Radiological Diagnosis of Small Bowel Obstruction: Ventral Hernia's Mechanical Obstruction, Study notes of Pathophysiology

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72 - year-old female presents with

abdominal pain, N/V. History of

abdominal surgery

John J. DeBevits IV, MD

Mechanical small bowel obstruction in setting of a ventral hernia

Transition point….

Mechanical small bowel obstruction

Obstruction or blockage of ≥1 small bowel (SB) segments by intrinsic or extrinsic narrowing of SB lumen Identifiable causes:

• Adhesions (~60%)
• Hernias (15%)
• Tumor Abdominal radiography first step in imaging
• Diagnostic in 50-60% of cases CT diagnosis of closed loop or strangulated SBO is crucial to guide surgical intervention

Imaging Abdominal radiography High-grade vs. low grade? Dilated SB loops exceeding 50% of largest visible colon loop 2.5 times increase in # of distended loops compared to normal number Presence of >2 air-fluid levels, wider than 2.5cm Air-fluid levels differing >2cm in height from one another within the same SB loop SB-colon diameter ratio >2.

MDCT

Clinical issues

• Closed loop obstruction: SB segments markedly

distended (>4cm) with fluid, little gas

• Whirlpool sign due to twisting mesenteric vessels
• “Balloons on strings”: dilated SB loops “hanging” by

stretched mesenteric vessels

• Strangulating SBO: blood supply is impaired
  • Bowel wall thickening (edema/hemorrhage)
  • Ischemic bowel may show increased, decreased, or

absent bowel wall enhancement

• Interloop edema
• Ascites
• Congested vessels

References http://pubs.rsna.org/doi/full/10.1148/radiol. 5131519 http://pubs.rsna.org/doi/pdf/10.1148/rg. 085514