Can constipation cause Small Bowel Obstruction (SBO)?

Can Constipation Cause Small Bowel Obstruction (SBO)?

No, constipation itself does not directly cause small bowel obstruction, as constipation primarily affects the colon while SBO occurs in the small intestine. 1 Small bowel obstruction is a mechanical blockage that prevents the passage of intestinal contents through the small intestine, whereas constipation is typically a large bowel (colonic) issue.

Etiology of Small Bowel Obstruction

The most common causes of SBO include:

1. Adhesions (26-100% of cases in virgin abdomen):

   • Adhesions are the leading cause of SBO, even in patients without prior surgery 1
   • In patients with virgin abdomen (no prior surgery), adhesions account for approximately 48% of SBO cases 1
   • These may be congenital adhesions that form during embryonic development 1

2. Malignancy (4-41% of cases):

   • Primary small bowel tumors (NETs, lymphoma, carcinomas)
   • Metastatic disease (commonly from colon, ovary, or prostate) 1

3. Other less common causes:

   • Bezoars
   • Small bowel volvulus
   • Intussusception
   • Meckel's diverticulum
   • Gallstone ileus
   • Internal hernias
   • Inflammatory bowel disease 1
   • Uterine fibroids (rare) 2
   • Endometriosis (rare) 3
   • Epiploic appendagitis (rare) 4
   • Congenital bands 5

Clinical Presentation of SBO

SBO typically presents with:

• Abdominal pain
• Vomiting
• Abdominal distension
• Constipation 1, 6

While constipation is a symptom of SBO, it's important to note that it's a result of the obstruction, not the cause. The mechanical blockage in the small intestine prevents the passage of intestinal contents, which secondarily leads to constipation.

Diagnostic Approach

CT imaging is the diagnostic method of choice with >90% accuracy for SBO, allowing visualization of:

• Colonic dilation without a transition point in pseudo-obstruction
• Identifiable transition point in mechanical obstruction
• Potential causes of obstruction 7

CT findings suggestive of mechanical SBO include:

• An identifiable transition point
• Visible obstructive cause
• "Small bowel feces sign" 7

Management Considerations

Management depends on whether the obstruction is:

1. Complete vs. partial
2. Complicated vs. simple 6

Complete and complicated SBOs more commonly require surgical intervention, while partial, simple obstructions may be managed conservatively.

Important Clinical Pitfalls

1. Misdiagnosis: Confusing SBO with constipation can lead to delayed appropriate treatment
2. Delayed diagnosis: Can lead to bowel ischemia and perforation with mortality rates up to 40% 7
3. Absence of surgical history: Many clinicians incorrectly rule out adhesions when there's no history of abdominal surgery, but congenital adhesions can cause SBO in virgin abdomens 1, 5
4. Normal laboratory values: Do not exclude the possibility of bowel ischemia 7

In summary, while constipation is a symptom of SBO, it is not a cause of it. The relationship is unidirectional - SBO can cause constipation, but constipation does not cause SBO. When evaluating a patient with constipation, other clinical features such as abdominal distension, vomiting, and abdominal pain should prompt consideration of SBO as a diagnosis.