What are the common causes of bowel obstruction?

Common Causes of Bowel Obstruction

The most common causes of bowel obstruction are adhesions (55-75% of small bowel obstructions), hernias (15-25% of small bowel obstructions), and malignancies (60% of large bowel obstructions). 1

Small Bowel Obstruction Causes

Small bowel obstruction (SBO) accounts for approximately 15% of hospital admissions for acute abdominal pain in the USA. The primary causes include:

1. Adhesions (55-75%) 1

   • Most common cause of SBO
   • Typically post-surgical adhesions
   • Even in patients with no prior abdominal surgery (virgin abdomen), adhesions can still be the leading cause (26-100% of cases) 1
   • May present as solitary band adhesions or more extensive matted adhesions 1

2. Hernias (15-25%) 1

   • Second most common cause
   • Include inguinal, femoral, umbilical, and internal hernias
   • Carry a significantly higher risk of strangulation compared to other causes 2
   • Require careful examination of all hernia orifices during physical examination

3. Malignancies (5-10%) 1

   • Primary small bowel tumors (NETs, lymphoma, carcinomas)
   • Metastatic disease (commonly from colon, ovary, or prostate)
   • In virgin abdomen cases, malignancy accounts for 4-13% of SBO 1

4. Other causes (15%) 1

   • Intussusception
   • Small bowel volvulus
   • Gallstone ileus
   • Meckel's diverticulum
   • Foreign bodies/bezoars
   • Inflammatory bowel disease strictures
   • Radiation-induced strictures

Large Bowel Obstruction Causes

Large bowel obstruction (LBO) has a different etiological profile:

1. Cancer (60%) 1

   • Most common cause of LBO
   • Typically colorectal adenocarcinoma

2. Volvulus (15-20%) 1

   • Sigmoid volvulus most common
   • Cecal volvulus less common
   • Often associated with chronic constipation and dolichocolon

3. Diverticular disease (10%) 1

   • Strictures from recurrent diverticulitis

4. Other causes (10%) 1

   • Fecal impaction
   • Inflammatory bowel disease
   • Radiation strictures
   • Ischemic strictures
   • Endometriosis

Clinical Presentation and Diagnosis

Key clinical features that suggest bowel obstruction include:

• Abdominal distension (highest predictive value with positive likelihood ratio of 16.8) 1
• Colicky abdominal pain
• Nausea and vomiting (earlier and more prominent in SBO)
• Absence of flatus or bowel movements
• Visible peristalsis

CT abdomen and pelvis with IV contrast is the preferred initial imaging modality for suspected bowel obstruction, with diagnostic accuracy >90% 3.

Risk Factors for Complications

Certain causes of bowel obstruction carry higher risks of complications:

• Hernias have the highest risk of strangulation (57.2% of bowel ischemia cases) 2
• Large bowel cancer (19.1% of ischemia cases) 2
• Advanced age increases risk of complications and mortality 3
• Signs of peritonitis, fever, or elevated WBC may indicate strangulation or perforation 3

Management Considerations

Management depends on the cause and severity:

• Conservative management is appropriate for partial obstruction without signs of complications
• Surgical intervention is necessary for complete obstruction, strangulation, or perforation
• Early surgical consultation is recommended for all patients with intestinal obstruction 3

Pitfalls to Avoid

1. Missing strangulation: Bowel ischemia occurs in approximately 14% of cases, necrosis in 9.3%, and perforation in 5.3% of bowel obstructions 2

2. Overlooking less common causes: While adhesions are most common, always consider other etiologies, especially in patients without prior surgery

3. Delayed surgical consultation: Early surgical evaluation is crucial even when planning conservative management initially

4. Inadequate imaging: Plain radiographs have limited sensitivity (60-70%); CT with IV contrast is preferred 3

5. Failing to examine all hernia sites: Careful examination of all potential hernia orifices is essential, as hernias carry the highest risk of strangulation 2