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(Radiographics. 1999;19:1237-1250.)
© RSNA, 1999

SCIENTIFIC EXHIBIT

CT of Bowel and Mesenteric Trauma in Children1

Peter J. Strouse, MD, Bradley J. Close, MD, Kelley W. Marshall, MD and Robert Cywes, MB, ChB

1 From the Section of Pediatric Radiology, Department of Radiology (P.J.S., B.J.C., K.W.M.), and Section of Pediatric Surgery, Department of Surgery (R.C.), C.S. Mott Children's Hospital, F3503, University of Michigan Health System, 1500 E Medical Center Dr, Ann Arbor, MI 48109-0252. Recipient of a Certificate of Merit award for a scientific exhibit at the 1998 RSNA scientific assembly. Received February 26, 1999; revision requested March 11 and received April 26; accepted May 3. Address reprint requests to P.J.S.


   Abstract
Top
 Abstract
INTRODUCTION
 EXAMINATION TECHNIQUE
 CLINICAL EXPERIENCE
 MECHANISMS OF TRAUMA
 CT FINDINGS
 SUMMARY
 References
 
Although most traumatic abdominal injuries in children are treated with conservative nonsurgical management, traumatic perforation or infarction of the gastrointestinal tract still necessitates surgical management. It is imperative to recognize the often subtle computed tomographic (CT) findings of bowel or mesenteric trauma in children. Pediatric patients with bowel perforation or infarction due to trauma usually demonstrate multiple abnormalities at CT. A specific history of lap belt injury, bicycle handlebar injury, or child abuse with an abdominal injury should heighten suspicion for a bowel injury. CT findings in children with bowel or mesenteric trauma include free intraperitoneal air, free retroperitoneal air, extraluminal oral contrast material, free intraperitoneal fluid, bowel wall defect, bowel wall thickening, mesenteric stranding, fluid at the mesenteric root, focal hematoma, active hemorrhage, and mesenteric pseudoaneurysm. Some findings, such as free intraperitoneal air and focal bowel wall thickening, are associated with a strong likelihood of a bowel injury that requires surgical repair. Other findings, such as free intraperitoneal fluid, mesenteric stranding, fluid at the mesenteric root, and focal hematoma, are less specific for an injury that requires surgical repair. The hypoperfusion complex can usually be differentiated from a traumatic bowel injury; however, in some patients the imaging findings overlap.

Index Terms: Children, injuries, 70.41 • Computed tomography (CT), in infants and children, 70.12112 • Intestines, injuries, 74.41, 75.41 • Mesentery, injuries, 792.41


   INTRODUCTION
Top
 Abstract
 INTRODUCTION
EXAMINATION TECHNIQUE
 CLINICAL EXPERIENCE
 MECHANISMS OF TRAUMA
 CT FINDINGS
 SUMMARY
 References
 
Although most traumatic abdominal injuries in children are now treated with conservative nonsurgical management, traumatic perforation or infarction of the gastrointestinal tract still necessitates surgical management. The introduction of laparoscopic abdominal exploratory surgery and bowel repair may lower the threshold for surgery (1). Therefore, it has become imperative to recognize the often subtle computed tomographic (CT) findings in bowel injury so that children with traumatic gastrointestinal perforation or infarction can be expediently treated with surgical repair. A delay in diagnosis can lead to substantial added morbidity and potential mortality (2).

In this article, CT of traumatic injury to the intestine and mesentery in children is discussed. The specific topics discussed are examination technique, clinical experience, mechanisms of trauma, and CT findings.


   EXAMINATION TECHNIQUE
Top
 Abstract
 INTRODUCTION
 EXAMINATION TECHNIQUE
CLINICAL EXPERIENCE
 MECHANISMS OF TRAUMA
 CT FINDINGS
 SUMMARY
 References
 
At our institution, CT studies done to check for blunt abdominal trauma in children are performed in the helical mode. A single dose of gastrointestinal contrast material (3% iodine by weight) is administered orally or via a nasogastric tube in a dose of 2–16 fl oz (60–480 mL); the dose depends on the size of the patient. Most of the children have undergone placement of a nasogastric tube, which eases the administration of gastrointestinal contrast material. Patients receive an intravenous bolus of 2 mL/kg of nonionic contrast material, with scanning commencing after a 60–90-second delay; the delay depends on the patient's size and age and the injection rate. A power injector can be used if a secure, 22-gauge or larger intravenous catheter has been placed; otherwise, the bolus is injected by hand. We measure the patient size from a scout image to determine the optimal field of view and vary the section thickness on the basis of the patient size. A 5- or 7-mm section thickness is used in infants and young children. In older children and teenagers, 7-mm-thick sections through the upper abdomen and 10-mm-thick sections through the pelvis are obtained. If the initial findings produce concern about a bladder injury, delayed images through the pelvis are obtained.

Children are accompanied to the CT suite by personnel from the pediatric emergency service, who monitor the child. Sedation is rarely necessary in the setting of a CT examination performed acutely for trauma. In the unusual event that sedation is necessary, it is performed by the pediatric emergency service personnel, who select the agent and monitor the child throughout the examination.

The routine use of oral contrast material is controversial (3,4). Currently, we still recommend administration of oral contrast material to all patients. In practice, many patients do not receive oral contrast material. In our experience, oral contrast material is rarely of benefit in diagnosis of acute bowel injuries; however, we do find it useful in exclusion of duodenal or pancreatic abnormality. Oral contrast material has proved valuable in diagnosis of bowel injuries with delayed manifestations. To our knowledge, there was no significant untoward complication related to the administration of oral contrast material during the period of our clinical experience.

