What is the differential diagnosis and management for a patient presenting with left lower quadrant pain and rebound tenderness?

Left Lower Quadrant Pain with Rebound Tenderness

Immediate Action Required

Obtain CT abdomen and pelvis with IV contrast immediately—rebound tenderness in the left lower quadrant indicates possible peritonitis, perforation, or abscess requiring urgent diagnosis and treatment. 1

Clinical examination alone is unreliable with misdiagnosis rates of 34-68%, and rebound tenderness has poor diagnostic accuracy for distinguishing between diverticulitis, appendicitis, and other pathology. 1

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Critical Red Flags Requiring Emergency Evaluation

The presence of rebound tenderness already indicates a serious condition, but additional findings mandate immediate surgical consultation:

• Free air on CT = perforation requiring emergency surgery 1
• Fecal peritonitis = emergency surgical intervention 1
• Signs of septic shock (fever, tachycardia, confusion, hypotension) = immediate broad-spectrum carbapenem therapy and ICU admission 1
• Diffuse peritonitis (guarding, absent bowel sounds, rigid abdomen) = emergency surgical consultation 1

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Differential Diagnosis

Most Common Causes in Adults

Acute diverticulitis is the most common cause of left lower quadrant pain with rebound tenderness in adults, though the classic triad (left lower quadrant pain, fever, leukocytosis) is present in only 25% of cases. 1

Other critical diagnoses to exclude:

• Perforated diverticulitis with abscess formation 1
• Colitis (infectious, inflammatory bowel disease) 1, 2
• Epiploic appendagitis 1, 2
• Bowel obstruction (complete obstruction presents with inability to pass gas/stool in 90% of cases) 1
• Atypical appendicitis with redundant cecum or long appendix projecting into left lower quadrant 3, 4
• Gynecologic pathology in premenopausal women (ovarian torsion, ectopic pregnancy, tubo-ovarian abscess) 1
• Urolithiasis or pyelonephritis 1, 2
• Perforated colon cancer (suspect if pericolonic lymphadenopathy >1 cm on CT) 1

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Essential Laboratory Tests

Order immediately while awaiting CT:

• C-reactive protein (CRP): CRP >170 mg/L predicts severe diverticulitis with 87.5% sensitivity and 91.1% specificity 1
• White blood cell count with differential: Left shift >75% suggests bacterial infection 1
• Lactate level: Elevated lactate indicates sepsis 1
• Pregnancy test in all women of reproductive age before CT 1

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Imaging Strategy

CT abdomen and pelvis with IV contrast is the gold standard with 98-100% diagnostic accuracy, rated 8/9 (usually appropriate) by the American College of Radiology. 1

Key CT Findings and Their Implications:

• Intestinal wall thickening with pericolonic fat stranding = diverticulitis 1
• Extraluminal gas or free intraperitoneal air = perforation requiring surgery 1
• Abscess size <4 cm = antibiotics alone for 7 days 1
• Abscess size ≥4 cm = percutaneous drainage + antibiotics for 4 days 1
• Pericolonic lymphadenopathy >1 cm = suspect cancer, not diverticulitis 1

Special Population Considerations:

• Premenopausal women: Obtain pelvic/transvaginal ultrasound first if gynecologic pathology suspected 1
• Pregnant patients: Use ultrasound or MRI instead of CT to avoid radiation 1

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Treatment Algorithm Based on CT Findings

Uncomplicated Diverticulitis (No abscess, perforation, or fistula)

Immunocompetent patients:

• Conservative management WITHOUT antibiotics 1
• Clear liquid diet advancement 1
• Oral analgesics for pain control 1
• Outpatient management if able to tolerate oral intake 1

Immunocompromised or elderly patients:

• Antibiotics for maximum 7 days: Ertapenem 1 g q24h OR Eravacycline 1 mg/kg q12h 1

Complicated Diverticulitis with Small Abscess (<4 cm)

• Antibiotics alone for 7 days without drainage 1
• Ertapenem 1 g q24h OR Eravacycline 1 mg/kg q12h 1

Complicated Diverticulitis with Large Abscess (≥4 cm)

• Percutaneous drainage + antibiotics for 4 days in immunocompetent, non-critically ill patients 1
• Stop antibiotics at 4 days if source control is adequate 1
• Continue up to 7 days in immunocompromised or critically ill patients 1

Septic Shock

• Immediate broad-spectrum carbapenem therapy: 1
  • Meropenem 1 g q6h by extended infusion, OR
  • Doripenem 500 mg q8h by extended infusion, OR
  • Imipenem/cilastatin 500 mg q6h by extended infusion

Perforation with Diffuse Peritonitis

Emergency surgical consultation required: 1

• Clinically stable patients without major comorbidities: Primary resection and anastomosis ± diverting stoma 1
• Critically ill or multiple comorbidities: Hartmann's procedure 1

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Critical Pitfalls to Avoid

1. Do NOT rely on clinical examination alone—rebound tenderness has poor diagnostic accuracy and misdiagnosis rates are 34-68% 1

2. Do NOT continue antibiotics beyond 7 days in uncomplicated cases—this increases resistance without improving outcomes 1

3. Do NOT order routine colonoscopy after CT-confirmed uncomplicated diverticulitis unless: 1

   • Age-appropriate screening not yet performed
   • Abscess, perforation, or fistula present
   • Pericolonic lymphadenopathy >1 cm on CT (suspect cancer)

4. Do NOT miss atypical appendicitis—appendicitis can present with left lower quadrant pain if the appendix is redundant or the patient has situs inversus 3, 4

5. Do NOT forget gynecologic causes in premenopausal women—obtain pelvic ultrasound if clinical suspicion exists 1

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When to Obtain Repeat Imaging

• Signs of infection persist beyond 7 days = repeat CT to assess for inadequate source control 1
• New symptoms develop during treatment 1
• Weight loss, anemia, or change in bowel habits = repeat colonoscopy to exclude malignancy 5