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70 M.G. Mutch, E.H. Birnbaum, and C.O. Menias
throughout the small and large bowel without bowel distention (<2.5 cm in diameter). An abnormal gas pattern is a variable amount of gas in the presence of one or more loops of
dilated small bowel (>2.5 cm in diameter).
6
The mucosal
markings of the small bowel, known as the plicae circularis,
traverse the entire diameter of the lumen and help to distinguish it from the colon, which has haustral markings that project into the lumen but do not reach the opposite wall. The
amount of intraluminal fluid or material also greatly affects
the radiographic appearance of the intestinal gas pattern. Airfluid levels, which are the dependent layering of fluid and air
within a dilated loop of intestine when viewed in the upright
position, are common radiographic findings of an SBO. A
complete or high-grade SBO is characterized by dilated loops
of small bowel, air-fluid levels, and absence of colonic gas
(Figure 6-1A and B). There can be a single or multiple dilated
loops of small bowel, and the dilated bowel loops may also be
stacked on top of each other giving it a ladder-like appearance. Generally, the more dilated loops of intestine present,
the more distal the obstruction is located. Several factors can
confound the radiographic appearance of an SBO. First, a distal bowel obstruction may appear to be more proximal when
the distal bowel is filled with fluid and not gas. If the obstruction has been longstanding or the patient has had excessive
vomiting, the bowel may be completely filled with fluid and
have a complete absence of gas. Clues that support the diagnosis of an SBO in a gasless abdomen are a ground-glass
appearance and loss of solid organ outlines such as the liver
edge, renal shadow, and the psoas shadow. These findings are
consistent with significant intraabdominal and intraluminal
sequestration of fluid. Second, the presence of colonic gas in
the setting of dilated small bowel and air-fluid levels is compatible with an early SBO without complete evacuation of
distal gas, a partial SBO, or an adynamic ileus. If the diagnosis is uncertain clinically and radiographically, then a followup study with either computed tomography (CT) or small
bowel contrast study is warranted.
Plain films are not able to reliably differentiate a simple
obstruction from a strangulating obstruction. Findings that are
considered to be high risk for vascular compromise include
complete bowel obstruction, extensive mucosal thickening or
edema, pneumatosis, portal venous gas, or a closed loop
obstruction. A study of 51 patients with radiographic findings
of a complete SBO found 29% of patients had infarcted bowel
requiring resection.
7
This highlights the importance of interpreting the radiographic data in the context of the patient’s
clinical condition.
Large Bowel Obstruction
Colonic obstructions typically present with the same signs
and symptoms as an SBO. The most common causes of large
bowel obstruction are carcinoma, volvulus, Ogilvie’s syndrome, and fecal impaction. Other etiologies include Crohn’s
FIGURE 6-1. A Plain film of SBO dilated loops, ladder. B SBO air-fluid levels.
6. Diagnostic Evaluations—Radiology, Nuclear Scans, PET, CT Colography 71
disease, diverticulitis, ischemic stricture, anastomotic stricture, and endometriosis.
Cancer
Typically the colon will be distended up to the point of obstruction with a paucity of distal gas. If the ileocecal valve (ICV) is
competent, the cecum can be markedly dilated and there may
be little dilation of the small bowel (Figure 6-2). With a competent ICV, the entire colon becomes dilated and the cecum
has the greatest distensibility. Once the cecal diameter reaches
>12 cm, it is generally agreed that the risk of impending perforation is high. However, if the ICV is incompetent, gas can
reflux back into the small bowel. As a result, the colon may
not be all that dilated and the small bowel may become dilated
with air-fluid levels mimicking an SBO (Figure 6-3). In this
case, careful review of clinical data is necessary to guide the
next diagnostic evaluation.
If a colonic obstruction is suspected, the diagnosis can be
confirmed with a water-soluble contrast enema. It is difficult
to differentiate the etiology of the obstruction with plain films
so a contrast enema can give significant information regarding the cause of the obstruction. Water-soluble contrast is preferred over barium in this situation for several reasons. First,
this avoids the risk of barium peritonitis if there is any concern for perforation or compromise in the integrity of the
colon wall. Second, by avoiding barium, subsequent radiologic studies are not compromised. Third, if the obstruction is
the result of fecal impaction, water-soluble contrast is both
diagnostic and therapeutic.