All CT scans are reviewed by a radiologist before the patient is removed from the scanner. Additional or delayed images may be obtained at the discretion of the radiologist. All images are printed at soft-tissue window settings, with images of the thorax printed at lung window settings and images of the liver and spleen printed at narrow liver window settings. Bone window images are reviewed on the console; hard copy images of sites of fracture are printed. Review of abdominal images on the console at lung window settings frequently assists in classifying abdominal gas as extraperitoneal, intraluminal, or free intraperitoneal.


   CLINICAL EXPERIENCE
Top
 Abstract
 INTRODUCTION
 EXAMINATION TECHNIQUE
 CLINICAL EXPERIENCE
MECHANISMS OF TRAUMA
 CT FINDINGS
 SUMMARY
 References
 
To identify pediatric patients with traumatic bowel or mesenteric injury, we reviewed all reports of abdominal CT examinations performed to check for blunt trauma in patients less than 18 years of age over a 7-year period. A total of 1,036 reports were reviewed. CT studies performed elsewhere in patients who were transferred to our institution for subsequent care were included. We also reviewed the diagnosis and procedure database of the pediatric surgery section for the same period to identify all patients who had undergone surgery for blunt abdominal trauma. All CT scans that showed findings potentially related to bowel or mesenteric trauma were reviewed, and all CT scans of patients who underwent surgery for bowel trauma were reviewed. Medical records were reviewed to determine the mechanism of trauma for each patient.

Thirty-one patients with traumatic bowel or mesenteric injury were identified. The mechanisms of trauma were motor vehicle accident (n = 21), child abuse (n = 6), bicycle handlebar injury (n = 2), hockey collision (n = 1), and falling furniture (n = 1). Of the 21 children who were injured in a motor vehicle accident, 18 were passengers in a vehicle and three were pedestrians struck by a vehicle. Of the 18 who were passengers, 11 were restrained and three were not restrained; the presence or absence of restraint was not specified in four cases. Three of the 11 restrained children had characteristic lap belt ecchymoses.

The CT findings are given in the Table. Twenty-five patients underwent surgery for a possible traumatic bowel or mesenteric injury demonstrated at CT. Of these 25 patients, 14 had bowel perforation and four had bowel infarction, which necessitated surgical bowel repair; seven patients underwent surgery but did not require surgical bowel repair. The remaining six patients had an unequivocal bowel or mesenteric abnormality at CT but were treated conservatively without surgery. The abnormalities were confirmed with clinical follow-up and an upper gastrointestinal contrast material study (n = 3), follow-up CT (n = 3), ultrasonography (n = 1), or percutaneous aspiration (n = 1). Patients with subtle or equivocal abnormalities at CT and no indication of bowel injury in their history, at physical examination, or at clinical follow-up were not included in this category.


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  		Bowel and Mesenteric Abnormalities Identified at CT
 
Four patients demonstrated CT findings of the hypoperfusion complex; one of these patients also had bowel perforation. All 18 patients who required surgical bowel repair demonstrated multiple CT findings. No patient with a surgically proved traumatic bowel injury had a normal CT scan. Among the 1,005 patients who underwent CT without a bowel injury being diagnosed, no patient has yet shown evidence of a "missed" bowel injury (ie, posttraumatic stricture) at follow-up.


   MECHANISMS OF TRAUMA
Top
 Abstract
 INTRODUCTION
 EXAMINATION TECHNIQUE
 CLINICAL EXPERIENCE
 MECHANISMS OF TRAUMA
CT FINDINGS
 SUMMARY
 References
 
The most common mechanism of traumatic bowel or mesenteric injury in children is a motor vehicle accident. Although many injuries from motor vehicle accidents are simply the result of a blunt force on the abdomen, restrained children may be at increased risk for bowel injury due to lap belts. Two other common mechanisms of bowel injury in children are bicycle handlebar injuries and child abuse.

Lap Belt Injury
Children are prone to injury from lap belts for the following reasons: (a) Children tend to ride in the backseat; (b) shoulder restraints are less effective in children; (c) lap belts tend to ride high over the abdomen rather than over the anterosuperior iliac spine, as is ideal (note that b and c are accentuated by slouching); and (d) young children have a relatively high center of gravity, which produces a shearing force by the belt (5). Although a lap belt injury can cause damage to virtually any organ in the abdomen, there is a strong association with bowel injury and bladder injury (6). Due to the acute flexion or shearing force, there is also a strong association with lumbar spinal fracture (Chance fracture) or dislocation. The presence of a lap belt ecchymosis is an indication for CT and should prompt a careful assessment for bowel, bladder, and spinal injuries (6).

The imaging appearance of bowel injuries due to lap belts does not differ from that of bowel injuries due to other causes. CT does allow identification of an accompanying spinal injury; identification of such an injury should increase suspicion for a bowel injury. In extreme injuries, the abdominal musculature may be disrupted and cause traumatic herniation of the intestine into the abdominal wall (Fig 1).



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  		Figure 1a.   Lap belt injury in a 16-year-old girl after a motor vehicle accident in which she was a backseat passenger. A Chance fracture of the third lumbar vertebra was seen on radiographs and scout CT scans. (a) Photograph shows prominent lap belt ecchymosis. (b) CT scan shows disruption of the rectus muscles and a diffuse traumatic hernia of the anterior abdominal wall (arrows). Fluid at the mesenteric root and moderate free intraperitoneal fluid were noted on other sections. No free intraperitoneal air or bowel wall thickening was seen. At surgery, multiple mesenteric defects were found with extensive areas of devascularization of the small intestine, cecum, and sigmoid colon. Most of the intestine was resected.

