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Original Report |
1 Department of Radiology, Hospital of the University of Pennsylvania, 3400
Spruce St., Philadelphia, PA 19104.
2 Present address: Department of Radiology, New York University School of
Medicine, 560 First Ave., New York, NY 10016.
Received May 13, 2002;
accepted after revision August 22, 2002.
Address correspondence to M. S. Levine.
Abstract
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CONCLUSION. The CT finding of pneumatosis does not always indicate transmural infarction of the bowel in intestinal ischemia. Patients with associated portomesenteric venous gas are more likely to have transmural infarction than those with pneumatosis alone.
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The widespread use of abdominal CT in ischemic bowel disease has enabled detection of more subtle pneumatosis at earlier stages of the disease [9,10,11]. This raises the possibility that pneumatosis can be detected in patients with partial ischemic damage of the bowel wall before the development of transmural infarction. Thus, some patients with intestinal ischemia could have viable bowel despite findings of pneumatosis on CT. A recent study by Wiesner et al. [12] supports this hypothesis; pneumatosis was observed on CT in patients with intestinal ischemia in the absence of transmural infarction. The purpose of our study was to reassess the CT finding of pneumatosis in ischemic bowel disease to determine whether it indicates transmural necrosis versus partial mural ischemia and also to determine whether other CT findings can be used to predict which patients with pneumatosis are more likely to have viable bowel.
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Our study group comprised the remaining 15 patients with clinical findings of ischemic bowel disease who underwent abdominal CT with a HiSpeed Advantage scanner (General Electric Medical Systems, Milwaukee, WI). Nine patients underwent contrast-enhanced CT with 150 mL of 60% iodinated contrast material (diatrizoate meglumine [Hypaque] or iohexol [Omnipaque 300]; Nycomed, Princeton, NJ) administered IV. The remaining six patients underwent unenhanced CT. All except one patient also received 20 mL of an oral contrast agent (diatrizoate meglumine and diatrizoate sodium [Gastroview]; Mallinckrodt, St. Louis, MO) diluted with 800 mL of water 30-45 min before the study. CT was routinely performed with the patient supine during full inspiration. Images were obtained at 5- and 7-mm slice collimations (pitch, 1.3:1; mAs, 200-220) and reconstructed with a soft-tissue algorithm.
All CT scans were analyzed by a consensus review of two abdominal radiologists who had no knowledge of the surgical or pathologic findings or eventual clinical outcome for these patients. The CT scans were reviewed at a computer workstation so that window settings could be adjusted to optimize visualization of pneumatosis. As in the study by Wiesner et al. [12], the pneumatosis was classified as curvilinear (if manifested predominantly by arclike bands of gas) or bubbly (if manifested predominantly by tiny circular collections of gas). The images were also reviewed for other CT findings of ischemia, including a mural stratification pattern (i.e., target sign), dilatation of bowel, mural thickening, mesenteric edema, mural or mesenteric hemorrhage, hemorrhagic ascites, visceral infarcts, pneumoperitoneum, mesenteric arterial or venous thrombi, and portomesenteric venous gas [9, 10].
The imaging findings were then correlated with the clinical and pathologic data to determine how often pneumatosis was associated with irreversible transmural infarction of bowel versus partial mural ischemia without full-thickness necrosis and also to determine whether other CT findings could be used to predict which patients with pneumatosis were more likely to have viable bowel. Patients were classified as having nonviable bowel with transmural infarction if the diseased bowel was resected at surgery and if pathologic examination of the resected specimen confirmed the presence of gangrenous bowel or if the patient died from complications of ischemic bowel disease without undergoing surgery. Conversely, patients were classified as having viable bowel with partial mural ischemia if they did not have necrotic bowel at surgery or if they recovered without surgery. A statistical analysis of the data was not performed because such an analysis would have limited value in our small study population.
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.
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Nine (60%) of the 15 patients with pneumatosis had infarcted bowel: three had resection of the gangrenous bowel at surgery (one patient died 3 days later), and six died from complications of bowel infarction without undergoing surgery within a mean interval of 5.8 days from presentation (range, 1-25 days). The other six patients (40%) had viable bowel without transmural infarction: three had partial mural ischemia at surgery and three recovered without surgery. Thus, seven (47%) of 15 patients with pneumatosis died from complications of bowel infarction.
CT Findings
Nine patients (60%) had transmural infarction. CT revealed pneumatosis that
was predominantly curvilinear in seven of these patients
(Fig. 1) and bubbly in two
(Fig. 2A). The small bowel was
affected in four patients (Fig.
2A), and the colon, in five
(Fig. 1). All nine patients
with transmural ischemia had other CT findings of ischemia, including
dilatation of bowel in nine (Fig.