FIGURE 6-2. Large bowel obstruction secondary to sigmoid cancer.
Competent ICV.
FIGURE 6-3. Large bowel obstruction secondary to sigmoid cancer.
Incompetent ICV.
Pseudoobstruction
Dr. Ogilvie first described acute colonic pseudoobstruction in
1948, which is a condition characterized by massive dilation
of the colon with no evidence of mechanical obstruction.
Radiographically, it is characterized by marked dilation of the
cecum, ascending colon, and transverse colon (Figure 6-4).
The descending colon and rectum are infrequently dilated. If
the diagnosis is in question, it can be confirmed by a watersoluble enema, where there should be free flow of contrast
into the cecum with no evidence of obstruction. Once again,
in the acute setting, barium should be avoided.
Colonic Volvulus
Plain films are able to diagnose sigmoid volvulus in 75% of
the cases. The classic plain film findings include a dilated,
U-shaped loop of colon that is projected toward the right
upper quadrant. This characteristic finding has also been
called the “bent inner tube” sign (Figure 6-5A). The direction
the volvulus points depends on the redundancy of the
involved segment of sigmoid colon. In the middle of this loop
is a vertically oriented white stripe that represents the two
6
72 M.G. Mutch, E.H. Birnbaum, and C.O. Menias
apposing walls of the obstructed loop of sigmoid colon. It is
not uncommon to see dilated colon and even small bowel
proximal to the volvulus because it does create a complete
obstruction. If the diagnosis cannot be made with plain films,
a water-soluble contrast enema will provide the diagnosis.
Gentle instillation of contrast will demonstrate a smooth,
tapered point of obstruction at the rectosigmoid junction
known as a “bird’s beak” (Figure 6-5B). If the diagnosis is
still in question a CT can be obtained.
The diagnosis of rotational cecal volvulus can be made
with plain films 75% of the time. Classically, the medially
placed ICV indents the dilated cecum giving it the characteristic “coffee bean” or “kidney” shape (Figure 6-6A). The
dilated right colon folds into the left upper quadrant (opposite
to sigmoid). Dilated proximal small bowel may obscure the
diagnosis. A CT will demonstrate dilated small bowel and
cecum centered around the “swirly” mesentery. The “bascule” type volvulus produces a sharp, flat cut off of retrograde
contrast as the mobile, redundant cecum flips up medially into
the upper abdomen, causing a dilated cecum and small bowel
on plain films.
FIGURE 6-4. Ogilvie’s syndrome.
Pneumoperitoneum
The plain film radiograph has been used since the early 1940s
to diagnose free air within the peritoneal cavity.
of air, patient position, direction of the X-ray projection, and
phase of respiration contribute to the sensitivity of detecting
pneumoperitoneum. In 1971, Miller and Nelson
strated that as little as 1 cc of free air could be detected by
upright chest plain film. The upright chest film is the most
sensitive view for identifying free air under the diaphragm.
8
The amount
9
demon-
10
FIGURE 6-5. A Plain film of sigmoid volvulus. B Contrast enema of sigmoid volvulus.
6. Diagnostic Evaluations—Radiology, Nuclear Scans, PET, CT Colography 73
between the liver and the anterior abdominal wall, between
loops of bowel, within the peritoneal ligaments, and in
Morison’s pouch. The appearance and configuration of the air
depends on the shape of the space in which it has accumulated. The most common plain film finding is the accumulation of air under the right hemidiaphragm (Figure 6-7A). The
relatively dense liver offers a sharp contrast to the air and the
diaphragm. The Rigler sign or double-wall sign, which has
been found in 32% of cases of pneumoperitoneum, is created
when gas accumulates on both sides of the intestinal wall.
Both sides of the wall are visualized as a thin, white stripe.
