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80 M.G. Mutch, E.H. Birnbaum, and C.O. Menias
FIGURE 6-16. Contrast enema of Crohn’s disease showing skip
lesions.
that project into the lumen. Other findings associated with
diverticulosis include a shortened, narrowed, and spastic sigmoid colon. Hyperelastosis leads to a stiff, thickened, and
nondistendible colon that is characteristic of extensive diverticulosis. The combination of a shortened, thickened colon and
extensive diverticula can disrupt the symmetric appearance of
the haustral clefts, giving the mucosal outline an irregular
zigzag appearance (Figures 6-18A and B). This is best seen
with single column contrast enemas.
In the acute setting, a water-soluble contrast agent should be
used rather than barium to avoid the highly morbid case of barium peritonitis. In acute diverticulitis, the inflammation is pericolonic and contrast studies are unable to directly demonstrate
the inflammation. They are able to infer the effects of the pericolonic inflammation on the mucosa. Findings such as narrowing of the sigmoid colon, extrinsic compression, mucosal
edema, and spasm in the presence of diverticula are all suggestive of diverticulitis but they lack significant specificity.
Contrast enemas are able to demonstrate complications of
diverticulitis such as perforation, abscess, fistula, and strictures.
Extraluminal leak of contrast is diagnostic of diverticulitis
with free perforation, when associated with the appropriate
clinical scenario. The contrast can flow freely into the peritoneal cavity, into a contained cavity, or a blind ending sinus.
Contrast that flows into the bladder, vagina, or early filling of
proximal loops of intestine are all findings consistent with a
FIGURE 6-17. Contrast enema of Crohn’s disease showing a stricture.
fistula. A colovesical fistula is the most common diverticularassociated fistula, but contrast enemas are able to make the
23
diagnosis only 20% of the time.
Therefore, a contrast enema
should not be the first test used to confirm the diagnosis of a fistula. A pericolonic abscess that impinges on the colon can be
seen as a smooth contour defect along one wall of the colon that
does not distend with the instillation of contrast material or air.
Stricture formation may occur after a single attack of diverticulitis but more frequently it is the result of recurrent
episodes of inflammation. The site of the stricture is at the
point of inflammation, which is typically within the sigmoid
colon. Benign strictures have a smooth, gentle transition to
the stricture with intact mucosa. The radiographic appearance
of the stricture and adjacent colon along with the clinical scenario should help to elucidate the cause of the stricture.
27
Submucosal and Extracolonic Lesions
Lipoma
On double contrast barium enema, lipomas can appear as a
submucosal mass or a polypoid lesion. The lesions can have
an oval, lobulated, or pear shape and the overlying mucosa is
smooth with sharp, well-demarcated borders. Lipomas are
soft and pliable, so during fluoroscopic examination, com-
6. Diagnostic Evaluations—Radiology, Nuclear Scans, PET, CT Colography 81
overlying mucosa remains intact and smooth with the edges of
the lesion being distinct (Figure 6-19). The involved segments
tend to be long, with discrete proximal and distal edges, and the
overlying mucosa remains intact. The barium may highlight
nodular, irregular mucosal edges, but there is no ulceration.
This is unlike annular carcinomas, which have short strictures
with shouldering and ulcerated mucosa. Second, the mass can
infiltrate the mesentery resulting in cavitation of the lesion into
the mesentery. On barium enema, this appears similar to the
annular lesions, but at some point within the affected segment,
there is a nodular projection that is beyond the lumen of the
colon. Finally, disseminated lymphoma appears as multiple,
long segments of nodular, narrowed colon.
Endometriosis
The findings on barium enema in the patient with endometriosis are consistent with an extracolonic process, because the
30
mucosa remains smooth and intact.
Mild involvement will
show a short, focal area with bunching of the mucosal folds,
which has been termed mucosal pleating. This short segment
will also show evidence of extraluminal narrowing. With
more extensive involvement with scarring and contracture,
stricturing can develop (Figure 6-20). Radiographically, this
appears as a short, benign stricture with a sharp transition,
mucosal pleating, and intact mucosa.
