What are the differential diagnoses for left lower quadrant pain?

Differential Diagnoses for Left Lower Quadrant Pain

The differential diagnosis for left lower quadrant pain is broad, but diverticulitis is the most common cause in adults, followed by colonic pathology, urologic conditions, and gynecologic disorders in women of reproductive age. 1, 2

Primary Differential Diagnoses

Gastrointestinal Causes

• Diverticulitis is the most frequent cause of left lower quadrant pain, particularly in elderly patients, though the classic triad of left lower quadrant pain, fever, and leukocytosis is present in only 25% of cases 1, 3
• Colitis (infectious, inflammatory bowel disease, ischemic) presents with left lower quadrant pain and altered bowel habits 2
• Fecal impaction causes left lower quadrant pain with constipation and abdominal distension 2
• Epiploic appendagitis is a benign self-limited condition that mimics diverticulitis 3, 2
• Perforated colon cancer must be considered, especially when CT shows pericolonic lymphadenopathy >1 cm with or without pericolonic edema 1
• Bowel obstruction presents with inability to pass gas or stool (present in 90% of large bowel obstructions) and abdominal distension (present in 65% of cases) 1
• Left-sided appendicitis in patients with situs inversus totalis or intestinal malrotation, though extremely rare, can present with left lower quadrant pain 4, 5

Urologic Causes

• Left-sided urolithiasis (renal colic) causes acute severe left lower quadrant or flank pain 3, 2
• Urinary tract infection including pyelonephritis can cause left lower quadrant pain 3

Gynecologic Causes (in premenopausal women)

• Ovarian pathology (cyst, torsion, rupture) requires evaluation with pelvic/transvaginal ultrasound as the preferred initial imaging 1, 6
• Ectopic pregnancy must be excluded with pregnancy testing before CT imaging 1
• Pelvic inflammatory disease presents with cyclical or persistent left lower quadrant pain 7
• Endometriosis causes cyclical pain related to menstrual cycle 7

Vascular and Musculoskeletal Causes

• Spontaneous retroperitoneal hemorrhage is detected on CT with IV contrast 2
• Rectus sheath hematoma causes abdominal wall pain 2
• Abdominal wall pathology including hernias and muscle strain 3

Functional Disorders

• Irritable bowel syndrome becomes the most likely diagnosis when structural pathology has been excluded by CT and colonoscopy, particularly when pain is related to bowel movements or dietary triggers 7

Critical Red Flags Requiring Emergency Evaluation

Immediate emergency department evaluation is mandatory for left lower quadrant pain accompanied by any of the following: 1

• Fever combined with left lower quadrant pain and elevated white blood cell count suggests complicated diverticulitis 1
• Inability to pass gas or stool with abdominal distension indicates possible bowel obstruction 1
• Severe abdominal tenderness with guarding or rebound tenderness suggests peritonitis or perforation 1
• Vomiting especially when persistent 1
• Bloody stools indicating possible ischemia or inflammatory process 1
• Signs of shock (hypotension, tachycardia, altered mental status) suggesting sepsis or hemorrhage 1
• Progressively worsening pain over several days 1

Diagnostic Approach

Initial Imaging Strategy

• CT abdomen and pelvis with IV contrast is the preferred imaging modality for most patients with left lower quadrant pain, with a diagnostic accuracy of 98% and rated 8/9 (usually appropriate) by the American College of Radiology 1, 6
• CT with IV contrast provides superior detection of complications, identifies alternative diagnoses, guides treatment decisions, reduces hospital admissions by >50%, and enables risk-stratification 1

Special Population Considerations

• For premenopausal women with suspected gynecologic pathology, pelvic/transvaginal ultrasound is the preferred initial imaging before proceeding to CT 1, 6
• Obtain pregnancy testing before ordering CT in women of reproductive age 1
• In pregnant patients, ultrasonography and MRI are preferred over CT to avoid radiation exposure 1

Alternative Imaging When CT Contraindicated

• CT without IV contrast is acceptable when IV contrast is contraindicated, though less accurate for detecting abscesses (rated 6/9 by the American College of Radiology) 1
• Ultrasound with graded compression can reduce unnecessary CT examinations but is operator-dependent and limited in obese patients 1
• Plain radiography is not useful as an initial test due to limited sensitivity 6

Common Diagnostic Pitfalls

• Clinical diagnosis alone is unreliable, with misdiagnosis rates between 34-68% 1
• Ultrasound may miss non-gynecologic causes of left lower quadrant pain that can be detected by CT 6
• Atypical appendicitis with a long appendix projecting into the left lower quadrant or left-sided appendicitis with situs inversus can be missed without imaging 4, 5
• Early diverticulitis might be missed even with CT, though sensitivity is 98-100% 7
• Malignancy masquerading as diverticulitis: pericolonic lymphadenopathy >1 cm with or without pericolonic edema suggests cancer rather than diverticulitis 1, 7