Approach to Assessment of Abdominal Pain
Definition
Abdominal pain is the cardinal symptom of a large number of intra-abdominal pathologies ranging from benign self-limited disease to surgical emergencies requiring immediate intervention. 1, 2
Classification
By Onset and Duration
- Acute: Sudden onset, typically requiring evaluation within hours to days 3
- Chronic: Pain persisting beyond 3 months, often representing functional disorders or benign causes 4
By Location (Guides Differential and Imaging)
- Right upper quadrant: Cholecystitis, hepatobiliary disease, cholangitis 5
- Right lower quadrant: Appendicitis (most critical to exclude), ectopic pregnancy in women 5, 3
- Left lower quadrant: Diverticulitis, colorectal pathology 6
- Epigastric: Pancreatitis, peptic ulcer disease, gastritis 6
- Diffuse/nonlocalized: Bowel obstruction, mesenteric ischemia, peritonitis 5
Differential Diagnosis
Common Surgical Causes
- Appendicitis: 15.9-28.1% of acute abdominal pain requiring surgery 6
- Bowel obstruction: 15% of acute abdominal pain admissions; small bowel (adhesions, hernias, neoplasms), large bowel (cancer, volvulus, diverticular disease) 6
- Cholecystitis: Evaluated by right upper quadrant pain and ultrasound 5
- Perforated viscus: Peritonitis, rigid abdomen 6
- Mesenteric ischemia: Pain out of proportion to examination findings 6
Common Medical Causes
- Gastroenteritis: Self-limited, no red flags 3
- Pancreatitis: Elevated lipase, epigastric pain 5
- Nephrolithiasis: Flank pain, hematuria 7
- Urinary tract infection: Dysuria, positive urinalysis 7
Gynecologic Causes (Women of Reproductive Age)
- Ectopic pregnancy: Mandatory β-hCG testing before imaging 5, 7
- Ovarian torsion: Acute onset, unilateral pelvic pain 5
- Pelvic inflammatory disease: Fever, cervical motion tenderness 5
Special Population Considerations
- Elderly: Higher likelihood of malignancy, diverticulitis, vascular causes; atypical presentations 5
- Post-bariatric surgery: Internal herniation, tachycardia as critical warning sign 6
History
Character of Pain
- Colicky pain: Bowel obstruction as bowel attempts to overcome occlusion 6
- Severe pain out of proportion to examination: Mesenteric ischemia 6
- Sudden onset: Perforation, vascular catastrophe 2
- Gradual onset: Inflammatory processes (appendicitis, diverticulitis) 3
Associated Symptoms
- Vomiting: Earlier and more prominent in small bowel obstruction versus large bowel obstruction 6
- Constipation and inability to pass gas: 85% sensitivity and 78% specificity for adhesive small bowel obstruction in patients with prior surgery 6
- Rectal bleeding with weight loss: Colorectal cancer 6
- Fever: Infection, abscess, cholangitis 6
Red Flags Requiring Urgent Evaluation
- Hemodynamic instability (tachycardia, hypotension): Bleeding or sepsis 6, 5
- Tachycardia: Most sensitive early warning sign of surgical complications, triggers urgent investigation even before other symptoms develop 6, 5
- Combination of fever, tachycardia, and tachypnea: Predicts anastomotic leak, perforation, or sepsis 6
- Signs of peritonitis (rigid abdomen, rebound tenderness): Perforation, ischemia 6
- Abdominal distension with vomiting: Bowel obstruction 6
- Asymmetric gaseous distension with emptiness of left iliac fossa: Pathognomonic for sigmoid volvulus 6
Risk Factors
- Prior abdominal surgery: Adhesive obstruction (55-75% of small bowel obstructions) 6
- Previous diverticulitis: Diverticular stenosis 6
- Chronic constipation: Dolichosigmoid and volvulus 6
- Psychotropic medications: Chronic constipation predisposing to volvulus, especially in elderly institutionalized patients 6
- Cardiopulmonary, renal, or hepatic comorbidities: Increase surgical risk 6
Physical Examination (Focused)
Vital Signs
- Fever, tachycardia, hypotension, tachypnea: Infection, bleeding, or complications 6
- Tachycardia alone: Most critical early warning sign 6, 5
Abdominal Examination
- Murphy's sign (pain when pressing right upper quadrant): Cholecystitis 6
- Rebound tenderness, guarding, rigidity: Peritonitis 6
- Abdominal distension: Bowel obstruction, volvulus 6
- Empty rectum on digital examination: Classic for sigmoid volvulus 6
- Asymmetric gaseous distension with emptiness of left iliac fossa: Pathognomonic for sigmoid volvulus 6
Critical Pitfall
- Absence of peritonitis does not exclude bowel ischemia: Patients with sigmoid volvulus often lack peritoneal signs despite established ischemia due to chronic distension masking examination 6
Investigations
Laboratory Tests (Initial Workup)
- Complete blood count (CBC): Leukocytosis indicates infection or inflammation 5, 7
- Comprehensive metabolic panel (CMP): Liver function tests (ALT, AST, alkaline phosphatase, bilirubin) for hepatobiliary pathology 5, 7
- Serum lipase: More specific than amylase for pancreatitis 5, 7
- Urinalysis: Urinary tract infection or nephrolithiasis 5, 7
