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Original Research |
1 Department of Radiology, Centre Hospitalier Universitaire St.-Pierre,
Université Libre de Bruxelles, 322 Rue Haute, Brussels 1000,
Belgium.
2 Department of Radiology, HIS Site Etterbeek-Ixelles, Brussels, Belgium.
3 Statistical Unit, Institut de Recherche Interdisciplinaire en Biologie Humaine
et Moléculaire, Université Libre de Bruxelles, Brussels,
Belgium.
4 Department of Gastrointestinal Surgery, Centre Hospitalier Universitaire
St.-Pierre, Université Libre de Bruxelles, Brussels, Belgium.
Received July 8, 2005;
accepted after revision September 18, 2005.
Address correspondence to B. Hainaux
(hainauxb{at}yahoo.fr).
Abstract
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SUBJECTS AND METHODS. We prospectively studied 85 consecutive patients with extraluminal air on MDCT who had surgically proven gastrointestinal tract perforations. All patients underwent surgery within 12 hours after MDCT was performed. Two experienced radiologists, blinded to the surgical diagnosis, reached a consensus prediction of the site of the perforation using the following eight MDCT findings: concentration of extraluminal air bubbles adjacent to the bowel wall, free air in supramesocolic or inframesocolic compartments, extraluminal air in both abdomen and pelvis, focal defect in the bowel wall, segmental bowel-wall thickening, perivisceral fat stranding, abscess, and extraluminal fluid. MDCT imaging results were compared with surgical and pathologic findings. Logistic regression analyses were performed to assess the significance of the different radiologic criteria.
RESULTS. Analysis of MDCT images was predictive of the site of gastrointestinal tract perforation in 73 (86%) of 85 patients. Logistic regression showed that concentration of extraluminal air bubbles (p < 0.001), segmental bowel wall thickening (p < 0.001), and focal defect of the bowel wall (p = 0.007) were strong predictors of the site of bowel perforation.
CONCLUSION. MDCT is highly accurate for predicting the site of gastrointestinal tract perforations. Three of eight CT findings significantly correlate with surgical diagnosis.
Keywords: abdominal imaging • bowel • CT • gastrointestinal radiology • gastrointestinal tract perforation • MDCT
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CT Examinations
Abdominal examinations were performed on a 4-MDCT scanner (Somatom Plus
Volume Zoom, Siemens Medical Solutions) with the following parameters:
collimation, 4 x 2.5 mm; table speed, 15 mm per 0.5 second of scanner
rotation; 120 kV; and 130 effective milliampere seconds. All the patients
underwent scanning in the supine position starting from the diaphragm down to
the pubic symphysis. None of the patients received oral or rectal contrast
material; unenhanced scanning was performed in all patients. In 46 patients,
additional contrast-enhanced images were acquired with the same parameters
after injection of 120 mL of a low-osmolarity contrast medium (iobitridol,
Xenetix 350 mg I/mL, Guerbet) at a rate of 2.5 mL/s via a power injector.
Scanning was started 80 seconds after initiating contrast material
injection.
Image Analysis
The images were stored on compact disks and reviewed on a workstation
(Wizard, Siemens Medical Solutions). Two experienced abdominal radiologists
evaluated axial and multiplanar reconstruction images. They were blinded to
all records but were informed that all patients presented with acute abdominal
pain and their abdominal CT scans showed pneumoperitoneum. Together, the
radiologists completed a questionnaire on the presence or absence of eight CT
findings indicative of acute bowel disease and gastrointestinal perforation.
The eight CT findings evaluated were few bubbles of extraluminal air
concentrated in close proximity to the bowel wall, extraluminal air
exclusively in supramesocolic or inframesocolic compartments, extraluminal air
in both abdomen and pelvis, focal defect in the bowel wall, segmental
bowel-wall thickening, perivisceral inflammatory fat stranding, abscess, and
extraluminal fluid. Bowel-wall thickening was a subjective criterion evaluated
without measurement of the bowel wall. After reviewing these eight findings,
the two radiologists were asked to determine by consensus the site of bowel
perforation. The predicted sites of perforation were categorized as follows:
stomach and duodenum, jejunum and ileum, appendix, cecum and ascending colon,
transverse colon, descending colon, sigmoid colon, and rectum.
Statistical Analysis
For each of the eight CT findings, the percentage of patients with positive
results for the finding among the correct diagnoses and the percentage of
patients with negative results for the finding among the 12 patients where the
perforation site could not be determined—no diagnosis was
false—were calculated. The percentage of correct diagnoses when each
finding was present and the percentage of correct diagnoses when each finding
was absent were also calculated. Logistic regression analyses were performed
to evaluate the probability of a correct diagnosis as a function of the
presence or absence of any of the eight findings. A first analysis was
performed using the enter procedure. Rao's efficient scores
[4] for each of the eight
findings were calculated to detect which findings were statistically
associated with a correct diagnosis. A second analysis was performed with a
stepwise forward procedure to detect the successive most relevant findings for
correctly predicting the localization of the perforation. Statistical analyses
were performed using SPSS version 13.0 (Statistical Package for the Social
Sciences) for Windows (Microsoft).