FIGURE 6-18. A Contrast enema single column showing severe diverticulosis with the sawtooth mucosa. B Air contrast enema of severe
diverticulosis.
pression can change the configuration of the lesion; this is
called the “pillow sign.”
28
Lymphoma
There are three basic radiographic morphologies that primary
colonic lymphomas can demonstrate.
29
First, they can appear as
discrete polypoid lesions. Typically occurring in the cecum,
these lesions can range from 2 to 20 cm in size. In contrast, adenomatous polyps have mucosal irregularities because of their
frond-like appendages. These are submucosal lesions, so the
FIGURE 6-19. Contrast enema showing colonic lymphoma.
82 M.G. Mutch, E.H. Birnbaum, and C.O. Menias
FIGURE 6-20. Contrast enema showing endometriosis.
Colonic Intussusception
Intussusception occurs when a proximal segment of bowel
(intussusceptum) telescopes into the lumen of the distal bowel
(intussuscipiens), much like turning a sock inside out. When
viewed in cross-section, there are three rings or six layers
across the diameter, which represent walls of the intestine—
the outer wall is the distal lumen, the middle ring is the distal
wall folded back onto itself, and the inner wall is the proximal
intussuscepting wall. Plain films may reveal the pathognomonic “crescent sign.” As the intussusceptum telescopes into
the intussuscipiens, the distal lumen folds into itself. At this
transition, air can get trapped within the lumen, and this is
seen as the “crescent sign.” Plain films may also show a
dilated proximal colon that is decompressed distally. As a
result, a contrast enema is often ordered to evaluate a large
bowel obstruction. The classic appearance of an intussusception on contrast enema is the spring coil appearance or crescent sign (Figure 6-21). Contrast gets trapped between the
lumens of the intussuscipiens and intussusceptum leaving a
thin, circular line that encircles the intussuscipiens.
Anastomotic Assessment
Contrast enema studies are frequently used postoperatively to
examine a colocolic, colorectal, coloanal, or ileal-anal anastomosis. The studies are used to evaluate for anastomotic leak
in a septic patient, before closure of a diverting stoma, or to
rule out an anastomotic stricture in patients with defecation
difficulties. When testing the integrity of an anastomosis,
FIGURE 6-21. Contrast enema showing colonic intussusception.
a water-soluble contrast agent should be used. Contrast should
be allowed to fill the colon under the weight of gravity, with
the bag placed no higher than 1 m above the patient. Initially,
the flow of contrast should be tightly controlled and increased
as the examination permits. As previously mentioned, there is
minimal peritoneal toxicity with water-soluble agents, and a
single column study provides adequate detail to detect the
majority of clinically significant leaks. The expected findings
depend on the clinical scenario for ordering the examination.
In the early postoperative period when evaluating for an anastomotic leak, water-soluble contrast enema is more sensitive
31
than CT with rectal contrast.
Radiographic findings of an
anastomotic dehiscence include the extravasation of contrast
freely into the peritoneal cavity or into a contained cavity
(Figures 6-22A and B). Key findings that influence the management of an early anastomotic leak are the size of the disruption, the containment of the leak, and how well it empties
back into the lumen after evacuation. A leak identified before
closure of a diverting stoma can be contained within a cavity
or be a blind sinus. Typically, delaying the closure of the
stoma will give the anastomotic disruption time to heal. There
are several views that are important to see before a leak can
be excluded. Obtaining anterior-posterior and lateral views of
early filling of the lumen, full distention of the colon, and the
postevacuation periods are necessary for an adequate study.
Early filling may reveal subtle leaks that are either obscured
by the distended rectum or empty readily when the bowel is
decompressed. Distention of the bowel is necessary to unroll
mucosal folds and provide some intraluminal pressure to test
6. Diagnostic Evaluations—Radiology, Nuclear Scans, PET, CT Colography 83
with an associated abscess. Anastomotic strictures are the
result of ischemia or a septic complication of the surgery.
