AJR 2001; 176:1105-1116
© American Roentgen Ray Society
CT of Bowel Wall Thickening
Significance and Pitfalls of Interpretation
Michael Macari1 and
Emil J. Balthazar
1
Both authors: Department of Radiology, NYU Medical Center, Tisch Hospital, 560
First Ave., Ste. HW 207, New York, NY 10016.
Received June 27, 2000;
accepted after revision November 1, 2000.
Address correspondence to M. Macari.
Introduction
CT has become the most important imaging technique for evaluating the
abdomen and pelvis. CT is used to examine patients with acute abdominal
complaints, known or suspected malignancy, abdominal and pelvic trauma, and
inflammatory conditions. When CT images of the abdomen and pelvis are
interpreted, the focus is often placed on the peritoneal cavity, the
mesentery, and the parenchymal organs. A common misconception is that CT
provides only limited information with respect to the gastrointestinal
tract.
In fact, recent technologic advances and accumulated experience in image
interpretation suggest that substantial information regarding gastrointestinal
tract disorders can be obtained. Normal variants—as well as abnormal
conditions—may cause thickening of the bowel wall. In this review, the
normal CT appearance of the bowel wall and the different causes of bowel wall
thickening will be described.
The various criteria that allow one to differentiate normal variants and
abnormal conditions are reviewed, including attenuation pattern of bowel wall
thickening; degree of bowel wall thickening; circumferential symmetric
thickening versus asymmetric thickening; focal, segmental, or diffuse
involvement; and associated perienteric abnormalities.
Normal Gastrointestinal Tract
The normal small-bowel wall is thin, measuring between 1 and 2 mm when the
lumen is well distended (Fig.
1). However, the thickness of the normal small-bowel wall varies
slightly depending on the degree of luminal distention. As a result, different
criteria have been used to diagnose small-bowel wall thickening
[1,2,3,4,5,6].
When the lumen of the small bowel is distended, the wall is often not seen. If
the bowel is partially collapsed, the wall measures between 2 and 3 mm and is
of symmetric thickness. In these cases it is important to compare the degree
of thickness of similarly distended segments to exclude disorders. A
measurement of 2-3 mm as the upper limit of normal thickness has been used by
some authors [3,
4]. Others have advocated any
perceptible thickening to indicate disorders
[5,
6]. However, potential pitfalls
exist with this latter approach. We have observed that when the normal small
bowel is filled with water, its wall may appear thicker
(Fig.
2A,Fig. 2B). In
case of uncertainty regarding the presence of a disease process, a small-bowel
series should be performed.
View larger version (130K):
[in this window]
[in a new window]
[as a PowerPoint slide]
|
Fig. 1. —Normal enhancement and appearance of small bowel in
77-year-old woman. Axial CT scan obtained at level of kidneys with IV contrast
material and water as oral contrast agent shows enhancement of normal bowel
wall. Note thinly enhancing valvulae conniventes (arrow). This
finding is often better seen when water alone is given as oral contrast agent.
Enhancement may be obscured with positive contrast in lumen.
|
|
View larger version (186K):
[in this window]
[in a new window]
[as a PowerPoint slide]
|
Fig. 2A. —Perceived pitfall in interpretation of bowel wall thickening
caused by mixing of water and oral contrast material in 47-year-old man with
history of lymphoma. Axial CT scan through upper abdomen shows apparent
homogeneous circumferential thickening of wall of jejunum loops
(arrow), a finding suspicious for lymphoma.
|
|
View larger version (147K):
[in this window]
[in a new window]
[as a PowerPoint slide]
|
Fig. 2B. —Perceived pitfall in interpretation of bowel wall thickening
caused by mixing of water and oral contrast material in 47-year-old man with
history of lymphoma. Radiograph from upper gastrointestinal series performed 2
days after A shows normal small bowel (arrow).
|
|
The normal thickness of the colonic wall varies greatly depending on the
degree of distention. When the colon is distended, the wall should measure
less than 3 mm; it is often imperceptible
[7]. Frequently, because of
fecal contents, fluid, or colonic redundancy, the true thickness is difficult
to ascertain. Carefully following the colonic wall to a region where the colon
is well distended with gas will often reveal the true thickness
(Fig. 3).
View larger version (161K):
[in this window]
[in a new window]
[as a PowerPoint slide]
|
Fig. 3. —Normal colonic wall thickness in 81-year-old woman with
breast cancer. Contrast-enhanced axial CT scan of cecum suggests bowel wall
thickening with target appearance (arrow). However, ventral wall is
thin, without target appearance (arrowhead). Occasionally, residual
fluid in bowel can mimic submucosal edema and bowel wall thickening, as in
this case. Identifying focal area of distention without adjacent fluid will
clarify wall thickness.
|
|
The normal bowel wall enhances after an adequate bolus of IV contrast
material (Fig. 1). The
enhancement is often more easily identified in patients who have been given
water as an oral contrast agent. In these cases, the enhancing bowel wall is
well depicted adjacent to the low-attenuation fluid in the lumen. Enhancement
is usually greater on the mucosal aspect of the bowel wall. This enhancement
should not be mistaken for a disease process. Recognizing that the wall is not
thickened and that no perienteric inflammation is present will allow one to
differentiate normal enhancement from a disease process.
