AJR 2004; 183:1667-1671
© American Roentgen Ray Society
Cecal Pneumatosis in Patients with Obstructive Colon Cancer: Correlation of CT Findings with Bowel Viability
Patrice Taourel1,
Fabrice Garibaldi1,
Jerome Arrigoni1,
Virginie Le Guen1,
Alvian Lesnik1 and
Jean Michel Bruel2
1 Department of Radiology, Lapeyronie Hospital, 371, avenue du Doyen Gaston
Giraud, 34295, Montpellier cedex 5, France.
2 Department of Radiology, Saint-Eloi Hospital, Montpellier, France.
Received December 18, 2003;
accepted after revision March 9, 2004.
Address correspondence to P. Taourel.
Abstract
OBJECTIVE. The purpose of our study was to reassess CT findings of
cecal pneumatosis in patients with acute large-bowel obstruction due to colon
cancer to determine whether this condition indicates transmural necrosis
versus viable bowel and also whether other CT findings could be used to
identify patients with transmural necrosis.
CONCLUSION. CT findings of cecal pneumatosis do not always indicate
transmural infarction in patients with acute large-bowel obstruction due to
colon cancer. Cecal pneumatosis may be related to viable bowel when it
displays a bubblelike pattern or when it is not associated with other findings
of ischemia.
Introduction
Pneumatosis is visible on abdominal radiography but is best viewed on CT
with lung window settings to enhance detection of subtle forms. Although
pneumatosis may be detected in patients with ischemic bowel disease, it may
also be seen in patients with a variety of nonischemic conditions, including
bowel distention, infectious enteritis, chronic obstructive pulmonary disease,
connective tissue disorders, leukemia, and AIDS as well as reactions to organ
transplants, steroid usage, and chemotherapy
[1]. In patients with acute
large-bowel obstruction, the presence of intramural cecal gas is classically
considered to be a sign of necrosis and incipient cecal rupture
[2]; however, pneumatosis may
also be caused by mucosal disruption due to overdistention of the cecum. The
differentiation of cecal necrosis from viable bowel can be essential to
treating patients with acute largebowel obstruction due to colon cancer,
because cecal necrosis contraindicates colonic stent placement and requires
resection of the cecum.
Our study was performed to assess the frequency of cecal pneumatosis
detected on CT in patients with acute large-bowel obstruction due to colon
cancer to determine whether this condition indicates transmural cecal necrosis
versus overdistention and also to determine whether other CT findings could be
used to predict which patients with cecal pneumatosis are most likely to have
a viable cecum.
Materials and Methods
Between March 2000 and September 2003, 23 consecutive patients referred by
the emergency department presented with acute bowel obstruction caused by
colon cancer that had been identified on CT. They constituted our study
population, 19 men and four women, with an age range of 48–89 years
(mean age, 70 years).
All CT examinations were performed with a helical CT scanner (HiSpeed or a
LightSpeed CT unit, GE Healthcare). All patients underwent contrast-enhanced
CT. Scanning began 70 sec after the start of an IV injection of 120 mL of
contrast material delivered at a rate of 2.5 mL/sec. Because of the presence
of the acute bowel obstruction, no patient received an oral contrast agent.
Images were obtained with a 5- or 2.5-mm collimation and were reconstructed
with a soft-tissue algorithm.
All CT examinations were interpreted via consensus review by two abdominal
radiologists who had no knowledge of the surgical or pathologic findings. The
CT scans were reviewed on a computer workstation so that window settings could
be adjusted to optimize visualization of pneumatosis. Pneumatosis was
classified as curvilinear if it manifested predominantly as arclike bands of
gas or as bubbly if it manifested predominantly as tiny circular collections
of gas. In the cecum, air trapped between the bowel mucosa and fecal debris or
fluid may mimic bubbly pneumatosis
[3,
4]; therefore, bubbly
pneumatosis was diagnosed only when the bubbles were detected on the dependent
aspect of the bowel and also on its more ventral aspect, a finding that is in
contrast to that of pseudopneumatosis
[4] (Figs.
1A,
1B and
2A,
2B). The images were also
reviewed for other CT findings of ischemia, including pneumoperitoneum,
portomesenteric venous gas, cecal mural thickening, and right mesocolic edema.
Lastly, the bowel caliber was evaluated to identify cecal dilatation with a
cecal caliber of between 8 and 12 cm and with a cecal caliber greater than 12
cm.
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Fig. 1A. —Cecal pneumatosis in 70-year-old man. CT scans obtained with
standard abdominal (A) and wider (B) window settings show small
gas bubbles in cecal wall. Bubbles raise air–fluid levels. Findings at
surgery and pathologic examination showed cecal transmural necrosis. Note also
fluid lateral relative to ascending colon.