Strictures typically occur remotely from surgery, therefore the
concern for a leak is low and barium can be used as the contrast agent of choice. Radiographically, they have abrupt,
short, symmetric narrowing with intact mucosa.
Small Bowel Series and Enteroclysis
The small bowel represents 75% of the length and 90% of the
mucosal surface of the entire GI tract, but the incidence of
pathology is much less frequent than that of the upper and
lower portions of the intestinal system. Consequently, radiologic studies of the small bowel are often used to finish an
examination of the GI tract for the sake of completeness.
Indications for small bowel studies include unexplained GI
FIGURE 6-22. A Contrast enema showing a contained anastomotic
leak. B Contrast enema showing a free-flowing leak.
the anastomotic integrity. Finally, the postevacuation films are
the most important because they identify any residual contrast
outside of the lumen, which may be the only finding that a
leak is present. The presence of smooth-bordered extraluminal compression at the level of the anastomosis is consistent
bleeding, evaluation for small bowel tumors, SBO, Crohn’s
disease, and malabsorption.
is challenging for several reasons. First, with the enormous
mucosal surface, it is difficult to adequately visualize all segments of the bowel. Second, the multiple overlapping loops of
the small bowel can make visualization difficult. Finally, the
flow of contrast through the small bowel cannot be controlled.
As a result, findings may be missed if the physician is not
paying close attention at all times. Nonetheless, small bowel
contrast studies have a vital role in the practice of surgeons.
Barium follow-through and enteroclysis are the principle
methods for examining the small bowel. During a small bowel
follow through (SBFT), the patient drinks a large volume of
dilute barium. The radiologist follows the flow of contrast
through the small bowel with the use of fluoroscopy and spot
films. The pylorus and gastric emptying limit the rate that the
contrast enters the small bowel. Various techniques that apply
pressure to the abdomen are used to manipulate and flatten
out the loops of bowel to improve visualization. The major
disadvantages are the inability to completely distend the
bowel, and the time and attention required by the patient, radiologist, and radiology staff to perform an adequate examina-
26
tion.
During enteroclysis, the contrast and methylcellulose
are administered through a small tube passed into the duodenum. This allows for rapid instillation of barium into the
small bowel allowing for better distention and visualization.
Advantages over SBFT include better filling and distention of
the bowel and decreased study time. The major disadvantages
are the placement of the nasoduodenal tube, the relatively
high radiation dose, and hyperosmotic nature of the methylcellulose. When comparing the diagnostic results between
SBFT and enteroclysis, the results are mixed. Regardless of
the indication for the examination, the quality of the study
depends on the radiologist’s preferred technique and their
attention to detail during the study.
The technical aspects of the SBFT begin with the oral
administration of a 40%–50% barium suspension with a volume of 300–500 mL. The flow of barium, which is limited by
pyloric emptying, is then followed under fluoroscopy. The
32
Examination of the small bowel
84 M.G. Mutch, E.H. Birnbaum, and C.O. Menias
patient and bowel are manipulated and spot images are taken
at points of interest or every 15 minutes. Normal transit time
for the small bowel can vary widely but is generally defined
as 90–120 minutes. Enteroclysis requires nasal or oral intubation of the pylorus so contrast may be rapidly administered to
maximize the distention of the small intestine. The catheter is
typically 12 French in caliber and can be passed with minimal
discomfort to the patient. The catheter is passed under fluoroscopic guidance to ensure its postpyloric position. The contrast is then infused at an initial rate of 75 mL/minute and then
is increased as needed and tolerated. Serial images are
obtained in the same manner as the SBFT.