Often, the air trapped between the loops of bowel or leafs of
mesentery will appear in a triangular configuration. Gas that
has entered the lesser sac appears as an ill-defined lucency
just above the lesser curve of the stomach. When air has
entered into Morison’s pouch, the inferior edge of the liver
becomes outlined (Figure 6-7B). If there is any question about
the diagnosis, the films should be repeated in another position
or a CT should be obtained, which is the most sensitive study
to detect free air.
Colitis
12
FIGURE 6-6. A Plain film of cecal volvulus. B CT of cecal volvulus.
In this position, the X-ray beam hits the diaphragm tangentially at its highest point and minimizes the collection of air
being obscured by other organs. The left lateral decubitus film
is also fairly sensitive for patients who are unable to be transported or stand. Some authors recommend keeping the patient
in the left lateral position for 10–15 minutes before shooting
the X-ray.
10
This allows adequate time for the air to rise above
the lateral edge of the liver. When the plain film is performed
during mid-expiration or mid-inspiration the ability to detect
small amounts of air is increased.
11
Intraperitoneal gas can be trapped in many locations such
as under the diaphragm, in the lesser sac, under the liver,
The diagnosis of colitis is typically a clinical one, but careful
inspection of plain film radiographs can provide a wealth of
valuable information. Plain films can give information
regarding the condition of the mucosa, extent of colonic
involvement, presence of perforation, evidence of bowel
infarction, severity of colitis, and presence of associated ileus
or obstruction.
When the colon is filled with gas, the gas/mucosa interface gives characteristic patterns associated with colitis.
Thumbprinting is a sign for bowel wall and mucosal edema
associated with most causes of acute colitis. Bowel wall
edema results in thickening of the mucosal or haustral folds
so that they appear as thick white lines projecting into the
lumen. Also, the angle of the haustral folds becomes blunted
and smooth versus the normal sharp angulation of the haustra.
The edema also causes the bowel wall to become thick and
stiff. As a result, the gas-filled loops tend to lie straight or
gently curve and the gas distribution changes little when the
patient is in different positions. When two edematous loops
are adjacent to each other, the distance between the two
lumens is greater than usual. An ominous sign is the presence
of massively dilated segment of colon associated with bowel
wall thickening and thumbprinting (Figure 6-8). This is diagnostic for toxic megacolon when associated with the clinical
findings of leukocytosis, severe abdominal tenderness, and
hemodynamic instability. All of these signs are suggestive of
bowel wall edema, inflammation, and ischemia, but give little
indication as to the underlying cause.
Examining five characteristics can provide considerable
data regarding the severity and extent of the Crohn’s or ulcerative colitis (UC).
13
First, the extent of solid colonic fecal
material gives a general sense of the extent of disease. Solid
74 M.G. Mutch, E.H. Birnbaum, and C.O. Menias
FIGURE 6-7. A Plain film of intraperitoneal free air under diaphragm.
B Plain film of free air under liver edge.
IGURE 6-8. Plain film of colitis with megacolon.
F
stool in the right and transverse colon indicates left-sided
colitis, and absence of solid stool anywhere in the colon suggests pancolitis. Second, examining the mucosal contours can
help determine which segments of the colon are involved.
Normally, the mucosal edge is smooth with sharp, narrow
haustral markings. In the presence of active or longstanding
inflammatory bowel disease (IBD), the mucosal contours are
altered. The mucosal edge becomes blurred and has a granular appearance because of inflammation and ulceration.
