Abdominal imaging - X-ray

Role

Plain abdominal X-ray (AXR) has a narrow, well-defined role in modern practice - largely limited to specific scenarios (suspected bowel obstruction, perforation screening, foreign body localisation) given its low sensitivity for most other abdominal pathology compared with CT
Increasingly superseded by CT for most acute abdominal presentations given CT's substantially higher diagnostic yield, but AXR retains a role as a rapid, low-radiation initial or monitoring test in specific circumstances

Distinguishes gas patterns (dilated bowel loops, air-fluid levels suggesting obstruction), calcifications (some renal/biliary stones, chronic pancreatitis calcification), and free air under the diaphragm on an erect film (though erect chest X-ray is actually more sensitive for detecting pneumoperitoneum than an erect AXR)
Dilated small bowel loops with air-fluid levels suggest small bowel obstruction; a markedly dilated colon (toxic megacolon threshold - transverse colon diameter >=6cm in the appropriate clinical context) is a specific, important, actionable finding in severe colitis
AXR has poor sensitivity for many common causes of acute abdominal pain (appendicitis, most inflammatory/ischaemic bowel disease, most solid organ pathology) - a normal AXR does not meaningfully lower suspicion for these conditions and should not be relied upon to exclude them

Used serially in some settings to monitor known bowel obstruction/ileus progression or resolution, and to track foreign body position, given its speed and low radiation burden compared with repeat CT
Findings suggesting a surgical emergency (free air, marked colonic dilatation, closed-loop obstruction pattern) warrant urgent escalation regardless of clinical severity appearing modest
Bowel obstruction, toxic megacolon (in severe ulcerative colitis), ingested foreign bodies, chronic pancreatitis (calcification)

AXR's main modern value is as a rapid triage/monitoring tool in specific known conditions (obstruction, colitis severity monitoring) rather than as a general-purpose diagnostic test for undifferentiated abdominal pain, where CT has largely superseded it

3 more sections, plus exam facts

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