Acute abdomen — workup by quadrant

Pain location → differential → imaging choice → when to operate. The classic Step 2 surgery question.

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◆RUQ pain

•Acute cholecystitis: Murphy sign, fever, leukocytosis → US first (wall thickening, pericholecystic fluid, sonographic Murphy) → laparoscopic cholecystectomy
•Ascending cholangitis: Charcot triad (fever, jaundice, RUQ pain) ± Reynolds pentad (+ AMS + hypotension) → IV antibiotics + emergent ERCP
•Hepatitis: ↑↑ AST/ALT (>1000), risk factors; viral serologies
•Liver abscess: amebic (travel) vs pyogenic (biliary disease); CT, drainage + antibiotics
•Choledocholithiasis: ↑ bilirubin + dilated CBD; ERCP

•Appendicitis: migration of pain from periumbilical to RLQ, McBurney point, Rovsing/Psoas/Obturator signs; CT (or US in kids/pregnant) → laparoscopic appendectomy
•Ovarian torsion (women): sudden severe pain, often after exertion, with adnexal mass; transvaginal US with Doppler; emergent laparoscopy
•Ectopic pregnancy: positive β-hCG + adnexal mass + free fluid; methotrexate vs salpingostomy/-ectomy
•Mesenteric adenitis: post-viral, mimics appendicitis (mostly in kids); supportive
•Crohn flare: ileitis; bowel wall thickening on imaging
•Cecal volvulus: distended colon with 'coffee bean' sign on plain film; colonoscopic detorsion or surgery

•Splenic rupture: trauma (Kehr sign — left shoulder pain) or mono with sport contact; FAST or CT; observe if stable, splenectomy if unstable
•Pancreatitis: epigastric → LUQ radiating to back; lipase >3x ULN; CT for complications
•Splenic infarct: SCD, AFib, endocarditis; CT
•Gastric ulcer perforation: free air on upright CXR; emergent surgery

•Diverticulitis: LLQ pain + fever + leukocytosis in middle-aged adults; CT (do NOT colonoscope acutely); antibiotics ± drainage of abscess; surgery for perforation/recurrent
•Ovarian torsion (left)
•Sigmoid volvulus: elderly, constipation, distended; 'coffee bean' or 'omega' sign; sigmoidoscopic detorsion → elective resection

•Mesenteric ischemia: pain OUT OF PROPORTION to exam, AFib (embolic) or atherosclerosis (thrombotic) or low flow (NOMI) or venous thrombosis; CTA → angiography + embolectomy or fluids + heparin
•Bowel obstruction: distention, vomiting, no flatus, high-pitched bowel sounds; X-ray (air-fluid levels, dilated loops) → CT; NG decompression, fluids, surgery if strangulated or complete
•Pancreatitis (see LUQ)
•Ruptured AAA: severe back/abdominal pain + hypotension + pulsatile mass; bedside US if stable, OR emergently if not
•Aortic dissection (covered in cardio): tearing chest/back pain + unequal BPs; CT angiography
•Perforated viscus: sudden severe pain + rigid abdomen + free air on upright CXR; emergent surgery

•Suspected perforation → upright CXR (free air under diaphragm) or CT abdomen
•Suspected appendicitis → CT (US in kids/pregnant)
•Suspected biliary → US first
•Suspected SBO → upright + supine abdominal X-rays first → CT
•Suspected mesenteric ischemia → CTA mesenteric arteries
•Suspected AAA rupture → bedside US if unstable, CTA if stable
•Pregnancy + abdominal pain → US first (avoids radiation), MRI if more detail needed

◆Pain out of proportion to exam = mesenteric ischemia until proven otherwise
◆Charcot triad = cholangitis → emergent ERCP
◆Free air under diaphragm = perforated viscus → emergent surgery
◆Pulsatile abdominal mass + hypotension = ruptured AAA → OR (don't waste time on CT)
◆Appendicitis in pregnancy or pediatrics → US first to minimize radiation; CT if non-diagnostic
◆Volvulus on plain film: cecal = 'coffee bean' in RLQ, sigmoid = 'omega/bent inner tube' in LLQ
◆Acute pancreatitis: lipase > amylase for specificity; CT for severity scoring only after 72 hours

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