Depending on the extent of ulceration, the haustral markings
may appear thick or be absent all together. Third, the character of the haustral markings provides information regarding
the severity of disease. The haustral clefts are normally narrow with sharp angulation from the mucosal edge and are
closely spaced. As the colitis progresses, the haustra become
thicker, the angulation with the mucosal edge becomes
blunted, and they are spaced farther apart. The haustra begin
to disappear as the mucosal ulcerations progress. Fourth, the
diameter of the colon can indicate the severity and chronicity
of the disease. A markedly dilated (>5 cm) colon with
thumbprinting and bowel wall edema is concerning for toxic
megacolon. At the other end of the spectrum, a chronic,
“burned out” colon takes on a tubular, narrowed appearance
(Figure 6-9). This is more characteristic of UC than Crohn’s
disease. Finally, the thickness of the wall becomes thicker
6. Diagnostic Evaluations—Radiology, Nuclear Scans, PET, CT Colography 75
Contrast Studies
Contrast Enemas
Barium studies of the colon are designed for the detection of
mucosal and intramural lesions. With the widespread use and
availability of colonoscopy, the role of single or double contrast barium studies has diminished. Despite the direct competition with colonoscopy, barium studies continue to be an
important player in the diagnosis of colonic pathology. The
advantages of barium as a contrast medium are its ability to
coat and adhere to the mucosa. This then allows for the instillation of air as second contrast medium. In air-contrast examinations, the colon is filled with barium. It is drained and then
the colon is insufflated with air as a second contrast medium.
The barium outlines the mucosal edges and the air distends
the colon allowing for maximum visualization of mucosal
detail. The indications for a barium study include screening
and diagnosis of mucosal disease processes in the elective setting. Its disadvantages are the need for a colon preparation,
the inherent characteristics of the medium, and the toxicity
when exposed to the peritoneal cavity. The exposure of barium to the peritoneal cavity results in an intense inflammatory
response that has a mortality rate of approximately 50%.
Therefore, the use of barium should be avoided in urgent sit-
FIGURE 6-9. Plain film of chronic burned out colitis.
over time in patients with IBD. The distribution of the bowel
wall thickening provides clues as to the extent of colonic
involvement. Plain films are also able to provide information
regarding the extraintestinal manifestations of IBD.
Abnormalities of the skeletal system such as sacroiliitis,
ankylosing spondylitis, and osteopenia secondary to chronic
steroid use can be seen.
Another manifestation of colitis is pneumatosis where gas
has accumulated within the wall of the intestine. This may be
a relatively benign process such as pneumatosis cystoides
intestinalis or it may represent the very grave situation of
bowel infarction. Pneumatosis has two characteristic radiographic patterns. It may show a bubbly appearance where
the gas accumulates within multiple cyst-like sacs in the
colonic wall or the pneumatosis may dissect along the axis of
the colon wall appearing as thin, linear streaks that are
aligned along the axis of the bowel. Other associated findings
that are concerning for vascular compromise of the colon
include bowel dilatation, thumbprinting of the mucosa, and
intraperitoneal free air. As the ischemia progresses to infarction, mucosal integrity is disrupted and gas may find its way
into the mesenteric and portal venous systems. This is characterized by thin, branching lucencies within the liver, typically seen near the periphery. In the clinical setting of
abdominal pain, known colitis, acidosis, or hemodynamic
compromise, no further radiographic studies are needed to
define the etiology of the pneumatosis or to indicate the
severity of disease.
uations such as studying the integrity of an anastomosis, evaluating a large bowel obstruction, examining acute colitis, or
when there is concern for bowel perforation. In these situations, a water-soluble contrast agent should be used. Watersoluble agents do not coat the mucosa. Instead, the bowel is
visualized by passive filling of the lumen with the contrast as
a single contrast study. As a result, water-soluble enemas do
not provide as much detailed information as barium studies.
Indications for a water-soluble study include evaluating the
integrity of a colonic anastomosis, evaluating colonic obstruction, the preoperative evaluation of the colon for evidence of
gross pathology, delineating colonic fistulas, and therapeutic
enema for fecal impaction. The peritoneal cavity tolerates
exposure of water-soluble contrast with very little reaction
and, therefore, it is the contrast agent of choice in urgent
situations.
Cancer and Polyps
The most common reason for ordering an air contrast barium
enema is for the screening and diagnosis of neoplastic lesions
of the colon and rectum, especially when screening for
colorectal cancer in conjunction with flexible sigmoidoscopy,
when colonoscopy is not possible.
trast barium enema depends on the quality of colonic preparation, the size of lesion, the ability to adequately distend the
colon with air, and obtaining multiple views. There are many
regimens available for cleansing the colon that range from
oral agents such as magnesium citrate and polyethylene
glycol to enemas and suppositories.
