Overview
For centuries, bowel trauma had a high mortality rate, and survivors escaped death by withstanding hemorrhage and sepsis.[1, 2] With the introduction of radiography, diagnostic accuracy improved. In 1971, the use of ultrasound (US) to evaluate blunt abdominal trauma was first reported. The use of CT to evaluate blunt abdominal trauma was first reported in 1979.
Since 1979, the resolution and scanning time of CT have improved, as well as its ability to detect bowel injury. Multi-row helical detector CT scans are capable of scanning the abdomen in less than 30 seconds and can detect free air, free fluid, abnormal bowel wall enhancement, bowel wall thickening, and mesenteric infiltration. These advances in CT have brought the debate of conservative management of abdominal trauma full circle. Currently, many patients with blunt abdominal trauma or retroperitoneal penetrating trauma can be managed without surgery and can avoid unnecessary laparotomy. See the images below.
A 47-year-old man with blunt trauma to the abdomen. Axial CT through upper abdomen reveals 2 spots of free intraperitoneal air (arrows). 
Female patient with right-sided colon perforation. Axial CT through the abdomen shows focal gas bubbles (red arrow) and anextraluminal fluid collection (blue arrow) adjacent to the contrast-filled colon. Multidetector CT scanning using 16- and 64-slice CT has increased the speed in which trauma patients are scanned. In addition, 16- and 64-slice multidetector CT imaging allows the creation of isotropic voxels that allow reformats to be performed in sagittal and coronal planes, which can allow better localization of bowel injuries.
Preferred examination
CT of the abdomen is the preferred diagnostic examination for the evaluation of blunt abdominal trauma in the hemodynamically stable patient with blunt abdominal trauma and in selected instances of penetrating trauma to the posterior abdomen. Unstable patients or patients with penetrating injuries to the abdomen undergo exploratory laparotomy.[3]
Abdominal CT examination should be systematic. Traumatic injury to the bowel is rarely isolated. First, evaluate the more commonly injured organs, such as the liver and spleen, as well as the pancreas, adrenals, kidneys, blood vessels, spine, and skeletal structures.
Evaluate traumatic injury to the bowel in the context of the mechanism and location of injury, as follows:
- Right upper quadrant: examine the right lung base, right hemi-diaphragm, liver, gallbladder, right colon, right adrenal, right kidney, and right abdominal small bowel loops
- Midline: evaluate the base of the heart, diaphragm, pancreas, duodenum, aorta, inferior vena cava, and small bowel mesentery
- Left upper quadrant: evaluate the base of the heart, base of the left lung, left hemi-diaphragm, stomach, spleen, tail of the pancreas, left adrenal, left kidney, left colon, and small bowel loops
- Lower abdomen and/or pelvis: evaluate the bladder, rectosigmoid, and small bowel loops.
Each imaging modality (eg, plain abdominal radiograph, US, CT) demonstrates typical findings that suggest a diagnosis of bowel trauma. In the hemodynamically stable patient with abdominal trauma, CT is the study of choice.
Limitations of techniques
The accuracy of CT for the evaluation of bowel injury is as high as 97.6%.
CT can be limited if diagnostic peritoneal lavage (DPL) is performed prior to the CT. Free intraperitoneal fluid and air from the DPL observed on CT makes the evaluation for bowel injury very difficult.
Although CT can suggest bowel injury by demonstrating free intraperitoneal air, free fluid, or thickened bowel wall, in many instances it cannot reliably localize the exact location of bowel injury.
