What is the appropriate diagnosis and treatment for lower left quadrant pain in a patient?

Diagnostic and Management Approach to Lower Left Quadrant Pain

Order CT abdomen and pelvis with IV contrast immediately as the first-line diagnostic test for lower left quadrant pain, as it has 98% diagnostic accuracy and is rated 8/9 (usually appropriate) by the American College of Radiology. 1

Initial Diagnostic Strategy

CT abdomen and pelvis with IV contrast is the preferred imaging modality for evaluating lower left quadrant pain, providing comprehensive assessment of diverticulitis (the most common cause), colitis, inflammatory bowel disease, bowel obstruction, gynecologic pathology, and other etiologies. 1 This imaging modality:

• Detects complications including abscess, perforation, fistula, and obstruction 1
• Identifies alternative diagnoses in 49% of patients, fundamentally altering management 2
• Reduces hospital admissions by >50% through accurate risk stratification 1
• Has sensitivity and specificity approaching 100% for sigmoid diverticulitis 1

Do not rely on clinical examination alone, as misdiagnosis rates range from 34-68% even in experienced hands. 1 The classic triad of left lower quadrant pain, fever, and leukocytosis is present in only 25% of diverticulitis cases. 1

Special Population Considerations

For premenopausal women with suspected gynecologic pathology, order pelvic/transvaginal ultrasound as the initial imaging study instead of CT. 1 Obtain pregnancy testing before ordering CT in women of reproductive age. 1

Plain radiography has no role in evaluating lower left quadrant pain due to very limited diagnostic value. 2

Red Flags Requiring Emergency Evaluation

Immediate emergency department evaluation is mandatory if any of the following are present:

• Fever with inability to pass gas or stool 1
• Severe abdominal tenderness with guarding or rebound tenderness (indicates peritonitis) 1
• Vomiting with progressively worsening pain 1
• Bloody stools 1
• Signs of shock (hypotension, tachycardia, altered mental status) 1
• Toxic appearance suggesting sepsis 1

These symptoms indicate potential perforation, abscess formation, complete bowel obstruction, or septic shock—all life-threatening complications requiring urgent intervention. 1

Treatment Algorithm Based on CT Findings

Uncomplicated Diverticulitis (No Abscess, Perforation, or Fistula)

For immunocompetent patients: Conservative management WITHOUT antibiotics is recommended. 1 This includes:

• Clear liquid diet with gradual advancement 1
• Oral analgesics for pain control 1
• Outpatient management if able to tolerate oral intake 1

For immunocompromised or elderly patients: Antibiotics for maximum 7 days. 1 Recommended regimens:

• Ertapenem 1 g IV q24h 1
• Eravacycline 1 mg/kg IV q12h 1

Complicated Diverticulitis with Small Abscess (<4 cm)

Antibiotics alone for 7 days without drainage. 1 Use the same antibiotic regimens as above. 1

Complicated Diverticulitis with Large Abscess (≥4 cm)

Percutaneous CT-guided drainage PLUS antibiotics for 4 days. 1 This approach is appropriate for immunocompetent, non-critically ill patients. 1

Stop antibiotics at 4 days if source control is adequate in immunocompetent patients. 1 Continue up to 7 days only in immunocompromised or critically ill patients, guided by clinical response and inflammatory markers. 1

Perforation with Diffuse Peritonitis

Emergency surgical consultation for immediate laparotomy. 1 Surgical options include:

• Primary resection and anastomosis with or without diverting stoma (clinically stable patients without major comorbidities) 3
• Hartmann's procedure (critically ill patients or those with multiple comorbidities) 3

Start broad-spectrum carbapenem therapy immediately if septic shock is present:

• Meropenem 1 g IV q6h by extended infusion 1
• Doripenem 500 mg IV q8h by extended infusion 1
• Imipenem/cilastatin 500 mg IV q6h by extended infusion 1

Critical Pitfalls to Avoid

Do not continue antibiotics beyond 7 days in uncomplicated cases, as this increases antibiotic resistance without improving outcomes. 1

Do not order routine colonoscopy after CT-confirmed uncomplicated diverticulitis except for:

• Age-appropriate colon cancer screening not yet performed 1
• Abnormal pericolic lymph nodes >1 cm on CT (suggests malignancy rather than diverticulitis) 1
• Luminal colon mass on CT 1
• Presence of abscess, perforation, or fistula 1

Obtain repeat imaging if fever and leukocytosis persist beyond 48-72 hours despite appropriate treatment, as this indicates inadequate source control. 1

Laboratory Markers for Risk Stratification

C-reactive protein (CRP) >170 mg/L predicts severe diverticulitis with 87.5% sensitivity and 91.1% specificity. 1, 3 However, 39% of patients with complicated diverticulitis have CRP below 175 mg/L, so do not exclude complicated disease based on low CRP alone. 3

When all three criteria are present (left lower quadrant tenderness, CRP >50 mg/L, absence of vomiting), the diagnosis of diverticulitis has 97% accuracy, but this occurs in only 24% of patients. 1