Crohn’s Disease
Barium studies of the small bowel are essential for staging the
severity and extent of bowel involvement in patients with
Crohn’s disease. Indications for the studies include routine
surveillance of known small bowel disease, assessing the
severity of disease during a flare, defining the disease distribution for a new diagnosis, preoperative assessment, and to
assist in the differentiation between Crohn’s disease and UC.
The radiographic appearance of Crohn’s disease depends on
the severity of disease and its distribution. Early or mild
Crohn’s disease is characterized by thickened, irregular
mucosal folds, a coarse villous pattern of the mucosa, and
aphthous ulcers (Figure 6-23A). The early edema and inflammation are typically confined to the mucosa, which can be
seen as a fine nodularity of the mucosal edge. The edema also
causes the villi to swell allowing barium to get trapped
between them, producing a fuzzy, ground-glass, or coarse villous pattern. Aphthous ulcerations appear as shallow collections of barium surrounded by a radiolucent halo. As the
disease progresses, more of the bowel wall becomes involved
and the edema and inflammation extend into the submucosa
and muscularis. The plicae circularis is made up of the
mucosa and submucosa so submucosal involvement causes
these folds to become even thicker and blunted producing the
characteristic thumbprinting. Chronic or severe inflammation
causes further distortion and disruption of the plicae circularis
and enlargement, deepening, and coalescence of the aphthous
ulcerations. The ulcers are classically located on the mesenteric border of the lumen, which is fairly specific to Crohn’s
disease. They enlarge and coalesce taking on various configurations such as stellate or rose thorn shapes and linear or
crescent shapes. Continued progression leads to the characteristic deep linear ulcers of Crohn’s disease.
Advanced disease is characterized by transmural inflammation that can be seen radiographically as deep, long linear
ulcers, sawtoothed nodularity of the mucosa, cobblestoning,
severe thickening of the bowel wall, luminal narrowing, and the
complications of the disease. Inflammation of the submucosa
and subserosa allows for the deep, knife-like clefts to burrow
into the bowel wall. These clefts and fissures begin to merge
into a longitudinal and transverse network of ulcerations.
FIGURE 6-23. A Small bowel series showing TI Crohn’s disease
strictures. B SBFT showing cobblestoning.
Between the ulcers remain pieces of relatively uninflamed
mucosa. This produces a sharp, sawtooth nodularity of the
mucosal edge, and ultimately develops a cobblestone pattern
(Figure 6-23B). Barium fills the clefts and fissures and does not
cling to the relatively spared mucosa in between, which is the
basis for the cobblestone pattern. As these islands of residual
mucosa attempt to regenerate, they heap up and branch giving
rise to pseudopolyps. Once again, the barium does not adhere
to these polyps so the cobblestoning becomes more irregular
and complex. Transmural inflammation leads to fat creeping
and bowel-wall thickening. The thickened bowel wall displaces
adjacent loops of intestine so the distance between loops is
6. Diagnostic Evaluations—Radiology, Nuclear Scans, PET, CT Colography 85
increased. During the barium study, these loops cannot be
compressed or manipulated. The thickening also causes narrowing of the lumen. Radiographically, this can be seen as
areas of nondistensible, ulceronodular bowel producing a string
sign. The narrowing is caused by reversible edema, spasm, and
inflammation or irreversible fibrosis.
Barium studies are more sensitive at identifying fistulas
than endoscopy. The fistula tract may be visualized directly or
indirectly. Early filling of the colon is highly suggestive of an
enterocolic fistula. For example, an ileal-transverse colon fistula will show contrast entering the transverse colon before
the right colon fills with contrast. An abscess may be seen as
an extraluminal mass or compression of the adjacent loops of
intestine.
