What is the differential diagnosis for a patient presenting with abdominal pain?

Differential Diagnosis for Abdominal Pain

The differential diagnosis for abdominal pain should be systematically organized by anatomic location, with consideration of gastrointestinal, gynecologic, urologic, vascular, and musculoskeletal etiologies, while immediately identifying critical red flags that require urgent intervention. 1

Differential Diagnosis by Anatomic Quadrant

Right Upper Quadrant Pain

• Acute cholecystitis is the primary diagnostic consideration 1
• Hepatobiliary pathology including choledocholithiasis and cholangitis 1
• Peptic ulcer disease or gastritis may present with right upper quadrant or epigastric pain 1

Right Lower Quadrant Pain

• Appendicitis is the most critical diagnosis to exclude 1
• Ectopic pregnancy must be considered in all women of reproductive age 1
• Ovarian torsion or pelvic inflammatory disease in women 2
• Incarcerated inguinal hernia 1

Left Lower Quadrant Pain

• Diverticulitis is the leading consideration in older adults 1
• Sigmoid volvulus, particularly with history of chronic constipation 1
• Ovarian pathology or pelvic inflammatory disease in women 2

Epigastric or Diffuse Pain

• Peptic ulcer disease or gastritis 1
• Acute pancreatitis 1
• Mesenteric ischemia (arterial or venous thrombosis), especially when pain is out of proportion to physical findings 1, 2
• Small bowel obstruction (55-75% from adhesions, 15-25% from hernias) 1
• Large bowel obstruction (60% from colorectal cancer, 15-20% from volvulus) 1

Differential Diagnosis by Mechanism

Inflammatory/Infectious Causes

• Appendicitis, cholecystitis, diverticulitis, pancreatitis, and pelvic inflammatory disease 1
• Abscess formation or perforation with peritonitis 1

Obstructive Causes

• Small bowel obstruction: adhesions (55-75%), hernias (15-25%) 1
• Large bowel obstruction: colorectal cancer (60%), volvulus (15-20%) 1

Vascular Causes

• Mesenteric ischemia from arterial or venous thrombosis 1
• Abdominal aortic aneurysm 3

Gynecologic Causes (Women of Reproductive Age)

• Ectopic pregnancy 1
• Ovarian torsion 2
• Pelvic inflammatory disease 1

Critical Red Flags Requiring Urgent Evaluation

These findings indicate potentially life-threatening conditions requiring immediate intervention:

• Hemodynamic instability (tachycardia, hypotension) suggests bleeding or sepsis 1
• Peritoneal signs (rigid abdomen, rebound tenderness) indicate perforation or ischemia 1
• Pain out of proportion to physical findings strongly suggests mesenteric ischemia 1, 2
• Abdominal distension with vomiting indicates bowel obstruction 1, 2
• Fever with severe pain suggests infection, abscess, or perforation 1, 2

Common Pitfalls to Avoid

• Failing to obtain β-hCG testing in all women of reproductive age before imaging can delay diagnosis of ectopic pregnancy 1, 4
• Overlooking hernia orifices and surgical scars during examination can miss incarcerated hernias 1
• Dismissing atypical presentations in elderly patients can lead to missed diagnoses, as symptoms may be subtle even with serious pathology 1, 2
• Over-relying on normal laboratory values early in disease can lead to missed diagnoses, as labs may not yet be abnormal 1
• Ordering conventional radiography routinely has limited diagnostic value and should not be the initial imaging approach 4

Algorithmic Approach to Diagnosis

Step 1: Identify Pain Location

• Determine the anatomic quadrant to narrow the differential diagnosis 2

Step 2: Assess for Red Flags

• Check vital signs for fever, tachycardia, hypotension, or tachypnea 2
• Examine for peritoneal signs, abdominal distension, or Murphy's sign 2

Step 3: Mandatory Laboratory Testing

• β-hCG in all women of reproductive age before any imaging 1, 4
• Complete blood count to assess for leukocytosis 2, 4
• Comprehensive metabolic panel including liver function tests 4
• Serum lipase (more specific than amylase for pancreatitis) 4
• Urinalysis for urinary tract infection or nephrolithiasis 4
• Consider lactate and D-dimer if mesenteric ischemia suspected 2, 4

Step 4: Imaging Based on Location and Suspected Pathology

• Right upper quadrant pain: Abdominal ultrasound for suspected cholecystitis 2
• Right lower quadrant pain: Abdominal ultrasound initially, then CT with contrast if needed 2
• Left lower quadrant pain: CT abdomen/pelvis with contrast for suspected diverticulitis 2
• Pelvic pain: CT abdomen/pelvis with contrast 2
• Non-specific or diffuse pain: CT abdomen/pelvis with contrast, especially with fever or serious illness 2
• Suspected mesenteric ischemia: CT angiography of the abdomen 2
• Suspected kidney stones: Non-contrast CT abdomen/pelvis 2