 


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  		Figure 1b.   Lap belt injury in a 16-year-old girl after a motor vehicle accident in which she was a backseat passenger. A Chance fracture of the third lumbar vertebra was seen on radiographs and scout CT scans. (a) Photograph shows prominent lap belt ecchymosis. (b) CT scan shows disruption of the rectus muscles and a diffuse traumatic hernia of the anterior abdominal wall (arrows). Fluid at the mesenteric root and moderate free intraperitoneal fluid were noted on other sections. No free intraperitoneal air or bowel wall thickening was seen. At surgery, multiple mesenteric defects were found with extensive areas of devascularization of the small intestine, cecum, and sigmoid colon. Most of the intestine was resected.

 
Bicycle Handlebar Injury
Handlebars on bicycles and similar vehicles cause a focally directed impact on the abdomen of a child. The injury typically occurs with an abrupt stop; the child is thrown forward, and the abdomen is impaled on the protruding handlebar. The site of impact may be identified externally as a focal bruise or skin disruption and internally as bowel wall thickening at CT. The bowel injury is usually focal (Fig 2).



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  		Figure 2a.   Bicycle handlebar injury in a 7-year-old boy. (a) Photograph shows focal ecchymosis in the left upper quadrant due to the impact of the end of a handlebar. (b) CT scan shows focal bowel wall thickening in the same region (arrows). A small amount of free fluid was present in the left upper quadrant and pelvis. A jejunal perforation was found at surgery. (Case not included in the Clinical Experience section or in the Table. Courtesy of Kathleen Emery, MD, Children's Hospital Medical Center, Cincinnati, Ohio.)

 


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  		Figure 2b.   Bicycle handlebar injury in a 7-year-old boy. (a) Photograph shows focal ecchymosis in the left upper quadrant due to the impact of the end of a handlebar. (b) CT scan shows focal bowel wall thickening in the same region (arrows). A small amount of free fluid was present in the left upper quadrant and pelvis. A jejunal perforation was found at surgery. (Case not included in the Clinical Experience section or in the Table. Courtesy of Kathleen Emery, MD, Children's Hospital Medical Center, Cincinnati, Ohio.)

 
Child Abuse
Visceral trauma is the second leading cause of death in child abuse after central nervous system injury. In addition to parenchymal organ injury, the abused child can suffer injury to any portion of the gastrointestinal tract (7). Classically, intramural duodenal hematoma is associated with child abuse and is usually attributed to a direct blow to the upper anterior abdomen; the duodenum is injured when it is compressed between the offending force and the spine. Unfortunately, injuries are often more serious than a simple intramural hematoma and perforation does occur (7–9). Abused children can present in a moribund state with sepsis days after the traumatic event and without a clear history of trauma or with a frankly misleading history. Duodenal hematoma or irregularity, diffuse mesenteric stranding, and copious intraperitoneal fluid are often present (Fig 3). Extraluminal gas or oral contrast material is indicative of perforation (10). If there is a question of abuse, careful inspection of the anterior ribs may reveal irregularity or frank fracture, which likely occurred at the time of the traumatic event or a preceding similar event (Fig 4) (11). Although classic posterior rib fractures may also be identified, their pathophysiologic origin is less specifically associated with bowel injury but is indicative of the repetitive and varied trauma seen in abused children.



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  		Figure 3a.   Confirmed child abuse in an 18-month-old girl with an initial history of "falling down steps." CT scans show a markedly irregular distal duodenum (black arrowheads) and marked diffuse mesenteric stranding (M in b) and free fluid (F). Small bubbles of free intraperitoneal air are present anteriorly (white arrowheads). The proximal jejunum is dilated (J in b). At surgery, a transection was found at the duodenal-jejunal junction.

 


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  		Figure 3b.   Confirmed child abuse in an 18-month-old girl with an initial history of "falling down steps." CT scans show a markedly irregular distal duodenum (black arrowheads) and marked diffuse mesenteric stranding (M in b) and free fluid (F). Small bubbles of free intraperitoneal air are present anteriorly (white arrowheads). The proximal jejunum is dilated (J in b). At surgery, a transection was found at the duodenal-jejunal junction.

 


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  		Figure 4a.   Increasing pain and fever in a 5-year-old boy with a 2-week history of gastrointestinal distress. CT was performed to "r/o [rule out] appy [appendectomy] vs. abscess." (a) CT scan shows an ill-defined mass (H) within the mesentery. The abnormality extends to the mesenteric root. A large amount of free fluid (F) is present, mainly within the pelvis. The anterior ends of several ribs were irregular and probably fractured. (b) CT scan shows a fracture of the left anterior sixth rib (arrow). The slight expansion of the right anterior sixth rib (?) distinguishes this rib from the adjacent ribs and was likely due to previous fracture. At surgery, a mesenteric tear with a large hematoma was found. Child abuse was subsequently substantiated.

