What is Adhesive Small Bowel Obstruction?
Adhesive small bowel obstruction (ASBO) is a surgical emergency where fibrous tissue bands (adhesions) connecting normally separated peritoneal surfaces mechanically block the small intestine, preventing passage of intestinal contents and presenting with abdominal pain, vomiting, distention, and constipation. 1
Definition and Pathophysiology
Adhesions are fibrous tissue bands that abnormally connect surfaces or organs within the peritoneal cavity that should normally be separated. 1 These bands result from pathological peritoneal healing after injury, rather than normal tissue repair. 1
- The adhesions physically obstruct the small intestine, hindering passage of intestinal contents through mechanical compression or kinking of the bowel. 1
- Adhesions represent the single most common cause of small bowel obstruction overall. 1
Etiology and Risk Factors
Prior abdominal surgery is the primary cause of adhesion formation, with adhesions developing in response to peritoneal injury during the surgical procedure. 1
Other causes of peritoneal injury leading to adhesion formation include: 1
- Radiotherapy
- Endometriosis
- Inflammation
- Local tumor response
The risk of developing at least one episode of small bowel obstruction is highest following colorectal surgery (10% within 3 years), oncologic gynecological surgery, and pediatric abdominal surgery. 1
Clinical Presentation
The classic tetrad of symptoms includes: 1, 2
- Abdominal pain (may be continuous in ischemia)
- Vomiting (typically bilious)
- Abdominal distention
- Constipation (may be absolute in complete obstruction)
Important caveat: Elderly patients may not present with all symptoms, making diagnosis more challenging in this population. 2
Additional concerning signs suggesting bowel compromise include: 3
- Fever
- Tachycardia
- Leukocytosis
- Peritonitis on physical examination
Diagnosis
Definitive confirmation of adhesive etiology is made during operative treatment, but non-invasive methods include history of previous adhesive obstruction episodes or CT scan exclusion of other causes. 1
Non-adhesive causes to exclude include: 1
- Incarcerated hernias
- Obstructing lesions (malignant or benign tumors)
- Bezoars
- Inflammatory bowel disease
- Volvulus
CT scan is the best imaging modality for initial assessment, helping confirm mechanical obstruction, locate the obstruction site, establish the cause, and detect complications. 4
CT findings predicting need for surgery include: 3
- Closed-loop obstruction
- Mesenteric edema
- Free intraperitoneal fluid
- "Small bowel feces sign"
Water-soluble contrast studies serve both diagnostic and therapeutic purposes—if contrast fails to reach the colon within 24 hours on follow-up X-ray, surgery is likely needed. 3, 2
Epidemiology and Recurrence
One in ten patients develops at least one episode of small bowel obstruction within 3 years after colectomy. 1
Recurrence is extremely common and represents a major pitfall in management: 1, 3
- 12% of non-operatively treated patients are readmitted within 1 year (20% at 5 years)
- 8% of operatively treated patients are readmitted within 1 year (16% at 5 years)
- After repeated conservative management, recurrence rates escalate dramatically: 21% after first admission, 41.7% after second, 60% after third, and 100% after fourth admission 5
Complications
ASBO is a surgical emergency because it can lead to bowel ischemia, perforation, and death if not promptly recognized and appropriately managed. 1
Surgical complications during adhesiolysis include: 1
- Seromuscular injury: damage to serosa and muscle layer without entering the bowel lumen
- Enterotomy: full-thickness bowel injury with visible mucosa or leaking intestinal contents
- Delayed diagnosed perforation: unrecognized bowel injuries that cause postoperative deterioration
The risk of iatrogenic bowel injury during laparoscopic adhesiolysis is 6.3-26.9%, which is higher than open surgery. 3