Dr. Tye is a Radiology Fellow and Dr. Desser is an Associate Professor of Radiology, Department of Radiology, Stanford University School of Medicine, Stanford, CA.
variety of infectious, inflammatory, neoplastic, and congenital
diseases affect the small bowel, resulting in myriad clinical
presentations that can often overlap. Computed tomography (CT) has
become an indispensable tool for evaluating the small bowel in both the
outpatient and emergency room settings, replacing the radiographic
small-bowel follow-through (SBFT) examination in most instances. The
development of multidetector CT (MDCT) scanners and their concomitant
shorter scan times has further increased the utility of CT in evaluating
vascular abnormalities affecting the small bowel because of the ability
to scan multiple acquisitions during different phases of enhancement.
The multiplanar capabilities of MDCT, along with the development of
neutral enteric contrast agents, has facilitated the development of CT
enterography as a useful tool for detailed characterization of
inflammatory diseases and improved detection of small-bowel neoplasms.
purpose of this article is, first, to review the technique for
performing MDCT of the small bowel, and second, to discuss its various
applications and indications.
different techniques have been established for MDCT of the small bowel.
At our institution, we routinely employ either a 16- × 1.25-mm or 64- ×
0.625-mm detector configuration, reconstructing at 1.25- and 5-mm-thick
axial sections for primary viewing. Coronal reformations are also
routinely performed. Intravenous contrast is routinely administered for
standard MDCT of the abdomen/pelvis, in which small bowel pathology is
suspected, unless there is a contraindication. We administer 150 mL of a
300-mg/mL iodinated contrast medium intravenously at a rate of 2 to 3
mL/second. Scanning commences during the portal venous phase, after a
High-density enteric contrast is not typically
administered for our routine CT scans for several reasons. First, the
presence of water-density fluid in the bowel lumen is preferred when
intravenous contrast has been administered, as this maximizes
visualization of mucosal enhancement patterns, which are of critical
importance in cases of bowel ischemia and a number of inflammatory
conditions. High-density contrast can also obscure intraluminal lesions,
such as gallstones in cases of gallstone ileus. Second, imaging cannot
commence until 1 to 2 hours following the administration of positive
enteric contrast in order to ensure adequate opacification of distal
small-bowel loops—a delay that is often not feasible in the
Positive enteric contrast agents, including
barium sulfate suspensions and water-soluble high osmolar iodinated
solutions, can be useful in a few situations, however. If intravenous
contrast cannot be given, positive enteric contrast will facilitate
delineation of the small-bowel loops and thus aid in distinction of
bowel loops from surrounding soft-tissue structures. Patients with
ovarian malignancies routinely ingest positive enteric contrast agents
prior to their staging/surveillance MDCT scans, which are also performed
with intravenous contrast, in order to improve our ability to
distinguish peritoneal tumor implants from normal small-bowel loops.
Patients in whom there is high clinical suspicion for fistulaeor
abscesses are also given positive enteric contrast prior to their
studies for optimal detection and characterization of these entities.
there is high clinical suspicion for bowel ischemia, our MDCT protocol
is modified to optimize visualization of the mesenteric arteries and any
associated abnormalities. A CT angiogram is obtained using a
bolus-tracking technique, with image acquisition occurring during the
arterial phase of enhancement.
CT enterography (CTE), another
modification of the MDCT protocol, is also being increasingly used in
select patients in whom specific clinical questions regarding
small-bowel architecture is needed, such as Crohn’s disease or occult
gastrointestinal (GI) bleeding. The protocol for CTE differs most
prominently from routine MDCT in the administration of large volumes of
neutral enteric contrast prior to theMDCT scan. Neutral enteric contrast
that is not resorbed is preferred to maximize distal-bowel luminal
distention and conspicuity of the enhancing bowel wall. In addition, the
beam hardening artifacts that can be seen with positive enteric
contrast agents are avoided. A number of studies have been performed
comparing various contrast agents, including a combination of water and
methylcellulose, polyethyleneglycol, mannitol, sorbitol, and
low-concentration barium solutions.1-5 The most commonly used
agent now is Volumen (Bracco Diagnostics,Inc., Princeton, NJ), a
low-concentration barium solution containing sorbitol, a nonabsorbable
sugar alcohol that limits water resorption and thereby helps maintain
The details of neutral enteric contrast administration for CTE vary slightly from institution to institution.1,7 but
generally involve ingestion of a total of 1350 mL of Volumen,
administered in three 450 mL portions at uniform time intervals
beginning 45 to 90 minutes prior to scanning.
