 4
Significant comorbidities (cirrhosis, chronic kidney disease, heart failure, poorly controlled diabetes). 1, 4, 5

Antibiotic Regimens When Indicated

Outpatient Oral Therapy (4-7 Days for Immunocompetent Patients)

First-line: Amoxicillin-clavulanate 875/125 mg orally twice daily. 1, 4, 5

Alternative: Ciprofloxacin 500 mg orally twice daily PLUS metronidazole 500 mg orally three times daily. 1, 4, 5

Inpatient Intravenous Therapy (Transition to Oral Within 48 Hours)

Indications for hospitalization:

Complicated diverticulitis (abscess ≥4-5 cm, perforation, fistula, obstruction). 1, 4
Inability to tolerate oral intake. 1, 4
Severe pain or systemic symptoms (fever, sepsis). 1, 4
Immunocompromised status. 1, 4
Significant comorbidities or frailty. 1, 4

IV regimens:

Ceftriaxone 1-2 grams IV daily PLUS metronidazole 500 mg IV every 8 hours. 4, 5
Piperacillin-tazobactam 3.375-4.5 grams IV every 6-8 hours. 4, 5
Amoxicillin-clavulanate 1.2 grams IV every 6 hours. 4

Transition to oral antibiotics as soon as the patient tolerates oral intake (typically within 48 hours) to facilitate earlier discharge. 1, 4

Duration of Therapy

Immunocompetent patients: 4-7 days total. 1, 4
Immunocompromised patients: 10-14 days total. 1, 4
After percutaneous drainage of abscess: 4 days post-drainage in immunocompetent patients; up to 7 days in immunocompromised or critically ill patients. 1, 4

Treatment of Complicated Diverticulitis

Small Abscess (<4-5 cm)

Treat with intravenous antibiotics alone for 7 days without percutaneous drainage. 1, 4 Hospital admission is required for IV therapy and close monitoring. 1, 4

Large Abscess (≥4-5 cm)

Perform CT-guided percutaneous drainage PLUS intravenous antibiotics. 1, 4 Continue antibiotics for 4 days after successful drainage in immunocompetent patients, or up to 7 days in immunocompromised or critically ill patients. 1, 4 Obtain cultures from drainage to guide antibiotic selection. 1, 4

Generalized Peritonitis or Sepsis

Obtain emergent surgical consultation for source control surgery (Hartmann procedure or primary resection with anastomosis). 1, 4 Start broad-spectrum IV antibiotics immediately (piperacillin-tazobactam or ceftriaxone plus metronidazole). 1, 4, 5 For septic shock, escalate to meropenem 1 gram IV every 6 hours by extended infusion. 4

Follow-Up and Monitoring

Mandatory re-evaluation within 7 days of diagnosis (earlier if clinical condition deteriorates). 1, 4
Obtain repeat CT imaging if symptoms persist beyond 5-7 days despite appropriate therapy to assess for complications (abscess formation, perforation). 1, 4
Instruct patients to return immediately for fever >101°F, severe uncontrolled pain, persistent vomiting, inability to eat/drink, or signs of dehydration. 4

Post-Acute Management

Colonoscopy Timing

Schedule colonoscopy 6-8 weeks after symptom resolution for:

First episode of uncomplicated diverticulitis (if no recent high-quality colonoscopy). 1, 4, 3
Any complicated diverticulitis (7.9% associated cancer risk). 1, 4
Patients ≥50 years requiring routine screening. 1, 4
CT findings of abnormal pericolonic lymph nodes >1 cm, luminal mass, or diagnostic uncertainty. 1, 2

Do not perform colonoscopy during the acute phase due to high risk of perforation. 4, 2

Recurrence Prevention

High-fiber diet (≥22 grams/day from fruits, vegetables, whole grains, legumes) combined with low intake of red meat and sweets. 4, 3
Regular vigorous physical activity. 4, 3
Achieve or maintain BMI 18-25 kg/m². 4, 3
Smoking cessation. 4, 3
Avoid nonaspirin NSAIDs and opioids when possible. 4, 5
Do not restrict nuts, corn, popcorn, or small-seeded fruits—they are not associated with increased diverticulitis risk. 4, 3

Medications to Avoid

Do not prescribe mesalamine or rifaximin for prevention of recurrent diverticulitis—high-certainty evidence shows no benefit but increased adverse events. 4

Surgical Considerations

Elective surgery should NOT be based on the number of episodes alone. 4 The traditional "two-episode rule" is no longer accepted. 4 Consider elective sigmoidectomy for:

≥3 episodes within 2 years with significant quality-of-life impairment. 4
Persistent symptoms >3 months (smoldering diverticulitis). 4
Complicated diverticulitis (stenosis, fistula, recurrent bleeding). 1
Immunocompromised patients (if fit for surgery). 1

The DIRECT trial demonstrated significantly better quality of life at 6 months and 5 years after elective surgery compared with continued conservative management. 4 However, surgery carries 10% short-term and 25% long-term complication rates. 4

Critical Pitfalls to Avoid

Do not prescribe routine antibiotics for uncomplicated diverticulitis without high-risk features—this contributes to antimicrobial resistance without clinical benefit. 1, 4
Do not assume all patients require hospitalization—most immunocompetent patients with uncomplicated disease can be safely managed outpatient. 1, 4
Do not rely on clinical examination alone—CT confirmation is mandatory before discharge decisions. 1, 2
Do not overlook immunocompromised patients—they require immediate antibiotics (10-14 days), lower threshold for repeat imaging, and early surgical consultation. 1, 4
Do not apply the "no antibiotics" approach to complicated diverticulitis (Hinchey 1b or higher with abscess)—the evidence specifically excluded these patients. 4
Do not stop antibiotics early if indicated, even if symptoms improve—complete the full regimen. 4
Do not extend antibiotics beyond 7 days in immunocompetent patients with adequate source control—this increases resistance without improving outcomes. 4

Special Populations

Immunocompromised Patients

Require immediate antibiotic therapy for 10-14 days, lower threshold for CT imaging, and early surgical consultation regardless of other factors. 1, 4 Corticosteroid use specifically increases risk of perforation and death. 4, 5

Elderly Patients (≥65 Years)

Maintain a lower threshold for antibiotic treatment and hospitalization even when disease appears uncomplicated, due to higher complication and mortality rates. 1, 4 Age >80 years is an independent high-risk factor mandating antibiotic therapy. 1, 4

Pregnant Patients

Pregnancy is an absolute indication for antibiotics regardless of disease severity. 1, 4, 5 Use ultrasound or MRI instead of CT when possible to avoid radiation exposure. 2

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