Abdominal and Gastrointestinal Imaging
Core concepts
Understand the acute abdomen: free air (pneumoperitoneum), obstruction, ischemia, and perforation. Learn the CT signs of bowel obstruction (transition point, small bowel feces sign) and ischemia (pneumatosis, portal venous gas, reduced enhancement). Know the patterns of liver disease: cirrhosis, steatosis, hemangioma versus metastasis, and HCC enhancement (arterial wash-in, portal washout). Understand biliary anatomy and the causes of biliary obstruction (stone versus stricture versus tumor). Learn pancreatic pathology: acute pancreatitis (Balthazar/severity), pancreatic adenocarcinoma (double duct sign). Understand the spleen, adrenals, and peritoneal spaces. Know the GI contrast series: barium swallow, meal, follow-through, and enema, and their indications. Understand the principles of CT colonography and the detection of polyps.
Traps
Free air on supine radiograph collects anteriorly; erect films show subdiaphragmatic gas. A normal amylase does not exclude pancreatitis. Distinguish hemangioma (peripheral nodular enhancement) from HCC (arterial hyperenhancement with washout). Do not confuse a gallstone ileus with simple obstruction. Remember that a small bowel obstruction with a transition point and no ischemia may be managed conservatively.
Rule of thumb
For any suspected bowel obstruction, look for the transition point and signs of strangulation (reduced wall enhancement, pneumatosis, closed loop). These determine surgical urgency.