The timing of CT
image acquisition relative to intravenous contrast injection is also
modified in the CTE protocol, with images acquired during the “enteric”
phase of contrast enhancement, after a 45-second delay (Figure 1).
number of congenital conditions affecting the small bowel can cause
symptoms that come to clinical attention and which can be detected on
MDCT. Some of these entities, including Meckel’s diverticulum,
malrotation, and annular pancreas, are detailed below, along with their
complications and associated MDCT findings.
diverticulum is the most common congenital anomaly of the
gastrointestinal tract and results from failure of regression of the
vitelline duct, resulting in a true diverticulum arising from the distal
ileum. It is estimated from autopsy series that approximately 2% to
4%of individuals have Meckel’s diverticula, although the vast majority
of individuals are asymptomatic.8-10
diverticulum is the most common cause of gastrointestinal bleeding in
patients under the age of 30 and is due to acid production and
subsequent ulceration by rests of ectopic gastric mucosa within the
diverticulum.11,12 Meckel’s diverticulum can also present with intestinal obstruction due to intussusception, volvulus, or hernia.13,14 Symptoms can also result from inflammation and/or perforation of the diverticulum.14 While
symptomatic Meckel’s diverticula in children are most often related to
hemorrhage or intussusception, in adults,symptoms are more commonly due
to obstruction or diverticulitis.11,15-17 In such a setting,
MDCT is frequently utilized for evaluation of these nonspecific
symptoms. As a result, Meckel’s diverticula and their associated
complications have been increasingly diagnosed by CTin both the
pediatric and adult populations.8,12 The usefulness of MDCT
in detecting a Meckel’s diverticulum as the cause of lower
gastrointestinal bleeding has also been recognized.13
a CT scan, a Meckel’s diverticulum typically appears as a blind-ending
pouch located in the midline or in the right lower quadrant, containing
air and fluid or particulate matter.11,12 Visualization of a
fibrous band connecting the diverticulum to the anterior abdominal wall
is helpful for confident diagnosis. Mural thickening and infiltration of
the surrounding mesenteric fat may be present if there is active
inflammation.Identification of a normal appendix on CT is also quite
useful for excluding the diagnosis of appendicitis in these patients, as
acute appendicitis is often clinically suspected.12 Olson et
al described the appearance of symptomatic Meckel’s diverticula in a
pediatric population, noting 3 typical patterns: isolated small bowel
obstruction (31%); intussusception with small bowel obstruction (19%);
and cystic mass with surrounding inflammatory change (25%) (Figure 2).8
Anomalies of midgut rotation
primitive midgut undergoes a number of complex rotations during the
first trimester of fetal development in order to establish its
finalnormal position, followed by peritoneal fixation of the broad-based
small-bowel mesentery, which extends from the ligament of Treitz to the
ileocecal valve. A number of anomalies can occur when these rotations
do not occur normally, including nonrotation, a spectrum of
malrotation,and reverse rotation. Classically, a complete midgut
malrotation presents in the neonatal period secondary to volvulus, with
neonatal bilious vomiting. However, many individuals, particularly those
with less severe degrees of midgut malrotation, may not present with
symptoms until later in life, with a range of clinical presentations,
from vague abdominal pain to intermittent symptoms of obstruction to
malabsorption and weight loss, at which point, these patients are often
evaluated by CT scan.18,19 Some may not develop symptoms at
all, with the abnormal positioning of their bowel noted only
incidentally on CT studies performed for other reasons.20 Given
the risk of volvulus associated with malrotation of any degree,
however, the recognition of these anomalies by radiologists is critical,
even when patients are asymptomatic.