Small Bowel Obstruction
A complete bowel obstruction is readily apparent based on clinical grounds and easily supported by plain films of the
abdomen. However, the diagnosis is not always clear in up to
one-third of cases.
lead to significant increases in morbidity and mortality. When
the diagnosis is uncertain and the clinical circumstances support further testing, contrast studies of the small bowel can be
very useful. Specific indications for either SBFT or enteroclysis
include equivocal plain films, unclear etiology, early postoperative obstructions, or when preoperative localization of the site
of obstruction is important. Dilute barium studies are the most
useful because they provide the best mucosal detail and the barium typically does not become inspissated in the small bowel,
therefore its use in the setting of a complete or partial SBO is
not contraindicated. However, the use of water-soluble agents
can be problematic in the setting of a complete SBO because of
their hypertonicity, which draws water into the bowel lumen
further exacerbating the fluid sequestration caused by the
obstruction. Finally, traditional SBFT is the preferred technique
for assessing the presence of partial SBO.
Findings consistent with an adhesive obstruction include a
smooth, sharp transition point with a straight or curved line
that stretches across the bowel (Figure 6-24). This is most
apparent when the band is a single, thin adhesion. If multiple
adhesions are present, the transition point is not as easily
depicted. Typically, adhesions will fix the loop of intestine to
the pelvis, retroperitoneum, or abdominal wall so that it does
not move with manipulation or respiration. Peritoneal metastasis can also fix the affected loop of intestine to the peritoneal cavity. These two etiologies can often be differentiated.
As mentioned, adhesions typically cause smooth transitions
that stretch across the entire lumen and the surrounding
mucosa appears normal. In contrast, metastasis will cause a
desmoplastic reaction in the surrounding bowel so the mucosa
at the transition point will appear irregular and tethered. Also,
the tumor begins at one edge of lumen and either directly
invades the lumen or infiltrates around the bowel circumference. This further exaggerates the mucosa irregularities and
33
Subsequent delays in the diagnosis can
FIGURE 6-24. SBFT showing a simple SBO.
may not completely obstruct the flow of barium into the distal, collapsed bowel. Metastasis can also cause obstruction by
external compression of the bowel. This will be seen as
an external mass effect and the overlying mucosa, in this case,
will appear more normal.
Lesions intrinsic to the small bowel can also be elucidated.
Primary adenocarcinomas of the small bowel are more common in the proximal bowel and occur with decreasing frequency more distal along the small intestine. Their findings
are very similar to those seen for colon cancers on barium
enema. There is mucosal destruction with sharp demarcation
between normal mucosa and the lesion. The lesion may be
semiannular or annular. Carcinoid tumors typically occur in
the terminal ileum and start as submucosal lesions. As they
grow, there may be mucosal destruction and tethering toward
the center of the abdomen as the mesenteric desmoplastic
reaction progresses.
Computed Tomography
CT has become a routine examination to evaluate a wide
range of disease processes because it is an easy, fast, and
accurate test that provides cross-sectional imaging. The benefit of cross-sectional imaging is the detailed imaging and resolution of the hollow viscus and solid organs. Accurate
interpretation requires optimal opacification of the GI tract
and vascular structures. The bowel is opacified by administering a water-soluble oral contrast agent. The density of barium interferes with the acquisition of data during the scan and
thus should be avoided as a contrast agent. The oral contrast
is typically administered 45–60 minutes before scanning to
86 M.G. Mutch, E.H. Birnbaum, and C.O. Menias
allow the contrast to opacify as much of the bowel as possible. If pelvic or rectal pathology is being evaluated, the contrast may also be administered per rectum at the time the scan
is being performed. Intravenous (IV) contrast agents typically
are iodinated so it is important to take a thorough history of
allergies. It is administered as a bolus at the time of the examination. The reason for the examination dictates the exact timing between when the contrast is administered and when the
CT images are acquired (i.e., venous versus arterial phase).
The CT scan uses ionizing radiation to acquire the images
with 5- to 10-mm collimation. Smaller collimation allows for
sharper, more detailed images.
CT scans are usually ordered for the staging of colorectal
cancer, evaluation of abdominal complaints, and evaluation of
postoperative complications. Once again, having a specific
question in mind when ordering the scan will allow the scan
to be tailored to the appropriate parameters.
