What is the appropriate diagnosis and treatment for left lower abdominal pain accompanied by nausea and tenderness?

Left Lower Quadrant Pain with Nausea and Tenderness

Obtain CT abdomen and pelvis with IV contrast immediately, as this is the preferred diagnostic test with 98% accuracy and will guide all subsequent management decisions. 1, 2

Immediate Diagnostic Approach

The clinical presentation of left lower quadrant pain with nausea and tenderness most commonly suggests diverticulitis, though the classic triad (left lower quadrant pain, fever, leukocytosis) is present in only 25% of cases, making clinical diagnosis alone unreliable with misdiagnosis rates of 34-68%. 2

Critical Red Flags Requiring Emergency Evaluation

Before proceeding with imaging, assess for the following features that mandate immediate emergency department evaluation:

• Fever combined with severe tenderness and guarding (suggests perforation or peritonitis) 2
• Inability to pass gas or stool (present in 90% of large bowel obstructions) 2
• Vomiting, bloody stools, or signs of shock (indicates complicated disease) 2
• Diffuse abdominal tenderness with rebound or absent bowel sounds (peritonitis requiring emergent surgery) 2

Imaging Strategy

CT abdomen and pelvis with IV contrast is rated 8/9 (usually appropriate) by the American College of Radiology and should be performed in most patients. 1, 2 This modality provides:

• Superior detection of complications including abscess, perforation, fistula, and obstruction 2
• Identification of alternative diagnoses with sensitivity ranging 50-100% versus only 33-78% for ultrasound 1
• Risk stratification that reduces hospital admissions by >50% 2
• Sensitivity and specificity approaching 100% for sigmoid diverticulitis 2

Alternative Imaging Considerations

• CT without IV contrast (rated 6/9) is acceptable when IV contrast is contraindicated, though less accurate for detecting abscesses 1, 2
• Transabdominal ultrasound has variable performance (sensitivity 77-98%, specificity 80-99%) and is operator-dependent and limited in obese patients, making it less reliable than CT 1, 2
• Plain radiography is not useful as the initial test—it can only detect large-volume free air and is significantly less sensitive than CT for all relevant pathology 1

Special Population: Premenopausal Women

If the patient is a premenopausal woman, obtain pelvic/transvaginal ultrasound as the initial imaging study to evaluate for gynecologic causes (ectopic pregnancy, pelvic inflammatory disease, ovarian torsion) that can present identically to diverticulitis. 1, 2 CT can follow if ultrasound is negative or equivocal. 1

Management Based on CT Findings

Uncomplicated Diverticulitis (Bowel Wall Thickening + Pericolonic Fat Stranding, No Abscess/Perforation)

Conservative management WITHOUT antibiotics is appropriate for immunocompetent patients. 2 This includes:

• Clear liquid diet with gradual advancement 2
• Oral analgesics for pain control 2
• Outpatient management if able to tolerate oral intake 2

Antibiotics for 7 days maximum should only be used in:

• Immunocompromised patients 2
• Elderly patients 2

Recommended regimens: 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 Use the same antibiotic regimens as above. 2

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

Percutaneous drainage combined with antibiotics for 4 days in immunocompetent, non-critically ill patients. 2 Stop antibiotics at 4 days if source control is adequate. 2

Perforation or Peritonitis

Emergent surgical consultation for operative intervention. 2 If septic shock is present, use:

• Meropenem 1 g q6h by extended infusion, OR
• Doripenem 500 mg q8h by extended infusion, OR
• Imipenem/cilastatin 500 mg q6h by extended infusion 2

Critical Pitfalls to Avoid

• Do not continue antibiotics beyond 7 days in uncomplicated cases—this increases resistance without improving outcomes 2
• Watch for CT findings suggesting cancer rather than diverticulitis: pericolonic lymphadenopathy >1 cm with or without pericolonic edema requires colonoscopy 3, 2
• Do not perform routine colonoscopy after CT-confirmed diverticulitis except for age-appropriate screening, unless abscess, perforation, or fistula is present 2
• Avoid contrast enema as initial imaging—it only shows secondary mucosal effects and increases perforation risk with colonic distention 1
• Do not use MRI for initial evaluation—it is less sensitive for free air and urinary calculi, more time-consuming, and more subject to motion artifacts 1

Alternative Diagnoses to Consider

If CT does not show diverticulitis, consider:

• Urolithiasis (unenhanced CT has near 100% sensitivity/specificity) 1
• Gynecologic pathology in women (requires pelvic ultrasound) 1, 2
• Inflammatory bowel disease (Crohn's disease, ulcerative colitis) 4
• Bowel obstruction (CT will show dilated bowel loops) 2
• Functional bowel disorders (diagnosis of exclusion after structural pathology ruled out) 3