What is the epidemiology of Small Bowel Obstruction (SBO) in adult populations, particularly those with a history of abdominal surgery?

Epidemiology of Small Bowel Obstruction

Small bowel obstruction accounts for nearly 50% of all emergency laparotomies and represents a common surgical emergency with significant morbidity and healthcare costs. 1

Incidence and Population Characteristics

• Most SBO patients (approximately 80%) have a history of prior abdominal surgery, making adhesions the predominant etiology in this population 1
• SBO in virgin abdomen (SBO-VA) accounts for only 5-16% of all SBO cases based on cohort studies screening 600-850 patients 1
• The median age at diagnosis ranges from 58 to 65 years, with a notable male predominance (65-83% of cases) 1
• Population-based studies remain lacking, with most available data coming from single-center retrospective cohorts 1

Etiologic Distribution

In Patients with Prior Abdominal Surgery

• Adhesions cause 55-75% of all SBO cases in patients with surgical history 1, 2, 3
• Having prior abdominal surgery demonstrates 85% sensitivity and 78% specificity for predicting adhesive SBO 2, 3
• Matted adhesions predominate (67%) over band adhesions in this population 2
• Hernias account for 15-25% of cases 2, 3
• Malignancies cause 5-10% of obstructions 2, 3

In Virgin Abdomen (No Prior Surgery)

• Adhesions still cause 26-100% of SBO-VA cases (pooled data shows 47.9% or 134/280 cases) 1, 2
• Notably, band adhesions are more common (65%) than matted adhesions (35%) in virgin abdomen—the opposite pattern from post-surgical patients 1, 2
• Malignancy accounts for 4-41% of SBO-VA cases (most studies report 4-13%), representing a higher proportion than in post-surgical SBO 1, 2
• Other causes include hernias (10%), Meckel's diverticulum, gallstone ileus, bezoars, internal hernias, intussusception, and volvulus 1, 2

Surgical Management Patterns

• Between 39-83% of SBO-VA patients undergo operative treatment, which is notably higher than contemporary rates for post-surgical SBO 1
• This high operative rate likely reflects historical bias toward surgical exploration when no prior surgical history exists to explain the obstruction 1
• Negative laparotomies occur in 6-40% of SBO-VA cases, where no definitive cause is identified at surgery 1

Clinical Outcomes and Recurrence

• Early postoperative morbidity reaches 48% in surgical SBO cases, with 10% requiring reoperation 4
• Early mortality is 5.2%, strongly correlated with advanced age and ASA class 4
• At median 66-month follow-up, 18% of patients experience recurrent SBO requiring readmission, with 26 of these requiring reoperation 4
• Risk factors for recurrence include multiple previous laparotomies, diffuse adhesions, and difficult index surgery (bowel injury, prolonged operative time, significant bleeding) 4
• Despite these recurrence rates, 81% of surviving patients have no SBO readmissions over 5 years following index admission 5

Important Clinical Caveats

The traditional teaching that malignancy is the primary cause of SBO-VA is outdated. Modern data shows adhesions remain the most common etiology even in virgin abdomen, likely due to improved cancer screening detecting malignancies before they present as obstruction 1. However, malignancy still accounts for approximately 1 in 10 cases of SBO-VA, mandating thorough evaluation with high-quality CT imaging 1, 2.

The high operative rate in SBO-VA (39-83%) may expose patients to unnecessary laparotomies, as non-operative management succeeds in most cases when attempted 1. Modern guidelines suggest treating SBO-VA similarly to adhesive SBO in post-surgical patients, with initial conservative trial unless signs of ischemia, strangulation, or peritonitis are present 1.