Colorectal Cancer
An abdominal and pelvic CT is the most common method for
staging colorectal cancer before definitive surgical resection.
The aims of the CT scan are to 1) evaluate the liver for distant
metastatic disease, 2) evaluate for regional lymphadenopathy,
especially in rectal cancer, where nodes may have been
missed during a transrectal ultrasound, and 3) assess for the
presence of intraperitoneal disease. CT is also used to follow
colorectal cancer patients longitudinally for the development
of recurrent disease. It is most effective when used to evaluate patients who have symptoms concerning for recurrent disease or have a rising carcinoembryonic antigen (CEA) level.
There are no strong data to support its use in routine surveillance for detecting metastasis in the absence of symptoms or
rising CEA.
34
There are several modalities, such as CT, ultrasound, and
magnetic resonance imaging (MRI), available to assess the
liver for metastatic disease. All of them have their advantages
and disadvantages, but they all have equivalent diagnostic accuracy for the detection of liver metastasis.
27,35
CT images are
typically obtained in two phases: the hepatic artery phase
(20–25 seconds after the IV contrast is initiated) and the portal
venous phase (65–70 seconds after the IV contrast is started).
The majority of colorectal metastases are hypovascular and
show up as hypodense lesions during the portal venous stage
because the majority of metastatic lesions derive their blood
supply from the arterial system. During the portal venous
phase, contrast enhances the hepatic parenchyma and portal
veins and the metastatic lesions do not enhance (Figure 6-25).
CT is able to differentiate many hepatic lesions based on
their imaging characteristics and the dynamic effects of contrast on these lesions. Common liver lesions that need to be
differentiated from colorectal metastasis include simple cysts,
hepatic adenomas, primary liver tumors, hemangiomas, and
focal nodular hyperplasia. Colorectal metastases typically are
round, well-circumscribed lesions that are fairly homoge-
FIGURE 6-25. CT scan showing liver metastasis.
neous in density, which is consistent with solid tissue. As
lesions grow they become more irregular in shape and their
enhancement becomes more heterogeneous. Central necrosis
and calcification may also be present. In contrast, simple cysts
have a density consistent with fluid, which is more hypodense
than solid tissue, and there is very little change in their
enhancement during the various phases of imaging. Hemangiomas can be differentiated from metastatic lesions by the
fact that they remain enhanced throughout the portal venous
phase. The other hepatic lesions are typically hypervascular
so they can be reliably differentiated from metastatic lesions
during dual-phase CT imaging. The accuracy of CT for the
detection and differentiation of liver lesions is greatest for
lesions >1 cm.
36,37
Lesions <1 cm generally do not have the
dynamic enhancing properties to be readily differentiated and,
as a result, they are named indeterminate lesions.
Other advantages of the CT scans include the ability to
detect regional adenopathy and to assess the relationship of
the primary tumor to adjacent structures (Figure 6-26).
Detecting regional adenopathy is most important for rectal
cancer because the presence of adenopathy may influence the
surgeon to give neoadjuvant chemoradiation therapy. The CT
criteria for pathologic adenopathy are based on size only.
Typically, nodes >1 cm in size are concerning for metastatic
disease.
Diverticulitis
The most common CT findings associated with diverticulitis
are pericolonic/mesenteric inflammation (98%), diverticula
(84%), colonic wall thickening (70%), and abscess (47%).
Normally, the colonic mesentery and pericolonic tissues are
28
6. Diagnostic Evaluations—Radiology, Nuclear Scans, PET, CT Colography 87
typically localized around a short segment of the colon, thus
if a long segment, several segments, or the entire colon is
involved, a different diagnosis should be sought. The presence
or absence of diverticula does not impact the radiographic
diagnosis. The development of diverticula is associated with
hyperelastosis of the colonic wall, which is evident by the
thickening of the wall. This leads to decreased compliance
and shortening of the involved segment of colon. When the
thickness of the colon wall is >5 mm, it is considered abnormal. The wall thickening may be circumferential or just localized to the segment adjacent to the inflammation.
