What is the appropriate work‑up and initial management for an adult with left lower abdominal pain?

Left Lower Abdominal Pain: Work-Up and Initial Management

Immediate Imaging Strategy

CT abdomen and pelvis with IV contrast is the preferred initial imaging modality for most adults with left lower quadrant pain, with 98% diagnostic accuracy and superior detection of complications. 1, 2

Primary Imaging Recommendation

• Order CT abdomen/pelvis with IV contrast (rated 8/9 "usually appropriate" by ACR) as it provides comprehensive evaluation of all abdominal organs, detects complications (abscess, perforation, fistula, obstruction), and identifies alternative diagnoses with sensitivity/specificity up to 100% for diverticulitis 1, 2
• CT with IV contrast is superior to all other modalities for depicting extracolonic disease extent and facilitating selection between medical versus surgical therapy 1

Special Population Exception

• For premenopausal women with suspected gynecologic pathology (ectopic pregnancy, pelvic inflammatory disease, ovarian pathology), order transvaginal/pelvic ultrasound first 1, 2
• Obtain pregnancy testing before CT in women of reproductive age 2
• Use CT only when ultrasound is equivocal or nongynecologic etiology is suspected 1

Alternative Imaging (When IV Contrast Contraindicated)

• CT without IV contrast is acceptable but less accurate for detecting abscesses (rated 6/9 by ACR) 2
• Transabdominal ultrasound with graded compression has variable performance (sensitivity 77-98%, specificity 80-99%) but is operator-dependent, limited by body habitus, and misses more alternative diagnoses than CT (sensitivity 33-78% vs 50-100%) 1, 2

Imaging NOT Recommended

• Plain radiography has no role—it is insensitive for small amounts of free air, abscesses, and most pathology compared to CT 1
• Contrast enema is not useful initially as diverticulitis is an extramucosal process; it shows only secondary effects and increases perforation risk 1
• MRI is not useful for acute evaluation—it is time-consuming, less sensitive for free air and urinary calculi, and more subject to motion artifacts 1

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Clinical Assessment: What to Look For

Classic Presentation (Present in Only 25% of Cases)

• Left lower quadrant pain + fever + leukocytosis suggests diverticulitis, but clinical diagnosis alone has 34-68% misdiagnosis rate 1, 3, 2
• When all three criteria present (LLQ tenderness, CRP >50 mg/L, absence of vomiting), diagnostic accuracy reaches 97%, but this occurs in only 24% of patients 2

Red Flag Symptoms Requiring Emergency Evaluation

• Fever with inability to pass gas/stool (suggests obstruction present in 90% of large bowel obstructions) 2
• Severe abdominal tenderness with guarding or rebound (suggests peritonitis/perforation) 3, 2
• Signs of shock (hypotension, tachycardia, confusion) indicating possible sepsis 3, 2
• Bloody stools or vomiting 2
• Progressively worsening pain over several days 2

Laboratory Studies to Obtain

• Complete blood count with differential (left shift >75% suggests bacterial infection) 3, 2
• C-reactive protein (CRP >170 mg/L predicts severe diverticulitis with 87.5% sensitivity and 91.1% specificity) 3, 2
• Lactate level (elevated indicates sepsis/systemic infection) 3
• Blood cultures if febrile 3

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Management Algorithm Based on CT Findings

Uncomplicated Diverticulitis (No Abscess, Perforation, or Fistula)

• Immunocompetent patients: Conservative management WITHOUT antibiotics—clear liquid diet advancement and oral analgesics only 3, 2
• Immunocompromised or elderly patients: Antibiotics for maximum 7 days using Ertapenem 1g q24h or Eravacycline 1mg/kg q12h 3, 2
• Most can be managed outpatient if able to tolerate oral intake and no peritonitis 2, 4

Complicated Diverticulitis with Small Abscess (<3-4 cm)

• Antibiotics alone for 7 days without drainage 3, 2
• Use Ertapenem 1g q24h or Eravacycline 1mg/kg q12h 3

Complicated Diverticulitis with Large Abscess (≥3-4 cm)

• Percutaneous CT-guided drainage PLUS antibiotics for 4 days in immunocompetent, non-critically ill patients 3, 2
• Stop antibiotics at 4 days if source control adequate 2
• Continue up to 7 days in immunocompromised/critically ill patients 2

Perforation with Diffuse Peritonitis or Septic Shock

• Immediate emergency surgical consultation for laparotomy 3, 2
• Start broad-spectrum carbapenem therapy immediately (Meropenem 1g q6h extended infusion, Doripenem 500mg q8h extended infusion, or Imipenem/cilastatin 500mg q6h extended infusion) 3
• Aggressive fluid resuscitation with crystalloids to restore BP >90 mmHg systolic 3

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Critical Pitfalls to Avoid

Diagnostic Errors

• Do not rely on clinical examination alone—misdiagnosis rates are 34-68%, and elderly patients present atypically (only 50% have LLQ pain, only 17% have fever) 1, 3, 2
• Do not assume low CRP excludes complicated disease—39% of complicated cases have CRP <175 mg/L 3
• Watch for CT findings suggesting cancer rather than diverticulitis: pericolonic lymphadenopathy >1 cm with or without pericolonic edema 2

Treatment Errors

• Do not delay antibiotics waiting for imaging in hypotensive/septic patients—mortality increases significantly with delayed treatment 3
• Do not continue antibiotics beyond 7 days in uncomplicated cases—this increases resistance without improving outcomes 2
• Do not perform routine colonoscopy after CT-confirmed uncomplicated diverticulitis except for age-appropriate screening not yet done, abnormal lymph nodes on CT, luminal mass, or presence of abscess/perforation/fistula 2

Imaging Errors

• Do not order plain radiographs—they add no value beyond clinical assessment and are insensitive for critical findings 1, 5
• Do not order contrast enema acutely—it increases perforation risk and misses extracolonic pathology 1

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When Imaging May Not Be Required

Patients with known diverticulosis presenting with mild, intermittent LLQ pain without fever or peritonitis can be managed conservatively without imaging 1, 2

Criteria for Conservative Management Without Imaging

• Prior history of diverticulitis with similar symptoms 1
• Relatively mild clinical symptoms 2
• No fever, no signs of peritonitis, able to tolerate oral intake 2
• No progressively worsening pain 2

When to Image Despite Mild Symptoms

• Fever develops 2
• Severe or progressively worsening pain 2
• Inability to tolerate oral intake 2
• Signs of peritonitis 2
• Persistent symptoms beyond 2-3 days despite conservative management 2

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Monitoring and Follow-Up

• Repeat imaging if clinical deterioration occurs or if fever/leukocytosis persist beyond 48-72 hours despite appropriate treatment 3
• Obtain surgical consultation immediately for high-risk presentations (hypotension, peritonitis, free perforation) 3, 2
• In-hospital mortality for acute diverticulitis increases with age: 1.6% in patients <65 years, 9.7% in patients 65-79 years, and 17.8% in patients >80 years 3