14
The sensitivity of air con-
15
The cleaner the colon,
76 M.G. Mutch, E.H. Birnbaum, and C.O. Menias
the better the barium is able to coat the mucosa and provide
more detailed images.
A barium enema can detect up to 90% of polyps and cancers that are >1 cm in size, but sensitivity decreases to 50%
for lesions <1 cm in size.
16,17
Lesions can appear sessile,
pedunculated, flat, exophytic, and circumferential. The outline of the mucosal edge helps to differentiate benign versus
malignant and intraluminal versus extraluminal processes.
The configuration and the location of the lesion within the
lumen dictate its radiographic appearance. Specifically,
the profile in which the lesion is imaged and the location
of the lesion within the lumen relative to retained pools of barium help to create its appearance on film. For example, lesions
on the dependent portion of the lumen that sit in a puddle of
barium will appear as filling defects. In contrast, lesions that are
outlined in barium and are away from pools of barium appear
as sessile, pedunculated, flat, or annular outlines that project
into the lumen of the colon. When pedunculated lesions are
viewed in profile, the stalk and head are easily identified.
Early cancers and polyps are very difficult to differentiate
radiographically. The size of the lesion is the most helpful
indicator of malignancy, with lesions >2 cm having a 50%
chance of invasive cancer.
18,19
Also, the presence of an ulcer
is highly suggestive of a malignant lesion. Polyps and early
cancers can be sessile, flat, or pedunculated. Tubular adenomas tend to have a more regular, smooth mucosal surface. In
contrast, villous lesions have many frondlike projections of
FIGURE 6-10. ACE of polyp or early cancer.
the mucosa and barium gets trapped in these projections giving them a very irregular mucosal pattern. Sessile lesions
when viewed in face take on a “bowlers hat” appearance that
project into the lumen (Figure 6-10). The brim of the hat corresponds to the base of the lesion and the dome of the hat represents the head of the lesion. Depending on the size and
mucosa abruptly transitions into a convexity with complex,
irregular borders. Given this characteristic shape, these lesions
are often described as saddle lesions. Annular lesions refer to
cancers that encompass the entire circumference of the colon’s
lumen. They are usually found in the sigmoid colon, but can
complexity of a sessile lesion, the dome may be smooth or
multi-lobulated. Pedunculated lesions are recognized by the
appearance of their discrete stalk. When viewed obliquely or
tangentially, the barium coats the stalk and it is easily identified. If viewed on end, it has the appearance of a “Mexican
hat,” which consists of two concentric circles where the outer
circle represents the head of the lesion and the inner circle
corresponds to its base.
20
As neoplastic lesions grow they tend to occupy greater portions of the circumference wall and lumen of the colon. As a
result, it is easier to distinguish the lesions as malignant. The
most common appearances of colon cancers found during an
air contrast barium enema are annular or semiannular (53%),
polypoid (38%), and flat (9%).
21
The size, complexity, and villous component of the lesion all contribute to its ability to
retain barium and thus its radiographic appearance. Once
again, its position within the lumen may require multiple
views to accurately visualize the lesion. Lesions that straddle
one-third to half of the circumference of the lumen are called
semiannular or saddle lesion (Figure 6-11). When viewed in
profile, semiannular cancers appear as convex lines with the
margins etched in barium. The smooth outline of normal
FIGURE 6-11. ACE of semiannular cancer.
