What is the most common cause of gut obstruction?

Most Common Cause of Gut Obstruction

Adhesions are the single most common cause of small bowel obstruction, accounting for 55-75% of all cases in the general population. 1, 2

Primary Etiologic Distribution

The hierarchy of causes follows a clear pattern:

• Adhesions: 55-75% of all small bowel obstructions 1, 2
• Hernias (incarcerated inguinal, femoral, umbilical, incisional): 15-25% of cases 2
• Malignancy (primary tumors or metastatic disease): 5-10% of cases 2
• Other causes (intussusception, volvulus, gallstone ileus, bezoars, inflammatory bowel disease): Less common 1, 2

Context-Dependent Variations

In Patients with Prior Abdominal Surgery

Adhesions become even more dominant, causing 60-70% of small bowel obstructions in patients with previous laparotomy. 3 The World Society of Emergency Surgery confirms that having a history of previous abdominal surgery has 85% sensitivity and 78% specificity for predicting adhesive small bowel obstruction. 2

The type of adhesion differs based on surgical history:

• Matted adhesions predominate (67%) in patients with previous surgery 2
• Band adhesions are less common (33%) in this population 2

High-risk surgical procedures include colorectal surgery, oncologic gynecological procedures, appendectomy, and rectal operations. 3

In Virgin Abdomen (No Prior Surgery)

Even without previous abdominal surgery, adhesions still account for 26-100% of small bowel obstructions (most studies show approximately 48%). 2 This is a critical clinical pearl often overlooked.

In virgin abdomen patients:

• Band adhesions are more common (65%) than matted adhesions (35%) 2
• Malignancy becomes relatively more prevalent (4-41% of cases) compared to post-surgical patients 2
• Hernias become a more prominent consideration 2

Special Population: Post-Bariatric Surgery

After Roux-en-Y gastric bypass (RYGB), the etiology shifts dramatically:

• Internal hernia: 53.9% of late small bowel obstructions 1
• Roux limb compression through mesocolic window: 20.5% 1
• Adhesions: Only 13.7% in this specific population 1

Clinical Implications

Diagnostic Approach

CT scan with IV contrast is the most accurate imaging modality, with 76% accuracy for determining the specific etiology compared to operative findings. 2 Look for:

• Transition point between dilated and normal caliber bowel 1
• Closed-loop obstruction suggesting strangulation risk 2
• Signs of ischemia requiring urgent surgery 2

Common Pitfall

Do not assume all obstructions in virgin abdomen are malignant. Adhesions remain the most common cause even without prior surgery, though malignancy must be excluded. 2 Negative laparotomies occur in 6-40% of virgin abdomen cases, which is frustrating but well-documented. 2

Timing Considerations

Adhesive obstruction can occur at any time after peritoneal injury:

• 50% occur within the first postoperative month 3
• 1% develop within the first year after surgery 3
• 20% appear more than 10 years after the initial operation 3

Mortality Risk

The stakes are high: mortality escalates from 3% for simple adhesive obstruction to 30% when bowel becomes necrotic or perforated. 3 Hernias carry a significantly higher risk of strangulation than adhesions or malignancy. 4