Bowel Wall Thickening
Bowel wall thickening may be related to a number of entities, including
normal variants, inflammatory conditions, and neoplastic disease. The CT
findings that need to be analyzed when assessing thickened bowel include
pattern of attenuation; degree of thickening; symmetric versus asymmetric
thickening; focal, segmental, or diffuse involvement; and associated
perienteric abnormalities. Evaluation of these parameters, which are reviewed
in the following text, will lead to a more accurate differential
diagnosis.
Attenuation of the Thickened Bowel Wall
The attenuation pattern of a thickened segment of bowel wall is an
important criteria for establishing a differential diagnosis. In most cases,
the attenuation pattern of a thickened bowel wall is directly related to the
administration of IV contrast material (Fig.
4A,4B).
If IV contrast material is not administered, most cases of bowel wall
thickening will show homogeneous attenuation. Two notable exceptions to this
are the presence of central fat deposition and intestinal pneumatosis (Figs.
5 and
6A,6B).
In these cases, variations in attenuation of the bowel wall can be depicted on
CT without IV contrast material because of the marked differences in tissue
attenuation.
View larger version (143K):
[in this window]
[in a new window]
[as a PowerPoint slide]
|
Fig. 4A. —"Target" sign detected only after IV contrast
administration in 64-year-old man with pain and bloody diarrhea. CT scan
obtained without IV contrast material shows moderate circumferential
thickening of sigmoid colon (arrow). Attenuation of bowel wall is
homogeneous. Without IV contrast material, further characterization is not
possible.
|
|
View larger version (114K):
[in this window]
[in a new window]
[as a PowerPoint slide]
|
Fig. 4B. —"Target" sign detected only after IV contrast
administration in 64-year-old man with pain and bloody diarrhea.
Contrast-enhanced axial CT image obtained 48 hr after A at same level
shows thickened sigmoid with target configuration (arrow). Findings
suggest inflammation or ischemia. Endoscopy and biopsy confirmed ischemic
colitis.
|
|
View larger version (158K):
[in this window]
[in a new window]
[as a PowerPoint slide]
|
Fig. 5. —Deposition of fat in submucosa producing "target"
sign in 85-year-old man with history of chronic ulcerative colitis.
Contrast-enhanced axial CT scan of rectum shows target configuration with
central low attenuation in submucosa (arrow). Central low attenuation
is same density (-80 H) as surrounding perirectal fat, indicating submucosal
fat deposition. Patient was asymptomatic at time of examination.
|
|
View larger version (117K):
[in this window]
[in a new window]
[as a PowerPoint slide]
|
Fig. 6A. —Improved detection and evaluation of intramural air with wide
window and low level settings in 34-year-old woman with AIDS and diarrhea.
Contrast-enhanced axial CT scan (window width and level, 420 and 30 H) at
level of cecum shows gas surrounding cecum (arrow).
|
|
View larger version (86K):
[in this window]
[in a new window]
[as a PowerPoint slide]
|
Fig. 6B. —Improved detection and evaluation of intramural air with wide
window and low level settings in 34-year-old woman with AIDS and diarrhea.
Same CT slice as A (window width and level, 1550 and -460 H,
respectively) better shows that central low attenuation (gas) is in wall
(arrow) of cecum, which is compatible with pneumatosis. Patient was
treated with antibiotics, improved within a week, and did not require
colectomy.
|
|
The presence or absence of enhancement can be evaluated in a number of
ways, including comparing the attenuation of the thickened segment with other
segments of bowel, comparing unenhanced and contrast-enhanced scans, or, if
unenhanced images are not available, obtaining delayed images. After IV
contrast material administration, there are two distinct patterns of bowel
wall attenuation: homogeneous and heterogeneous (Appendix 1).
Homogeneous Attenuation
The differential diagnosis of a thickened bowel wall that shows homogenous
attenuation on CT includes submucosal hemorrhage or hematoma
[8,
9], infarcted bowel
[10,
11], neoplasm
[12,13,14,15],
chronic Crohn's disease [3],
radiation injury [10], and
pseudothickening related to incomplete distention and residual fluid
[1].
Submucosal hemorrhage.—The diagnosis of submucosal
intestinal hemorrhage is usually made when CT depicts circumferential and
symmetric bowel wall thickening in patients who are undergoing anticoagulation
therapy or who have an underlying bleeding diathesis
(Fig. 7). On CT, most cases of
submucosal hemorrhage show homogeneous high attenuation of the thickened
segment and lack of enhancement
[8,
9]. Patients often have a
history of coagulopathy and, in most cases, the small bowel is affected in a
segmental distribution [9]. In
patients with suspected submucosal hemorrhage, an unenhanced CT examination is
often helpful in establishing the diagnosis by showing high attenuation in the
thickened segment [8,
9]. The high attenuation is due
to acute bleeding in the bowel wall.
View larger version (165K):
[in this window]
[in a new window]
[as a PowerPoint slide]
|
Fig. 7. —Intramural hemorrhage in 64-year-old man with bowel wall
thickening (homogeneous attenuation). Contrast-enhanced axial CT scan of
abdomen shows segmental circumferential thickening with homogeneous
attenuation of a loop of jejunum (arrow). Differential diagnosis
includes hemorrhage, ischemia, and lymphoma. Because of history of
anticoagulation therapy and abrupt onset, hemorrhage is most likely.
