An Abdominal X-ray (AXR) is a first-line imaging test used in the evaluation of suspected bowel and urological disease.
It is quick, inexpensive, and widely available, but sensitivity and specificity are lower than CT. AXR is often a screening or triage tool in the acute setting.

📋 Indications (Suspected Pathology)

👉 Large and small bowel obstruction (including volvulus).
👉 Perforation of an abdominal viscus (though erect CXR is more sensitive for free air).
👉 Constipation – faecal loading assessment.
👉 Renal/ureteric calculi (though CT KUB is now gold standard).
👉 Foreign bodies (swallowed, inserted, or penetrating).

🛠️ Different Types of AXR Views

Supine AP: Standard view, patient on their back – best for obstruction, stones, faecal loading.
Erect AXR: Patient upright; shows air-fluid levels in obstruction and can help detect perforation.
Decubitus: Patient lies on side; gas-fluid levels rise and can help confirm free air if erect film not possible.

✅ Normal Abdominal X-ray

Small bowel: Central, valvulae conniventes (lines crossing entire width), diameter < 3 cm.
Large bowel: Peripheral, haustra (do not cross whole lumen), diameter < 6 cm (caecum < 9 cm).
Stomach: Left upper quadrant gas bubble is normal.

🚨 Large Bowel Obstruction (LBO)

Grossly dilated colon (>6 cm).
Haustra visible but stretched and thickened.
Common causes: colorectal cancer, volvulus, strictures (e.g., diverticular disease).

🚨 Small Bowel Obstruction (SBO)

Central dilated loops >3 cm.
“Stack of coins” / “step-ladder” appearance with multiple air-fluid levels on erect film.
Causes: adhesions (most common), hernia, Crohn’s disease.

💥 Perforation

Free intraperitoneal gas, best seen under diaphragm (erect CXR more sensitive).
Look for Rigler’s sign (gas outlining both sides of bowel wall).
Urgent surgical referral needed.

🧩 Ulcerative Colitis – “Thumb Printing”

Mucosal oedema causes thickened haustral folds → “thumb-print” appearance.
Seen in severe colitis (IBD or infective).
Beware of toxic megacolon if gross dilatation present.

🌀 Sigmoid Volvulus

Massively dilated loop, often extending from pelvis to diaphragm.
Classic “coffee bean” or “omega loop” sign.
Common in elderly, institutionalised, or neuropsychiatric patients.

🌀 Caecal Volvulus

Dilated caecum, often displaced into left upper quadrant.
More acute and surgical than sigmoid volvulus.

🔧 Post-Operative Ileus

Diffuse gaseous distension of small and large bowel.
No clear transition point (contrast with SBO).
Common post-op, due to inflammation, analgesia (opioids), or electrolyte imbalance.

📚 Clinical Pearls

Always assess: gas pattern, bowel size, air-fluid levels, free air, calcifications, soft tissue masses.
Compare with clinical context – AXR alone rarely definitive.
In suspected obstruction/perforation, CT abdomen is gold standard for diagnosis and surgical planning.

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Abdominal X-Ray (AXR)

📸 Introduction