- β-hCG: Mandatory in all women of reproductive age before imaging to rule out ectopic pregnancy 5, 7
Additional Laboratory Tests Based on Clinical Suspicion
- C-reactive protein (CRP): Superior sensitivity and specificity compared to WBC for ruling in surgical disease; elevated CRP and abnormal imaging are significant predictive factors for hospital admission 6, 8
- Lactate: Elevated suggests ischemia or sepsis, but normal levels do not exclude internal herniation or early ischemia 6, 7
- D-dimer: Consider if mesenteric ischemia suspected 6, 7
- Procalcitonin: Helpful for assessing inflammatory response in suspected sepsis 6
- Blood cultures: If sepsis suspected 7
Imaging Strategy by Pain Location
- Right upper quadrant: Ultrasonography is initial test of choice for cholecystitis and hepatobiliary disease 5, 3
- Right lower quadrant: CT abdomen/pelvis with contrast for suspected appendicitis 5, 3
- Left lower quadrant: CT abdomen/pelvis with contrast for suspected diverticulitis 6
- Pelvic pain: CT abdomen/pelvis with contrast 6
- Nonlocalized/diffuse pain: CT abdomen/pelvis with IV contrast is preferred due to broad differential; changes leading diagnosis in 51% of patients and alters admission decisions in 25% 5
Imaging Strategy by Suspected Condition
- Acute cholecystitis: Abdominal ultrasound 6
- Acute appendicitis: CT abdomen/pelvis with contrast 6
- Kidney stones: Non-contrast CT abdomen/pelvis 6
- Bowel obstruction: CT abdomen/pelvis with contrast 6
- Mesenteric ischemia: CT angiography of abdomen 6
Expected Findings
- Appendicitis: Periappendiceal fat stranding, appendiceal diameter >6mm, appendicolith 3
- Cholecystitis: Gallbladder wall thickening, pericholecystic fluid, positive sonographic Murphy's sign 5
- Bowel obstruction: Dilated bowel loops, air-fluid levels, transition point 6
- Diverticulitis: Colonic wall thickening, pericolonic fat stranding, abscess 6
Empiric Treatment
Resuscitation and Stabilization
- IV fluids: For hemodynamic instability or dehydration 1
- NPO status: If surgical intervention likely 1
- Nasogastric decompression: For bowel obstruction with vomiting 6
Analgesia
- Opioids or NSAIDs: Pain control does not mask surgical findings and should not be withheld 1
Antibiotics (When Indicated)
- Broad-spectrum antibiotics: For suspected intra-abdominal infection (appendicitis, diverticulitis, cholangitis, peritonitis) 1
- Initiate early if sepsis suspected: Do not delay for imaging 1
Specific Conditions
- Sigmoid volvulus: Endoscopic decompression if no peritonitis 6
- Adhesive small bowel obstruction: Conservative management with NPO, IV fluids, nasogastric decompression if no signs of strangulation 6
Indications to Refer
Immediate Surgical Consultation
- Signs of peritonitis (rigid abdomen, rebound tenderness) 6
- Hemodynamic instability (tachycardia, hypotension) 6, 5
- Suspected perforation or ischemia 6
- Bowel obstruction with signs of strangulation (fever, tachycardia, peritonitis) 6
- Acute appendicitis 6
- Acute cholecystitis not responding to conservative management 5
Urgent Specialist Referral
- Suspected mesenteric ischemia: Vascular surgery 6
- Ectopic pregnancy: Obstetrics/gynecology 5
- Ovarian torsion: Obstetrics/gynecology 5
- Pancreatitis with complications: Gastroenterology or surgery 5
Elective Referral
- Chronic abdominal pain without red flags: Gastroenterology after organic pathology excluded 4
- Functional disorders (irritable bowel syndrome): Consider psychological support (cognitive therapy) and pharmacological options; repetitive testing not recommended 4
Critical Pitfalls
Diagnostic Pitfalls
- Failing to obtain β-hCG in women of reproductive age before imaging: Delays diagnosis of ectopic pregnancy, a life-threatening condition 5, 7
- Relying on conventional radiography: Limited diagnostic value in most patients with abdominal pain; should not be routinely ordered 5, 7
- Assuming normal lactate excludes ischemia: Normal lactate does not exclude internal herniation or early ischemia 6
- Assuming absence of peritonitis excludes bowel ischemia: Chronic distension can mask peritoneal signs despite established ischemia 6
- Ignoring tachycardia: Most sensitive early warning sign of surgical complications; triggers urgent investigation even before other symptoms develop 6, 5
- Underestimating atypical presentations in elderly: May require more thorough evaluation even if laboratory tests are normal 5
Management Pitfalls
- Overuse of CT scans: Minimize ionizing radiation exposure, especially in young patients; consider ultrasound first for suspected appendicitis 6
- Withholding analgesia: Pain control does not mask surgical findings and should not be delayed 1
- Repetitive testing in functional disorders: Once functional pain is established, repetitive testing is not recommended 4
- Delaying antibiotics in sepsis: Initiate early if sepsis suspected; do not delay for imaging 1