Unenhanced study can better define high attenuation.
|
|
Ischemia and infarction.—The appearance of the
gastrointestinal wall varies on IV contrast-enhanced CT as the bowel wall
progresses from ischemia to infarction. When the wall is ischemic, it is often
circumferentially thickened and may contain a target or halo configuration of
attenuation [9,
10] (Fig.
8A,8B).
In other cases of ischemic bowel, the wall is thickened and no enhancement is
identified [10,
11]. In these cases,
homogeneous attenuation of the bowel wall will be seen. Detecting lack of
enhancement can be difficult, but comparing adjacent loops helps to show this
finding [11]
(Fig. 9). In our experience,
complete lack of enhancement is rarely identified in these patients.
Etiologies of ischemia and infarction include thromboembolism, low flow
(related to poor cardiac output), and strangulation obstruction
[10].
View larger version (159K):
[in this window]
[in a new window]
[as a PowerPoint slide]
|
Fig. 8A. —Ischemic bowel with mural thickening and target configuration
of attenuation in 71-year-old woman. Contrast-enhanced axial CT scan at level
of terminal ileum shows circumferential small-bowel wall thickening with
target configuration (arrow).
|
|
View larger version (153K):
[in this window]
[in a new window]
[as a PowerPoint slide]
|
Fig. 8B. —Ischemic bowel with mural thickening and target configuration
of attenuation in 71-year-old woman. Contrast-enhanced axial CT scan at level
of superior mesenteric artery shows intraluminal filling defect
(arrow) consistent with mural thrombus. Thrombus was confirmed at
follow-up angiography.
|
|
View larger version (147K):
[in this window]
[in a new window]
[as a PowerPoint slide]
|
Fig. 9. —Closed-loop small-bowel obstruction with ischemic bowel in
83-year-old woman. Contrast-enhanced axial CT image at level of pelvis shows
typical configuration of closed-loop obstruction with dilated small-bowel
loops in radial distribution, minimal to no mural thickening, and homogeneous
attenuation (open arrows). Note loops in closed-loop obstruction do
not enhance to same degree as loops not in closed loop (solid arrow),
suggesting ischemia. Ischemic bowel with infarction was present at subsequent
surgery.
|
|
Chronic Crohn's disease and chronic radiation
changes.—Chronic Crohn's disease and chronic radiation enteritis
may show homogenous attenuation on contrast-enhanced CT
[3,
10]. In patients with
long-standing Crohn's disease or radiation injury, transmural fibrosis
develops. In the chronic phase, the typical findings on IV
contrast—enhanced CT of a target appearance are no longer present
[3,
10].
Neoplasm.—Gastrointestinal neoplasms can present with
homogeneous attenuation of the thickened segment on contrast-enhanced CT
[12,13,14].
In these instances, other criteria (degree, symmetry, length of involved
segment, and associated perienteric abnormalities) are important in
establishing the correct diagnosis. In cases of neoplasm, homogeneous
attenuation correlates with size of the tumor
[15]. Smaller tumors present
either as circumferential areas of bowel wall thickening or as asymmetric
areas of bowel wall thickening with homogeneous enhancement
(Fig. 10).
View larger version (104K):
[in this window]
[in a new window]
[as a PowerPoint slide]
|
Fig. 10. —Well-differentiated adenocarcinoma in 26-year-old man with
bowel obstruction. Contrast-enhanced axial CT scan at level of cecum shows
homogeneous attenuation (enhancement) of circumferentially thickened cecum
(straight arrows). Small amount of fluid is seen in lumen
(arrowhead). Note multiple obstructed loops of small bowel with
air—fluid levels (curved arrow). Surgery revealed
well-differentiated adenocarcinoma of cecum.
|
|
Small-bowel lymphoma is often depicted on CT as a segmental area of
circumferential thickening with homogeneous attenuation and enhancement
[12,
14]. A recent study found that
in 33 (72%) of 46 patients with small-bowel lymphoma, the involved bowel
showed single or multiple focal areas of gross circumferential wall thickening
with homogeneous attenuation
[14]
(Fig. 11).
View larger version (147K):
[in this window]
[in a new window]
[as a PowerPoint slide]
|
Fig. 11. —Lymphoma of small bowel in 30-year-old man. Contrast-enhanced
axial CT image of mid abdomen shows homogeneous attenuation (enhancement) of
markedly thickened small bowel (arrows). Thickening involves a short
segment of small bowel. Despite small-bowel thickening, mild dilatation of
lumen is seen. Findings are strongly suggestive of small-bowel lymphoma. Note
retroperitoneal lymphadenopathy (arrowhead). Biopsy revealed
non-Hodgkin's lymphoma.
|
|
Pitfalls.—Residual fluid within the lumen coating the mucosa
of the bowel wall may be perceived as a thickened segment without enhancement
(Fig.
2A,2B).
In these cases, a disease process may be difficult to exclude, and correlation
with a small-bowel series may be needed
[1].
Heterogeneous (Stratified) Attenuation
Heterogeneous attenuation is the second pattern that may be depicted in a
thickened segment of bowel wall. When the attenuation of a thickened bowel
wall is heterogeneous, the wall may display a stratified pattern or a mixed
pattern of attenuation.