As mentioned, not only does CT allow for confirmation of
the diagnosis of diverticulitis, but it can also identify associated complications. Abscess formation is the most common
complication of diverticulitis. An abscess appears as a fluid
collection typically near the area of diverticulitis (Figure
6-28). Often, oral and IV contrast are needed to distinguish an
abscess from adjacent loops of intestine. When the surround-
FIGURE 6-26. CT scan showing primary lesion and adenopathy.
ing loops of bowel are able to be opacified with oral contrast
and the rim of the abscess is enhanced with IV contrast, the
accuracy of diagnosing an abscess is maximized. The pres-
hypodense because of the high water content of the surrounding fat and sharp edges between adjacent structures. As the
inflammatory process begins, the tissue becomes edematous
and more vascular. This causes the pericolonic tissue to
become more enhanced and the sharp contrasts between the
various tissue plains become hazy, resulting in the so-called
“dirty fat.” When the inflammatory response is centered on a
portion of colon that is thickened (>5 mm), the diagnosis of
diverticulitis is confirmed. Often, the inflammatory process
can be extensive, producing a phlegmon in the absence of an
organized abscess (Figure 6-27). Depending on the size of the
perforation, there may be small flecks of extraluminal air
within the mesentery or pericolonic tissue or in the upper
abdomen above the liver. The inflammatory process is
ence of air or an air-fluid level within the abscess cavity is
also highly suggestive of an abscess.
A colovesical fistula in the most common fistula associated
with diverticulitis, and a CT scan is the most sensitive for the
29
detection of such a fistula.
Air within a bladder that has not
been instrumented is diagnostic for an enterovesical fistula
(Figure 6-29). When the wall of the bladder is thickened and
in close proximity to the area of sigmoid colon that is thickened and contains diverticula, the etiology is likely related to
diverticular disease. If the fistula is large enough, contrast,
either administered orally or per rectum, may fill the bladder.
Rectal contrast filling the bladder can help distinguish the
source of fistula from a terminal ileal fistula associated with
Crohn’s disease.
FIGURE 6-27. CT scan showing uncomplicated diverticulitis.
FIGURE 6-28. CT scan showing a diverticular abscess.
88 M.G. Mutch, E.H. Birnbaum, and C.O. Menias
FIGURE 6-29. CT scan demonstrating a colovesical fistula.
Crohn’s Disease
The role of CT in the diagnosis and evaluation of Crohn’s disease continues to evolve. A CT scan is used in two general situations during the management of Crohn’s disease. First, a CT is
obtained to evaluate a patient with new onset abdominal pain,
and findings consistent with Crohn’s disease are incidentally
found. Second, a CT scan is obtained to evaluate for complications in a patient that is known to have Crohn’s disease. The distribution of the disease greatly impacts the findings seen on CT.
The most common findings associated with Crohn’s disease are
bowel wall thickening, peri-intestinal inflammation, and
regional lymphadenopathy. The bowel wall can reach 11–13
mm in thickness, which can be either symmetric or asymmetric.
The halo sign, which is a low-attenuation ring caused by submucosal deposition of fat between the enhancing mucosa and
bowel musculature, is a common finding associated with
Crohn’s disease (Figure 6-30A). The transmural nature of the
inflammatory process allows it to extend into the mesentery and
adjacent structures so there is often an extensive inflammatory
response centered on the affected bowel. There are many features that help to distinguish Crohn’s disease from other inflammatory diseases of the GI tract. First, Crohn’s disease is usually
found to involve the terminal ileum and right colon. Second,
there may be skip lesions. For example, multiple segments of
small bowel and/or colon may be involved (Figure 6-30B).