An abnormal position of the
cecum on CT can be useful for determining the presence of a malrotation,
with an increasingly abnormal position generally corresponding with a
more severe degree of malrotation. The duodenum may also lie in an
abnormal position, anterior to the superior mesenteric artery (SMA). An
important clue to the presence of a midgut malrotation or nonrotation is
the reversal of the normalrelative positions of the superior mesenteric
vein (SMV) and artery, first described by Nichols and Li as the “SMV
rotation sign.”21 That is,if the SMV lies to the left of or
directly anterior to the SMA rather than in its normal position to the
right of the SMA, a midgut malrotation or nonrotation is likely present,
as this results from failure of completion of the normal 270-degree
counterclockwise rotation of the midgut around the axis of the SMA
during fetal development. This abnormal relationship of the SMA and SMV
can be demonstrated on ultrasound in patients with a favorable body
habitus, but is even more easily seen on CT.18-24 The
“whirlpool sign” can be seen on both CT and ultrasound in cases of
malrotation complicated by midgut volvulus and describes the twisting of
the small bowel and SMV around the SMA.18,19,25,26
pancreas is a rare congenital anomaly that is typically diagnosed in
early childhood, either due to symptoms of complete duodenal obstruction
and/or frequently associated additional congenital abnormalities. In
adults, however, annular pancreas is often not clinically suspected, but
is increasingly diagnosed on imaging studies performed to evaluate
symptoms of gastric outlet obstruction or pancreatitis.27,28 An
annular pancreas results from failure of rotation and fusion of the 2
ventral pancreatic anlages to the dorsal anlage during the first
trimester of fetal development. It is a rare congenital anomaly,
although the increased use of MDCT and MRCP in recent years has
suggested that there may be a higher incidence than previously thought,
particularly when also taking into consideration the incidence of
incomplete annular pancreas, which can also cause clinical symptoms.27 CT,
particularly with imaging during the pancreatic phase of enhancement,
enables visualization of the pancreatic tissue encircling the duodenum
either completely or partially.27,28 Sandrasegaran et al
found that identification of pancreatic tissue posterolateral to the
second portion of the duodenum is 92% sensitive and 100% specific for
diagnosis of annular pancreas, whether complete or incomplete. That is, a
complete ring of pancreatic tissue surrounding the duodenum is not
necessary for a diagnosis of annular pancreas.27
ischemia can be either acute or chronic, with acute mesenteric ischemia
far more common than chronic ischemia. CT, and more recently, MDCT,
play a critical role in the diagnosis of patients with acute mesenteric
ischemia. Acute mesenteric ischemia is an infrequent but important cause
of abdominal pain, as it is associated with an average mortality rate
of 71%. There has been little improvement in outcomes in the past 10
years, despite medical, surgical, and technological advances.29
mesenteric ischemia can be due either to occlusive disease (80%) or to
nonocclusive disease (20%). The majority of occlusive cases are due to
thromboembolic disease affecting the SMA, with 50% secondary to embolus
and 20% secondary to thrombosis. SMV occlusion is less common,
responsible for 5% to 10% of cases. Vasculitis from a variety of
underlying conditions is also an important, although less common,
occlusive cause of acute mesenteric ischemia. The CT appearance can be
quite variable, as it is in large part a reflection of the pathologic
stage of ischemic injury to the bowel, which ranges from mild mural
edema to transmural infarction, depending on the duration of ischemia,
the cause (arterial or venous), and the extent of involvement.30
occlusive ischemia due to thromboembolic disease is best evaluated with
a biphasic MDCT angiography technique, in which both arterial and
portal venous phase scans are acquired. An occlusive thrombus can be
identified as a hypodense filling defect within the proximal portion of
the SMA, usually adjacent to a site of preexisting calcified
atherosclerotic plaque. An occlusive acute embolus also appears as a
hypodense filling defect, but is typically located at arterial branch
points. Three-dimensional reconstructions and volume-rendered images of
the mesenteric vasculature can often be quite helpful for confident
diagnosis. Ischemic small bowel due to arterial occlusive disease is
characterized by a loss of motor tone, resulting in distention of the
small- bowel loops, but generally no significant bowel wall thickening.