2A), mural thickening in eight
(Fig. 1), mural stratification
in three, mesenteric edema in five, mural or mesenteric hemorrhage in two,
hemorrhagic ascites in two, visceral infarcts in two, pneumoperitoneum in
three, and portomesenteric venous gas in four
[9,
10]
(Fig. 2B). The remaining six
patients (40%) had partial mural ischemia without transmural infarction. CT
depicted pneumatosis that was predominantly curvilinear in four of these
patients (Figs. 3 and
4) and bubbly in two. The small
bowel was affected in four patients (Fig.
3); the colon, in one (Fig.
4); and the small bowel and colon, in one. Four of the six
patients with partial mural ischemia had other CT findings of ischemia,
including dilatation of the bowel in three
(Fig. 3), mural thickening in
three (Fig. 3), and
pneumoperitoneum in three; two patients had isolated pneumatosis without other
CT findings of ischemia; and none had portomesenteric venous gas.
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Of the 15 patients with pneumatosis on CT, both patients (100%) with isolated pneumatosis and no other CT findings of ischemia had viable bowel and recovered without surgery. Five (56%) of nine with pneumatosis and other CT findings of ischemia but no portomesenteric venous gas, and all four (100%) with pneumatosis and other CT findings of ischemia, including portomesenteric venous gas, had gangrenous bowel. When the CT findings were correlated with clinical outcome, both patients (100%) with isolated pneumatosis survived. Three (33%) of nine patients with pneumatosis and other CT findings of ischemia but no portomesenteric venous gas, and all four (100%) with pneumatosis and other CT findings of ischemia including portomesenteric venous gas, died.
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In our study, six (40%) of 15 patients with pneumatosis on CT and clinical findings of intestinal ischemia had viable bowel at surgery or recovered without surgery (Figs. 3 and 4), indicating partial mural ischemia without transmural necrosis. Our findings independently corroborate the findings of Wiesner et al. [12] that pneumatosis on CT does not always indicate transmural necrosis of the bowel in patients with intestinal ischemia. Both of these studies refute the long-held concept that pneumatosis is a specific sign of bowel infarction in ischemic bowel disease. Presumably, gas can enter the ischemic bowel wall via a disrupted mucosa in the absence of transmural infarction. This observation explains our ability to detect pneumatosis on CT in patients with viable bowel in whom surgical resection is not required.
Further analysis of our cases revealed that both patients (100%) with isolated pneumatosis had viable bowel (Fig. 4). Five (56%) of nine with pneumatosis and other CT findings of ischemia but no portomesenteric venous gas (Fig. 1), and all four (100%) with pneumatosis and other CT findings of ischemia including portomesenteric venous gas (Fig. 2A,2B), had transmural infarction. Our data suggest that patients with isolated pneumatosis are more likely to have partial mural ischemia, whereas patients with pneumatosis and portomesenteric venous gas are more likely to have transmural infarction. Similarly, Wiesner et al. [12] found that patients with findings of pneumatosis and portomesenteric venous gas on CT were more likely to have transmural infarction than those with pneumatosis alone. Thus, preliminary data from both studies indicate that the presence of portomesenteric venous gas can be used to predict which patients with pneumatosis are more likely to have transmural infarction necessitating emergency surgical intervention.
Our study has limitations. Because ours was a retrospective investigation, the need for strict inclusion criteria limited the total number of cases in our study population, precluding a meaningful statistical analysis of the data. Small sample sizes could also have magnified the effect of selection bias on our study population. In addition, we cannot exclude the possibility that one or more patients with clinically suspected intestinal ischemia may have had coincidental pneumatosis from a nonischemic cause. We also cannot totally exclude the possibility that the two patients with isolated pneumatosis had false-positive findings on CT resulting from an unusual configuration of trapped intraluminal gas, nor can we exclude the possibility that one or more of the three patients who recovered without surgery might have had a tiny segment of transmural infarction. Conversely, some patients excluded from the analysis because of a benign clinical presentation may actually have had ischemic bowel disease, so we could have underestimated the frequency of pneumatosis in patients with intestinal ischemia who had viable bowel. Finally, some patients in our study underwent unenhanced CT, limiting our ability to detect other CT findings of ischemia, such as a mural stratification pattern.
In conclusion, our data suggest that the CT finding of pneumatosis does not always indicate transmural infarction of the bowel in intestinal ischemia. Patients with associated portomesenteric venous gas are more likely to have transmural infarction than those with pneumatosis alone. Thus, some patients with intestinal ischemia may have partial mural ischemia with viable bowel despite the presence of pneumatosis on CT.
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