Expansion
Bowel gas pattern, then solid organs, bones and calcification
Expansion
Bowel gas pattern first
- Small bowel: central, valvulae conniventes crossing the full width, normally under 3 cm
- Large bowel: peripheral, haustra crossing part of the width, normally under 6 cm
- Caecum: up to 9 cm, and above this the perforation risk is high
Dilatation patterns
- Small bowel dilated, colon collapsed: small bowel obstruction
- Both dilated: large bowel obstruction with an incompetent ileocaecal valve, or ileus
- Coffee bean sign arising from the pelvis: sigmoid volvulus
- Thumbprinting and mucosal oedema: colitis, ischaemia
- Toxic megacolon: transverse colon over 6 cm with mucosal islands, in acute colitis
Free air (pneumoperitoneum)
- Best seen on an erect chest radiograph as air under the diaphragm
- Rigler’s sign: both sides of the bowel wall visible, so gas on the inside and outside
- Football sign, falciform ligament sign, triangles of air between loops
Then the rest
- Solid organs: liver, spleen, kidney and psoas outlines
- Calcification: renal and ureteric stones along the line of the ureters, gallstones (only 10 to 15 per cent are radio-opaque), pancreatic calcification, aortic aneurysm, phleboliths in the pelvis, which are round with lucent centres
- Bones: lumbar spine, pelvis, sacroiliac joints, hips, lower ribs, and metastases
- Lines, tubes, drains, stents and foreign bodies
The abdominal radiograph is a low yield test with a substantial radiation dose, and CT has replaced it for most indications; it retains a role in suspected obstruction, in known inflammatory bowel disease and in foreign bodies.