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Fig. 1B. —Cecal pneumatosis in 70-year-old man. CT scans obtained with
standard abdominal (A) and wider (B) window settings show small
gas bubbles in cecal wall. Bubbles raise air–fluid levels. Findings at
surgery and pathologic examination showed cecal transmural necrosis. Note also
fluid lateral relative to ascending colon.
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Fig. 2A. —Cecal pseudopneumatosis in 76-year-old man. Standard
abdominal (A) and wider (B) window settings show tiny gas
bubbles in periphery of lumen contiguous to colonic wall. Bubbles do not raise
air–fluid levels. Surgery did not reveal cecal necrosis.
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Fig. 2B. —Cecal pseudopneumatosis in 76-year-old man. Standard
abdominal (A) and wider (B) window settings show tiny gas
bubbles in periphery of lumen contiguous to colonic wall. Bubbles do not raise
air–fluid levels. Surgery did not reveal cecal necrosis.
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The imaging findings were then correlated with the surgical and pathologic
data to determine how often pneumatosis was associated with cecal necrosis
versus viable bowel and also whether other CT findings could be used to
predict which patients with pneumatosis were most likely to have cecal
necrosis. Patients were classified as having cecal necrosis if the diseased
cecum was resected at surgery and pathologic examination of the resected
specimen confirmed the presence of gangrenous bowel.
A statistical analysis of the data was not performed because our study
population was too small to establish meaningful significance levels. Our
institutional review board approved all aspects of this retrospective study
and did not require the informed consent of patients whose records were
included in our study.
Results
Surgical and Pathologic Findings
In all patients, surgery was performed within 24 hr after the CT
examination. The bowel obstruction was due to occlusive colon cancer in the
sigmoid colon in 14 patients, in the descending colon in three patients, in
the splenic flexure in one patient, in the transverse colon in two patients,
and in the hepatic flexure in three patients. In two patients, a second
nonocclusive colon cancer was found in the right part of the transverse colon
and in the hepatic flexure. Surgery revealed necrosis of the cecum in six
patients (26%), and a resection of the ascending colon was performed with
pathologic analysis confirming the cecal necrosis. In the other 17 patients,
surgery did not reveal any sign of necrosis or ischemia in the cecum.
Pathologic findings confirmed the lack of cecal ischemia in the seven patients
who had a resection of the right part of the ascending colon to excise a tumor
in the ascending colon or the hepatic flexure that was isolated in two
patients or associated with a descending colon cancer in five patients.
Surgery revealed peritonitis due to perforation of the infarcted cecum in five
patients or to perforation of the sigmoid cancer in two patients.
CT Findings
The CT findings according to the presence of cecal necrosis at surgery are
summarized in Table 1.
For four of the six patients with cecal necrosis, CT showed cecal
pneumatosis that was predominantly curvilinear in three patients (Fig.
3A,
3B,
3C) and bubbly in one patient.
All six patients with cecal ischemia had other CT findings of ischemia of the
cecum, including thickening of the colonic wall in two patients, right
mesocolic edema in five patients, and pneumoperitoneum in five patients. The
cecum was dilated in five of these patients—in three patients, the
caliber was greater than 12 cm and in two patients, the caliber was between 8
and 12 cm. The cecum was not dilated in one patient with a perforated
cecum.
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Fig. 3B. —83-year-old man with occlusive sigmoid cancer and
pneumatosis. CT scans of cecum obtained with standard abdominal (B) and
wider (C) window settings show curvilinear pneumatosis. Note also huge
pneumoperitoneum. Findings at surgery and pathology confirmed necrosis of
cecum.
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Fig. 3C. —83-year-old man with occlusive sigmoid cancer and
pneumatosis. CT scans of cecum obtained with standard abdominal (B) and
wider (C) window settings show curvilinear pneumatosis. Note also huge
pneumoperitoneum. Findings at surgery and pathology confirmed necrosis of
cecum.
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In three of the 17 patients without cecal necrosis, CT revealed
predominantly bubbly cecal pneumatosis (Fig.
4A,
4B,
4C,
4D). The right hemicolon was
dilated in these three patients, with a diameter ranging from 8 to 12 cm. One
of the three patients had right mesocolic edema, another indication of
ischemia. In 14 of the 17 patients without ischemic findings at surgery, CT
revealed no other ischemic finding. Among the three patients with ischemic
findings revealed on CT, one showed thickening of the right wall of the colon,
two had right mesocolic edema, and two had pneumoperitoneum (both patients
with perforation of the sigmoid tumor). In all 17 patients without cecal
necrosis, the colon was dilated. The caliber of the cecum was greater than 12
cm in three patients and ranged from 8 to 12 cm in 14 patients.