Recognizing alternating (stratified) layers of attenuation in a thickened
segment of bowel wall helps in the differential diagnosis. The stratified
pattern may be in the form of a double halo or a target configuration. The
double halo sign consists of an inner low-attenuation (edema) ring surrounded
by an outer higher attenuation ring. In the "target" sign, inner
and outer layers of high attenuation surround a central area of decreased
(edema) attenuation [1]. These
signs are best visualized during the late arterial and early portal venous
phases of IV contrast material enhancement
[1]. On unenhanced or delayed
(>2 min) IV contrast—enhanced CT, these signs may not be visualized
(Fig.
4A,4B).
The high attenuation present with these signs is related to hyperemia
[1].
Inflammation and ischemia.—The double halo and target signs
have similar significance in that they usually indicate an acute inflammatory
or ischemic condition. The double halo sign was first reported by Frager et
al. [16] in patients with
Crohn's disease. In addition to Crohn's disease, this pattern of attenuation
may be present in ulcerative colitis, infectious enterocolitis, radiation
enteritis, vasculitis, lupus erythematosus, and bowel edema in patients with
cirrhosis [1,
3,
16,17,18,19,20,21,22,23,24,25,26,27,28,29,30,31,32,33,34,35,36,37,38,39]
(Figs.
12,13,14).
The finding of stratified attenuation in a thickened segment, although
nonspecific, is used mainly to exclude malignant conditions. Correlation with
clinical history and associated findings on CT related specifically to the
bowel wall and the surrounding mesentery may allow one to narrow the
differential diagnosis.
View larger version (142K):
[in this window]
[in a new window]
[as a PowerPoint slide]
|
Fig. 12. —"Target" sign in 35-year-old woman with history
of ulcerative colitis. Contrast-enhanced axial CT image of rectum shows mild
wall thickening with classic target appearance and inner enhancement of mucosa
(short white arrow) and outer enhancement of muscular layer (long
white arrow) surrounding low-attenuation edematous submucosa (black
arrow).
|
|
View larger version (127K):
[in this window]
[in a new window]
[as a PowerPoint slide]
|
Fig. 13. —"Target" sign in 37-year-old man with history of
acute Crohn's disease. Contrast-enhanced axial CT image shows marked
circumferential thickening of terminal ileum. Target appearance is present,
with enhancement of mucosa (short arrow) and outer enhancement of
muscular layer (long arrow) surrounding low-attenuation edematous
submucosa (arrowhead).
|
|
View larger version (119K):
[in this window]
[in a new window]
[as a PowerPoint slide]
|
Fig. 14. —"Target" sign in 37-year-old woman with history
of lupus erythematosus. Contrast-enhanced axial CT image at level of mid
abdomen shows diffuse marked circumferential thickening of colon. Target
appearance is present, with enhancement of mucosa (short white arrow)
and outer enhancement of muscular layer and serosa (long white arrow)
surrounding low-attenuation edematous submucosa. Small amount of ascites is
present (arrowhead).
|
|
Neoplasm.—A notable exception to this accepted general rule
(target sign = inflammation) is the rare occurrence of this sign in
infiltrating scirrhous carcinoma of the stomach and colon. Rigidity (after
attempted air insufflation), severe luminal narrowing, abrupt transition, and
regional lymphadenopathy usually help in establishing the correct
diagnosis.
Pitfalls.—A potential pitfall may arise when residual fluid
and oral contrast material fill the bowel lumen to mimic a target sign
[2]. Seeing that the bowel is
partially filled with fluid and that adjacent areas of the bowel are well
distended with gas will usually allow these pitfalls to be recognized
(Fig. 3). Moreover, usually no
perienteric disease is associated with these fluid-filled segments, which also
tends to exclude an acute inflammatory process.
The deposition of submucosal fat in the large and small bowels has been
documented in patients with both acute and chronic inflammatory disorders of
the bowel [40,
41]. One study found
submucosal fat deposition in 61% of patients with ulcerative colitis but in
only 8% of patients with Crohn's disease
[23]. Although a stratified
pattern of attenuation is present with submucosal fat deposition, recognizing
the very low attenuation (negative Hounsfield unit value) of the submucosa
will allow an accurate diagnosis to be established
(Fig. 5).
Finally, pneumatosis may present as a striated pattern of attenuation
[42]. Occasionally, small
amounts of gas may be overlooked when CT scans are viewed at standard
abdominal window and level settings (Fig.
6A,6B).
In these cases, viewing the scans at wider window and lower level settings
facilitates visualization of the gas. Air trapped between the bowel wall and
residual fluid in the lumen may mimic pneumatosis
(Fig. 15), which usually
occurs in the cecum or stomach. In these cases, the perceived pneumatosis will
be seen on the dependent aspect of the bowel where the residual fluid is
present. Recognizing that the more ventral aspect of the bowel wall does not
show the appearance will usually allow this pitfall to be avoided.
View larger version (159K):
[in this window]
[in a new window]
[as a PowerPoint slide]
|
Fig. 15. —Intraluminal air mimicking pneumatosis in 58-year-old man.
