Discussion: - Detection of bowel and mesenteric injury can be challenging in patients after blunt abdominal trauma. Early diagnosis and treatment are critical to decrease patient morbidity and mortality. Computed tomography (CT) has become the primary modality for the imaging of these patients. Signs of bowel perforation such as free air and contrast material are virtually pathognomonic. Bowel-wall thickening, free fluid, and mesenteric infiltration may be seen with this type of injury and partial thickness injuries.
- Hemoperitoneum detected with diagnostic peritoneal lavage or ultrasonography is no longer an unequivocal indication for exploratory laparotomy in a stable patient. More emphasis is now placed on nonsurgical management of liver and spleen injuries . The concurrent presence of significant bowel or mesenteric injury, however, would make conservative treatment inappropriate and necessitate exploratory laparotomy. Therefore, greater sensitivity and specificity of imaging studies are demanded for these types of injury.
CT Findings of Bowel or Mesenteric Injury:
Bowel Discontinuity
Discontinuity of bowel is the primary finding of bowel injury,direct visualization is unusual, one must generally rely on secondary findings.
Extraluminal Oral Contrast Material
Free intraperitoneal oral contrast material is 100% specific for bowel perforation . if concentrated intravenous contrast material from genitourinary tract perforation is not a confounding factor.
Extraluminal Air
The finding of pneumoperitoneum has a sensitivity of 44%—55%,Extraluminal intra- or retroperitoneal air is not diagnostic of bowel perforation. Although bowel perforation is a major source of this finding, barotrauma and mechanical ventilation can result in air below the diaphragm. Air introduced during CT cystography may escape through a bladder laceration . Whenever free air is detected, other secondary indications of bowel injury should be sought to determine its significance.
Intramural Air
Major bowel injuries (those requiring laparotomy, such as perforations) and minor bowel injuries (which can be treated conservatively, such as serosal abrasions) have findings of bowel-wall thickening and free fluid in common. CT does not appear to be able to readily help distinguish the two in all instances . Along with extraluminal air, the presence of intramural air will highlight a probable full-thickness rather than partial-thickness injury.
Bowel-Wall Thickening
Bowel-wall thickening, seen in 75% of transmural injuries, is more sensitive for bowel-wall injury than is extravasation of oral contrast material or pneumoperitoneum . Isolated mesenteric lacerations may also demonstrate this sign, probably as a result of interruption of the arterial supply or venous drainage. Unfortunately, this finding can often be very subjective. Some authors say wall thickness greater than 3 or 4 mm is abnormal in an attempt to better quantify this abnormality. Only a few articles in the trauma literature take into account the degree of luminal distention . We use a combination of observations by Kunin et al and Strouse et al : Disproportionate thickening compared with normal segments or bowel-wall thickness greater than 3 mm with adequate bowel distention is abnormal. In an attempt to reduce the number of false-positive findings, we also require circumferential involvement. Normal bowel with small amounts of air distention can have wall thickening in a dependent position but a normal thin wall outlined by air on the inner mucosal surface in the nondependent position.
Bowel-Wall Enhancement
Taylor et al initially described bowel-wall enhancement without perforation as part of the hypoperfusion complex (shock bowel) in children. Results of subsequent studies have shown that bowel-wall enhancement can also occur in a high percentage of children with perforation but no evidence of the hypoperfusion complex . An adult form of the complex with a lower frequency of bowel-wall enhancement has been reported . These patients also had diffuse thickening of the wall of the small bowel and fluid distention, but unlike the series of children, some had bowel perforation along with signs of hypoperfusion. The proposed cause of enhancement of reduced perfusion and interstitial leak of contrast material fits into the categories of either local vascular damage related to bowel or mesenteric injury or the more systemic hypoperfusion complex.
The definition of bowel-wall enhancement is not uniform. Empiric assessment , enhancement greater than that of the psoas muscle , or enhancement equal to that of adjacent blood vessels have all been used. None of our cases showed full-thickness wall enhancement equal to that of adjacent vessels, but three cases demonstrated mucosal enhancement . These cases involved limited segments, and one was in the region of perforation and the other two were not. It is unclear how the normal high levels of contrast enhancement achieved with spiral CT scanners will affect the specificity of this sign.
Mesenteric Infiltration
Mesenteric infiltration or “stranding” can be associated with mesenteric injury with or without bowel perforation, but bowel-wall thickening associated with stranding is highly suggestive of significant bowel injury. Sensitivities and specificities of 69%—77% and 44%—100%, respectively, have been reported for this sign . Mesenteric findings are more common when bowel injury is along the mesenteric border . A localized hematoma within the mesentery in the absence of a bowel abnormality points to an isolated laceration of a mesenteric vessel.
Intraperitoneal and Retroperitoneal Fluids:
Periduodenal hematoma is a fairly specific sign of duodenal injury because retroperitoneal blood tends to localize at the site of injury. This is in contrast with intraperitoneal blood for which the absence of restriction allows blood from solid organ injury to flow freely where it may be associated with normal bowel loops. It follows that hemoperitoneum in the absence of solid organ injury would imply bowel or mesenteric laceration as the source of bleeding,However, fluid location may be helpful. Interloop fluid specifies fluid between the folds of mesentery and bowel . These usually polygonal collections are uncommonly associated with solid organ injury and more likely to be related to bowel or mesenteric injury.
Fluid in the intra- or extraperitoneal compartments may not be from hemorrhage but rather may be due to leakage of bowel contents, urine, bile, or pancreatic juice, or the introduction of diagnostic peritoneal lavage fluid. Of these fluids, opacified intraperitoneal urine would most completely mask the presence of intraperitoneal blood or bowel contents . Hemorrhage from damage to other organs in the same anatomic space can also be misleadin
Differential Diagnosis
Free air (also seen with pneumomediastinum, pneumothorax, recent DPL, laparotomy, barotrauma)
Free fluid (also caused by injury to other organs including liver, spleen, gallbladder, urinary bladder)
Bowel wall thickening (also seen with various enteritis or colitides including ischemic, inflammatory, pseudomembranous)
Abnormal bowel wall enhancement (also seen in hypotensive "shock bowel")
Ultrasonography
Findings
Typically, the role of US in evaluating bowel trauma is limited to detecting free intraperitoneal fluid in trauma patients who are not sufficiently hemodynamically stable to undergo CT. However, the identified fluid cannot be further defined. Considerations include benign ascites, blood, urine, or bile and must be confirmed with CT.
Other findings of bowel injury include dilated bowel loops secondary to an ileus or obstruction. US is insensitive in detecting intraperitoneal free air.
