Most Commonly Injured Organ in Patients with Seatbelt Sign
The small intestine is the most commonly injured organ in patients with a seatbelt sign. 1
Mechanism and Patterns of Injury
The seatbelt sign is a clinical finding characterized by ecchymosis of the abdominal wall following blunt trauma, typically from a motor vehicle collision. This sign indicates that significant force was transmitted to the abdomen and should prompt high suspicion for internal injuries.
The mechanism of bowel injury in seatbelt syndrome involves:
- Posterior crushing of the bowel segment between the seatbelt and vertebra or pelvis 2
- This can result in:
- Local lacerations of the bowel wall
- Mural and mesenteric hematomas
- Transection of the bowel
- Localized devascularization
- Full-thickness contusions
Evidence for Small Intestinal Injury Predominance
The 2020 study on intestinal injuries in seatbelt syndrome found:
- Significantly more bowel perforations occurred in the small intestine than in the large intestine (p = 0.003) 1
- Significantly more mesenteric injuries occurred in the small intestine than in the large intestine (p < 0.001) 1
- Within the small intestine, the jejunoileal junction was more vulnerable to mesenteric injury than the proximal jejunum (p = 0.015) 1
Distribution of Injuries
Research shows that in patients with seatbelt sign:
- The small intestine is more vulnerable to perforation and mesenteric injury than the large intestine 1
- Two-thirds of all intestinal and mesenteric injuries cluster in three sites: the ileocecal region, the sigmoid colon, and the jejunum 3
- 90% of patients experience two or more intestinal lesions, suggesting simultaneous action of different traumatic mechanisms 3
Clinical Implications
The presence of a seatbelt sign is associated with a significantly increased risk of abdominal injury:
- 64% of patients with a seatbelt sign had abdominal injury compared to only 8.7% without the sign 4
- 36% of patients with seatbelt sign required operative intervention versus 3.8% without the sign 4
- 21% of patients with seatbelt sign had small bowel perforation compared to only 1.9% without the sign 4
Diagnostic Approach
The World Society of Emergency Surgery (WSES) guidelines recommend:
- The presence of a seatbelt sign should prompt a CT scan and a high index of suspicion for bowel injury (GRADE: High) 2
- Patients with seatbelt sign and non-specific CT findings should be admitted for observation including serial clinical examination (GRADE: Moderate) 2
- CT findings highly specific for bowel injury include extraluminal air, extraluminal oral contrast, or bowel-wall defects 2
Pitfalls to Avoid
- Delayed diagnosis: Hollow visceral injury has an insidious presentation, often resulting in delayed diagnoses 2
- Relying solely on initial CT: Approximately 20% of bowel injuries may be missed on initial CT 5
- Dismissing normal initial labs: Serum biomarkers like amylase may be normal initially despite significant injury 2
- Early discharge: Even with a negative CT, patients with seatbelt sign should be observed due to the risk of delayed perforation 6
In conclusion, when evaluating a patient with a seatbelt sign, clinicians should maintain a high index of suspicion for small intestinal injury, which is the most commonly injured organ in this clinical scenario.