Delayed presentation of bowel injury occasionally occurs. Patients returning with continued symptoms several hours or days after a negative trauma should undergo repeat CT.[4]
Radiography
Plain radiography findings in bowel injury include the following[5] :
- Nonspecific findings may include small and/or large bowel dilation suggestive of ileus or obstruction secondary to peritonitis
- Soft tissue density and/or mass effect on bowel gas loops suggest fluid collections, hematoma, or scoliosis resulting from splinting toward the side of injury
- Loss of right psoas shadow suggests a retroperitoneal fluid collection from a duodenal injury
- Free intraperitoneal air suggests bowel perforation
- Upright abdominal films and left lateral decubitus films can detect as little as 1 mL or 2 mL of free intraperitoneal air under the diaphragm or over the liver edge, respectively
- On supine abdominal radiographs, free air can be observed outlining the serosa of the bowel loops ("Rigler" or serosa sign) or the falciform ligament
- Retroperitoneal air from duodenal or sigmoid injury can outline the diaphragmatic crura or the kidneys
- GI studies using contrast can identify areas of extravasation from perforated bowel. GI studies also can help identify a duodenal hematoma
Plain radiographs are not highly specific or sensitive for evaluating bowel injury. Findings of free air, abdominal fluid, scoliosis, and psoas shadow obliteration are observed in fewer than 43% of patients with intestinal trauma. Fluid collections must be large (>800 mL) to be visible on plain radiographs.
Pneumoperitoneum does not always indicate bowel rupture and can be observed in patients with pneumomediastinum or pneumothorax and in patients on mechanical ventilation.
Computed Tomography
CT is the modality of choice for evaluating abdominal trauma in the hemodynamically stable patient (see the images below).[6, 7, 8, 9, 10, 11, 12, 13, 14, 15, 16, 17, 18, 19, 20, 21, 22] CT evaluation for blunt abdominal trauma can be difficult and requires strict attention to meticulous techniques.
A 47-year-old man with blunt trauma to the abdomen. Axial CT through upper abdomen reveals 2 spots of free intraperitoneal air (arrows). 
A 15-year-old boy with blunt trauma to the abdomen and a perforated stomach. Axial CT demonstrates large amount of free intraperitoneal air (green arrow). An air/fluid level with fluid is seen in the right paracolic gutter (red arrow). Extravasated oral contrast is seen in the left paracolic gutter (blue arrow) adjacent to the stomach. 
Patient in a motor vehicle collision with injury to the spleen. Axial CT through the abdomen shows thickening and enhancement of bowel wall in the left lower quadrant resulting from hypotension and hypoperfusion of the bowel. No bowel injury was seen. 
A 47-year-old man with blunt trauma to the abdomen. Axial CT through the level of the pelvis shows small bowel wall thickening and enhancement (red arrow) from blunt small bowel injury. Free intraperitoneal air visualized (blue arrow) is from a perforated sigmoid colon. Image from AJR 2000;174:1538 printed with permission from American Roentgen Ray Society. 
A 19-year-old man with right-sided chest trauma. Axial CT through the upper abdomen shows a large amount of right retroperitoneal air surrounding the right kidney (arrows). Some air is seen in the right subcutaneous tissues. Retroperitoneal air dissected downwards from a right-sided chest pneumothorax. 
Patient with blunt abdominal trauma with duodenal hematoma. Axial CT through the abdomen shows soft tissue density and mild stranding surrounding duodenum (arrow) consistent with a duodenal hematoma. 
Female patient with blunt abdominal trauma and duodenal perforation. Focal axial CT of the right upper abdomen shows free intraperitoneal air (red arrow) and contrast extravasation (blue arrow) from the duodenum (yellow arrow). Female patient with right-sided colon perforation. Axial CT through the abdomen shows focal gas bubbles (red arrow) and anextraluminal fluid collection (blue arrow) adjacent to the contrast-filled colon. 
A 79-year-old woman after a motor vehicle collision. Axial CT through the level of the pelvis shows a focal area of small bowel wall thickening (red arrow) consistent with focal blunt small bowel injury. Fat stranding is seen in the mesentery (yellow arrow) consistent with a mesenteric hematoma. 
