Gastrointestinal Imaging
What the exam tests
GI imaging tests fluoroscopy, bowel obstruction, inflammatory bowel disease, liver lesions, pancreaticobiliary disease, and postoperative complications. CT and MR enterography are high-yield.
Core rules
- Small bowel obstruction: dilated loops >3 cm with a transition point and decompressed distal bowel. Look for closed-loop obstruction, ischemia, and strangulation.
- CT enterography uses neutral oral contrast and intravenous contrast to assess Crohn disease activity and complications.
- LI-RADS applies to patients at risk for HCC: arterial phase hyperenhancement plus washout and capsule favors HCC.
- Acute pancreatitis is diagnosed clinically with enzyme/lipase and imaging; CT is most useful for complications.
Worked example
A 70-year-old with vomiting and abdominal distension has CT showing dilated small bowel loops, a transition point in the right lower quadrant, and collapsed distal ileum. Reasoning: this is a mechanical small bowel obstruction, not ileus. The next step is to identify the cause, such as adhesions or hernia, and to look for closed-loop features, reduced wall enhancement, or pneumatosis. If signs of ischemia or closed loop are present, urgent surgical consultation is required.
Traps
Calling ileus obstruction without a transition point; missing a closed loop; giving oral contrast in high-grade obstruction; and misclassifying a liver lesion without evaluating the appropriate phase.
Key points
- A transition point distinguishes mechanical obstruction from ileus.
- Closed-loop obstruction is a surgical emergency.
- LI-RADS requires arterial hyperenhancement and washout/capsule in at-risk patients.
- CT enterography evaluates Crohn complications, not just luminal disease.