 


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  		Figure 4b.   Increasing pain and fever in a 5-year-old boy with a 2-week history of gastrointestinal distress. CT was performed to "r/o [rule out] appy [appendectomy] vs. abscess." (a) CT scan shows an ill-defined mass (H) within the mesentery. The abnormality extends to the mesenteric root. A large amount of free fluid (F) is present, mainly within the pelvis. The anterior ends of several ribs were irregular and probably fractured. (b) CT scan shows a fracture of the left anterior sixth rib (arrow). The slight expansion of the right anterior sixth rib (?) distinguishes this rib from the adjacent ribs and was likely due to previous fracture. At surgery, a mesenteric tear with a large hematoma was found. Child abuse was subsequently substantiated.

 

   CT FINDINGS
Top
 Abstract
 INTRODUCTION
 EXAMINATION TECHNIQUE
 CLINICAL EXPERIENCE
 MECHANISMS OF TRAUMA
 CT FINDINGS
SUMMARY
 References
 
With the exception of the hemodynamically unstable patient, most pediatric patients with blunt abdominal trauma are treated conservatively without surgery. Unless there is evidence of active hemorrhage, even severe parenchymal organ injuries are treated conservatively. Therefore, there are relatively few imaging findings that indicate an acute need for surgery. CT has the greatest potential to alter patient treatment by demonstrating bowel injury because bowel perforation or infarction remains a firm indication for surgical intervention (12). Although relatively infrequent, these injuries do have the potential for considerable morbidity. Clinical manifestations of bowel injury may be subtle, absent, or masked by other pathologic conditions. Often, bowel injury is first suspected when findings are seen at CT.

Findings identified at CT in our patients and in the literature as indicative of bowel or mesenteric trauma are free intraperitoneal air, free retroperitoneal air, extraluminal oral contrast material, free intraperitoneal fluid, bowel wall defect, bowel wall thickening, mesenteric stranding, fluid at the mesenteric root, focal hematoma, active hemorrhage, and mesenteric pseudoaneurysm (10,13–25).

Free Intraperitoneal Air
Free intraperitoneal air is highly suggestive of perforation of the gastrointestinal tract (13). However, this finding was present in only half of our patients with perforation. Prior studies have shown free intraperitoneal air in a similar proportion of patients with perforation (13–16). In cases of perforation, the amount of air may be substantial or minimal; often, only minimal air is present in perforations of the small intestine (Figs 5–7). CT is valuable in detection of very small quantities of free air. Review of abdominal images at lung window settings aids in identification of extraluminal gas. Free air is most commonly identified anteriorly near the liver but can be trapped within leaves of the mesentery. Care must be taken not to mistake extraperitoneal intraabdominal air dissecting down from the thorax for free intraperitoneal air (17). Intraperitoneal air is introduced during diagnostic peritoneal lavage and can be viewed with less suspicion in this setting. Free intraperitoneal air can also result from dissection of a pneumomediastinum or introduction of a catheter into the bladder with intraperitoneal rupture (5). A study by Kane et al (18) in adults demonstrated bowel perforation in four of 18 patients with free intraperitoneal air detected at CT. These investigators postulated that pneumoperitoneum may have resulted from pneumothorax in some patients, but in other patients the cause was unknown. Other CT evidence of bowel injury is helpful in confirming that pneumoperitoneum is a consequence of perforation.



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  		Figure 5.   Free intraperitoneal air in a 14-year-old boy with a bicycle handlebar injury. CT scan shows a small amount of free fluid (F). The free fluid and subtle bowel wall thickening (seen on other images) were considered equivocal findings. However, the presence of small bubbles of free intraperitoneal air (arrowheads) confirms the diagnosis of bowel perforation.

 


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  		Figures 6, 7.   (6) Free intraperitoneal air in a 16-year-old boy who was hit by an automobile. CT scans show a large amount of free intraperitoneal fluid (F), which is not accounted for by parenchymal or osseous pelvic injury. There is slight bowel wall thickening (arrows in a). A tiny bubble of extraluminal gas is seen anteriorly (arrowhead in b). Fluid is seen at the mesenteric root (M in a). Two sites of small bowel perforation and a degloving injury of the sigmoid colon were found at surgery. (7) Free intraperitoneal air in a 6-year-old boy with abdominal pain after a motor vehicle accident. The patient was treated conservatively for 3 days. CT was performed due to increasing pain and new fever. CT scans show free intraperitoneal fluid (F), free intraperitoneal air (arrowheads in a), bowel wall thickening (arrows), and mesenteric stranding (M), which are indicative of bowel perforation with peritonitis.

 


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  		Figures 6, 7.   (6) Free intraperitoneal air in a 16-year-old boy who was hit by an automobile. CT scans show a large amount of free intraperitoneal fluid (F), which is not accounted for by parenchymal or osseous pelvic injury. There is slight bowel wall thickening (arrows in a). A tiny bubble of extraluminal gas is seen anteriorly (arrowhead in b). Fluid is seen at the mesenteric root (M in a). Two sites of small bowel perforation and a degloving injury of the sigmoid colon were found at surgery. (7) Free intraperitoneal air in a 6-year-old boy with abdominal pain after a motor vehicle accident. The patient was treated conservatively for 3 days. CT was performed due to increasing pain and new fever. CT scans show free intraperitoneal fluid (F), free intraperitoneal air (arrowheads in a), bowel wall thickening (arrows), and mesenteric stranding (M), which are indicative of bowel perforation with peritonitis.