Rather, the walls appear paper-thin. Lack of mural enhancement is a
highly specific sign of mesenteric ischemia,but can be difficult to
detect (Figure 3).31,32 In more advanced cases, in which
ischemia has progressed to infarction, pneumatosis and portalvenous gas
may be seen. However, it is important to note that these can also be
seen in nonischemic conditions, in which the integrity of the intestinal
mucosa has been breached.30,33,34
Findings on MDCT in
cases of bowel ischemia due to venous occlusion are typically different
from those due to arterial occlusion, characterized by more pronounced
wall edema, mesenteric edema, and interloop free fluid. Bowel-wall
thickening in ischemia is typically symmetric, but can have various
patterns of attenuation, including homogeneous hypodensity or a
halo/target appearance. Mural hemorrhage is frequently seen as well in
cases of venous ischemia, and can cause a heterogeneous attenuation
within the bowel wall due to areas of hemorrhage juxtaposed with areas
of edema and hypoperfusion.32 Venous occlusion can be seen in
patients with an underlying hypercoagulable state, or may be due to a
complicated small-bowel obstruction, an infiltrative neoplasm, or an
infection. Occasionally, a thrombus can be directly visualized within
the affected mesenteric vein as a hypodense filling defect that may
expand the vein.
The gastrointestinal tract is involved in 50% of
patients with vasculitis. Vasculitides involving the large vessels
include Takayasu arteritis and giant cell arteritis. Medium vessels are
affected in polyarteritis nodosa, typically seen in older females, and
Kawasaki disease, a pediatric disease. Systemic lupus erythematosis
(SLE), Henoch-Schonlein purpura, and Wegener’s disease affect small
vessels and are typically seen in younger patients. These vasculitides
cause ischemia at unusual sites, such as the stomach and duodenum, as
well as the small bowel and the colon. Infarcts in other organs, such as
the kidney and spleen, are often seen as well. Bowel ischemia in these
patients is secondary to narrowing and occlusion of small mesenteric
arteries, resulting in long segments of diffuse, marked bowel wall
edema, and hemorrhage(Figure 4).
Generalized states of systemic
hypotension, such as heart failure and shock, may produce nonocclusive
small-bowel ischemia. Reperfusion injury occurs once blood flow to the
bowel is restored to normal, leading to mucosal injury and submucosal
edema. On MDCT,this may produce the dramatic appearance of marked
mucosal hyperemia and bowel wall thickening known as “shock bowel.”
mesenteric ischemia is also known as “intestinal angina” and results
from inadequate blood flow to the bowel, typically in the setting of
underlying atherosclerotic disease in elderly patients causing
significant occlusion or narrowing of the celiac axis, SMA, and/or
inferior mesenteric artery. Symptoms typically occur in a postprandial
setting, when increased splanchnic blood flow demand is greater than the
blood supply available from the diseased arteries. Chronic mesenteric
ischemia is often suspected based on the clinical presentation, in
conjunction with arteriographic evaluation of the splanchnic vessels.
MDCT utilizing the CT angiography technique described above, calcified
and noncalcified atherosclerotic plaque is well demonstrated, as well as
the extensive collateral formation that occurs due to the chronic
nature of the disease. MDCT also allows the exclusion of extrinsic
causes of vascular occlusion, such as tumors. MDCT images can also be
used for preoperative planning for revascularization.30
obstruction (SBO) is a common cause of abdominal pain, accounting for
4% of all emergency room visits for abdominal pain and 20% of surgical
admissions. Rapid diagnosis and identification of complicated cases,
such as closed-loop obstruction, volvulus,or superimposed ischemia, are
of critical importance, as these patients require emergent surgical
management. At our institution, MDCTis routinely performed for the
evaluation of suspected SBO, having essentially replaced the small-bowel
follow-through examination and sometimes even plain radiography as the
initial examination of choice.
