Which radiologic tests should be ordered to evaluate the patient with acute abdominal pain?
The selection of tests depends on the likelihood of the pretest clinical diagnosis and the ability of the radiologic test to confirm clinical suspicion.
• Plain radiographs of the abdomen are quick and readily available, and can be done at the bedside. They can detect bowel obstruction (dilated loops of bowel with air/fluid levels), volvulus, and viscus perforation (free air). Occasionally, they may suggest stone disease (≈ 20% of gallbladder stones and ≈ 80% of renal stones are calcified) or ruptured aortic aneurysm (separation of aortic wall calcium and mass effect). Calcium in the area of the pancreas might suggest pancreatitis as the cause of pain. A gasless abdomen, air in the bowel wall, or air in the portal venous system suggests bowel infarction or severe infection. Free intraabdominal air is best detected with the patient in the left lateral decubitus position for 10 minutes, but a computed tomography (CT) scan is more sensitive for small amounts of air.
• Ultrasound (US) of the abdomen is quick, noninvasive, and can be performed at the bedside. The disadvantages of US include variable operator expertise and suboptimal examination in the obese or gaseous abdomen. US is excellent for evaluating the gallbladder, bile ducts, liver, kidneys, appendix, and pelvic organs.
• CT of the abdomen provides a detailed view of the anatomy. Oral and intravenous contrast agents are usually required. CT has become an extension of the physical examination and the single most helpful radiologic examination of the patient with acute abdominal pain. CT is better than US for evaluation of the pancreas, but often lacks the spatial resolution to identify biliary stone disease.
• Hepatoiminodiacetic (HIDA) scan is the most accurate test for acute cholecystitis