MDCT of the Small Bowel

Grace A. Tye, MD; Terry S. Desser, MD

Disclosures

Appl Radiol. 2012;41(8):6-17. 

In This Article

Trauma

Injury to the bowel and/or mesentery is seen in 1% to 5% of cases of blunt trauma at exploratory laparotomy, but can be difficult to diagnose both clinically and radiographically. Bowel injury can be due to deceleration forces that induce shear injury at transitions between mobile and fixed segments of bowel; direct force causing crush injuries; or bursting forces that cause sudden increases in intraluminal pressure.The most common locations of bowel injury are in the proximal jejunum near the ligament of Treitz and the distal ileum near the ileocecalvalve. MDCT has become the imaging test of choice to evaluate for injury to the bowel and/or mesentery due to its relatively high level of accuracy compared to other imaging modalities such as ultrasound and peritoneal lavage.[53,54]

One of the most important MDCT findings in cases of small-bowel injury is free fluid in the absence of obvious visceral organ injury. Enteric fluid in the peritoneal cavity secondary to bowel injury can be of water-density if there is no associated hemorrhage and no administration of enteric contrast. The presence of free fluid in the peritoneal cavity in the absence of an obvious solid organ injury generally warrants further evaluation with exploratory laparoscopy.[53] Small amounts of free, water-density fluid are often seen in menstruating females, however, and should be interpreted with caution. It is worthwhile to note also that very small amounts of simple free fluid can rarely be seen in a male, deep in the pelvis, even without any obvious traumatic injury on surgical exploration.[53] However, generally, even small amounts of free fluid are abnormal in males and should raise suspicion of visceral organ injury.

Free intraperitoneal or retroperitoneal air is a highly specific finding for bowel perforation. However, extraluminal air is not present inmost patients presenting with full-thickness bowel injury, present in only 20% to 55% of cases.[53,54] When seen, it is located in the nondependent portions of the abdomen. A careful search using wide window settings is critical for detection of small amounts of extraluminal air. Direct visualization of the defect in the bowel wall is rare, but if seen, highly specific for bowel wall perforation. We do not typically administer enteric contrast prior to imaging trauma patients. However, if it is administered, the detection of extraluminal contrast material is specific for bowel injury.[53,54]

Bowel wall thickening can be seen with tramatic injury to the bowel in 45% to 75% of cases (Figure 12).[53,54] It is important to distinguish underdistended bowel, which appears artifactually thickened, from truly thickened bowel. An isolated, truly thickened segment of bowel wallis likely due to an underlying contusion of the bowel.[54] Abnormal enhancement is neither a sensitive nor specific sign of bowel injury, although occasionally patchy areas of hyperenhancement can be seen in areas of injury. When diffuse bowel wall thickening with diffuse mucosal hyper-enhancement is seen, this does not indicate injury to the bowel itself, but rather represents reperfusion injury to the bowel after a severe episode of hypotension (ie "shock bowel") (Figure 13).

Figure 12.

Small-bowel contusion and perforation resulting from motor vehicle collision. (A) Axial scan with intravenous contrast and without oral contrast shows thick-walled, hyperdense loop of small bowel (arrow), indicating intramural hematoma. (B) Adjacent image shows water-density fluid between loops of bowel (arrow), indicating associated small-bowel perforation.

Figure 13.

Reperfusion injury due to trauma and ensuing hypotension ("shock bowel"). (A) Axial contrast-enhanced image shows splenic injury with active arterial extravasation (arrow) and perisplenic blood (arrowhead). Note flattened inferior vena cava and diminutive aorta suggesting systemic hypotension. (B) Dramatic appearance of small bowel with hyperenhancing mucosa and edematous submucosa due to reperfusion injury, the so-called "shock-bowel."

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