MDCT findings in SBO include
dilated loops of small bowel measuring >3 cm in diameter, with a
transition to normal caliber or collapsed bowel loops seen distally. The
“small bowel feces” sign has been identified as a specific but not
sensitive sign for SBO, and describes the presence of solid material
intermixed with gas bubbles (ie, the appearance of fecal material)
within the small bowel, typically just proximal to the site of
obstruction.35-37 This finding can be helpful in identification of the transition point.38 The
fecal material should be present within dilated loops of bowel,
however, as fecal material can be seen within the small bowel in
nonobstructed bowel of cystic fibrosis patients as well as individuals
with metabolic or infectious enteropathies. Furthermore, fecal material
within the distal ileum can be seen in patients with an incompetent
ileocecal valve, but no SBO.37,39
facilitates the identification of the cause of an SBO, whether it is
extrinsic or intrinsic to the bowel. The most common causeo f SBO in
developed countries is adhesions, with the vast majority secondary to
prior abdominal or pelvic surgery. Adhesions are not visualized on CT,
with only a beak or sharp angulation in the bowel seen at the transition
point from normal to dilated bowel (Figure 5). A diagnosis of adhesions
as the cause of SBO can only be made when other causes have been
excluded and an appropriate clinical history is present.38 The reported accuracy of CT in the diagnosis of adhesive SBO is 70% to 95%.38
second most common cause of SBO is hernias, which are most commonly
external but may also be internal. There are several typesof external
hernias, including but not limited to inguinal, femoral, umbilical,
ventral, obturator, lumbar, and Spigelian hernias, all of which occur at
points of structural weakness in the abdominal or pelvic wall
musculature. These areas of weakness may be iatrogenic in nature,such as
in the cases of parastomal, incisional, and laparoscopic port site
hernias. When small bowel protrudes into these areas of weakness and
becomes entrapped, passage of enteric contents proximal to this may
Internal hernias are less common than external
hernias, but are important to identify as they are associated with
significant morbidity and mortality, yet are difficult to diagnose both
clinically and radiographically. Internal hernias can occur in many
locations, including paraduodenal, the foramen of Winslow, pericecal,
and intersigmoid. Transmesenteric internal hernias are becoming
increasingly common because of the increasing number of bariatric
surgeries performed in which a mesenteric defect is created to
accommodate a Roux loop. When small bowel herniates through this
surgically created defect, causing an SBO, small bowel is seen in an
abnormal position lateral to the colon, with omentum and small bowel
located directly adjacent to the abdominal wall (Figure 6).38
rare cause of SBO is intussusception, responsible for only 1% of cases.
A “bowel-within-bowel” appearance on CT is pathognomonic for an
intussusception and describes the telescoping of a small-bowel loop,
often with its associated mesenteric fat and vessels, into a downstream
loop of bowel. Most small-bowel intussusceptions identified on CT are
transient, cause no associated obstruction, and have no underlying tumor
acting as a lead-point (Figure 7). Rather, the majority of
entero-enteric intussusceptions may be idiopathic. In a minority of
cases, however, a mass lesion may be acting as the lead-point for the
intussusception. In these cases, the intussusception is more likely to
cause significant SBO requiring surgical treatment (Figure 8).40
intrinsic and extrinsic to the bowel can also cause SBO, with some
common causes including adenocarcinomas of the GI tract, pancreas, and
ovary, carcinoid tumor and its associated desmoplastic reaction, and
extraenteric nonHodgkin’s lymphoma.38
intraluminal causes of SBO include gallstones that migrate from the
gallbladder via a biliary-enteric fistula into the adjacent duodenum,
typically lodging itself in the distal ileum to create the entity known
as “gallstone ileus.” Foreign bodies, bezoars, enteroliths,and
inspissated fecal material in patients with cystic fibrosis can also
MDCT plays a role not only in diagnosing
the presence of an SBO and determining its cause, but also in
identifying potential complications, one of the most important of which
is a closed loop obstruction. A closed loop obstruction results when 2
points along the same length of small bowel are obstructed at a single
point. This is most often caused by an adhesion, although internal and
external hernias are also common causes. The segment of bowel between
the 2 obstructed points is predisposed to volvulus, leading to venous
outflow obstruction,and high risk of strangulation of the incarcerated
segment of bowel. Findings of closed loop obstruction on MDCT depend on
the length and angle of the incarcerated segment. Typically, a C-shaped,
U-shaped, or coffee bean-shaped loop of bowel is seen, with radiating
folds and accompanying mesenteric vessels seen converging to the point
of obstruction, often called the “beak sign” (Figure 9). A “whirl sign”
can be seen in the presence of a volvulus, describing the twisting of
the mesentery and its vessels around the point of obstruction.41,42
enteritis is a common cause of acute diarrheal illness in the United
States and can be caused by viruses, bacteria, or, less commonly,
protozoa. The most common viral causes include norovirus (formerly
Norwalk virus) and rotavirus, with the most common bacterial causes
including Salmonella, Escherichia coli, and Clostridium perfringens. Protozoa that typically involve the small bowel include Cryptosporidium, Microsporidium, Isospora, Cyclospora, and Giardia lamblia.