 


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  		Figures 6, 7.   (6) Free intraperitoneal air in a 16-year-old boy who was hit by an automobile. CT scans show a large amount of free intraperitoneal fluid (F), which is not accounted for by parenchymal or osseous pelvic injury. There is slight bowel wall thickening (arrows in a). A tiny bubble of extraluminal gas is seen anteriorly (arrowhead in b). Fluid is seen at the mesenteric root (M in a). Two sites of small bowel perforation and a degloving injury of the sigmoid colon were found at surgery. (7) Free intraperitoneal air in a 6-year-old boy with abdominal pain after a motor vehicle accident. The patient was treated conservatively for 3 days. CT was performed due to increasing pain and new fever. CT scans show free intraperitoneal fluid (F), free intraperitoneal air (arrowheads in a), bowel wall thickening (arrows), and mesenteric stranding (M), which are indicative of bowel perforation with peritonitis.

 


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  		Figures 6, 7.   (6) Free intraperitoneal air in a 16-year-old boy who was hit by an automobile. CT scans show a large amount of free intraperitoneal fluid (F), which is not accounted for by parenchymal or osseous pelvic injury. There is slight bowel wall thickening (arrows in a). A tiny bubble of extraluminal gas is seen anteriorly (arrowhead in b). Fluid is seen at the mesenteric root (M in a). Two sites of small bowel perforation and a degloving injury of the sigmoid colon were found at surgery. (7) Free intraperitoneal air in a 6-year-old boy with abdominal pain after a motor vehicle accident. The patient was treated conservatively for 3 days. CT was performed due to increasing pain and new fever. CT scans show free intraperitoneal fluid (F), free intraperitoneal air (arrowheads in a), bowel wall thickening (arrows), and mesenteric stranding (M), which are indicative of bowel perforation with peritonitis.

 
Free Retroperitoneal Air
Free retroperitoneal air indicates traumatic disruption of a retroperitoneal portion of the gastrointestinal tract, usually the duodenum (Fig 8) but also potentially the colon (10). Dissection of a pneumomediastinum and extraperitoneal bladder rupture are alternative causes.



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  		Figure 8a.   Free retroperitoneal air in a 7-year-old boy after a motor vehicle accident. Copies of CT scans (marks included) from the referring institution show not only free intraperitoneal air (arrows) but also free retroperitoneal air (arrowheads). Free intraperitoneal fluid (F in b) and mesenteric stranding (M in b) are also seen. At surgery, perforations were found in the distal duodenum and the hepatic flexure of the colon.

 


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  		Figure 8b.   Free retroperitoneal air in a 7-year-old boy after a motor vehicle accident. Copies of CT scans (marks included) from the referring institution show not only free intraperitoneal air (arrows) but also free retroperitoneal air (arrowheads). Free intraperitoneal fluid (F in b) and mesenteric stranding (M in b) are also seen. At surgery, perforations were found in the distal duodenum and the hepatic flexure of the colon.

 
Extraluminal Oral Contrast Material
Although extraluminal oral contrast material is probably the most specific sign of bowel perforation next to direct visualization of the perforation, the finding is quite uncommon (19). Extraluminal contrast material is typically most dense near the perforation; however, it may be seen elsewhere in the abdomen (Fig 9). Differential causes of hyperattenuating fluid in the peritoneum include blood (which typically is not as hyperattenuating as contrast material), actively extravasating vascular contrast material, and extraluminal contrast material due to a leak from the urinary tract. Associated findings will usually help identify a vascular or urinary tract injury.



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  		Figure 9.   Extraluminal oral contrast material in a 6-year-old boy after a motor vehicle accident. CT scan shows a thin rim of high attenuation peripheral to the liver (arrows); this finding presumably represents extraluminal oral contrast material. Free fluid was seen within the pelvis, and there was slight bowel wall thickening in the lower abdomen. The bladder was intact. A perforation of the ileum was found at surgery.

 
Free Intraperitoneal Fluid
In the absence of parenchymal organ injury, osseous pelvic injury, large vessel injury, or bladder perforation, the presence of free intraperitoneal fluid should cause concern about an injury to the bowel or mesentery (15,20). In a study by Sivit et al (20), four of six children with peritoneal fluid as an isolated finding had a bowel injury. The finding of unexplained free fluid therefore warrants a careful search for other findings of bowel injury. In our experience, it is unusual for free intraperitoneal fluid to be the sole manifestation of a bowel perforation. The minimum amount of free fluid that should warrant concern is not defined. A small amount of free fluid is a normal physiologic finding in the menstruating female.

Bowel Wall Defect
Direct visualization of a defect in the bowel wall due to perforation is rare, but visualization of such a defect is diagnostic (16). Even with careful retrospective review, we did not see this finding in any of our 14 patients with bowel perforation.

Bowel Wall Thickening
What thickness of the bowel wall is abnormal? A value of 3–4 mm has been given in the literature (13,19,21); however, the distinction between abnormal and normal is often better made by means of a "gestalt" interpretation than direct measurement. In our patients, we considered the bowel wall to be abnormally thick if it was at least 3 mm thick or clearly disproportionate to normal bowel wall segments (Figs 10, 11). In addition, an abnormal bowel wall segment frequently enhances more than a normal bowel wall segment (Fig 6a) (22). Abnormal bowel wall enhancement is difficult to define. Bowel wall enhancement may also vary considerably depending on the technique of contrast material administration. An abnormal bowel wall segment can be identified by means of bowel wall thickening even in the absence of intravenous contrast material (Fig 12).



