The clinician evaluates acute abdomen using a systematic differential diagnosis framework organized by onset rapidity, pain character, and anatomical location. Sudden-onset (seconds to minutes) severe pain suggests vascular catastrophe (ruptured AAA, mesenteric ischemia, splenic rupture) or hollow viscus perforation (perforated peptic ulcer, perforated diverticulitis). Rapidly progressive (minutes to hours) pain suggests inflammation or obstruction (appendicitis, cholecystitis, pancreatitis, bowel obstruction, incarcerated hernia, testicular or ovarian torsion). Gradual onset (hours to days) suggests developing infection or inflammation (diverticulitis, pyelonephritis, inflammatory bowel disease flare). The clinician applies the acute abdomen algorithm: hemodynamic assessment (unstable patients with peritoneal signs require emergent surgical consultation before further workup), focused history (onset, character, radiation, associated symptoms -- vomiting preceding pain suggests medical cause, pain preceding vomiting suggests surgical cause), focused examination (inspection, auscultation, percussion for peritoneal irritation, careful palpation starting away from the area of maximal tenderness, assessment for hernias, costovertebral angle tenderness, pelvic examination when indicated), and targeted diagnostics (CBC, CMP, lipase, lactate, urinalysis, beta-hCG, upright chest X-ray for free air, CT abdomen/pelvis with IV contrast as the imaging modality of choice for most acute abdominal...