However, there is a limited role for radiologic imaging studies in the
diagnosis and management of infectious enteritis, as most patients do
not seek medical attention, and, in those who do, diagnosis can
generally be made from the history, physical exam, stool studies, and,
when needed, endoscopy. Imaging studies are only necessary in rare cases
or special situations, such as that of the immunocompromised patient.
The proximal small bowel is the typical site of infection by Giardia lamblia,
the most common parasite to cause infection in the United States.
Findings on CT are fairly nonspecific, with diffuse bowel-wall
thickening and mesenteric lymphadenopathy.43
enteritis affecting the distal ileum, often in combination with the
cecum, can cause a confusing clinical picture, mimicking appendicitis.
Frequent pathogens causing an infectious ileocecitis include Salmonella, Yersinia, Shigella, and Campylobacter.44,45
a well-recognized cause of colitis, is increasingly recognized as a
cause of enteritis as well. As in the colon, histologic changes include
extensive ulceration and sloughing of the bowel mucosal surface. In
contrast to cases of pseudomembranous colitis, bowel-wall thickening is
not as prominent of a feature in cases of C. difficile enteritis,
sometimes only seen in a very short segment of small bowel.
Distended,fluid-filled small-bowel loops, ascites, and mesenteric-fat
stranding were the predominant features in one small published series
and were described in several other reports as well. Abnormalities may
also be seen in the cecum, possibly heralding early involvement of the
colon as well.46
Important causes of enteritis in patients with HIV include Mycobacterium avium intracellulare (MAI), cytomegalovirus, and Crypto sporidium.
MAI more frequently affects the jejunum, causing bowel wall thickening
that can be nodular. The finding of low-density, bulky mesenteric and
retroperitoneal lymphadenopathy is helpful in suggesting the diagnosis,
although Whipple disease and lymphoma can have the same appearance.
Cytomegalovirus enteritis is often hemorrhagic, secondary to mucosal
ulcerations, which can sometimes be seen onCT. Cryptosporidium infection
results in bowel wall thickening, also typically involving the proximal
small bowel, which can be indistinguishable from MAI and giardiasis.47
variety of inflammatory conditions of the bowel are well depicted on
MDCT, although the manifestations can often be nonspecific, making a
precise diagnosis difficult. However, a systematic approach to the
interpretation of small-bowel abnormalities detected on CT can improve
specificity in some cases.
with Crohn’s disease who present with an acute flare often demonstrate
bowel wall thickening, with mural stratification that results in a
target-like or “halo” appearance of the bowel. Bowel wall thickening is
defined as a wall thickness >3 mm in a well-distended loop. The“halo”
appearance refers to alternating layers of hyperdense mucosa, hypodense
intramural edema, and hyperdense serosa (Figure 10). The presence of
low-density intramural edema suggests an active inflammatory process. A
more sensitive yet less specific indicator of active disease ismucosal
hyperemia, which is optimally demonstrated on a CT enterography
protocol. Luminal narrowing may be seen secondary to edema or spasm and
is reversible at this stage, although it can be severe enough to cause
an associated SBO.7With chronic inflammation, intramural
fatdeposition can be seen, with fat attenuation seen within the
thickened bowel wall rather than the water-density intramural edema seen
with acute disease. Alternatively, chronic inflammation can also result
in muscular hypertrophy, collagen deposition, and fibrosis, resulting
in strictures that can cause small-bowel obstruction.