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  		Figures 10-12.   (10) Bowel wall thickening in a 4-year-old boy who was ejected from an automobile during a high-speed motor vehicle accident. CT scan shows focal small bowel thickening on the left side (arrows). Note the fluid at the mesenteric root (M). There is a moderate amount of free fluid (F); the free fluid was predominantly located within the pelvis. A small jejunal perforation was found at surgery. (11) Bowel wall thickening in a 6-year-old boy who suffered a direct blow to the right lower quadrant during a motor vehicle accident. CT scan shows a thickened bowel wall in the right lower quadrant (arrows) with underlying mesenteric stranding (M). Note the small hematoma around the mesenteric vessels (arrowheads). F = free intraperitoneal fluid. At laparoscopy, a small area of jejunal infarction and perforation that corresponded to the CT abnormality was seen. This area was repaired laparoscopically. (12) Bowel wall thickening in a 17-year-old girl with complex pelvic fractures from a motor vehicle accident. An extraperitoneal bladder rupture was demonstrated with cystography. Owing to the contrast material load from angiography and pelvic embolization, the subsequent abdominal CT study was performed without additional intravenous contrast material. CT scan shows free intraperitoneal air (arrowheads). Despite the absence of contrast material, bowel wall thickening is seen on the right side (arrows). Note the difference in comparison with the imperceptible bowel wall on the left side. An ileal perforation was found at surgery.

 


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  		Figures 10-12.   (10) Bowel wall thickening in a 4-year-old boy who was ejected from an automobile during a high-speed motor vehicle accident. CT scan shows focal small bowel thickening on the left side (arrows). Note the fluid at the mesenteric root (M). There is a moderate amount of free fluid (F); the free fluid was predominantly located within the pelvis. A small jejunal perforation was found at surgery. (11) Bowel wall thickening in a 6-year-old boy who suffered a direct blow to the right lower quadrant during a motor vehicle accident. CT scan shows a thickened bowel wall in the right lower quadrant (arrows) with underlying mesenteric stranding (M). Note the small hematoma around the mesenteric vessels (arrowheads). F = free intraperitoneal fluid. At laparoscopy, a small area of jejunal infarction and perforation that corresponded to the CT abnormality was seen. This area was repaired laparoscopically. (12) Bowel wall thickening in a 17-year-old girl with complex pelvic fractures from a motor vehicle accident. An extraperitoneal bladder rupture was demonstrated with cystography. Owing to the contrast material load from angiography and pelvic embolization, the subsequent abdominal CT study was performed without additional intravenous contrast material. CT scan shows free intraperitoneal air (arrowheads). Despite the absence of contrast material, bowel wall thickening is seen on the right side (arrows). Note the difference in comparison with the imperceptible bowel wall on the left side. An ileal perforation was found at surgery.

 


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  		Figures 10-12.   (10) Bowel wall thickening in a 4-year-old boy who was ejected from an automobile during a high-speed motor vehicle accident. CT scan shows focal small bowel thickening on the left side (arrows). Note the fluid at the mesenteric root (M). There is a moderate amount of free fluid (F); the free fluid was predominantly located within the pelvis. A small jejunal perforation was found at surgery. (11) Bowel wall thickening in a 6-year-old boy who suffered a direct blow to the right lower quadrant during a motor vehicle accident. CT scan shows a thickened bowel wall in the right lower quadrant (arrows) with underlying mesenteric stranding (M). Note the small hematoma around the mesenteric vessels (arrowheads). F = free intraperitoneal fluid. At laparoscopy, a small area of jejunal infarction and perforation that corresponded to the CT abnormality was seen. This area was repaired laparoscopically. (12) Bowel wall thickening in a 17-year-old girl with complex pelvic fractures from a motor vehicle accident. An extraperitoneal bladder rupture was demonstrated with cystography. Owing to the contrast material load from angiography and pelvic embolization, the subsequent abdominal CT study was performed without additional intravenous contrast material. CT scan shows free intraperitoneal air (arrowheads). Despite the absence of contrast material, bowel wall thickening is seen on the right side (arrows). Note the difference in comparison with the imperceptible bowel wall on the left side. An ileal perforation was found at surgery.

 
An equivocal finding of bowel wall thickening becomes more worrisome when coupled with other findings of bowel injury. The pathophysiologic mechanism of bowel wall thickening may vary from patient to patient. Vascular compromise and inflammation due to spilling of bowel contents are likely causes. In our experience and that of others, focal bowel wall thickening is associated with a high likelihood of bowel injury that requires surgical repair (21, 22). Early after injury, bowel wall thickening is limited to the area of injury; thus, a focal abnormality on CT scans can guide the surgeon's exploration. When detection of perforation is delayed, peritoneal inflammation may become generalized and the bowel wall thickening may be more diffuse.

Mesenteric Stranding and Fluid at the Mesenteric Root
Bowel and mesenteric injuries are frequently associated with inhomogeneous increased attenuation within the mesentery (ie, stranding), which likely represents hemorrhage or an inflammatory response (Figs 3b, 7, 8, 11) (15,19,23). Fluid is also often seen at the mesenteric root adjacent to the aorta and inferior vena cava (Figs 6a, 10). In two of our patients, fluid at the mesenteric root was surgically confirmed to represent hemorrhage. Mesenteric stranding and fluid at the mesenteric root are frequently seen together. These findings were seen in most of our patients with bowel injury that required surgical repair. In the setting of unexplained free fluid, mesenteric stranding or fluid at the mesenteric root corroborates the presence of a bowel or mesenteric injury. However, mesenteric stranding and fluid at the mesenteric root were also frequently present when surgical repair was not necessary and thus do not indicate a need for surgery. Mesenteric abnormalities seen in combination with focal bowel wall thickening are associated with a high likelihood of an injury that requires surgical repair (21).

