What are the differential diagnoses and management options for left lower quadrant pain?

Left Lower Quadrant Pain: Differential Diagnoses and Management

Most Common Differential Diagnoses

Acute colonic diverticulitis is the most common cause of left lower quadrant pain in adults, accounting for the majority of cases, with prevalence rising 50% between 2000-2007. 1

Primary Differential Diagnoses by Frequency:

• Acute diverticulitis of the sigmoid or descending colon is the leading diagnosis, affecting 5-25% of patients with diverticulosis 1
• Colitis (infectious, ischemic, or inflammatory) presents with similar left lower quadrant pain and bowel symptoms 1
• Inflammatory bowel disease (Crohn's disease or ulcerative colitis) causes chronic or acute left-sided pain 1
• Epiploic appendagitis is a self-limited inflammatory condition of colonic fat appendages 1
• Bowel obstruction from adhesions, hernia, or malignancy 1
• Urolithiasis and pyelonephritis cause flank pain radiating to the left lower quadrant 1
• Gynecologic pathology including ovarian cyst, torsion, ectopic pregnancy, or pelvic inflammatory disease in women of reproductive age 1
• Perforated colon cancer may mimic diverticulitis 1
• Left-sided appendicitis in patients with intestinal malrotation (rare but important not to miss) 2, 3

Initial Diagnostic Approach

Clinical Assessment Limitations:

• Clinical diagnosis alone is unreliable with misdiagnosis rates of 34-68% 4
• The classic triad of left lower quadrant pain, fever, and leukocytosis is present in only 25% of diverticulitis cases 4
• When all three criteria (left lower quadrant tenderness, CRP >50 mg/L, absence of vomiting) are present, diagnostic accuracy reaches 97%, but this occurs in only 24% of patients 4

Imaging Strategy:

CT abdomen and pelvis with IV contrast is the preferred initial imaging modality for most patients with left lower quadrant pain, with 98% diagnostic accuracy. 4

• The American College of Radiology rates CT with IV contrast as 8/9 (usually appropriate) 4
• CT detects complications (abscess, perforation, fistula), identifies alternative diagnoses, guides treatment decisions, and reduces hospital admissions by >50% 4
• IV contrast improves characterization of bowel wall pathology, pericolic abnormalities, vascular pathology, and intra-abdominal fluid collections 1
• CT is sensitive for detecting small quantities of extraluminal air indicating perforation 1

Special Population Considerations:

• For premenopausal women with suspected gynecologic pathology, obtain pelvic/transvaginal ultrasound as initial imaging 4
• Obtain pregnancy testing before CT in women of childbearing age 4
• Unenhanced CT is acceptable when IV contrast is contraindicated (renal insufficiency, contrast allergy), though less accurate for detecting abscesses, rated 6/9 by ACR 4
• Ultrasound with graded compression can reduce unnecessary CT but is operator-dependent and limited in obese patients 4

Critical Red Flags Requiring Emergency Evaluation

Immediate emergency department evaluation is required for:

• Fever combined with severe abdominal tenderness and guarding (suggests perforation with peritonitis) 4
• Inability to pass gas or stool with abdominal distension (90% sensitive for large bowel obstruction) 4
• Signs of peritonitis: diffuse tenderness, rebound, absent bowel sounds 4
• Vomiting, bloody stools, or progressively worsening pain over several days 4
• Toxic appearance with fever, tachypnea, tachycardia, confusion, or signs of septic shock 4

Management Algorithm Based on CT Findings

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

• Conservative management WITHOUT antibiotics is appropriate for immunocompetent patients 4
• Antibiotics for maximum 7 days ONLY in immunocompromised or elderly patients 4
• Recommended antibiotic regimens: Ertapenem 1g q24h or Eravacycline 1mg/kg q12h 4
• Outpatient management with clear liquid diet advancement and oral analgesics 4

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

• Antibiotic therapy alone for 7 days without drainage 4
• Use same antibiotic regimens as uncomplicated cases 4

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

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

Perforation with Diffuse Peritonitis:

• Emergency surgical consultation for laparotomy with colonic resection 4
• Primary resection and anastomosis with or without diverting stoma for clinically stable patients 4
• Hartmann's procedure for critically ill patients or those with multiple major comorbidities 4
• Start broad-spectrum carbapenem therapy immediately: Meropenem 1g q6h, Doripenem 500mg q8h, or Imipenem/cilastatin 500mg q6h by extended infusion 4

Critical Pitfalls to Avoid

Diagnostic Pitfalls:

• Do not rely on clinical examination alone—misdiagnosis rates are 34-68% 4
• CT findings suggesting cancer rather than diverticulitis: pericolonic lymphadenopathy >1 cm with or without pericolonic edema 4
• Do not assume low CRP excludes complicated diverticulitis—39% of complicated cases have CRP <175 mg/L 5
• Consider left-sided appendicitis in young patients with intestinal malrotation—this rare condition presents with left lower quadrant pain and requires surgical intervention 2, 3

Management Pitfalls:

• Do not continue antibiotics beyond 7 days in uncomplicated cases—this increases resistance without improving outcomes 4
• Do not delay antibiotics waiting for imaging in hypotensive patients with suspected sepsis 5
• Repeat imaging if fever and leukocytosis persist beyond 48-72 hours despite appropriate treatment 5

Follow-Up Considerations

Colonoscopy Timing:

Routine colonoscopy after CT-confirmed uncomplicated diverticulitis is NOT warranted, except for:

• Age-appropriate colon cancer screening not yet performed 4
• Abnormal pericolic lymph nodes on CT (>1 cm) 4
• Luminal colon mass on CT 4
• Uncertain diagnosis 4
• Presence of abscess, perforation, or fistula 4

When Outpatient Management is Appropriate:

• Mild and stable pain without fever or systemic symptoms 4
• Ability to tolerate oral intake with normal bowel movements 4
• No signs of peritonitis on examination 4
• Reliable patient with access to follow-up care 4