6. Diagnostic Evaluations—Radiology, Nuclear Scans, PET, CT Colography 77
occur anywhere within the colon. Annular lesions are characterized as a circumferential narrowing of the lumen of the
colon. Characteristic findings implicating a malignant lesion
include destruction and irregularity of the overlying mucosa
with shelf-like, overhanging borders, and there is a sharp transition from normal mucosa into the annular lesion. Benign
strictures from ischemic colitis, diverticulitis, anastomotic
strictures, or Crohn’s disease, in contrast, tend to have smooth,
tapering borders. Malignant strictures are best identified when
viewed in profile. If a large bowel obstruction is suspected,
barium should be avoided and a water-soluble contrast agent
should be used, and only a single column contrast study is
needed to define the pathology. Annular lesions in this setting
can present as a completely obstructing lesion or a near
obstructing lesion, where only a string of contrast may get past
the lesion. A completely obstructing lesion will have an abrupt
cutoff of contrast at the level of the lesion. There will be shouldering or evidence of mucosal destruction at the point of
obstruction. If the lesion permits some contrast to flow past the
lesion, a “string sign” may be seen (Figure 6-12). This will be
seen as a thin line of contrast extending from the column of
contrast at the level of the obstruction. There is an abrupt cutoff of normal mucosa to a shouldering, overhanging lesion.
The “string” of contrast will show irregular, destroyed mucosa
along the length of the lesion.
FIGURE 6-12. Contrast enema of apple-core cancer string sign.
Polyposis Syndromes—Familial Adenomatous
Polyposis, Peutz-Jeghers, Juvenile Polyposis
It is not possible to distinguish between the sporadic adenomatous polyps and these polyposis syndromes using contrast
studies. Confirming the diagnosis of these polyposis syndromes requires histologic examination of the polyps. The
polyps can be seen with contrast as previously described in
the majority of instances, but contrast studies should only be
used if endoscopy is not possible.
Ulcerative Colitis
Barium enema is used 1) to confirm the diagnosis of UC and
differentiate it from Crohn’s disease, 2) to assess the extent
and severity of disease, and 3) for surveillance of the disease
and its complications. The radiographic appearance of UC
seen during barium enema examination depends on the state
of the disease process. Changes consistent with acute colitis
involve mucosal loss to varying degrees and bowel wall
edema. The pattern by which the barium outlines the mucosa
depends on the depth and size of ulceration. A granular
mucosal pattern is one of the earliest changes seen, which corresponds to the accumulation of inflammatory cells and
edema within the mucosa but the mucosa maintains its
integrity. When the barium coats the swollen and edematous
mucosal edge, it appears fuzzy and indistinct rather than the
normal sharp edges. As the inflammatory process progresses,
the integrity of the mucosa is broken, leading to the development of ulcers. These ulcerations are shallow, punctate lesions
confined to the mucosal layer. They appear as small, dense
collections of barium that are on the same plane as the rest of
the mucosa. This pattern is known as mucosal stippling
(Figure 6-13A). With continued inflammation, the crypt
abscesses rupture, exposing the submucosa. The ulcers begin
to extend laterally and undermine the adjacent mucosa. These
are called collar button ulcers and are characterized by a narrow neck and wide base that extends below the level of the
mucosal edge. As the ulcerations enlarge and coalesce, small
islands of residual mucosa are left, and as these mucosal
islands regenerate in the face of ongoing inflammation, they
develop into inflammatory pseudopolyps. Pseudopolyps are
irregular projections into the lumen of the bowel (Figure
6-13B). The projections can be round, linear, or have a complex branching pattern that represents mucosal bridging. The
depth of ulcerations seen on air contrast enema has been
found to correlate reliably with the depth and extent of ulceration seen on histopathologic examination.
The chronic changes of UC are related to the effects of
repeated ulceration and regeneration of the colonic mucosa.
Over time, the persistent inflammation causes the muscular
tone of tenia to relax and muscular hypertrophy of the muscularis mucosa. The changes of the musculature of the colon and
the chronic scarring of the mucosa are what lead to the loss of
all normal mucosal folds and haustra, narrowing of the bowel
lumen, and foreshortening of the colon. Radiographically, this
22,23
24
78 M.G. Mutch, E.H. Birnbaum, and C.O. Menias
FIGURE 6-13. A Contrast enema of UC showing stippling ulcers or
early colitis. B Contrast enema of UC with pseudopolyps.
appears as blunting or complete loss of the haustral markings,
a narrow tubular appearance to the colon, and loss of the
redundant course of the sigmoid and transverse colon (Figure
6-14). The point of transition from narrowed and flat mucosa
FIGURE 6-14. Contrast enema of chronic UC.
to normal haustral configuration can help determine the extent
of the colitis. There may be areas of the colon where the contraction of the bowel wall is worse giving rise to the appearance of symmetric, gentle narrowing resulting in a stricture.
