Bowel Injury/Perforation

               In a trauma setting, CT detection of peritoneal fluid, in the absence of any visible solid organ injury, suggests bowel injury.About half of these patients have small bowel or diaphragmatic injury, although isolated intraperitoneal fluid can be associated with unsuspected injury from bowel and mesenteric injuries, to solid organ trauma.
               Complicating the issue is that some patients with subsequently detected major bowel injury have no hemoperitoneum on admission CT and US, but bowel and mesenteric injury is detected only hours later; even then, bowel and mesenteric injury can be difficult to diagnose. Currently such injury is probably best studied with CT. Both IV and oral contrast are helpful. A prospective CT study achieved a sensitivity of only 64% but a specificity of 97% in detecting bowel injury in patients with blunt abdominal trauma; findings used to detect bowel injury included mesenteric infiltration, bowel wall thickening, extravasation either of vascular or enteric contrast, and the presence of pneumoperitoneum.
                Bowel wall thickening, in particular, is difficult to put in proper perspective as a finding of major bowel injury. If associated with a mesenteric hematoma, sufficiently severe mesenteric or bowel injury is generally presumed to warrant considering surgery. On the other hand, a focal mesenteric hematoma without adjacent bowel wall thickening occurs both in those patients requiring surgery and those who do not. Computed tomography has a high specificity in detecting a mesenteric hematoma. Nevertheless, the true accuracy of CT in establishing major bowel or mesenteric injury is difficult to judge, and published conclusions vary.
               With a perforation, imaging rarely identifies bowel wall discontinuity. Intraperitoneal spill of oral or rectal contrast identified by CT is usually assumed to represent a bowel perforation, but although diagnostic, it is rarely detected. Spill of instilled contrast from a urinary tract perforation is in the differential diagnosis. In pediatrics the role of CT in detecting bowel perforation appears even more limited than in adults, and CT identifies small bowel injury only in a minority. Clinicians should be aware of this CT limitation and not be lulled into a false sense of security, leading to a delay in surgery.
                Mesenteric stranding, often in association with adjacent blood, suggests mesenteric injury, although laceration of an adjacent loop of bowel results in similar findings. With rare exceptions, the presence of extraluminal gas (either pneumoperitoneum or extraperitoneal gas) is diagnostic of bowel perforation. Extraluminal gas is readily detected with both conventional radiography and CT.
               The inability to reliably and consistently detect a pneumoperitoneum is a limitation of US. The small bowel normally contains little gas, and a number of bowel perforations manifest later as an intraabdominal abscess rather than as an immediate pneumoperitoneum. Colonic perforation, on the other hand, commonly results in a pneumoperitoneum,which is readily detected. Other indirect signs for perforation include intraperitoneal fluid, bowel wall thickening, bowel wall contrast enhancement, and bowel lumen dilation.None of the latter signs is specific for a perforation.
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