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Small bowel obstruction
AbdomenCT
Dilated small bowel (>3 cm) with a transition point and collapsed distal loops. The task is to find the cause at the transition and exclude ischaemia.
Differential
Adhesions
common- •Abrupt transition with NO mass or wall thickening
- •Prior surgery; most common cause
Hernia
common- •Bowel loop within a hernia sac at the transition
- •Inguinal/femoral/incisional/internal location
Neoplasm
less-common- •Focal wall thickening or a mass at the transition
- •Metastatic serosal deposits; primary adenocarcinoma
Crohn disease stricture
less-common- •Mural thickening with enhancement, comb sign
- •Terminal ileal disease, fistulae, prior known Crohn
Gallstone ileus
rare- •Ectopic gallstone at the transition (Rigler triad)
- •Pneumobilia and cholecystoduodenal fistula
Closed-loop / volvulus
rare- •C-/U-shaped loop with radial mesentery and whirl sign
- •Two adjacent transition points; high ischaemia risk
Key discriminators
- •Presence and nature of a mass at the transition point
- •Hernia sac containing bowel
- •Closed-loop configuration and whirl sign
- •Signs of ischaemia (reduced/absent wall enhancement, pneumatosis, mesenteric oedema)
- •Surgical history (adhesions)
Work-up / next steps
- 1.Contrast-enhanced CT to localise transition and assess viability
- 2.Assess for closed-loop and strangulation urgently
- 3.Nasogastric decompression; surgical review for ischaemia/closed loop
- 4.Conservative trial for uncomplicated adhesive obstruction
References
- Radiopaedia: Small bowel obstruction.
- Silva AC et al. Small bowel obstruction: CT. RadioGraphics.
Educational clinical decision support only. This differential does not make a diagnosis, is not a medical device, and must never substitute for interpretation by a qualified radiologist correlated with the full clinical picture and prior imaging.