Causes of Intestinal Obstruction
Adhesions are the leading cause of small bowel obstruction (55-75% of cases), while colorectal cancer is the most common cause of large bowel obstruction (60% of cases). 1, 2
Small Bowel Obstruction Causes
Mechanical Causes (in order of frequency)
Adhesions account for 55-75% of all small bowel obstructions, with post-surgical adhesions being the predominant type—a history of prior abdominal surgery has 85% sensitivity and 78% specificity for predicting adhesive obstruction. 1, 2
Hernias cause 15-25% of small bowel obstructions, including inguinal, femoral, umbilical, and incisional hernias. 1, 2
Malignancies represent 5-10% of cases, including both primary small bowel tumors and metastatic disease. 1, 2
Other mechanical causes (15% collectively) include: 1, 2
- Carcinomatosis peritonei
- Endometriosis (particularly in women of reproductive age)
- Inflammatory bowel disease stenosis (especially Crohn's disease)
- Intussusception
- Volvulus
- Ischemic stenosis
- Radiation-induced strictures
- Post-anastomotic stenosis
- Gallstones (gallstone ileus)
- Foreign bodies and bezoars
Post-Bariatric Surgery Specific Causes
After Roux-en-Y gastric bypass (RYGB), the most common causes of small bowel obstruction differ from the general population and include: 1
- Internal hernia (through Petersen's space, jejuno-jejunostomy mesenteric defect, or transverse mesocolon)
- Adhesions
- Incisional/trocar site hernias
- Intussusception
- Volvulus
- Obstruction at the jejuno-jejunostomy
- Twisted alimentary limb
- Alimentary limb mesenteric ischemia
Large Bowel Obstruction Causes
Mechanical Causes (in order of frequency)
Colorectal cancer is responsible for approximately 60% of large bowel obstructions and requires urgent evaluation to exclude malignancy. 1, 2
Volvulus accounts for 15-20% of cases, with sigmoid volvulus being the most common type—chronic constipation history (dolichosigmoid) may suggest this diagnosis. 1, 2
Diverticular disease causes approximately 10% of large bowel obstructions, with previous diverticulitis episodes suggesting diverticular stenosis. 1, 2
Other causes (10% collectively) include: 1, 2
- Inflammatory bowel disease stenosis
- Ischemic strictures
- Radiation-induced fibrosis (particularly in sigmoid colon after pelvic radiation)
- Post-anastomotic strictures
Functional (Non-Mechanical) Obstruction
Adynamic ileus and pseudo-obstruction result from lack of enteric propulsion rather than mechanical blockage and must be distinguished from true mechanical obstruction. 2
Common Causes of Functional Obstruction
Opioid-induced bowel dysfunction is increasingly prevalent and can cause both acute ileus and chronic pseudo-obstruction (narcotic bowel syndrome). 1, 2
Postoperative state and trauma commonly cause temporary ileus. 2
Metabolic disturbances, including electrolyte abnormalities (particularly hypokalemia), can impair intestinal motility. 2, 3
Medications affecting peristalsis beyond opioids include anticholinergics (like cyclizine), which should be avoided for long-term use. 1, 2
Chemotherapy agents including bevacizumab (causes ulceration/perforation in 0.9% within 1 year) and tyrosine kinase inhibitors are associated with bowel complications. 2
Critical Diagnostic Distinctions
Each hernia orifice (umbilical, inguinal, femoral) and all laparotomy/laparoscopy incision scars must be carefully examined, as incarcerated hernias have a 33.3% strangulation rate compared to 9% for adhesions. 1, 4
Strangulation shows positive correlation with: 4
- Age greater than 70 years
- Feculent vomiting
- Abnormal peristaltic sounds
- White blood cell count higher than 18,000/mm³
Key clinical clues to differentiate causes: 1
- Sudden onset distension suggests volvulus
- Progressive distension suggests colorectal cancer
- Rectal bleeding and unexplained weight loss suggest malignancy
- Intermittent colicky pain with resolution followed by diarrhea suggests partial adhesive obstruction