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ABDOMINAL QUADRANT DIFFERENTIAL DIAGNOSIS & MANAGEMENT GUIDE

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LEFT UPPER QUADRANT (LUQ) PAIN

Key Anatomic Structures

• Spleen, stomach, pancreas (tail), left kidney, left adrenal, bowel, left liver lobe

Most Common Etiologies

Referred pain predominates (>95% of cases):

• Peptic ulcer disease, gastritis, esophagitis
• Pancreatitis
• Renal colic
• Cardiac angina/pericarditis
• Pneumonia (pleuritic)
• Spinal pathology 1

Primary LUQ Pathology (Rare)

• Splenic infarction, rupture, torsion
• Splenic aneurysm rupture
• Splenic vein thrombosis
• Splenomegaly complications 1

Imaging Algorithm

Variant 1: LUQ Pain + Suspected Splenomegaly

• First-line: CT abdomen/pelvis WITH IV contrast 1
• Alternate: Ultrasound abdomen (for splenic size, parenchyma, vasculature) 1
• Choose ONE initially; do not order simultaneously

Variant 2: LUQ Pain + Fever

• CT abdomen/pelvis WITH IV contrast (evaluate for abscess, infectious process) 1

Variant 3: Nonspecific LUQ Pain

• CT abdomen/pelvis WITH IV contrast (broad differential coverage) 1
• MRI abdomen with/without contrast is appropriate alternative 1

Critical Pitfalls

• LUQ has lowest physical exam interrater agreement among all quadrants 1
• Elderly patients present atypically with higher complication rates 1
• Plain radiographs NOT recommended (contributes to management in only 4% of cases) 1
• US alone has inferior sensitivity; should not delay cross-sectional imaging 1

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LEFT LOWER QUADRANT (LLQ) PAIN

Key Anatomic Structures

• Sigmoid/descending colon, left ovary/fallopian tube, left ureter, bowel

Most Common Etiologies (in order)

1. Acute diverticulitis (most common; 50% increase 2000-2007) 2
2. Colitis/inflammatory bowel disease
3. Epiploic appendagitis
4. Bowel obstruction
5. Hernia
6. Ovarian/fallopian pathology (women)
7. Pyelonephritis
8. Urolithiasis 2

Epidemiology

• 10% have diverticulosis at age 40
• 70% have diverticulosis in elderly
• 5-25% with diverticulosis develop diverticulitis 2

Imaging Algorithm

Nonspecific LLQ Pain (Broad Differential)

• CT abdomen/pelvis WITH IV contrast 2, 3
• Detects extraluminal air (perforation), bowel pathology, fluid collections
• Sensitivity/specificity near 100% for urolithiasis 2

Special Considerations:

• Unenhanced CT acceptable in elderly (≥75 years): accuracy 64-68% vs 68-71% with contrast (P=0.97-0.98) 2
• Suspected urolithiasis: Unenhanced CT preferred 2
• Women of reproductive age: Consider gynecologic causes first (see separate guidelines) 2

Critical Pitfalls

• Diverticulitis symptoms overlap with multiple conditions 2
• Elderly have higher comorbidity-related complications 2
• Large-volume extraluminal air = higher mortality 2

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RIGHT UPPER QUADRANT (RUQ) PAIN

Key Anatomic Structures

• Gallbladder, liver, right kidney, duodenum, pancreas (head), hepatic flexure

Most Common Etiologies

• Cholecystitis/cholelithiasis (most common)
• Hepatobiliary disease
• Peptic ulcer disease
• Pancreatitis
• Pneumonia (referred)
• Cardiac disease (referred) 4, 5

Imaging Algorithm

• Ultrasound abdomen (first-line for RUQ pain) 3, 6, 4
• CT abdomen/pelvis WITH IV contrast if US inconclusive 3, 6

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RIGHT LOWER QUADRANT (RLQ) PAIN

Key Anatomic Structures

• Appendix, cecum, right ovary/fallopian tube, right ureter

Most Common Etiologies

• Appendicitis (most common)
• Ovarian/adnexal pathology
• Urolithiasis
• Inflammatory bowel disease
• Ectopic pregnancy 3, 6

Imaging Algorithm

• CT abdomen/pelvis WITH IV contrast 3, 6
• Point-of-care ultrasound can aid diagnosis of appendicitis, urolithiasis 3
• Women of reproductive age: Pelvic US if gynecologic cause suspected 3

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GENERAL APPROACH TO ACUTE ABDOMINAL PAIN

Initial Laboratory Workup

• Complete blood count
• C-reactive protein
• Hepatobiliary markers
• Electrolytes, creatinine, glucose
• Urinalysis
• Lipase
• Pregnancy test (all women of reproductive age) 3

Risk Stratification

Normal WBC AND normal CRP:

• Re-evaluate in 12 hours 7

Elevated inflammatory markers:

• Proceed to imaging 7

Imaging Selection by Location

Pain Location	First-Line Imaging
RUQ	Ultrasound [3,6]
LUQ	CT with IV contrast [1,3]
RLQ	CT with IV contrast [3,6]
LLQ	CT with IV contrast [2,3]
Diffuse/generalized	CT with IV contrast [3,7]

Special Populations

Pregnant Patients:

• Ultrasound first-line
• MRI preferred over CT if US inconclusive 3

Elderly (≥75 years):

• Atypical presentations common
• Higher complication rates
• Unenhanced CT acceptable if contrast contraindicated 2

Shock/Respiratory Insufficiency:

• CT scan immediately 7

Critical "Can't Miss" Diagnoses

• Ruptured abdominal aortic aneurysm
• Mesenteric ischemia
• Ectopic pregnancy
• Perforated viscus
• Appendicitis with perforation
• Cholecystitis with perforation 3, 4

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IMAGING MODALITY SPECIFICS

CT Advantages

• Detects small amounts of extraluminal air
• Evaluates bowel wall, vasculature, fluid collections
• Broad differential coverage 2

Ultrasound Advantages

• No radiation
• Rapid bedside evaluation
• Preferred for RUQ, pregnancy, pediatrics 3, 4

Ultrasound Limitations

• Operator-dependent
• Limited by body habitus, bowel gas
• Should not delay definitive cross-sectional imaging when needed 1

Plain Radiography

• NOT recommended for acute abdominal pain workup
• Low sensitivity (30-70% for obstruction)
• Contributes to management in only 4% of cases
• Causes delays in definitive diagnosis 1