What are the causes of bowel obstruction?

Causes of Bowel Obstruction

Adhesions, hernias, and malignancies account for approximately 90% of small bowel obstructions, while colorectal cancer, volvulus, and diverticular disease cause the vast majority of large bowel obstructions. 1

Small Bowel Obstruction Causes

Most Common Etiologies

• Adhesions are the single most common cause of small bowel obstruction, representing 55-75% of all cases 1

  • Post-surgical adhesions are the predominant type, with previous appendectomy being particularly important 2
  • A history of prior abdominal surgery has 85% sensitivity and 78% specificity for predicting adhesive small bowel obstruction 1

• Hernias account for 15-25% of small bowel obstructions 1

  • Incarcerated hernias carry a significantly higher risk of strangulation compared to other causes 3
  • Hernias are responsible for 57.2% of bowel ischemia cases, 42.8% of necrosis cases, and 50% of perforation cases 3

• Malignancies cause 5-10% of small bowel obstructions 1

  • Both primary small bowel tumors and metastatic disease can be responsible 1

Less Common Small Bowel Causes

• Carcinomatosis peritoneal represents a less frequent but important cause 1, 4
• Endometriosis can cause small bowel obstruction, particularly in women of reproductive age 1, 4
• Inflammatory bowel disease stenosis, particularly Crohn's disease, causes obstruction through stricture formation 1, 4
• Intussusception, ischemic stenosis, radiation stenosis, and post-anastomotic stenosis collectively account for remaining cases 1
• Bezoars, gallstones, and foreign bodies are rare mechanical causes 1

Large Bowel Obstruction Causes

Most Common Etiologies

• Colorectal cancer is the leading cause of large bowel obstruction, responsible for approximately 60% of cases 1, 4

  • This represents a critical diagnosis requiring urgent evaluation to exclude malignancy 1

• Volvulus accounts for 15-20% of large bowel obstructions 1, 4

  • Sigmoid volvulus is the most common type 4, 3
  • Chronic constipation history (dolichosigmoid) may suggest volvulus 1

• Diverticular disease causes approximately 10% of large bowel obstructions 1, 4

  • Previous diverticulitis episodes may suggest diverticular stenosis 1

Less Common Large Bowel Causes

• Inflammatory bowel disease can cause colonic stenosis and obstruction 1, 4
• Megacolon from Hirschsprung's disease or Chagas disease 4

Functional (Non-Mechanical) Obstruction

Adynamic Ileus and Pseudo-Obstruction

These conditions are caused by lack of enteric propulsion rather than mechanical blockage and must be distinguished from true mechanical obstruction 1, 5

• Drugs that affect peristalsis, particularly opioids 1, 4
• Trauma and the postoperative period 1, 4
• Metabolic disturbances including electrolyte abnormalities 1, 4
• Sepsis 4
• Endocrine disorders 4
• Neuropathy or myopathy of the intestine in chronic intestinal pseudo-obstruction 4
• Connective tissue diseases and neurological disorders 4

Cancer Treatment-Related Causes

Chemotherapy and Radiation Complications

• Bevacizumab (anti-VEGF monoclonal antibody) causes ulceration, fistulation, or perforation in 0.9% of patients within 1 year 1
• Tyrosine kinase inhibitors (erlotinib, gefitinib) are associated with bowel perforation 1
• Radiotherapy-induced fibrosis can cause chronic strictures, particularly in the sigmoid colon after pelvic radiation 1
• Adhesions from previous cancer surgery 1
• Mesenteric ischemia from chemotherapy-associated hypercoagulable states 1

Critical Clinical Pitfalls

Never assume all obstructions with prior surgery are adhesive—always exclude hernias, malignancy, and other causes with appropriate imaging 1. History of rectal bleeding and unexplained weight loss are suggestive of colorectal cancer and require urgent evaluation 1. In patients with incarcerated hernias, maintain high suspicion for strangulation as this carries the highest risk of bowel ischemia, necrosis, and perforation compared to all other causes 3.