The presence of backwash ileitis is also a sign of chronic disease because the ICV has been scarred open. Barium contrast
studies are also able to detect other colonic complications of
UC such as adenomatous polyps and cancers. These appear as
the neoplastic lesions previously described. However, it
should be remembered that IBD-associated cancers tend to be
more flat and infiltrating and do not always appear as typical
neoplasms. Some authors argue that double contrast enemas
25
are able to identify areas of dysplasia,
but contrast enemas
are not recommended for routine surveillance.
Crohn’s Disease
Contrast studies help differentiate Crohn’s disease from UC,
define the severity and extent of the colitis, and identify complications of the disease. Contrast enemas are better than
colonoscopy at identifying and characterizing fistulas,
strictures, and the distribution of disease.
26
6. Diagnostic Evaluations—Radiology, Nuclear Scans, PET, CT Colography 79
As with UC, the radiographic appearance of Crohn’s disease depends on the acuity or chronicity of the disease.
Aphthous ulcerations are the earliest mucosal lesions seen in
Crohn’s disease.
22
Barium accumulates within the lesions and
they appear as small, shallow, or punctate collections with a
surrounding radiolucent halo (Figure 6-15A). These lesions
occur more frequently in the colon than the small intestine,
and they help to distinguish Crohn’s disease from UC. As the
aphthous lesions progress, the ulcerations deepen, widen,
and coalesce. The transmural nature of the inflammation
allows the ulcerations to extend into the musculature of the
bowel wall and even lead to fistulization. The result is deep
longitudinal and transverse fissuring with edematous mucosa
in between that gives the colon a cobblestone appearance.
Barium deposits in the deep fissures and appear as multiple
irregular white stripes (Figure 6-15B). The deepest portions
of the fissures penetrate beyond the submucosa and the
resulting image is one of “rose thorns” extending below the
level of the mucosal edge. Once the ulcerations progress
through the submucosa, the distinction of Crohn’s disease
can be made. Also, the identification of skip lesions or areas
of normal mucosa in between areas of active colitis distinguish Crohn’s disease from UC (Figure 6-16). Severe colitis
leads to the development of long, deep linear ulcers typically
along the mesenteric border of the colon. These long ulcers
are known as “rake” or “bear claw” ulcers. If the ulcerations
continue to burrow in the wall of the bowel, a fistula or sinus
tract can result. Fistulas can be identified by early filling of
the small bowel before opacification of the proximal colon or
as irregular projections of contrast outside of the lumen.
Another significant feature of Crohn’s disease is the development of strictures. Crohn’s strictures are a result of
transmural fibrosis. Radiographically, the strictures are
asymmetric, have irregular borders, and are not circumferential (they are centered on the mesenteric edge) (Figure 6-17).
This is in contrast to the strictures associated with UC, which
are symmetric, smooth, and circumferential.
FIGURE 6-15. A Contrast enema of Crohn’s disease showing
ulcers. B Contrast enema of Crohn’s with fissures, and long linear
ulcers.
Diverticulitis
Air contrast barium enemas are more sensitive than single contrast studies at detecting diverticula because of better colonic
distension and mucosal detail. The radiographic appearance of
diverticula varies based on their size, number, angle at which
they are viewed, amount of barium within the diverticula, and
amount of colonic distention. When viewed in profile, they are
flask-shaped with an associated neck that point away from the
lumen. When filled with barium, they will appear as white projections or a white line outlining the mucosa when the barium
has emptied from the diverticula. When viewed en face, they
have the appearance of a bowler’s hat projecting away from the
lumen when they are empty of barium. If filled with barium,
they will appear as a white spot or when partially filled, they
will appear as a bowler’s hat with a white meniscus. Diverticula
can be distinguished from polyps and small cancers because
they project away from the lumen as compared with neoplasms
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