Introduction
This topic covers how the small bowel and colon are examined with radiological methods, which modality is chosen for which clinical question, and how colorectal cancer appears on imaging, is staged and is distinguished from other causes of bowel wall thickening and stenosis.
Imaging of the small bowel
Plain abdominal radiography is the first step in acute abdominal pain. It can show dilated small bowel loops with air-fluid levels and a step-ladder pattern in mechanical obstruction, free intraperitoneal air in perforation, and it helps exclude other causes of acute pain. Its sensitivity is limited, so a normal film does not exclude obstruction.
- CT with oral and intravenous contrast is the main test in suspected obstruction, ischaemia, perforation, abscess and tumour; it shows the level and cause of obstruction and the bowel wall enhancement pattern.
- CT enterography and MR enterography distribute oral contrast and map the whole small bowel; MR enterography is preferred in young patients and for repeated imaging of Crohn disease.
- Ultrasound assesses bowel wall thickness, peristalsis, mesenteric fluid and abscesses without radiation. It is useful in children, pregnancy and thin patients, but it is operator-dependent and gas-containing loops limit it.
- Barium small bowel follow-through (SBFT) and enteroclysis are the two common ways to study the small intestine without CT; enteroclysis is reserved for difficult cases. They are now largely replaced by cross-sectional imaging but still give detailed mucosal and fistula information when used. Indications: chronic diarrhoea, IBD, gluten sensitivity, weight loss of unknown cause.