A 24-year-old man with blunt abdominal trauma and duodenal hematoma. Upper gastrointestinal series of the region of the duodenum shows large filling defect (arrow) compressing the contrast-filled second portion of duodenum lumen. Findings are consistent with an intramural duodenal hematoma. No extravasation of contrast is observed that suggests duodenal perforation. Administer oral and intravenous contrast. Extend sections from the base of the lungs to below the symphysis pubis. View these sections in the "abdominal, lung, liver" and "bone" windows. Carefully search for associated injuries, including Chance or vertebral burst fractures; abdominal bruising; and pancreatic, liver, spleen, adrenal, and kidney injury. Consider administering rectal contrast in patients with suggested penetrating injury to the rectum or retroperitoneal colon.
Multidetector CT scanning using a 16- or 64-slice CT allows for coronal and sagittal reformats. Examination of these off-axis images allows for improved detection and localization of bowel injuries.
The coronal plane is especially helpful because it provides an anatomic view and helps referring physicians/surgeons better understand the location and extent of injury.
The sagittal plane is helpful in the evaluation of the thoracic and lumbar spine and can detect associated compression fractures of the spine, which may be missed when viewed in the axial plane alone.
CT findings in bowel injury include the following (also see Table 1, below):
- Bowel injury is suggested by free intraperitoneal air, free intraperitoneal or retroperitoneal fluid, focal areas of bowel wall thickening, abnormal bowel wall enhancement, bowel wall hematoma (ie, duodenal hematoma), and intramural air.
- The most specific finding is the visualization of oral contrast extravasation and bowel wall disruption.
- A pattern of more diffuse bowel wall thickening, abnormal enhancement, and mesenteric infiltration can suggest mesenteric vascular injury resulting in ischemic bowel.
- In intestinal vascular injury, evaluate the celiac axis, superior mesenteric artery, and superior mesenteric vein. A mesenteric hematoma or a focal area of higher density clotted blood (ie, "sentinel clot") can suggest vascular injury.
- Focal contrast extravasation can indicate active hemorrhage.
Table 1. CT Findings in Bowel Injury (Open Table in a new window)
| Abdominal CT | Direct Findings | Indirect Findings |
| Bowel injury | Bowel wall disruption and oral contrast extravasation | Free intraperitoneal/retroperitoneal air, free intraperitoneal/retroperitoneal fluid Focal areas of bowel wall thickening, abnormal bowel wall enhancement |
| Mesenteric vascular injury | Intravenous contrast extravasation from the area of the mesentery | Diffuse bowel wall thickening, diffuse bowel wall enhancement, mesenteric infiltration/mesenteric hematoma |
The accuracy of CT for evaluating bowel injury is 82%, with a sensitivity of 64% and a specificity of 97%.
Some findings on CT suggesting bowel injury can represent false-positive findings, such as the following:
- Free intraperitoneal air in a trauma patient also can be observed in a patient with pneumomediastinum, pneumothorax, recent DPL, laparotomy, or barotrauma with no associated bowel injury
- Free fluid in a trauma patient can originate from injury to other organs, including the liver, spleen, gallbladder, and urinary bladder, without any injury to the bowel
- Bowel wall thickening and abnormal wall enhancement also can be observed in patients with hypotension or hypoperfusion without direct bowel injury
Ultrasonography
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.[23]
Other findings of bowel injury include dilated bowel loops secondary to an ileus or obstruction. US is insensitive in detecting intraperitoneal free air.
Angiography
The only role of angiography in acute bowel trauma is to identify the site of visceral bleeding.[24]
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| Abdominal CT | Direct Findings | Indirect Findings |
| Bowel injury | Bowel wall disruption and oral contrast extravasation | Free intraperitoneal/retroperitoneal air, free intraperitoneal/retroperitoneal fluid Focal areas of bowel wall thickening, abnormal bowel wall enhancement |
| Mesenteric vascular injury | Intravenous contrast extravasation from the area of the mesentery | Diffuse bowel wall thickening, diffuse bowel wall enhancement, mesenteric infiltration/mesenteric hematoma |
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