Abdominal and Gastrointestinal Imaging
Abdominal and gastrointestinal imaging rewards protocol knowledge and a search for transition points. The exam tests CT phase selection, recognition of obstruction and perforation, and characterisation of focal liver lesions.
Technique and phases
- Non-contrast CT: stones, calcification, acute haemorrhage.
- Arterial phase (about 30-40 s): hypervascular tumours and active bleeding.
- Portal venous phase (about 70-80 s): liver metastases and bowel wall.
- Delayed phase: urothelium and some cholangiocarcinomas.
Core diagnoses
- Small bowel obstruction: loops over 3 cm, a transition point and collapsed distal bowel. Ileus lacks a transition point.
- Pneumoperitoneum is most sensitively detected on CT lung windows.
- Appendicitis: appendix over 6 mm, fat stranding and appendicolith.
- Liver haemangioma shows peripheral nodular enhancement with centripetal fill-in; HCC in cirrhosis is assessed by LI-RADS.
Worked example
A 55-year-old with vomiting and colicky pain has dilated small bowel loops and a transition point in the right lower quadrant with collapsed distal ileum. That is mechanical small bowel obstruction, likely adhesive. If there is pneumatosis or reduced wall enhancement, ischaemia is present and surgery is urgent.
Traps
- Labeling ileus as obstruction; always look for a transition point.
- Missing free air because only soft-tissue windows were reviewed.
- Calling a haemangioma malignant because it enhances brightly.