Differentiation of Simple and Strangulated Small-Bowel Obstructions ...

greatly aids the diagnosis of smallbowel
strangulation (15). The high
attenuation of ascites on CT images
of strangulated obstruction is probably
caused by increased protein content
in the fluid. However, in our study,
the attenuation of ascites was cornpared
with that of bile in the gallbladder
or cysts in the liver or kidney, and
images of both simple and strangulated
obstructions revealed hyperattentuating
asdtes. Since a large amount
of ascites may be caused by many
conditions, confirmation of other CT
findings in the mesentery or bowel is
required so that the diagnosis of strangulation
is not made incorrectly.
We defined the mesenteric changes
(haziness or vascular engorgement) as
focal or diffuse because these changes
may be observed on CT images of patients
with simple small-bowel obstruction.
As expected, focal mesenteric
changes were seen on CT images
of both simple and strangulated obstructions
(Fig 9). Diffuse mesenteric
changes, however, had high specificities
(>95%) for the detection of strangulation.
An unusual course of mesenteric
vasculature (indicated with a
reversed position of superior mesenteric
artery and vein, the whirl sign,
or convergence of vessels) has been
seen also in cases of closed-loop obstruction
(1,2,8) or malrotation (21).
Although further study is necessary,
some of these findings may be seen
on CT scans of asymptomatic patients.
Furthermore, strangulation does not
always occur in patients with closedloop
obstruction. Therefore, this finding-an
unusual course of the mesenteric
vasculature-alone on CT scans
of patients with small-bowel obstruction
does not always indicate bowel
strangulation.
Some drawbacks of our study could
have reduced the reliability of the results.
There were some differences in
the scanning and contrast-infusion
techniques at the two institutions where
patients were evaluated; these might
have affected the true frequency of CT
findings that were analyzed. In addition,
because strangulation can develop
in only a few hours, the relatively long
time (mean, 2 days) between CT examination
and the surgery for obstruction
in this study might have affected
the severity of the obstructions exammed.
Nevertheless, our study demonstrated
the lack of sensitivity of known
CT criteria when used alone and their
relative diagnostic values. Furthermore,
the use of a combination of
highly specific CT findings enabled
differentiation of simple and strangulated
obstruction in 85% of the patients
in this retrospective study. Prospective
application, however, of these
CT criteria may not yield results as
accurate as ours, as implied by Frager
etal(6).
In conclusion, the usefulness of
known CT criteria for aiding the diagnosis
of strangulated small-bowel obstruction
was examined with review
of CT scans of a large number of patients
with simple and strangulated
small-bowel obstructions. Statistical
analyses of various CT findings revealed
that poor or no contrast enhancement
of bowel wall, a serrated
beak, a large amount of ascites, an unusual
course of mesenteric vasculature,
diffuse engorgement of mesenteric
vasculature, and mesenteric
haziness were the most useful CT
findings for identifying strangulated
obstruction. Detection of a combination
of these CT findings increases the
diagnostic accuracy of CT to enable
differentiation of simple and strangulated
small-bowel obstructions. #{149}
Acknowledgment The authors thank Bonnie
Hami, MA, for editorial assistance in preparation
of the manuscript.
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