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AbdomenDemonstration data

Abdominal X-Ray: Intestinal Obstruction (Resource-Limited)

The plain abdominal radiograph remains a first-line, low-cost investigation for suspected intestinal obstruction in resource-limited settings, where CT is often unavailable. It reliably demonstrates bowel dilatation, air-fluid levels and free intraperitoneal air, helping distinguish small from large bowel obstruction and identify surgical emergencies. Findings must always be interpreted alongside clinical assessment, as a normal film does not exclude early or closed-loop obstruction.

Indications

  • Acute abdomen with distension, colicky pain, bilious vomiting or absolute constipation
  • Suspected mechanical obstruction from incarcerated/strangulated external hernia (a leading cause in African settings)
  • Suspected sigmoid or caecal volvulus, especially in older patients with chronic constipation
  • Paediatric intussusception (currant-jelly stool, palpable mass) as a screening step before ultrasound/enema
  • Suspected ascariasis-related obstruction in children in endemic regions
  • Assessment for pneumoperitoneum in suspected perforation
  • Monitoring response to conservative management (serial films)

Contraindications & Cautions

  • No absolute contraindication; radiography is the accessible first-line study
  • Pregnancy: justify exposure, use tight collimation and abdominal shielding where possible; ultrasound preferred for some paediatric/obstetric contexts
  • Apply ALARA principles, particularly in children and for serial imaging
  • Do not delay surgical referral in a clinically unstable patient to obtain imaging
  • Barium contrast studies are contraindicated if perforation is suspected (use water-soluble contrast)

Patient Preparation

  • No fasting required for the plain film itself
  • Explain procedure and obtain verbal consent; reassure regarding brief breath-hold
  • Remove metallic objects, belts and clothing with fasteners from the field
  • Positioning: supine AP and erect PA/AP; if the patient cannot stand, a left lateral decubitus film (right side up) after 5-10 minutes of positioning
  • Ensure the diaphragm is included on the erect/decubitus view to detect subdiaphragmatic free air
  • Document nasogastric tube position if present; a decompressing NG tube may alter gas pattern

Technique & Parameters

  • Supine AP abdomen: include from diaphragms to symphysis pubis and both flanks
  • Erect abdomen (or erect chest to show diaphragm) to demonstrate air-fluid levels and free subdiaphragmatic gas
  • Left lateral decubitus alternative for non-ambulant patients: free air rises over the right lobe of liver
  • Typical exposure ~70-80 kVp with appropriate mAs; use grid for larger patients
  • Full inspiration and expiration considerations; avoid rotation (symmetry of iliac wings)
  • Resource-limited alternative/adjunct: bedside ultrasound can detect dilated fluid-filled loops, to-and-fro peristalsis and free fluid when radiography is equivocal
  • Water-soluble contrast follow-through may be used to confirm level and can be therapeutic in adhesive obstruction where available

Systematic Review

  • Assess overall bowel gas pattern: is dilated bowel small (central, valvulae conniventes spanning full width) or large (peripheral, haustra not crossing lumen)?
  • Measure calibre: small bowel >3 cm, transverse colon >6 cm, caecum >9 cm are abnormal
  • Count and localise air-fluid levels on the erect film (>2 levels or levels >2.5 cm suggests obstruction)
  • Search hernial orifices (inguinal, femoral, umbilical) for gas-containing loops
  • Look for a transition point and paucity of gas distally
  • Evaluate for volvulus signs (coffee-bean/inverted-U in sigmoid, embryo/kidney sign in caecal)
  • Check for free intraperitoneal air (Rigler sign, subdiaphragmatic lucency, football sign)
  • Review solid organs, calcifications, renal/biliary stones and the visualised bony skeleton

Key Findings & Significance

  • Small bowel obstruction: multiple dilated central loops >3 cm with valvulae conniventes (crossing the full width) and a stepladder of air-fluid levels
  • Large bowel obstruction: peripheral dilated colon >6 cm with haustral folds; competent ileocaecal valve raises perforation risk at the caecum
  • Sigmoid volvulus: massively dilated inverted-U 'coffee-bean' loop arising from the pelvis pointing to the right upper quadrant
  • Caecal volvulus: dilated caecum displaced to the left upper quadrant with a single long air-fluid level
  • Intussusception (paediatric): soft-tissue mass, target/crescent sign and paucity of gas in the right lower quadrant
  • Ascariasis: whorled or parallel tubular filling defects (worm bodies) within gas-filled bowel; 'whirlpool' of worms
  • Pneumoperitoneum: free subdiaphragmatic air, Rigler double-wall sign, indicating perforation
  • Gasless abdomen or fluid-filled loops may indicate closed-loop obstruction or strangulation

Differential Considerations

  • Dilated central small bowel with air-fluid levels -> mechanical SBO (adhesions, hernia, ascariasis) vs paralytic ileus (generalised gas including colon and rectum)
  • Dilated peripheral colon -> large bowel obstruction (colorectal cancer, volvulus, diverticular stricture) vs pseudo-obstruction (Ogilvie)
  • Coffee-bean sign -> sigmoid volvulus vs closed-loop small bowel obstruction
  • Right-lower-quadrant mass with obstruction in a child -> intussusception vs appendiceal mass vs Burkitt lymphoma (endemic in equatorial Africa)
  • Tubular intraluminal filling defects -> ascaris bolus vs faecal debris vs gallstone ileus
  • Free air -> perforated viscus (peptic ulcer, typhoid ileal perforation, tumour) vs post-operative/post-laparoscopy residual air
  • Generalised distension with no transition -> ileus from sepsis, electrolyte disturbance, or peritonitis

Pearls & Pitfalls

  • Valvulae conniventes cross the full bowel lumen; haustra do not - the key to distinguishing small from large bowel
  • A closed-loop or strangulating obstruction can show a deceptively gasless, fluid-filled abdomen - correlate with severe pain out of proportion
  • Always scrutinise the hernial orifices; a missed obstructed hernia is a common and avoidable error
  • In sigmoid volvulus the apex points to the right upper quadrant and the loop overlies the lower thoracic spine ('northern exposure' when it rises above transverse colon)
  • A competent ileocaecal valve in LBO produces a closed loop with high caecal perforation risk (caecum >9 cm)
  • Erect chest film is more sensitive than erect abdomen for small volumes of free air under the diaphragm
  • Pseudo-free air from Chilaiditi interposition of colon between liver and diaphragm - look for haustra
  • In children, ascaris worms may be seen only after they ingest contrast, appearing as linear lucent/opaque tubes

Structured Report

  • State views obtained (supine, erect/decubitus) and adequacy including diaphragm coverage
  • Describe bowel gas pattern, maximal calibre with measurement, and small vs large bowel involvement
  • Report presence, number and level of air-fluid levels and any transition point
  • Comment specifically on hernial orifices, volvulus signs, intraluminal filling defects and free intraperitoneal air
  • Note visualised solid organs, calcifications and skeleton
  • Impression: presence/absence and probable level and cause of obstruction, evidence of strangulation or perforation, and urgency
  • Recommend next step where relevant (surgical review, CT if available, contrast study, or ultrasound in children)

References

  • ACR Appropriateness Criteria: Suspected Small-Bowel Obstruction
  • WHO Surgical Care at the District Hospital manual
  • Grainger & Allison's Diagnostic Radiology (gastrointestinal imaging chapters)
  • Royal College of Radiologists: iRefer Making the Best Use of Clinical Radiology
  • RadioGraphics: Imaging of Bowel Obstruction reviews

Educational clinical decision support only. Protocols vary by institution and equipment; always confirm with a qualified radiologist and local guidelines before clinical use.