findings can also be helpful indicators of active disease. The “comb
sign” (Figure 10) describes the engorged vasa rectae within the
mesentery that run perpendicular to the bowel wall and correlates with
more advanced, active disease that may warrant more aggressive medical
therapies, given its correlation with more frequent hospital admissions.48 An
increase in the density of the mesenteric fat surrounding an abnormal
loop of bowel is a highly specific indicator of active Crohn’s disease
and correlates with elevated C-reactive protein levels and
histopathologic severity of disease.7 Fibrofatty
proliferation, or fatty deposition along the mesenteric border of
inflamed bowel segments, is highly specific for transmural inflammation
secondary to Crohn’s disease, but can be seen with both active and
Other important extra-enteric findings include
abscesses and fistulas, as these may determine a need for surgical
intervention. When abscesses or fistulas are suspected clinically,
positive enteric contrast should be administered prior to the CT scan.
disease is a chronic intolerance to gluten in genetically predisposed
patients that can lead to mucosal inflammation in the small bowel, most
often affecting the duodenum and proximal jejunum. Although definitive
diagnosis is made via endoscopic biopsy showing characteristic
histopathologic changes, as well as resolution of these changes after
institution of a gluten-free diet, MDCT is increasingly being used for
evaluation. Several authors have recently advocated the use of CT
enteroclysis for evaluation of suspected celiac disease. CT enteroclysis
differs from the routine MDCT protocol in that a large volume of
room-temperature water (generally >2 L) is infused through a
nasojejunal tube during image acquisition. Detailed protocol information
can be obtained from previously published literature.49,50
et al in a retrospective analysis of their experience with CT
enteroclysis in patients with suspected celiac disease, found that
reversal of the jejuno-ileal fold pattern had the highest specificity
for the disease (100%), but a sensitivity of only 63.6% (Figure 11).
Other findings that were strongly correlated with celiac disease
included ileal-fold thickening, vascular engorgement, and splenic
atrophy.50 Intussusception can be seen in celiac sprue due to
hypertrophied lymphoid tissue acting as lead-points. Lymphadenopathy is
often present as well. Patients with celiac disease are also at
increased risk for development of small-bowel adenocarcinomas and
lymphomas, and the bowel should be carefully evaluated for evidence of
administered in the course of cancer therapy can cause both acute and
chronic inflammatory changes in any bowel loops included within the
radiation port. Radiation enteritis is characterized by segmental areas
of abnormal bowel wall thickening. Chronic radiation enteritis can
result in development of homogeneously enhancing scar tissue within the
bowel wall, similar to that seen with fibrotic changes in chronic
Crohn’s disease.32 Given the somewhat nonspecific findings,
knowledge of the clinical history and note of the location of the
abnormal small bowel within the site of previous radiation are critical
to a confident diagnosis.
Primary neoplasms of the small bowel, both
benign and malignant, are rare. They are also difficult to diagnose, as
direct visualization of most of the small bowel is not possible with
conventional endoscopic procedures. Capsule endoscopy has been
increasingly used, but its utility is controversial. Double-contrast
enteroclysis has been considered the test of choice for evaluation of
the small bowel, but its required technical expertise and invasiveness
are drawbacks.51 MDCT, particularly with the CT enterography
protocol, has improved the ability ofCT to detect small-bowel tumors,
and provides the added advantage of characterizing the extraluminal
extension of disease.