Unenhanced axial CT scan at level of stomach shows gas (arrow)
between wall of stomach and residual gastric fluid mimicking pneumatosis. Note
pneumobilia (arrowhead) from previous procedure.
|
|
Heterogeneous (Mixed) Attenuation
The final category of attenuation pattern in thickened bowel is mixed
attenuation. In these cases, the grossly thickened bowel wall shows several
irregular zones of lower attenuation hap-hazardly located adjacent to areas of
higher attenuation. The findings are related to ischemia and necrosis and are
seen in high-grade, poorly differentiated gastrointestinal neoplasms such as
adenocarcinoma and stromal cell tumors. Larger tumors frequently undergo
central necrosis and will show heterogeneous enhancement on contrast-enhanced
scans. This heterogeneous enhancement is seen in large tumors and is related
to rapid growth, ischemia, and necrosis. Mucinous adenocarcinomas often
contain poorly defined central areas of low attenuation related to
intracellular tumor mucin deposition and may show heterogeneous attenuation
after contrast administration (Fig.
16).
View larger version (179K):
[in this window]
[in a new window]
[as a PowerPoint slide]
|
Fig. 16. —Heterogeneous low-attenuation enhancement in mucinous
adenocarcinoma with irregular circumferential bowel wall thickening in
64-year-old man with abdominal pain. Contrast-enhanced axial CT image of
splenic flexure shows irregular wall thickening (arrows) with
heterogeneous areas of low attenuation in colon wall (arrowhead).
Large mucinous adenocarcinoma was found at surgery.
|
|
Degree of Bowel Wall Thickening
The second variable that aids in establishing a differential diagnosis when
evaluating bowel wall thickening is the degree of thickening (Appendix 2).
Entities that cause mild bowel wall thickening (1-2 cm) often overlap and
include inflammatory conditions and neoplasms. In general, benign conditions
result in bowel wall thickening of less than 2 cm, whereas wall thickening
greater than 3 cm is usually present in neoplastic conditions
[1,
12,
14,
43].
Mild Thickening
In cases of mild bowel wall thickening, a nonneoplastic (inflammatory or
infectious) condition is usually present. Two of the more common inflammatory
conditions of the bowel are ulcerative colitis and Crohn's disease. Because
the disease process is limited to the mucosa in patients with ulcerative
colitis and is often transmural in Crohn's disease, bowel wall thickening is
usually greater in Crohn's disease. One study found the mean thickness of the
colon wall in Crohn's disease was 11.0 mm compared with 7.8 mm in patients
with ulcerative colitis [23]
(Figs. 12 and
13). In most cases of
intestinal infection involving the small bowel, the wall is either normal or
mildly thickened.
Marked Thickening
Infection and inflammation.—With severe infections of the
colon, the wall may become markedly thickened by edematous haustral folds (up
to 2 cm or even greater) (Fig.
17). On CT, the finding of barium trapped between these folds is
known as the "accordion" sign
[24]
(Fig. 18). The accordion sign
has been detected in 4-19% of patients with documented Clostridium
difficile colitis and has been considered specific
[24,25,26].
However, other causes, especially cytomegalovirus in AIDS patients, as well as
a variety of other infectious and inflammatory conditions, have shown massive
colonic wall thickening and a similar mucosal pattern to that shown by the
accordion sign [27,
28]
(Fig. 14). The usefulness of
the accordion sign relates to the depiction of severe submucosal edema in a
segmental or diffuse colitis caused by either an infection or ischemia.
View larger version (115K):
[in this window]
[in a new window]
[as a PowerPoint slide]
|
Fig. 17. —Diffuse marked colonic thickening with target appearance in
pseudomembranous colitis in 18-year-old woman with diarrhea. Contrast-enhanced
axial CT image of mid abdomen shows diffuse marked circumferential wall
thickening of cecum and descending colon with target appearance
(arrows). Findings are consistent with inflammatory colitis; stool
was positive for Clostridium difficile cytotoxin.
|
|
View larger version (133K):
[in this window]
[in a new window]
[as a PowerPoint slide]
|
Fig. 18. —"Accordion" sign in 44-year-old man with diarrhea
and Clostridium difficile colitis. Contrast-enhanced axial CT image
of mid abdomen shows marked thickening of haustra (arrowheads).
Barium (arrow) trapped between thickened haustra mimic appearance of
accordion.
|
|
Neoplasm.—Primary intestinal neoplasms often present as
short segments of bowel wall thickening
(Fig. 10). Sarcoma
(gastrointestinal stromal tumors) usually presents as a bulky exophytic mass
with heterogeneous attenuation (Fig.
19). Small-bowel lymphoma rarely obstructs the lumen, and it often
presents as a markedly thickened segment ranging from 1.5 to 7 cm (mean, 2.6
cm) [14]
(Fig. 11).
View larger version (152K):
[in this window]
[in a new window]
[as a PowerPoint slide]
|
Fig. 19. —Exophytic intestinal mass in 84-year-old man with bowel
obstruction. Contrast enhanced axial CT image shows large bulky exophytic mass
extending from jejunum with heterogeneous attenuation (white arrows).
Small bubble of gas is present in mass (black arrow), suggesting
fistula in bowel. Surgery revealed malignant gastrointestinal stromal
tumor.
|
|
Symmetric Versus Asymmetric Thickening
Another feature to evaluate in cases of bowel wall thickening is whether
the involved segments are symmetrically or asymmetrically thickened (Appendix
3). Symmetric thickening is present when the involved segment shows the same
degree of thickening throughout the circumference of the abnormal segment.
Asymmetric thickening relates to different degrees of eccentric thickening
around the circumference of the involved segment.
Symmetric thickening is seen in intestinal inflammatory conditions,
infections, bowel edema, and ischemia
[1] (Figs.
12,13,14).
