What is the appropriate grading and treatment approach for a small bowel injury in an adult patient with no significant past medical history?

Small Bowel Injury Grading and Treatment

Use the McNutt CT-based mesenteric injury grading system (Grades 1-5) combined with the AAST Organ Injury Scale to stratify small bowel injuries, with Grade 5 findings (active extravasation, bowel wall transection, or pneumoperitoneum) mandating immediate surgical exploration. 1

Grading Systems for Small Bowel Injury

McNutt CT Grading System (Mesenteric Injury)

The most clinically useful grading system combines CT findings with injury severity: 1

• Grade 1: Isolated mesenteric contusion 1
• Grade 2: Mesenteric hematoma < 5 cm 1
• Grade 3: Mesenteric hematoma > 5 cm 1
• Grade 4: Mesenteric contusion or hematoma (any size) with bowel wall thickening and adjacent interloop fluid collection 1
• Grade 5: Active vascular or oral contrast extravasation, bowel wall transection, or pneumoperitoneum 1

CT Findings and Their Diagnostic Performance

When evaluating CT scans, prioritize highly specific findings over sensitive ones: 1

Highly Specific Signs (99-100% specificity):

• Bowel wall hematoma (100% specificity, 23% sensitivity) 1
• Oral contrast extravasation (100% specificity, 10% sensitivity) 1
• Intravenous contrast extravasation in mesentery (100% specificity, 23% sensitivity) 1
• Free intraperitoneal air (99% specificity, 32% sensitivity) 1
• Bowel wall discontinuity (99% specificity, 22% sensitivity) 1

Sensitive but Less Specific Signs:

• Free peritoneal fluid (66% sensitivity, 85% specificity) 1
• Bowel wall thickening (35% sensitivity, 95% specificity) 1
• Mesenteric stranding (34% sensitivity, 92% specificity) 1

Treatment Algorithm Based on Grading

Immediate Surgical Exploration (Grade 5 or High-Specificity CT Findings)

Proceed directly to laparotomy without delay if any of the following are present: 1

• Extraluminal air 1
• Extraluminal oral contrast 1
• Bowel wall defects 1
• Active contrast extravasation 1
• Hemodynamic instability with suspected intra-abdominal injury 2

Observation with Serial Examination (Grades 1-4 or Equivocal Findings)

For patients with non-specific CT findings or high-risk mechanisms (seatbelt sign, handlebar injury): 1

• Admit for minimum 48 hours of observation 1
• Serial clinical examinations by experienced clinicians every 3-6 hours 1, 3
• Monitor vital signs continuously 1
• Serial inflammatory markers (CRP, procalcitonin) 1
• Repeat CT scan at 6 hours if clinical signs evolve or initial CT equivocal 1

Critical pitfall: Approximately 20% of bowel injuries are missed on initial CT, making serial examination mandatory. 4

Scoring Systems for Surgical Decision-Making

Faget's scoring system provides quantitative risk stratification: 1

• Small hemoperitoneum: 1 point 1
• Pneumoperitoneum: 5 points 1
• Score ≥5 indicates 11-fold increased risk of bowel injury requiring surgery (AUC 0.98) 1

Bonomi criteria (4 or more findings are pathognomonic for surgical bowel injury): 1

• Free air 1
• Free fluid without solid organ injury 1
• Intra-mesenteric fluid 1
• Contrast extravasation 1
• Bowel wall abnormality 1
• Mesenteric alteration 1

Time-Critical Considerations

Mortality increases significantly with delayed diagnosis: 1

• <8 hours to surgery: 2% mortality 1
• 8-16 hours: 9% mortality 1
• 16-24 hours: 17% mortality 1

• 24 hours: 31% mortality 1

Delays beyond 5-8 hours are associated with increased sepsis and serious complications. 1

Surgical Management Principles

Repair vs. Resection

The decision depends on injury extent and patient physiology: 1

• Primary repair for isolated perforations in stable patients 5
• Resection with anastomosis for multiple perforations or devitalized bowel 5
• Both handsewn and stapled anastomoses have equivalent outcomes (no superiority demonstrated) 1
• Surgeon experience and patient condition should guide technique choice 1

Special Populations

Penetrating Trauma:

• Nonoperative management possible only in highly selected stable patients at specialized centers 1
• Requires 48 hours minimum observation with serial exams 1
• Any hemoglobin drop >2 g/dL or worsening vital signs mandates exploration 1

Obtunded/Unreliable Exam:

• Diagnosis relies on injury pattern, vital signs trends, and inflammatory markers 1
• Lower threshold for repeat CT imaging 1
• Consider diagnostic peritoneal lavage if CT equivocal 6

Common Pitfalls to Avoid

• Never discharge a patient based solely on negative CT - 20% of injuries are missed initially 4
• Do not rely on serum amylase - abnormal in only 2 of 18 cases in one series 7
• Seatbelt sign mandates CT and high suspicion even with normal initial imaging 1
• Failed enteral feeding is a red flag - 15% of ICU patients who fail feeding have GI injury 1
• Physical examination is 100% sensitive in conscious patients - serial exams are superior to isolated diagnostic tests 7