What is the most common cause of large bowel obstruction?

The Most Common Cause of Large Bowel Obstruction

Colorectal cancer is the most common cause of large bowel obstruction, accounting for approximately 60% of all cases. 1

Etiology of Large Bowel Obstruction

Large bowel obstruction can be caused by various conditions, with the following distribution:

• Colorectal cancer (60% of cases) - Most common etiology of large bowel obstruction in adults 1, 2
• Volvulus (15-20% of cases) - Second most common cause, particularly sigmoid volvulus 1, 3
• Diverticular disease (10% of cases) - Third most common cause, usually due to stricture formation following repeated episodes of diverticulitis 1, 3, 4
• Other causes (10-15% of cases) - Including carcinomatosis, endometriosis, inflammatory bowel disease stenosis, ischemic strictures, radiation stenosis, and post-anastomotic stenosis 1, 5

Pathophysiology and Clinical Significance

• The sigmoid colon is the most common site for malignant large bowel obstruction, with approximately 75% of obstructing colorectal cancers occurring distal to the splenic flexure 1
• Approximately 20% of patients diagnosed with colorectal cancer will present with left-sided large bowel obstruction as their initial presentation 1
• Large bowel obstruction represents almost 80% of emergencies related to colorectal cancer 1
• Changes in colonic motility and increased blood flow may play a role in the dissemination of tumor cells and bacteria 3

Diagnostic Approach

• CT scan is the most accurate diagnostic tool with approximately 90% accuracy for identifying the site, severity, and etiology of large bowel obstruction 6, 7
• Key CT findings in malignant large bowel obstruction include:
  • Colonic wall thickening
  • Abrupt transition point
  • Presence of local lymph nodes
  • Proximal bowel dilation 7
• Plain abdominal radiographs have limited diagnostic value (sensitivity 50-60%) but may show dilated large bowel with air-fluid levels 6, 3
• Water-soluble contrast studies are important in distinguishing mechanical obstruction from pseudo-obstruction 3

Management Considerations

• For obstructing right-sided colon cancers, primary resection and ileocolic anastomosis is generally the treatment of choice 1
• For left-sided malignant large bowel obstruction, management options include:
  • Primary resection with or without anastomosis
  • Subtotal colectomy with or without anastomosis
  • Defunctioning stoma with interval resection
  • Self-expanding colonic stents as a bridge to surgery 1
• Self-expanding colonic stents have been successfully used as a non-invasive technique to relieve left-sided malignant bowel obstruction, allowing surgical resection to be performed electively rather than emergently 1
• Emergency surgery for large bowel obstruction is associated with high morbidity and mortality rates, almost three times that of elective resections 1, 2

Differential Diagnosis Pitfalls

• Colonic pseudo-obstruction can mimic mechanical large bowel obstruction and must be distinguished as it typically does not require surgical intervention 1, 7, 3
• Other conditions that can mimic malignant large bowel obstruction include:
  • Diverticulitis with stricture formation
  • Ischemic colitis
  • Inflammatory bowel disease
  • Endometriosis 7, 8
• Careful evaluation of the patient's history, imaging findings, and clinical presentation is essential for accurate diagnosis 6, 3