Third, the presence of mesenteric adenopathy suggests Crohn’s
or UC, but is not specific for IBD. Finally, the presence of complications such as abscess, fistula, or perforation points to a
diagnosis of Crohn’s disease. Abscesses can be located between
intestinal loops, within the mesentery, in the psoas muscle,
pelvic sidewall, and subcutaneous tissues (Figure 6-31). Fistulas
FIGURE 6-30. A CT scan showing Terminal Ileum (TI) Crohn’s
disease with abscess. B CT scan showing Crohn’s colitis.
FIGURE 6-31. CT scan showing a psoas abscess related to Crohn’s
disease.
6. Diagnostic Evaluations—Radiology, Nuclear Scans, PET, CT Colography 89
from the diseased segment of bowel to the bladder, skin, vagina,
or normal bowel can also be delineated on CT.
Small Bowel Obstruction
As mentioned above, SBO is a clinical diagnosis based on the
signs, symptoms, and clinical condition of the patient.
Radiologic studies are obtained to confirm the clinical diagnosis. Typically, the first line investigation is plain films of the
abdomen, but their accuracy varies from 46% to 80%.
result, there is often a delay in the diagnosis, which can lead
to an increase in morbidity and mortality. The use of CT in the
evaluation of an SBO is expanding and in many cases can
eliminate the delay in diagnosis. CT has the advantages of
being able to identify the site of obstruction, cause of obstruction, and it can provide information regarding vascular
compromise of the bowel. Indications when a CT scan is particularly helpful include 1) a patient with no prior surgery, 2)
a patient with equivocal plain films and an uncertain diagnosis, and 3) a patient with known intraabdominal pathology
such as Crohn’s disease or cancer.
Oral contrast is not always necessary and should be
avoided in patients with a high-grade or complete bowel
obstruction. The intraluminal fluid often distends the bowel
and acts as a natural contrast agent. The low-density intestinal
fluid also extenuates the enhancement of the bowel wall after
the administration of IV contrast, which can provide information regarding the flow of blood of the bowel.
The diagnostic criteria of an SBO by CT are based on the
presence of dilated proximal small bowel (>2.5 cm) and collapsed distal bowel. When a transition between dilated and
collapsed bowel is identified, then the diagnosis is confirmed
(Figure 6-32). But when a transition point is not identified, it
30
As a
is difficult to distinguish between an SBO and adynamic
ileus. In such cases, one must search for other clues to differentiate the processes. For example, the presence of “small
bowel feces,” which is gas bubbles mixed within particulate
matter, in the dilated bowel is a reliable indicator of an SBO.
The presence of other intraabdominal pathology, particularly
inflammatory processes, would generally indicate an adynamic ileus. This is a case in which oral contrast may be particularly helpful because if contrast reaches the colon, a
complete SBO is not present.
CT can also provide significant information regarding the
cause of the obstruction. Once again, the findings must be
interpreted in context with the patient’s clinical situation.
When there is a sharp transition from dilated to decompressed
bowel in the absence of other findings, this is highly suggestive of an SBO secondary to adhesions. CT does an excellent
job identifying hernias such as inguinal, umbilical, incisional,
or more of the atypical types. Often these hernias contain
bowel but not all are obstructing. Clues indicating obstruction
include dilate bowel going into the hernia and collapsed
bowel exiting the hernia, oral contrast proximal to the hernia
and no contrast distal to the hernia, and a localized inflammatory process surrounding the hernia, particularly in the
subcutaneous tissues (Figure 6-33). Another common extrinsic cause of obstruction is recurrent cancer. A CT scan is often
able to demonstrate a mass at the site of obstruction and may
also provide evidence of more widespread peritoneal disease.
Unexpected causes of obstruction may also be identified such
as Crohn’s disease, intussusception, or small bowel cancers.
When the affected bowel becomes strangulated, the morbidity and mortality associated with an SBO increase significantly. No test is able to provide definitive proof
of strangulated bowel, but CT is able to provide a wealth of
FIGURE 6-32. CT scan showing a simple SBO.
FIGURE 6-33. CT scan showing an incarcerated hernia.
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