In addition, the bowel is usually symmetrically thickened in cases of
submucosal hemorrhage [8,
9]
(Fig. 7). Some neoplasms may
also display symmetric thickening, especially scirrhous carcinoma and,
occasionally, lymphoma [1,
14]
(Fig. 11).
Asymmetric or eccentric bowel thickening is mainly seen with malignant
conditions. An exception to this is cases of long-standing Crohn's disease in
which the bowel may be asymmetrically thickened. Usually, associated
mesenteric findings will help establish the diagnosis of Crohn's disease in
these cases. Most neoplasms present with asymmetric thickening, including
stromal tumors, adenocarcinoma, carcinoids, metastases, and, occasionally,
lymphoma. A bulky exophytic mass is usually present in patients with
gastrointestinal stromal tumors, metastases, and, occasionally, lymphoma.
Irregular short asymmetric lesions with abrupt margins are the hallmark of
primary intestinal adenocarcinoma and metastatic disease
[12] (Fig.
20A,20B).
View larger version (140K):
[in this window]
[in a new window]
[as a PowerPoint slide]
|
Fig. 20A. —CT scans of focal asymmetric thickening in 59-year-old man
show importance of rectal distention. Axial scan at level of rectum shows lack
of distention (arrow), which limits the examination.
|
|
View larger version (134K):
[in this window]
[in a new window]
[as a PowerPoint slide]
|
Fig. 20B. —CT scans of focal asymmetric thickening in 59-year-old man
show importance of rectal distention. Axial scan at same level as A
performed after administration of rectal air shows focal asymmetrically
thickened ulcerated mass (arrow) on nondependent wall of rectum.
Biopsy revealed rectal adenocarcinoma.
|
|
Focal, Segmental, or Diffuse Bowel Wall Thickening and Location
The extent and location of bowel wall involvement should be evaluated. It
is important to determine if the bowel wall thickening is focal (a few
centimeters), segmental (10-30 cm), or diffuse (involving most of the small
bowel or colon). Although inflammatory or neoplastic conditions may overlap in
the length of involvement, the analysis helps in narrowing the differential
diagnosis (Appendix 4). With few exceptions, long segments of involvement are
seen in benign conditions.
Focal Involvement
Focal thickening is seen in both benign and malignant processes. Most
neoplasms of the gastrointestinal tract present as a focal area of bowel wall
thickening (Figs. 10 and
20A,20B).
Inflammatory processes that may present as focal areas of bowel wall
thickening include diverticulitis, appendicitis, and, occasionally,
tuberculosis.
Segmental Involvement
A segmental distribution of involvement is usually caused by an
inflammatory process. Conditions associated with segmental involvement include
Crohn's disease, infectious ileitis, radiation enteritis, and ischemia
[1,
38]. Other considerations for
segmental involvement include intramural hemorrhage and lymphoma (Figs.
7 and
11).
Diffuse Involvement
Diffuse thickening of the bowel wall is seen with a variety of inflammatory
conditions, including ulcerative colitis, infectious enteritis, edema from
low-protein states, portal hypertension associated with cirrhosis, and
low-flow ischemia [30,
32,
33,
39]
(Fig. 21). Segmental or
diffuse thickening may be seen in patients with small-bowel vasculitis, as
often occurs in systemic lupus erythematosus
[35,36,37]
(Fig 12).
View larger version (121K):
[in this window]
[in a new window]
[as a PowerPoint slide]
|
Fig. 21. —Diffuse mild colonic wall thickening in 35-year-old woman.
Contrast-enhanced axial CT image shows mild circumferential wall thickening of
ascending and descending colons (arrows). Diffuse mild colitis
suggests infection or ulcerative colitis. Endoscopy revealed ulcerative
colitis.
|
|
Associated Abnormalities
Last, a major advantage of CT over endoscopy or barium studies is the
ability of CT to show extraintestinal manifestations of disease. These
associated findings include lymph nodes; mesenteric stranding and
calcification; abscess, sinus tracts, and fistulas; proliferation of fat;
vascular occlusion; and solid organ abnormalities.
Lymph Nodes
The number, size, location, and attenuation of lymph nodes in the abdominal
and pelvic cavities are important associated findings when examining patients
with thickened bowel
[43,44,45,46].
Attenuation.—The attenuation of lymph nodes and the presence
or absence of calcification should be evaluated
[45,
46]. Low-attenuation lymph
nodes with a rim of contrast enhancement or calcified lymph nodes should alert
one to the possibility of tuberculosis, other mycobacterial infections, or
histoplasmosis (Fig.
22A,22B).
In a patient with AIDS, the presence of high-attenuation lymph nodes suggests
the possibility of Kaposi's sarcoma. In this condition, the lymph nodes are
hyperemic and will show enhancement during CT performed with IV contrast
material.
View larger version (146K):
[in this window]
[in a new window]
[as a PowerPoint slide]
|
Fig. 22A. —42-year-old woman with low-attenuation caseating lymph nodes
in intestinal tuberculosis. Contrast-enhanced axial CT image of cecum shows
irregular focal thickening (arrow) with associated small regional
lymph nodes (arrowhead). Findings mimic cecal carcinoma.
|
|
View larger version (149K):
[in this window]
[in a new window]
[as a PowerPoint slide]
|
Fig. 22B. —42-year-old woman with low-attenuation caseating lymph nodes
in intestinal tuberculosis. Contrast-enhanced axial CT image 1 cm cephalad to
A shows larger lymph node with central low attenuation
(arrow). Endoscopy and biopsy revealed cecal tuberculosis.
|
|
Neoplasm.—On CT, focal colonic wall thickening may present a
challenge in the differential diagnosis. When present, especially in the
sigmoid or descending colon, the main differential diagnosis is adenocarcinoma
versus diverticulitis (Fig.