A detailed description of the wide variety
of small-bowel neoplasms is beyond the scope of this paper, but can be
found in a number of previous publications.51,52 Benign
neoplasms include leiomyomas, gastrointestinal stromal tumors (GIST),
lipomas, adenomas, and hemangiomas. A number of polyposis syndromes also
affect the small bowel; they include familial adenomatous polyposis,
Peutz-Jeghers syndrome, Gardner’s syndrome, juvenile polyposis,
Cronkihite-Canada syndrome, and Cowden’s disease.
account for up to 70% of small-bowel neoplasms. Adenocarcinomas are the
most common of these, occurring most often in the duodenum, followed by
the proximal jejunum. Risk factors for adenocarcinoma include celiac
disease, Crohn’s disease, and familial adenomatous polyposis. The CT
appearance of adenocarcinoma can vary, but typically a focal segment of
asymmetric bowel-wall thickening is seen, with moderate, heterogeneous
enhancement and areas of mucosal ulceration. Extension through the
serosa into the adjacent mesentery can be evaluated on CT, as well as
the identification of metastases to lymph nodes and solid organs.
Adenocarcinomas often narrow or occlude the bowel lumen and can cause
obstruction, which can also be characterized on MDCT.
most common malignant neoplasm in the small bowel is the neuroendocrine,
or carcinoid tumor, which originates from enterochromaffin cells. Fifty
percent of neuroendocrine tumors are located in the appendix, with the
second most common site being the ileum. Although they are
hypervascular, these tumors are often small and difficult to identify on
routine CT, although CT enterography may increase their conspicuity.
Nodal metastases incite a desmoplastic reaction within the mesentery,
resulting in a mass-like density with spiculated margins,calcifications,
and marked tethering of adjacent bowel loops (Figure 1). This
desmoplastic reaction is more easily detected on CT and can helpin
establishing the diagnosis. Patients often present with fairly advanced
disease, after the development of flushing, diarrhea, and intermittent
hypertension. These symptoms of the “carcinoid syndrome” occur when
liver metastases are present. Neuroendocrine metastases to the liver are
hypervascular lesions that are best detected during the arterial phase
Lymphoma is the third most common malignant
neoplasm of the small bowel and may arise from mucosa-associated
lymphoid tissue (MALT). A systemic lymphoma can also affect the small
bowel. Lymphoma has a variety of appearances on CT, ranging from a short
segment of symmetric bowel wall thickening to a solitary mass
infiltrating the surrounding mucosa to multifocal enhancing mucosal
nodules.Secondary obstruction is uncommon, although intussusception can
be seen. Lymphoma most often affects the ileum.
While most GISTs
are benign tumors, they also have the potential for malignant
transformation. No radiologic imaging findings other than metastatic
disease can reliably differentiate benign from malignant disease, and
thus, surgical resection of all GISTs is recommended. These mesenchymal
tumors are more common in the stomach, but can occasionally be seen in
the jejunum, where the typical appearance is that of an exophytic, bulky
mass, often with areas of central cavitation and calcification.
Metastases to the liver, in contrast to neuroendocrine metastases, are
Metastatic disease affecting the small bowel
can result from direct extension, intraperitoneal seeding, or
hematogeneous spread. Malignancies that tend to directly invade the
small bowel include pancreatic, biliary, or colonic neoplasms. Ovarian
and colon adenocarcinomas can cause tumor implants along the serosal
surface of the small bowel, and in their advanced stages, can result in
obstruction.Common sources of hematogenously spread metastatic disease
to the small bowel include lung, breast, and renal cell carcinomas, as
well as melanoma (Figure 9).51, 52
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
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.
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).
MDCT has become the test of choice for
evaluation of known and suspected small-bowel pathology. Dedicated
angiographic protocols can be used for investigation of occult GI
bleeding or suspected ischemia. Enterography protocols have proven
useful for evaluation of small bowel inflammatory disease, especially
Crohn’s, and for detection and characterization of small-bowel
neoplasms. MDCT has largely replaced the small-bowel follow-through as
the preferred technique for evaluation of small-bowel obstruction, and
is invaluable in numerous other clinical settings in which the bowel is
the primary source of pathology or secondarily involved by other
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