Differential Diagnosis for Abdominal Pain
The differential diagnosis for abdominal pain is primarily determined by pain location, with gastrointestinal, gynecologic, urologic, vascular, and musculoskeletal etiologies to consider systematically based on anatomic quadrant and associated clinical features. 1
Approach by Pain Location
Right Upper Quadrant Pain
- Acute cholecystitis is the primary diagnostic consideration 1
- Hepatobiliary pathology including choledocholithiasis and cholangitis 2
- Hepatitis or hepatic abscess 2
- Peptic ulcer disease (duodenal) 3
- Pancreatitis (may present in RUQ) 1
- Right lower lobe pneumonia or pulmonary embolism (referred pain) 3
Right Lower Quadrant Pain
- Appendicitis is the most critical diagnosis to exclude 1, 4
- Ectopic pregnancy in women of reproductive age 1, 2
- Ovarian torsion or ruptured ovarian cyst 1, 4
- Pelvic inflammatory disease 1
- Nephrolithiasis 1
- Crohn disease (terminal ileitis) 1
- Incarcerated inguinal or femoral hernia 1
Left Lower Quadrant Pain
- Diverticulitis is the leading consideration in older adults 1
- Sigmoid volvulus (especially with chronic constipation history) 1
- Colorectal cancer (with weight loss or rectal bleeding) 1
- Ectopic pregnancy or ovarian pathology in women 1
- Nephrolithiasis 1
- Incarcerated hernia 1
Epigastric/Diffuse Pain
- Peptic ulcer disease or gastritis 4
- Acute pancreatitis 1, 2
- Gastroenteritis 1
- Mesenteric ischemia (pain out of proportion to exam) 4
- Abdominal aortic aneurysm (life-threatening) 3
- Acute myocardial infarction (referred pain) 3
- Small bowel obstruction 1
- Irritable bowel syndrome 1
Differential by Mechanism
Obstructive Causes
- Adhesions account for 55-75% of small bowel obstructions 1
- Hernias cause 15-25% of small bowel obstructions 1
- Colorectal cancer causes 60% of large bowel obstructions 1
- Volvulus causes 15-20% of large bowel obstructions 1
- Diverticular stricture causes 10% of large bowel obstructions 1
Inflammatory/Infectious Causes
- Appendicitis 1
- Cholecystitis 1
- Diverticulitis 1
- Pancreatitis 1
- Pelvic inflammatory disease 1
- Gastroenteritis 1
- Urinary tract infection 1
Vascular Causes
- Mesenteric ischemia (arterial or venous thrombosis) 1, 4
- Abdominal aortic aneurysm rupture 3
- Splenic rupture 3
Gynecologic Causes (Women of Reproductive Age)
- Ectopic pregnancy (must be excluded first) 1, 2, 5
- Ovarian torsion 1
- Ruptured ovarian cyst 4
- Pelvic inflammatory disease 1
- Intrauterine pregnancy complications 1
Functional Disorders
Critical Red Flags Requiring Urgent Evaluation
- Hemodynamic instability (tachycardia, hypotension) suggests bleeding or sepsis 4
- Peritoneal signs (rigid abdomen, rebound tenderness) indicate perforation or ischemia 1, 4
- Pain out of proportion to physical findings strongly suggests mesenteric ischemia 4
- Abdominal distension with vomiting indicates bowel obstruction 4
- Fever with severe pain suggests infection, abscess, or perforation 4
- Pulsatile abdominal mass indicates possible aortic aneurysm 3
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, 2, 5
- Overlooking hernia orifices (umbilical, inguinal, femoral) and surgical scars during examination misses incarcerated hernias 1
- Dismissing atypical presentations in elderly patients who may have minimal symptoms despite serious pathology 4
- Over-relying on normal laboratory values early in disease when clinical suspicion remains high for serious pathology 5
- Assuming functional disorder without excluding organic disease through appropriate targeted evaluation 6
Subsequent Diagnoses After Initial Unspecified Abdominal Pain
Patients initially diagnosed with unspecified abdominal pain have significantly increased likelihood of subsequent diagnosis of: