What is the appropriate evaluation and management of an adult presenting with new left lower‑quadrant abdominal pain?

Evaluation and Management of Left Lower Quadrant Abdominal Pain in Adults

For adults presenting with new left lower quadrant abdominal pain, obtain CT abdomen and pelvis with IV contrast as the initial imaging study—this is the American College of Radiology's primary recommendation with a rating of 8/9 (usually appropriate) and achieves 98% diagnostic accuracy. 1, 2

Initial Clinical Assessment

Begin by evaluating for the classic triad of left lower quadrant pain, fever, and leukocytosis, though recognize this triad appears in only 25% of diverticulitis cases. 2 More importantly:

• Do not rely on clinical examination alone—misdiagnosis rates range from 34-68% without imaging. 2
• Check for red flag symptoms requiring immediate emergency evaluation:
  • Fever with inability to pass gas or stool 2
  • Severe abdominal tenderness with guarding or rebound tenderness 2
  • Vomiting, bloody stools, or signs of shock 2
  • Progressively worsening pain over several days 2

Laboratory testing should include:

• Complete blood count with differential 2
• C-reactive protein (CRP >50 mg/L combined with left lower quadrant tenderness and absence of vomiting yields 97% accuracy for diverticulitis, though this occurs in only 24% of patients) 2
• Beta-hCG in all women of reproductive age before imaging 1

Imaging Strategy

CT abdomen and pelvis with IV contrast is the gold standard for the following reasons: 1, 2

• Diagnostic accuracy of 98% for diverticulitis 2
• Detects complications (abscess, perforation, fistula, obstruction) 2
• Identifies alternative diagnoses in 49% of patients with nonlocalized pain 2
• Reduces hospital admissions by >50% through accurate risk stratification 2
• Guides treatment decisions between medical management, percutaneous drainage, or surgery 2

Alternative imaging considerations:

• CT without IV contrast is acceptable when IV contrast is contraindicated (rated 6/9 by ACR), though less accurate for detecting abscesses 2
• Graded-compression ultrasound can reduce unnecessary CT examinations but is operator-dependent and limited in obese patients 2, 3
• For premenopausal women with suspected gynecologic pathology, obtain pelvic/transvaginal ultrasound first 2

Differential Diagnosis

The most common cause in adults >50 years is acute sigmoid diverticulitis. 2 Other considerations include:

• Colitis and inflammatory bowel disease 2
• Epiploic appendagitis 3
• Bowel obstruction or hernia 4
• Ovarian/fallopian tube pathology in women 2
• Pyelonephritis or nephrolithiasis 1
• Rare: appendicitis with situs inversus or unusually long appendix projecting to left lower quadrant 5, 6

Management Based on CT Findings

Uncomplicated Diverticulitis (no abscess, perforation, or fistula):

• Immunocompetent patients: Conservative management WITHOUT antibiotics (clear liquid diet advancement, oral analgesics for pain control) 2
• Immunocompromised or elderly patients: Antibiotics for maximum 7 days 2
  • Ertapenem 1 g q24h OR Eravacycline 1 mg/kg q12h 2

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

• Antibiotic therapy alone for 7 days without drainage 2

Complicated Diverticulitis with Large Abscess (≥4 cm):

• Percutaneous drainage PLUS antibiotics for 4 days (for immunocompetent, non-critically ill patients) 2
• Stop antibiotics at 4 days if source control is adequate 2
• Continue up to 7 days in immunocompromised or critically ill patients 2

Perforation with Diffuse Peritonitis:

• Emergency surgical consultation required 2
• Primary resection and anastomosis ± diverting stoma (clinically stable patients) 2
• Hartmann's procedure (critically ill patients or multiple major comorbidities) 2

Septic Shock:

• Escalate to broad-spectrum carbapenem therapy immediately: 2
  • Meropenem 1 g q6h by extended infusion OR
  • Doripenem 500 mg q8h by extended infusion OR
  • Imipenem/cilastatin 500 mg q6h by extended infusion

Special Populations

Women of reproductive age:

• Obtain pregnancy test before CT imaging 1
• Consider gynecologic causes first—obtain pelvic ultrasound if clinically indicated 2
• In pregnant patients, use ultrasonography or MRI instead of CT 2

Elderly patients:

• May present with atypical symptoms and normal laboratory tests despite serious pathology 2
• Higher likelihood of malignancy, diverticulitis, and vascular causes 2

Critical Pitfalls to Avoid

• CT findings suggesting cancer rather than diverticulitis: pericolonic lymphadenopathy >1 cm with or without pericolonic edema 2
• Do not order routine colonoscopy after CT-confirmed uncomplicated diverticulitis except for: 2
  • Age-appropriate colon cancer screening not yet performed
  • Abnormal pericolic lymph nodes on CT
  • Luminal colon mass on CT
  • Presence of abscess, perforation, or fistula
• Do not continue antibiotics beyond 7 days in uncomplicated cases—this increases resistance without improving outcomes 2
• If signs of infection persist beyond 7 days, obtain repeat imaging to assess for inadequate source control 2

When Imaging May Not Be Necessary

For patients with known diverticulosis presenting with mild, intermittent left lower quadrant pain without fever or signs of peritonitis, conservative outpatient management without imaging may be appropriate. 2 However, order CT immediately if any of the following develop: 2

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