Acute Abdomen

An acute abdomen is not one diagnosis. It is a clinical presentation in which abdominal or pelvic pathology may deteriorate quickly enough to threaten perfusion, bowel viability, or life. The differential is most useful when organized by mechanism: - Inflammation or infection: appendicitis, cholecystitis, cholangitis, pancreatitis, and diverticulitis. - Perforation: a perforated peptic ulcer or another perforated hollow viscus releases air, gastric contents, bile, or intestinal contents into the peritoneal cavity. - Obstruction: adhesions are a common cause of small bowel obstruction; incarcerated hernia and other mechanical causes can also compromise blood flow. - Vascular catastrophe: acute mesenteric ischemia and ruptured abdominal aortic aneurysm. - Gynecologic or extra-abdominal disease: ruptured ectopic pregnancy, ovarian torsion, renal colic, pyelonephritis, and lower-lobe pulmonary disease can all mimic an intra-abdominal emergency. The location and quality of pain reflect the structure being irritated. Distension of a hollow organ and early inflammation activate visceral afferents, producing vague, poorly localized midline pain. Once inflammation reaches the parietal peritoneum, somatic afferents create sharper, localized pain with guarding or rebound. A patient with peritonitis often lies still because movement...