Approach to Abdominal Pain
A board-focused framework for acute abdominal pain: characterize the pain, stabilize unstable or peritonitic patients and check a β-hCG first, then let location drive the top diagnosis, best initial test, and management across the classic acute-abdomen emergencies.
The board approach: stabilize, then localize
Abdominal pain is tested as a stabilize-then-localize problem. Understand the pain first: visceral pain is dull, midline, and poorly localized (foregut → epigastric, midgut → periumbilical, hindgut → suprapubic), while parietal (somatic) pain becomes sharp and well-localized once inflammation irritates the parietal peritoneum — which is why appendicitis pain migrates from periumbilical to RLQ.
Two reflexes win points before any imaging:
- In any reproductive-age woman, send a β-hCG first — ectopic pregnancy is the can't-miss diagnosis.
- If the patient is hemodynamically unstable or shows peritoneal signs (rigidity, rebound, involuntary guarding), resuscitate and involve surgery now — do not delay for a CT.
Otherwise, let the location of maximal pain drive your top differential and your first test.
Two reflexes before imaging: β-hCG in every reproductive-age woman (ectopic = can't-miss); unstable or peritonitic (rigidity/rebound) → resuscitate + surgery now, don't wait for CT.
Then location drives the first test:
- RUQ: cholecystitis (Murphy, fatty meal) or cholangitis (Charcot triad) → RUQ ultrasound
- Epigastric: pancreatitis (lipase ≥3× ULN, radiates to back), PUD/perforation; also inferior MI → lipase, upright CXR/CT for free air
- RLQ: appendicitis (periumbilical → RLQ, McBurney) → CT in adults, US in children/pregnancy; in women also ectopic/torsion
- LLQ: diverticulitis (older adult, fever) → CT with contrast; no acute colonoscopy
- Flank → groin: nephrolithiasis (colicky, hematuria) → noncontrast CT
- Periumbilical, pain out of proportion to exam: mesenteric ischemia (elderly, AFib, lactic acidosis) → CT angiography
- Diffuse + pulsatile mass + hypotension: ruptured AAA (older male smoker) → unstable = OR, stable = CT
Acute abdomen: buzzword → best test → management
| Diagnosis | Classic clue | Best test | Management |
|---|---|---|---|
| Acute cholecystitis | RUQ pain, +Murphy, fatty meal | RUQ US (HIDA if equivocal) | IV fluids, abx, cholecystectomy |
| Appendicitis | Periumbilical → RLQ, McBurney | CT (US if child/pregnant) | Appendectomy ± abx |
| Acute pancreatitis | Epigastric → back, lipase ≥3× | Clinical + lipase (CT for complications) | Aggressive IV fluids, analgesia, early enteral feeding |
| Ascending cholangitis | Charcot triad: fever, jaundice, RUQ | RUQ US, labs | Abx + ERCP decompression |
| Diverticulitis | LLQ pain, fever, older adult | CT abd/pelvis w/ contrast | Abx; colonoscopy in 6–8 wk |
| Perforated PUD | Sudden epigastric, rigid abdomen | Upright CXR/CT: free air | Emergent surgery |
| Mesenteric ischemia | Pain out of proportion, AFib | CT angiography | Resuscitate, revascularize |
| Ruptured AAA | Pulsatile mass, hypotension, smoker | US/CT (OR if unstable) | Emergent surgery |
A 72-year-old with atrial fibrillation (not anticoagulated) develops sudden, severe, diffuse abdominal pain. The exam is striking for a soft, only mildly tender abdomen despite the severe pain. Labs show a metabolic acidosis with elevated lactate.
Diagnosis: Acute mesenteric ischemia — SMA embolism (AFib is the embolic source).
Next best step: CT angiography of the abdomen. Give IV fluids and anticoagulation, and consult surgery for embolectomy/revascularization; proceed to laparotomy if peritonitis or bowel necrosis develops.
Trap: "Pain out of proportion to exam" + a cardiac embolic source = mesenteric ischemia until proven otherwise. A normal early lactate does not exclude it.
A 45-year-old obese woman has RUQ pain after a fatty meal, low-grade fever, and inspiratory arrest on RUQ palpation (Murphy sign). RUQ ultrasound shows gallstones but no wall thickening or pericholecystic fluid, and is read as equivocal.
Next best step: HIDA scan (cholescintigraphy) — non-visualization of the gallbladder confirms acute cholecystitis (cystic duct obstruction).
Management: NPO, IV fluids, antibiotics, and early laparoscopic cholecystectomy (same admission).
Contrast: RUQ pain + fever + jaundice = Charcot triad → ascending cholangitis, which requires ERCP biliary decompression plus antibiotics — not just cholecystectomy.
A 26-year-old woman with 6 weeks of amenorrhea presents with sudden left-lower-quadrant pain and light vaginal bleeding; BP 88/54.
First step (always): urine/serum β-hCG — positive.
Because she is hemodynamically unstable with a positive test, treat as a ruptured ectopic: resuscitate (two large-bore IVs, fluids/blood) and take her to the OR — a bedside/FAST ultrasound showing free intraperitoneal fluid confirms the need for surgery. Do not delay for a formal workup.
Stable-patient pathway: transvaginal ultrasound — no intrauterine pregnancy with a β-hCG above the discriminatory zone (~1500–2000 mIU/mL) = ectopic. Small, unruptured, stable → methotrexate; ruptured/unstable → salpingectomy.
Rule: every reproductive-age woman with abdominal pain gets a pregnancy test before imaging or opioids — ectopic pregnancy and ovarian torsion are the can't-miss diagnoses.
- 5 F's (gallstone risk): Fat, Female, Forty, Fertile, Fair
- Charcot triad (cholangitis): RUQ pain + fever + jaundice
- Reynolds pentad: Charcot triad + hypotension + altered mental status (suppurative cholangitis)
- Appendicitis signs: Rovsing (LLQ press → RLQ pain), Psoas (pain on hip extension), Obturator (pain on internal hip rotation)
- Murphy sign: inspiratory arrest on RUQ palpation → cholecystitis
- Cullen sign (periumbilical bruising) & Grey Turner sign (flank bruising): retroperitoneal hemorrhage / severe pancreatitis
- I GET SMASHED (pancreatitis causes): Idiopathic, Gallstones, Ethanol, Trauma, Steroids, Mumps, Autoimmune, Scorpion sting, Hypercalcemia/Hypertriglyceridemia, ERCP, Drugs
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