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.

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

📋 Indications

⛔ Contraindications & Cautions

🧑‍⚕️ Patient Preparation

⚙️ Technique & Parameters

🔎 Systematic Review

🩻 Key Findings & Significance

🧠 Differential Considerations

💡 Pearls & Pitfalls

📝 Structured Report

📚 References