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Fig. 4C. — 65-year-old man with occlusive sigmoid cancer and
pneumatosis. CT scans obtained with standard abdominal (C) and wider
(D) window settings show bubbly pneumatosis in cecal wall. Surgery did
not reveal any findings of ischemia or necrosis of cecum.
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Fig. 4D. — 65-year-old man with occlusive sigmoid cancer and
pneumatosis. CT scans obtained with standard abdominal (C) and wider
(D) window settings show bubbly pneumatosis in cecal wall. Surgery did
not reveal any findings of ischemia or necrosis of cecum.
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Discussion
The role of CT in the evaluation of bowel obstruction has mainly been as an
aid to the diagnosis and treatment of small-bowel obstruction. Published data
on large-bowel obstruction are more limited than the data on small-bowel
obstruction, but CT has been reported to be a suitable technique for
diagnosing colonic obstruction and identifying the site and cause of
obstruction [5]. In large-bowel
obstruction due to colon cancer, which accounts for approximately 60% of
large-bowel obstruction cases, CT allows evaluation of the entire colon for
detection of synchronous cancers
[6] and may be helpful for
distinguishing tumoral from ischemic segments in patients with ischemic
colitis proximal to a colonic carcinoma
[7]. The development of
ischemia in the cecal wall remote from the tumoral colonic segment could be
explained by Laplace's law: The tension in the bowel wall increases both with
increasing intraluminal pressure and with increasing diameter of the
obstructed bowel; the mucosal blood flow decreases, which may lead to mucosal
necrosis and, in the worst cases, to transmural necrosis. In the clinical
setting of acute large-bowel obstruction, the presence of intramural cecal gas
has been considered to be a sign of transmural cecal necrosis and incipient
rupture [2]. However, use of CT
improves the ability to detect even subtle cases of pneumatosis, so this
finding could theoretically be observed in patients with mucosal disruption in
the absence of transmural necrosis. To our knowledge, no studies have analyzed
the significance of cecal pneumatosis in the setting of an obstructive colonic
carcinoma and whether this condition indicates that cecal resection is
required. This information may be of importance, particularly because the
presence of transmural cecal necrosis contraindicates the use of
self-expanding metallic stents for treatment of acute malignant obstruction,
which is a promising option as a decompression therapy before surgery or as a
final palliative treatment in patients with advanced stages of the disease
[8].
In our study, seven (30%) of the 23 patients had cecal pneumatosis. This
high rate could be due to the way in which we selected our patients, all of
whom were referred from the emergency department with acute large-bowel
obstruction. In a recently published retrospective study that included 184
patients, acute large-bowel obstruction constituted the clinical presentation
in only 12% of the patients who underwent surgery for colon cancer
[9]. Our selection method also
could explain our high rate (26%) of cecal necrosis revealed at surgery. We
found that three of the seven patients who showed pneumatosis on CT had a
viable cecum at surgery. Our findings refute the long-held concept that cecal
pneumatosis is a specific sign of transmural infarction in patients with
obstructive colon cancer and support recently published data
[10,
11] showing that pneumatosis
seen on CT does not always indicate transmural necrosis of the bowel in
patients with intestinal ischemia.
We found it interesting that among our patients, bubblelike pneumatosis was
more often associated with a viable cecum than with band-like pneumatosis. The
same findings were obtained in patients with intestinal ischemia and
pneumatosis affecting either the small or large bowel or both
[10]. Further analysis of our
cases revealed that all patients with cecal necrosis had ischemic CT findings
other than pneumatosis, whereas only 18% of patients without cecal necrosis
had such CT findings. Moreover, two of the three patients with cecal
pneumatosis and viable bowel had isolated pneumatosis. The preliminary data
thus suggest that in patients with large-bowel obstruction due to colon
cancer, cecal pneumatosis that displays a bubblelike pattern or is not
associated with other findings of ischemia may be related to viable bowel.
Our study has some limitations. The number of cases of pneumatosis was
limited, precluding a meaningful statistical analysis of the data. Small
sample sizes could also have magnified the effect of selection bias in our
population. Second, we cannot totally exclude the possibility that the
patients with pneumatosis and viable cecum had false-positive findings on CT
because of an unusual configuration of trapped intraluminal gas. However, as
noted, we used very strict criteria for diagnosing pneumatosis to avoid
confusing pneumatosis with intraluminal gas collections that cling to the
mucosa. Third, in the three patients with pneumatosis who did not have cecal
ischemia findings at surgery, we cannot exclude the possibility that one or
more might have had a tiny segment of transmural infarction at the pathologic
analysis of the cecum if cecal resection had been performed.
In conclusion, our data suggest that CT findings of cecal pneumatosis do
not always indicate transmural infarction in patients with acute large-bowel
obstruction due to colon cancer. Cecal pneumatosis when in a bubblelike
pattern or when not associated with other findings of ischemia may be related
to viable bowel.
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Abstract
Introduction