Focal Hematoma
Occasionally, bowel or mesenteric injury produces a focal hematoma, which is seen as a well-defined mass. Hematomas contained within the wall of the gastrointestinal tract (intramural hematomas) are most commonly duodenal but can occur elsewhere in the small intestine or, less commonly, in the stomach or colon (Fig 13). The manifestations are often delayed (Figs 14, 15). Hematomas can also form within the mesentery due to mesenteric injury (Figs 16, 17). Injuries to the mesentery often involve disruption or occlusion of large arteries. Thus, there may be associated bowel ischemia or infarction, which causes bowel wall thickening in the absence of perforation. A bowel or mesenteric hematoma is not a strict indication for surgery (21). In the absence of other CT or clinical signs of bowel perforation or infarction, a patient with an isolated mesenteric hematoma can potentially be treated conservatively (19).



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  		Figure 13a.   Focal hematoma in a 4-year-old boy with a lap belt injury. (a) CT scan shows fluid distending the proximal duodenum (arrow). (b) CT scan shows a periduodenal or intramural hematoma (H). (c) Radiograph from an upper gastrointestinal study shows complete obstruction due to the hematoma (arrowheads).

 


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  		Figure 13b.   Focal hematoma in a 4-year-old boy with a lap belt injury. (a) CT scan shows fluid distending the proximal duodenum (arrow). (b) CT scan shows a periduodenal or intramural hematoma (H). (c) Radiograph from an upper gastrointestinal study shows complete obstruction due to the hematoma (arrowheads).

 


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  		Figure 13c.   Focal hematoma in a 4-year-old boy with a lap belt injury. (a) CT scan shows fluid distending the proximal duodenum (arrow). (b) CT scan shows a periduodenal or intramural hematoma (H). (c) Radiograph from an upper gastrointestinal study shows complete obstruction due to the hematoma (arrowheads).

 


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  		Figures 14, 15.   (14) Focal hematoma in a 5-year-old girl with a 12-hour history of increasing abdominal pain and vomiting. She had fallen against bicycle handlebars 36 hours earlier. CT scan shows a large duodenal-jejunal hematoma (H, arrows). (15) Focal hematoma in a 6-year-old boy with a 3-day history of vomiting. He had had an on-ice collision with his hockey coach 2 weeks earlier. The serum amylase level was normal. CT scan shows a large mass (H) in the left upper quadrant that drapes over bowel loops (B). An upper gastrointestinal study showed complete obstruction due to the mass. The mass was thought to be a large intramural jejunal hematoma. The patient was initially treated conservatively and received total parenteral nutrition. However, the symptoms did not improve and the mass persisted, and thus it was drained percutaneously. The contents were consistent with old blood and showed no amylase.

 


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  		Figures 14, 15.   (14) Focal hematoma in a 5-year-old girl with a 12-hour history of increasing abdominal pain and vomiting. She had fallen against bicycle handlebars 36 hours earlier. CT scan shows a large duodenal-jejunal hematoma (H, arrows). (15) Focal hematoma in a 6-year-old boy with a 3-day history of vomiting. He had had an on-ice collision with his hockey coach 2 weeks earlier. The serum amylase level was normal. CT scan shows a large mass (H) in the left upper quadrant that drapes over bowel loops (B). An upper gastrointestinal study showed complete obstruction due to the mass. The mass was thought to be a large intramural jejunal hematoma. The patient was initially treated conservatively and received total parenteral nutrition. However, the symptoms did not improve and the mass persisted, and thus it was drained percutaneously. The contents were consistent with old blood and showed no amylase.

 


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  		Figures 16, 17.   (16) Focal hematoma in a 13-month-old girl with an initial history of "fall from couch." Later, child abuse was confirmed. CT scan shows a mesenteric hematoma (H). The patient also had a liver contusion, a renal contusion, a skull fracture, a subdural hematoma, and bilateral retinal hemorrhage. (17) Focal hematoma in a 7-year-old boy with lap belt ecchymosis. CT scan shows a hematoma (H) surrounding the distal superior mesenteric artery and vein. The patient was treated conservatively. The finding had resolved at follow-up CT performed 1 month later.

 


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  		Figures 16, 17.   (16) Focal hematoma in a 13-month-old girl with an initial history of "fall from couch." Later, child abuse was confirmed. CT scan shows a mesenteric hematoma (H). The patient also had a liver contusion, a renal contusion, a skull fracture, a subdural hematoma, and bilateral retinal hemorrhage. (17) Focal hematoma in a 7-year-old boy with lap belt ecchymosis. CT scan shows a hematoma (H) surrounding the distal superior mesenteric artery and vein. The patient was treated conservatively. The finding had resolved at follow-up CT performed 1 month later.

 
Active Hemorrhage
Recent hemorrhage from the intestine or mesentery into the peritoneum may be more hyperattenuating than older hemorrhage that has diffused throughout the abdomen (Fig 18). This difference in attenuation is particularly likely if the hemorrhage is initially confined within a smaller portion of the peritoneal space (eg, between the leaves of the mesentery). This appearance has been termed the sentinel clot sign (24). Active hemorrhage may be enhanced by intravenous contrast material. Mesenteric stranding, fluid at the mesenteric root, and focal hematoma are seen in association with active hemorrhage but are of lower attenuation. Patients with active hemorrhage identified at CT usually require surgery (21,25). The CT findings guide the surgeon to the site of injury.



