Case cc -  Mesenteric tear and introduction to bowel injury

There is an ill defined area of soft tissue stranding in the root of the mesentery (1, 2, 3) located adjacent to a branch of the SMA. The stranding does not surround abdominal organs.  It is localized to the mesentery. There is no fluid or hemorrhage seen free within the peritoneum. There is no evidence of solid organ injury, free air, or bowel wall thickening.

This subtle finding is the most common manifestation of mesenteric injury.  Tearing of small mesenteric veins or arteries is the most common form of bowel injury and is indication for surgical exploration of the bowel. Localized stranding in the mesentery is the most common sign of bowel injury.

Twenty years ago it was believed that blunt abdominal trauma caused solid organ injury and penetrating injury caused viscous injury.  This is now known to be false.  Bowel injury is common following blunt trauma.  Unfortunately, signs of bowel injury are subtle and uncommon.  The most sensitive sign of bowel injury is free air or extravasation of oral contrast.  However, this is rarely seen for three reasons.  First, we rarely give oral contrast in the acute trauma setting.  Second, free air can be secondary to bladder rupture, deep peritoneal lavage, diaphragmatic injury, barotrauma, or penetrating injury.  Lastly, frank bowel rupture is not common.  More common and specific findings of bowel injury include localized areas of bowel underperfusion, focal areas of bowel wall thickening, stranding localized to a single bowel loop, and wedge shaped areas of peritoneal  fluid interdigitating between loops of bowel.  Bowel wall thickening can be difficult to evaluate on a trauma CT because no oral contrast is present.

Mesenteric shear injuries are more common than direct bowel injury.  Small tears of mesenteric arteries and veins result in hematoma and stranding that is localized to the mesentery.  Loops of bowel downstream from the injury are prone to ischemia and infarction.  In this particular case the trauma surgeons attributed the mesenteric stranding to non-specific hemoperitoneum from a subclinical solid organ injury.  The patient continued to have abdominal pain and was reimaged the following day.  View the second scan.  The hematoma is much larger and contains areas of increased density (at this point you should be able to find it yourself)..  The increased density is similar to a sentinal clot sign.  These findings suggested hematoma originating from the root of the mesentery.  Neither scan demonstrates findings of acute arterial hemorrhage.  Neither scan shows definite evidence of bowel wall thickening.  The following day the patient was taken to the opertating room for continued abdominal pain.  He had a small mesenteric tear and slow oozing from a small branch of the SMA.  A short segment of jejunum was ischemic and surgically removed. 

Did you notice the thin hypoattenuating line in the spleen.  This could be confused for a splenic laceration but it is really just a cleft in the spleen.  It is located very peripherally and there is no surrounding hematoma.

Take home points:

• Focal mesenteric hematomas (1, 2, 3) are specific for mesenteric tears
• Additional signs of bowel injury include:
  • extravasation of enteric contrast
  • pneumoperitoneum
  • underperfusion of a focal segment of bowel
  • stranding surrounding as focal loop of bowel
  • wedged shaped fluid collections in the mesentery which interdigitate between loops of bowel.
• Findings on CT suspicious for bowel injury are indication for surgical exploration, even in the absence of arterial hemorrhage or bowel wall thickening.