Dr. Melotti is with the Department of Diagnostic Radiology,
University of Maryland Medical Center and Maryland Shock-Trauma
Center, Baltimore, MD.
Although not a common sequela of blunt abdominal trauma, bowel
and mesenteric injury can be a major cause of early morbidity and
mortality if not detected quickly.
Bowel and mesenteric injuries occur in approximately 5% of patients
following blunt abdominal trauma, the most common mechanism of
injury is motor vehicle accidents.
Typical locations of injury include the fixed segments of bowel
that undergo shearing forces, such as the retroperitoneal
duodenal-jejunal junction at the ligament of Treitz and the
The bowel can also sustain injury by compression if caught between
the spine and an object such as the steering wheel or seat belt.
Due to the nature of such accidents, many patients have more
apparent multi-system injuries that can initially mask the
A reliable history and physical examination are often difficult
to obtain in the trauma patient due to distracting injuries,
neurologic injury, altered sensorium, or impairment of respiratory
function necessitating ventilatory support. The initial physical
examination may yield benign results as peritoneal signs may be
delayed. The classic clinical triad of rigidity, absent or
decreased bowel sounds, and abdominal pain is seen in approximately
one-third of patients with bowel and mesenteric injury.
The presence of an anterior abdominal hematoma or ecchymosis, also
known as the "seat-belt sign," may be apparent and suggests a
significant impact, although it is not highly correlated with bowel
(figure 1). Hypotension and tachycardia can suggest intra-abdominal
bleeding but are not specific for bowel or mesenteric injury,
and clinical findings can be confounded by injury to other
The timely diagnosis of bowel and/or mesentery injury is vital
since a significant delay can lead to peritonitis, sepsis, or
continued hemorrhage. Peritoneal lavage can be helpful in
diagnosing bowel and mesenteric injury in that it is sensitive for
intraperitoneal hemorrhage; however, lavage findings are
nonspecific for determining which organ is injured and the extent
The presence of bowel contents obtained by lavage is specific for
bowel perforation, although this is only detected in 30% of
surgically verified bowel perforations.
An increased white blood cell count in the peritoneal lavage fluid
also suggests full-thickness bowel injury, but may not be present
until several hours after injury. A drawback of diagnostic
peritoneal lavage is that retroperitoneal bowel injuries will not
be detected, and the use of lavage limits the ability to diagnose
bowel injury with CT since fluid and often air are introduced into
the peritoneal cavity.
Although sonography of the abdomen can be used to detect
intraperitoneal free fluid, it cannot specify the injured organ. In
the majority of patients with isolated bowel and mesenteric injury,
intraperitoneal free fluid is often not seen by sonography, thus
limiting the diagnostic sensitivity of this modality.
There are many studies in the radiologic and surgical literature
the accuracy of CT in diagnosing bowel and/or mesenteric injury in
the blunt trauma patient. Despite continued controversy, CT has
increasingly replaced peritoneal lavage as the diagnostic study of
choice in many trauma centers.
This is in part due to the widespread use and availability of
helical CT in many centers as well as the increased recognition and
understanding of CT signs of bowel and mesenteric injury by
interpreting radiologists. Scans are typically performed using oral
and intravenous iodinated contrast, and preferably prior to the
performance of peritoneal lavage.
CT findings specific for full-thickness bowel injury include
free intraperitoneal air (without an obvious source such as
previous peritoneal lavage or dissection of thoracic air) and
extravasated oral contrast.
In a study by Mirvis et al,
CT findings found to be diagnostic of full-thickness bowel
perforation include pneumoperitoneum without an alternate etiology;
intramesenteric, intramural, or retroperitoneal free air; direct
discontinuity of the bowel wall; and extravasation of oral contrast
Findings suggestive of bowel injury include intraperitoneal or
anterior pararenal fluid without CT evidence of a specific
abdominal organ injury, and thickened bowel wall or bowel wall
Abnormal enhancement of a segment of bowel wall may indicate bowel
injury, but is not specific.