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  		Figure 18.   Active hemorrhage in a 9-year-old boy who was ejected from an automobile during a motor vehicle accident. CT scan shows evidence of active bleeding into the mesentery (arrowheads), thickening of the bowel wall (arrow), fluid at the mesenteric root (M), and free fluid (F). At surgery, a large ileal mesenteric tear was found with ischemia of the ileum and mesoappendix but no perforation.

 
Mesenteric Pseudoaneurysm
Mesenteric pseudoaneurysms are rare. A sizable pseudoaneurysm probably indicates a substantial mesenteric injury with a vascular injury and a high likelihood of bowel ischemia or infarction (Fig 19). As with pseudoaneurysms within other abdominal structures, there is a high likelihood of continued or renewed hemorrhage.



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  		Figure 19.   Mesenteric pseudoaneurysm in an 8-year-old boy who was hemodynamically stable after a head-on motor vehicle accident in which he was restrained. CT scan shows a large hematoma (H) in the midabdomen on the right side with an enhancing pseudoaneurysm (*) and evidence of active hemorrhage (arrowheads). F = free intraperitoneal fluid. At surgery, a large mesenteric tear with right colonic ischemia was found.

 
Hypoperfusion Complex
Bowel injury produces CT findings that overlap with those of the hypoperfusion complex (26, 27). Although children with bowel perforation may also have manifestations of the hypoperfusion complex, it is important to differentiate those with the hypoperfusion complex only so that the patient receives the aggressive resuscitative therapy indicated and does not undergo unnecessary abdominal surgery. In the hypoperfusion complex, bowel wall thickening is diffuse but is usually limited to the small intestine (Figs 20, 21). The intestine is usually dilated and filled with fluid. Other findings indicative of hypoperfusion include diminished aortic caliber, collapse of the inferior vena cava, abnormal parenchymal organ enhancement, and associated traumatic intraabdominal injury. Free fluid and mesenteric stranding are usually present. The hypoperfusion complex can be distinguished from bowel wall thickening due to focal bowel or mesenteric injury by means of the associated findings and the diffuse nature of the small bowel abnormality. The CT findings of bowel perforation may overlap with those of the hypoperfusion complex (26). Such overlap is particularly likely if the diagnosis of bowel perforation is delayed and peritonitis causes diffuse bowel wall thickening.



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  		Figures 20, 21.   (20) Hypoperfusion complex in an 8-year-old boy after a motor vehicle accident. The patient appeared to be in stable condition on entering the CT scanner but experienced cardiac arrest during scanning (after this image was obtained) and could not be resuscitated. CT scan shows diffuse distended small intestine with diffuse wall thickening, findings consistent with the hypoperfusion complex. The aorta (a) is small in caliber. A large amount of free intraperitoneal fluid (F) and a large liver laceration are present. (21) Hypoperfusion complex in a 4-year-old boy after a motor vehicle accident in which he was unrestrained. In the ensuing fire, the patient suffered full-thickness burns over 90% of his body surface area. CT scan shows marked diffuse wall thickening of the small intestine. The aorta (a) and inferior vena cava (i) are small in caliber. C = air-filled colon (not free air), F = free intraperitoneal fluid. The patient died shortly after the CT study.

 


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  		Figures 20, 21.   (20) Hypoperfusion complex in an 8-year-old boy after a motor vehicle accident. The patient appeared to be in stable condition on entering the CT scanner but experienced cardiac arrest during scanning (after this image was obtained) and could not be resuscitated. CT scan shows diffuse distended small intestine with diffuse wall thickening, findings consistent with the hypoperfusion complex. The aorta (a) is small in caliber. A large amount of free intraperitoneal fluid (F) and a large liver laceration are present. (21) Hypoperfusion complex in a 4-year-old boy after a motor vehicle accident in which he was unrestrained. In the ensuing fire, the patient suffered full-thickness burns over 90% of his body surface area. CT scan shows marked diffuse wall thickening of the small intestine. The aorta (a) and inferior vena cava (i) are small in caliber. C = air-filled colon (not free air), F = free intraperitoneal fluid. The patient died shortly after the CT study.

 
The findings of the hypoperfusion complex may be striking. Although patients with this entity often appear to be in stable condition during scanning, they are actually on the brink of hemodynamic decompensation and require close monitoring and aggressive intervention (27).


   SUMMARY
Top
 Abstract
 INTRODUCTION
 EXAMINATION TECHNIQUE
 CLINICAL EXPERIENCE
 MECHANISMS OF TRAUMA
 CT FINDINGS
 SUMMARY
References
 
In our experience, all pediatric patients with traumatic perforation or infarction of the intestine had multiple abnormalities at CT. A specific history of lap belt injury, bicycle handlebar injury, or child abuse with an abdominal injury should heighten suspicion for a bowel injury. Some findings, such as free intraperitoneal air and focal bowel wall thickening, are associated with a strong likelihood of a bowel injury that requires surgical repair. Other findings, such as free fluid, mesenteric stranding, fluid at the mesenteric root, and hematoma, are less specific for an injury that requires surgical repair. The hypoperfusion complex can usually be differentiated from a traumatic bowel injury; however, in some patients the imaging findings overlap.


   References
Top
 Abstract
 INTRODUCTION
 EXAMINATION TECHNIQUE
 CLINICAL EXPERIENCE
 MECHANISMS OF TRAUMA
 CT FINDINGS
 SUMMARY
 References
 

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