23A,23B).
A recent study found that pericolonic lymph nodes adjacent to the focal area
of colonic thickening are more commonly seen in patients with colon cancer.
Pericolonic inflammatory changes are more commonly seen in diverticulitis
[43].
View larger version (152K):
[in this window]
[in a new window]
[as a PowerPoint slide]
|
Fig. 23A. —Benign versus malignant colonic lesion: importance of
lymphadenopathy. Contrast-enhanced axial CT scan of descending colon in
43-year-old man shows mild bowel wall thickening (straight arrow)
with fluid in adjacent paracolic gutter (arrowhead). Small
diverticulum is present (curved arrow). Findings are consistent with
mild focal diverticulitis, which resolved after antibiotic therapy.
|
|
View larger version (169K):
[in this window]
[in a new window]
[as a PowerPoint slide]
|
Fig. 23B. —Benign versus malignant colonic lesion: importance of
lymphadenopathy. 66-year-old man with left-sided abdominal pain.
Contrast-enhanced axial CT image at level of descending colon shows mild
thickening (long arrow) with fluid and stranding in adjacent
paracolic gutter (arrowhead). In addition, cluster of small lymph
nodes is seen in adjacent pericolonic fat (short arrow). This finding
(lymphadenopathy) is more commonly present in focal adenocarcinoma than in
diverticulitis. Surgery revealed adenocarcinoma, and seven of nine lymph nodes
tested positive for lymphadenopathy.
|
|
In addition to low-attenuation lymph nodes caused by tuberculosis,
metastatic lymphadenopathy from mucinous tumors of the colon will often be of
low attenuation. When large bulky retroperitoneal lymph nodes are present
adjacent to or in areas removed from a region of bowel wall thickening, a
diagnosis of lymphoma is suggested (Fig.
11).
Mesenteric Stranding and Calcification
Stranding.—When stranding of the perienteric fat is present
adjacent to a thickened segment of bowel, an inflammatory process should be
suspected. When this finding is not present, the differential diagnosis
includes lymphoma and hemorrhage (Figs.
7 and
11). A frequent pitfall when
interpreting CT with apparent bowel wall thickening is differentiating a
disease process from pitfalls related to residual fluid. When the perienteric
fat is normal adjacent to a thickened segment of bowel, an acute inflammatory
condition is less likely (Fig.
2A,2B).
Calcification.—Mesenteric calcifications are seen in benign
and malignant conditions.
Benign mesenteric calcifications may be present in granulomatous processes
such as tuberculosis, sarcoidosis, or, rarely, fungus. These calcifications
may be present in mesenteric lymph nodes or solid organs such as the liver or
spleen. The presence of mesenteric calcification does not imply that the
abnormal bowel wall thickening is related to a granulomatous disease; it
merely suggests that these conditions should be considered in the differential
diagnosis.
Malignant neoplasms may present on CT with calcifications in the mesentery,
which is occasionally seen in patients with treated lymphoma. Calcified foci
in the mesentery can also be seen in mucinous metastases from ovarian or
gastrointestinal neoplasms. Another neoplastic process that can present with a
calcified soft-tissue mass in the mesentery is carcinoid tumor
[12]. In these cases, a
significant desmoplastic process in the mesentery is sometimes present,
tethering adjacent loops of small bowel toward the calcified central mass
(Fig. 24). The small bowel is
often thickened, which is likely related to the peptides secreted by the
carcinoid tumor and secondary edematous changes.
View larger version (110K):
[in this window]
[in a new window]
[as a PowerPoint slide]
|
Fig. 24. —Mesenteric mass with calcification and adjacent desmoplastic
reaction in 80-year-old woman with abdominal pain. Contrast-enhanced axial CT
image of abdomen shows soft-tissue mass with small calcifications (black
arrow) in mesentery (straight white arrow). Note desmoplastic
response with stranding of adjacent fat and associated bowel wall thickening
(curved arrow). Surgery revealed carcinoid tumor.
|
|
Abscess, Sinus Tracts, and Fistulas
CT findings of mild, symmetric bowel wall thickening with or without a
target configuration in the distal ileum lead to a differential diagnosis of
infectious enteritis, Crohn's disease, vasculitis, and radiation enteritis.
Secondary findings that help establish the diagnosis of Crohn's disease
include fistulas, sinus tracts, perienteric abscess, and fibrofatty
proliferation [3,
20]
(Fig. 25).
View larger version (128K):
[in this window]
[in a new window]
[as a PowerPoint slide]
|
Fig. 25. —Abscess in Crohn's disease in 21-year-old man.
Contrast-enhanced axial CT image of pelvis shows segmental distal ileal
thickening with "target" sign (white arrow) and abscess
in right iliopsoas muscle (black arrow).
|
|
Fibrofatty Proliferation
Intestinal tuberculosis is particularly difficult to distinguish from
Crohn's disease [21,
22]. Important clues in
differentiating the cause of the abnormal bowel are fibrofatty proliferation
or marked lymphadenopathy. Marked low-attenuation lymphadenopathy in abdominal
tuberculosis is often the cause of displacement of small-bowel loops on barium
studies, whereas fibrofatty proliferation is usually the cause of bowel
displacement in Crohn's disease
[22].