CT findings indicating mesenteric injury associated with bowel
injury include triangular-shaped collections of free fluid between
the leaves of the mesentery (mesenteric triangles) or infiltration
within the mesenteric fat of fluid or hematoma
(figure 5). between bowel loops and mesenteric fat infiltration or
(figure 3).It is important to note that hemoperitoneum secondary to
solid abdominal organ injury does not commonly infiltrate the
or appear as triangular-shaped collections between the mesenteric
folds, thus lending greater specificity to this CT finding. Tiny
gas bubbles in the leaves of the mesentery can also be seen with
A careful search of the abdominal and pelvic CT images is needed to
exclude small amounts of pneumoperitoneum. Common sites of air
accumulation include the anterior peritoneal space and porta
hepatis region. Review of images in lung or bone windows
facilitates detection of minimal amounts of free air (figure
CT findings can be categorized as those associated with a need
for immediate surgery and those that may be observed. CT findings
sensitive for surgical bowel injury include extraluminal gas and
free fluid. Specific findings included extraluminal oral contrast
and extraluminal gas.
In one of the largest studies to date, Killeen
evaluated not only the accuracy of helical CT for detecting bowel
and mesenteric injury, but also its accuracy in determining which
patients required surgical management. CT was found to be 88%
accurate in detecting bowel injury, and 88% accurate in determining
surgical versus nonsurgical cases.
In diagnosing mesenteric injury, specific findings include
active mesenteric bleeding, bowel wall thickening associated with
mesenteric hematoma, and mesenteric hematoma alone
(figure 5). Mesenteric infiltration and free fluid suggest injury
to the mesentery, although these are not diagnostic findings for
injuries requiring surgical repair.
In the study by Killeen,
CT was found to be 96% accurate in diagnosing mesenteric injury and
75% accurate in determining surgical versus nonsurgical cases. CT
findings found to be sensitive for surgical mesenteric injury are
free intraperitoneal fluid and mesenteric hematoma; specific
findings include active bleeding and bowel wall thickening
associated with a mesenteric hematoma (figure 6). These findings
are similar to those of a study of mesenteric injury by Dowe et al.
Patients with CT findings of mesenteric bleeding or bowel wall
thickening associated with mesenteric hematoma or infiltration were
found to have a high incidence of mesenteric or bowel injury
requiring surgery. Focal mesenteric hematoma or infiltration alone
was found to be nonspecific, occurring in both bowel and mesenteric
injuries requiring surgery and those that did not.
Mimics and masks of bowel and mesenteric injury
Certain pathologic processes can either mask or mimic the CT
findings of bowel and mesenteric injury. Prolonged shock can
produce relatively diffuse bowel wall thickening
and obscure bowel wall contusion (figure 7). Shock bowel tends to
produce diffuse small bowel wall thickening associated with
mesenteric edema, whereas blunt trauma to the bowel is more likely
to manifest as focal or localized wall thickening (figure 8).
Increased central venous pressure (CVP) can cause periportal low
density on CT, bowel wall and mesenteric edema, free peritoneal
fluid, and retroperitoneal edema,
thus mimicking the intraperitoneal fluid, mesenteric edema, and
bowel wall thickening seen with primary bowel injury. Again, the
changes occurring with elevation of CVP are diffuse in extent
rather than focal as usually occurs with bowel injury (figure 9).
Signs of shock bowel, increased CVP, and bowel injury can
Despite its relative rarity, bowel and mesenteric injury is a
major cause of morbidity and mortality if not diagnosed in a timely
Controversy remains in the radiologic and surgical literature
concerning the diagnostic accuracy of CT in diagnosing these
injuries. Widespread availability of helical CT at emergency
centers and increasing familiarity by radiologists with diagnostic
and suspicious CT findings should lead to increased confidence and
reliance on this diagnostic modality. The increasing adoption of
nonoperative management of liver and spleen injuries requires high
confidence in the exclusion of surgical bowel and mesenteric injury
by CT. Further data from large, prospective studies should increase
the confident reliance on CT as an expeditious and accurate
diagnostic study for bowel and mesenteric injuries in the trauma
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