What is the differential diagnosis and management for left lower quadrant pain?

Left Lower Quadrant Pain: Differential Diagnosis and Management

Primary Differential Diagnoses

The most common cause of left lower quadrant (LLQ) pain is acute diverticulitis, particularly in patients over 40 years old, though clinical diagnosis alone is unreliable with misdiagnosis rates of 34-68%. 1

Gastrointestinal Causes

• Diverticulitis (most common): Classic triad of LLQ pain, fever, and leukocytosis present in only 25% of cases 1
• Epiploic appendagitis: Self-limited inflammation of colonic fat appendages, important mimicker of diverticulitis 2, 3
• Colitis (infectious, ischemic, inflammatory bowel disease) 4
• Colorectal carcinoma: Consider when pericolonic lymphadenopathy >1 cm present 5
• Fecal impaction 4
• Bowel obstruction: Inability to pass gas/stool in 90% of large bowel obstructions 5

Urologic Causes

• Left-sided urolithiasis/renal colic 6, 4
• Urinary tract infection/pyelonephritis 6

Gynecologic Causes (Premenopausal Women)

• Ovarian cyst/torsion 1
• Ectopic pregnancy 1
• Pelvic inflammatory disease 6
• Endometriosis 6

Other Causes

• Spontaneous retroperitoneal or rectus sheath hemorrhage 4
• Abdominal wall pathology 6
• Atypical appendicitis (long appendix projecting to LLQ or situs inversus) 7

Diagnostic Approach Algorithm

Step 1: Clinical Assessment

Evaluate for red flag symptoms requiring immediate emergency evaluation: 5

• Fever with severe abdominal tenderness and guarding (peritonitis)
• Inability to pass gas or stool (obstruction)
• Vomiting with bloody stools
• Signs of shock (hypotension, tachycardia, altered mental status)
• Progressively worsening pain over several days

Step 2: Initial Imaging Strategy

CT abdomen and pelvis with IV contrast is the preferred imaging modality for most patients with LLQ pain, with 98% diagnostic accuracy. 1, 5

CT Indications and Benefits 1, 5:

• Superior detection of complications (abscess, perforation, fistula, obstruction)
• Identifies alternative diagnoses with similar presentations
• Reduces hospital admissions by >50%
• Guides operative versus nonoperative treatment decisions
• Risk-stratifies patients for inpatient versus outpatient management

Alternative Imaging Based on Patient Population:

• Premenopausal women with suspected gynecologic pathology: Pelvic/transvaginal ultrasound first 1, 5
• Contraindication to IV contrast: Unenhanced CT acceptable (less accurate for abscesses but superior to clinical evaluation alone) 1
• Radiation dose reduction: 50-90% reduced-dose CT maintains similar sensitivity/specificity 1

Imaging NOT Recommended:

• MRI: Insufficient data to support routine use; less sensitive for extraluminal air and urinary calculi, more time-consuming 1
• Plain radiography: Less accurate than CT for all relevant pathology 1
• Fluoroscopic contrast enema: Not useful for initial evaluation 1

Step 3: Diagnosis-Specific Management

Uncomplicated Diverticulitis 1, 5:

Conservative treatment WITHOUT antibiotics is appropriate for immunocompetent patients with CT-confirmed uncomplicated diverticulitis. 1, 5

• Antibiotic therapy only for: Immunocompromised or elderly patients, duration ≤7 days 1, 5
• Outpatient management: Most uncomplicated cases can be managed outpatient 1
• Imaging may not be required: In patients with typical symptoms, prior diverticulitis history, and no complications 1

Complicated Diverticulitis with Abscess 1, 5:

• Small abscess (<3 cm): Antibiotics alone for 7 days 1, 5
• Large abscess (≥3 cm): Percutaneous drainage + antibiotics for 4 days 1, 5

Antibiotic Regimens (When Indicated) 1:

• Standard therapy: Ertapenem 1 g q24h OR Eravacycline 1 mg/kg q12h
• Septic shock: Meropenem 1 g q6h by extended infusion OR Doripenem 500 mg q8h by extended infusion OR Imipenem/cilastatin 500 mg q6h by extended infusion

Surgical Indications 1, 5:

• Free perforation with peritonitis: Emergent surgery required
• Hartmann's procedure: For critically ill patients with multiple comorbidities
• Primary resection and anastomosis: For clinically stable patients without comorbidities

Critical Pitfalls to Avoid

Misdiagnosis of Malignancy 5:

CT findings suggesting cancer rather than diverticulitis include pericolonic lymphadenopathy >1 cm with or without pericolonic edema. 5

• Weight loss, anemia, or change in bowel habits warrant colonoscopy despite prior normal study 8

Overlooking Epiploic Appendagitis 2, 3:

• Classic CT findings: Ovoid mass 1.5-3.5 cm with hyperattenuating ring and central hyperdense area 3
• Self-limiting condition; correct diagnosis prevents unnecessary antibiotics or surgery 3
• Important mimicker in patients with history of recurrent diverticulitis 2

Unnecessary Colonoscopy 5:

Routine colonoscopy after CT-confirmed diverticulitis is NOT warranted except for age-appropriate screening, unless abscess, perforation, or fistula is present. 5

Recurrent Pain Evaluation 8:

• When structural pathology excluded by CT and colonoscopy, functional bowel disorders become most likely 8
• New symptoms or significant time passage may warrant repeat imaging 8
• Cyclical pain in women suggests gynecologic etiology requiring pelvic ultrasound 8

Predictors of Recurrence 1:

• Colonic wall thickness <9 mm at initial presentation associated with 19% recurrence risk 1
• Extent of diverticulitis-related complications predicts recurrence 1