Solid Organs
When evaluating diffuse or segmental bowel wall thickening, findings in the
parenchymal organs can be helpful in establishing the differential diagnosis.
Focal or segmental bowel wall thickening with associated splenomegaly suggests
the diagnosis of lymphoma.
The differential diagnosis for diffuse colonic edema is infectious,
idiopathic (ulcerative), or ischemic colitis. However, patients with cirrhosis
may also develop intestinal edema. The edema most often occurs in the small
bowel and occasionally in the stomach and colon, especially the right colon
[6,
39]
(Fig. 26).
View larger version (138K):
[in this window]
[in a new window]
[as a PowerPoint slide]
|
Fig. 26. —Colonic edema in cirrhosis in 50-year-old man.
Contrast-enhanced axial CT image of right colon shows mild circumferential
wall thickening in right colon and target appearance consistent with edema
(arrow). Patient did not have pain or diarrhea. CT of liver (not
shown) showed findings consistent with cirrhosis.
|
|
Conclusion
Bowel wall thickening revealed on CT is seen as normal variants,
inflammatory conditions, and gastrointestinal neoplasms. A careful analysis of
several parameters described in this review—pattern of attenuation and
enhancement; degree, symmetry, and extent of thickening; and associated
abnormalities—will avoid most pitfalls, indicate a diagnosis of primary
intestinal lesions, or offer a pertinent differential diagnosis. Although none
of the solitary CT findings is by itself specific, the association of several
abnormal parameters will lead to a correct diagnosis or will narrow the
differential diagnosis in most cases. When confusing or overlapping CT
parameters are encountered or uncertainties persist, barium examinations
should be liberally used as complementary diagnostic studies.
,,,
References
-
Balthazar EJ. CT of the gastrointestinal tract: principles and
interpretation. AJR
1991;156:23
-32[Abstract/Free Full Text]
-
Shirkhoda A. Diagnostic pitfalls in abdominal CT.
RadioGraphics
1991;11:969
-1002[Abstract]
-
Gore RM, Balthazar EJ, Ghahremani GG, Miller FH. CT features of
ulcerative colitis and Crohn's disease. AJR
1996;167:3
-15[Free Full Text]
-
James S, Balfe DM, Lee JKY, Picus D. Small-bowel disease:
categorization by CT examination. AJR
1987;148:863
-868[Abstract/Free Full Text]
-
Scanlon MH, Blumberg ML, Ostrum BJ. Computed tomographic
recognition of gastrointestinal pathology.
RadioGraphics
1983;3:201
-227
-
Karahan OI, Dodd GD III, Chintapalli KN, Rhim H, Chopra S.
Gastrointestinal wall thickening in patients with cirrhosis: frequency and
patterns at contrast-enhanced CT. Radiology
2000;215:103
-107[Abstract/Free Full Text]
-
Horton KM, Corl FM, Fishman EK. CT evaluation of the colon:
inflammatory disease. RadioGraphics
2000;20:399
-418[Abstract/Free Full Text]
-
Lane MJ, Katz DS, Mindelzun RE, Jeffrey RB Jr. Spontaneous
intramural small bowel hemorrhage: importance of non-contrast CT.
Clin Radiol
1997;52:378
-380[Medline]
-
Balthazar EJ, Hulnick D, Megibow AJ, Opulencia JF. Computed
tomography of intramural intestinal hemorrhage and bowel ischemia.
J Comput Assist Tomogr
1987;11:67
-72[Medline]
-
Rha SE, Ha HK, Lee SH, et al. CT and MR imaging features of bowel
ischemia from various primary causes. RadioGraphics
2000;20:29
-42[Abstract/Free Full Text]
-
Zalcman M, Van Gansbeke D, Lalmand B, Braude P, Closset J, Struyven
J. Delayed enhancement of the bowel wall: a new CT sign of small bowel
strangulation. J Comput Assist Tomogr
1996;20:379
-381[Medline]
-
Buckley JA, Fishman EK. CT of small bowel neoplasms: spectrum of
disease. RadioGraphics
1998;18:379
-392[Abstract]
-
DiSario JA, Burt RW, Vargas H, McWhorter WP. Small bowel cancer:
epidemiological and clinical characteristics from a population-based registry.
Am J Gastroenterol
1994;89:699
-701[Medline]
-
Balthazar EJ, Noordhoorn M, Megibow AJ, Gordon RB. CT of
small-bowel lymphoma in immunocompetent patients and patients with AIDS:
comparison of findings. AJR
1997;168:675
-680[Abstract/Free Full Text]
-
Horton KM, Abrams RA, Fishman EK. Spiral CT of colon cancer:
imaging features and role in management. RadioGraphics
2000;20:419
-430[Abstract/Free Full Text]
-
Frager DH, Goldman M, Beneventano TC. Computed tomography in Crohn
disease. J Comput Assist Tomogr
1983;7:819
-824[Medline]
-
Jacobs JE, Birnbaum BA. CT of inflammatory disease of the colon.
Semin Ultrasound CT MR
1995;16:91
-101[Medline]
Top
Introduction
Normal Gastrointestinal Tract