The link between the location of free intraabdominal air and the site of the perforation was assessed with a chi-square test. Exact p values were reported. Statistical analysis software (StatXact version 5.0, Cytel Software) was used.
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The prediction of the site of gastrointestinal tract perforation using the eight CT findings was correct in 73 (86%) of 85 patients. The diagnostic values for each CT finding are listed in Table 1. Rao's scores for each finding (Table 2) showed that three findings—concentration of extraluminal air bubbles (Figs. 1A and 1B), focal defect of the bowel wall (Figs. 2A and 2B), and segmental bowel-wall thickening (Fig. 3)—were statistically significant predictors of correct localization of the perforation. The logistical analysis regression with the stepwise procedure also showed that the best predictors for perforation localization were the presence of concentrated extraluminal air bubbles (p < 0.001) followed by the presence of segmental bowel-wall thickening (p = 0.046). The three most predictive findings of the site of perforation were not present in any of the 12 patients for whom the site was undetermined by the radiologists. We also detected a link (p < 0.001) between the location of free intraabdominal air and the site of perforation, which is summarized in Table 3. The 37 patients with upper gastroduodenal perforation all had free intraabdominal air around the liver or stomach. Eight of these patients also had free air in the pelvis. None of them presented with pelvic pneumoperitoneum alone. In contrast, all of the 39 patients with colon perforation had free air in the pelvis. For 15 of these patients, free air was only observed in the pelvis, and no patient had free air only in the supramesocolic compartment. Of the nine patients with small-bowel perforation, six had free air in both the abdomen and pelvis.
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In our study, multiplanar reconstruction images were routinely performed, which we found to be useful for determining the precise location of bubbles of extraluminal air and defects in the bowel wall. Several articles stress the value of intraluminal gastrointestinal contrast material in the evaluation of patients with blunt abdominal trauma. The detection of free extraluminal contrast material is considered a direct sign of bowel perforation. However, in a literature review, the reported sensitivity of extravasation of oral contrast material varies from 19-42% [8]. The study of Shanmuganathan et al. [9] shows that triple-contrast helical CT (CT with administration of rectal, oral, and IV contrast material) is highly accurate for evaluating patients with penetrating injuries into the thoracoabdominal region. Nevertheless, only 15% of patients with bowel injury showed oral or rectal contrast material extravasation. Our study concerns mainly patients with nontraumatic bowel perforations who present with peritonitis. In these patients, it is often difficult to obtain oral or rectal opacification. One of the aims of our study was to determine the accuracy of CT to diagnose the site of bowel perforation using CT findings other than extravasation of contrast material.
The overall accuracy in predicting the site of bowel perforation was 86% in our study. These results are similar to the three previously published retrospective series [10-12]. Maniatis et al. [10] reported a sensitivity of 85.5% in a series of 76 patients presenting with bowel perforation secondary to various causes. Kim et al. [11] reported an overall accuracy of 82% in a series of 57 patients with gastrointestinal tract perforation after blunt abdominal trauma. The same result, 82%, was also reported by Catalano [12] in a series of 38 patients.
Previous reports have emphasized CT manifestations of bowel perforation secondary to various causes. However, no previous reports have compared CT findings to statistically evaluate the most useful findings. Ongolo-Zogo et al. [13] reported on a series of 10 perforated gastroduodenal peptic ulcers in which two important CT findings were indicative of the site of perforation: discontinuity in the bowel wall in six patients and tiny extraluminal air bubbles in close proximity to the bowel wall in two patients. Miki et al. [14] also reported on the direct visualization of a ruptured colonic wall in four of six patients with colonic perforation. However, these two findings did not occur in the series of 42 proximal and distal gastrointestinal tract perforations reported by Yeung et al. [15]. In our series of 85 perforations, free air bubbles in close proximity to the bowel wall indicated the site of perforation in 65 patients, with segmental bowel-wall thickening observed in 42 patients. Those two findings were strong predictors of the site of perforation (p <0.001). The third predictor of the site of perforation was the direct visualization of a focal defect in the bowel wall, seen in 29 patients (p =0.007). Moreover, in the 12 patients where CT was unable to predict the site of the perforation, none of these three findings was present.
As has been previously reported in other studies, our series also shows a link between the location of free intraabdominal air and the site of perforation [10, 16]. Gastroduodenal and colonic perforation can both appear as massive pneumoperitoneum with free air in the abdomen and in the pelvis. However, if free air is present only around the liver and stomach and not in the pelvis, proximal gastrointestinal perforation is likely. Conversely, if free air is present only in the pelvis, the likely site of perforation is the colon or, less frequently, the small bowel.
In conclusion, MDCT allows physicians not only to detect free intraabdominal air but also to precisely determine the anatomic site of gastrointestinal tract perforation without the use of oral or rectal contrast material. Three CT findings—concentrated bubbles of extraluminal air in close proximity to the bowel wall, focal defect in the bowel wall, and segmental bowel-wall thickening—have a high predictive value for the site of perforation.
Acknowledgments
We thank Anne Hepburn for reviewing the manuscript and Catherine Gerard and
Johan Grymonprez for editorial assistance.
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