CT Scan for Suspected Acute Abdominal Process: Impact of Combinations of IV,
Oral, and Rectal Contrast
World j of surgery 4 2010
Brian C. Hill1, 3
, Scott C. Johnson1, Emily K. Owens1, Jennifer L. Gerber1 and
Anthony J. Senagore2
(1) Michigan State University-College of Human Medicine, East Lansing, MI 49519,
USA
(2) Spectrum Health, Michigan State University-College of Human Medicine, Grand
Rapids, MI, USA
(3) 1631 Glenboro Ct., Wyoming, MI 49519, USA
Brian C. Hill
Email: hillbri3@msu.edu
Published online: 7 January 2010
Abstract
Background
There are limited data available on the ability of computed tomography (CT) to
accurately diagnose abdominopelvic pathology in acutely ill inpatients suspected of
having an acute abdominal process. The purpose of this study was to evaluate the
diagnostic accuracy of abdominal/pelvic CT with varying use of contrast agents in
hospitalized patients.
Methods
A retrospective review of all hospital inpatients (3/1/07–5/31/07) who underwent
urgent or emergent abdominal/pelvic CT with any combination of contrast,
intravenous (IV), oral, rectal, or unenhanced for a suspected acute abdominal process
was performed. Data collected included demographics, combination of contrast used,
CT diagnosis, time from CT scan to subsequent intervention, intervention type, and
actual diagnosis of the acute abdominal process. Accuracy of CT was compared
between enhanced and unenhanced imaging using Fisher’s exact test.
Results
A total of 661 patients were identified. Use of IV contrast alone was found in 54.2%
of CT scans and was correct in 92.5% of cases. IV and oral contrast was used in
22.2% of CT scans and was 94.6% correct. Unenhanced imaging was performed in
16.2% and was correct in 92.5%. Oral contrast alone was used in 7.0% and was
93.5% correct. There was no significant difference in the ability to correctly diagnose
a suspected acute abdominal process when enhanced CT imaging was compared to
unenhanced (p > 0.05).
Conclusions
CT contrast administration in critically ill hospitalized patients is not necessary to
accurately diagnose an acute abdominal process. Eliminating the use of contrast may
improve patient comfort, decrease patient risk, and minimize financial cost.
Introduction
Optimal evaluation of a patient with a potential acute abdominal process with CT is
generally considered to include administration of oral, rectal, and IV contrast.
However, administration of contrast through these three routes in an urgent or
emergent clinical setting may be constrained by underlying medical conditions or
patient care issues. Few reports in the literature describe the interpretation of
abdominal CT examinations in critically ill patient populations in the absence of the
use of contrast. The majority of studies assessing the use of contrast with CT for
abdominal/pelvic evaluation have focused on emergency department patients with a
limited differential diagnosis. Therefore, the purpose of this study was to evaluate
retrospectively the diagnostic accuracy of abdominal/pelvic CT with varying use of
contrast agents in a surgical teaching service located at a large teaching hospital.
Methods
This study was a retrospective review of all hospital inpatients from the Spectrum
Health, Butterworth Campus, undergoing urgent or emergent abdominal/pelvic CT
with any combination of contrast (unenhanced, IV, oral, or rectal) for a suspected
acute abdominal process from March 1, 2007 through May 31, 2007. The indication
for imaging was at the discretion of the treating physician, but the primary indication
was failure to improve or clinical deterioration with concern for an abdominopelvic
source of pathology. Patients who received CT as part of a kidney stone protocol or
for suspicion of appendicitis or diverticulitis were excluded. Approval of the study
was obtained from the Institutional Review Board at Spectrum Health.
Procedure notes, operative notes, and discharge summaries were reviewed to
determine accuracy of the CT diagnosis and time and type of definitive treatment.
Patient demographics, contrast used, CT diagnosis, time from CT scan to subsequent
intervention, intervention type, and actual diagnosis of the acute abdominal process
were recorded for all patients. Accuracy of CT diagnosis, as well as differences in
sex, was compared between enhanced and unenhanced imaging using the Fisher’s
exact test. In addition, differences in age between each of the contrast groups and the
unenhanced group were determined using the one-way ANOVA, followed by
Dunnett’s test. Significance was assessed at p < 0.05 for the quantitative data. Due to
the need to perform multiple Fisher’s exact tests to compare each of the three contrast
groups to the unenhanced group, the p value for significance was adjusted to
p < 0.017.
Results
A total of 1,457 CTs were performed during the study period. We identified 661
patients who fit the inclusion and exclusion criteria. Patient demographic information
is shown in Table 1. By far, IV contrast alone was the most common agent used in CT
imaging (54.2% of cases; Fig. 1). The CT diagnoses were divided into general
categories (Table 2). The most common diagnosis was no acute pathology followed
by inflammatory and infectious. After the CT scan, a subsequent procedural
intervention took place in 32.7% of the cases (216/661 patients), 18 of which had the
diagnosis of no acute pathology on CT scan. Table 3 shows the frequency of
intervention type after a CT scan that suggested acute pathology. The percentages of
cases requiring an intervention, broken down by contrast type, are displayed in Fig. 2.
The average time to intervention post-CT was 44.9 h.
Table 1 Patient demographic information
IV contrast
IV and oral
Oral contrast
Unenhanced
alone
contrast
alone
Age (year)a 55.9 ± 17.8*
54.8 ± 17.8*
66.7 ± 17.4
65.8 ± 17.8
Sex (%
149/358
62/107
71/147 (48.3%)
20/46 (43.5%)
b
Male)
(41.6%)*
(57.9%)
a
Mean ± standard deviation; values followed by an asterisk are significantly different
from the unenhanced group (p < 0.05)
b
Values followed by an asterisk are significantly different from the unenhanced group
(p < 0.017); a lower p value was used to control for the use of multiple χ2 tests
Fig. 1 Percentage of various combinations of CT contrast used (n = 661)
Table 2 Percentage of common CT diagnoses by category (n = 661)
Diagnosis
Number (%)
No acute findings 231 (34.9%)
Inflammatory
118 (17.9%)
Infectious
81 (12.3%)
Obstructed bowel 80 (12.1%)
Other
65 (9.8%)
Vascular
51 (7.7%)
Neoplastic
28 (4.2%)
Posttraumatic
7 (1.1%)
Table 3 Percentage of procedural intervention type performed after a CT diagnosis of
an acute abdominal process (n = 430)
Intervention
Number (%)
No intervention
232 (54%)
Surgical
87 (20.2%)
Aspiration/drainage
56 (13%)
Further imaging
19 (4.4%)
Sigmoid/colonoscopy 14 (3.3%)
EGD/ERCP
10 (2.3%)
Other
8 (1.9%)
Cystoscopy
4 (0.9%)
Fig. 2 Percentage of CT scans resulting in a procedural intervention based on contrast
combination used
Regardless of the combination of contrast used, the correct diagnosis was made 93%
of the time (Fig. 3). The combination of IV and oral contrast led to an accurate
diagnosis 94.6% of the time. There was no significant difference in the accuracy of
CT diagnosis when any combination of contrast was compared to CTs performed
without contrast.
Fig. 3 Percentage of correct CT results based on contrast combination used
Discussion
There have been concerns regarding the possible overuse of CT as a diagnostic tool
[1]. In 2000, the United States Food and Drug Administration estimated that a total of
45.1 million CTs had been performed in the United States [2]. Due to the radiation
exposure, indiscriminate use of CT increases the risk of cancer, thereby minimizing
the favorable benefit to risk ratio [1]. Our results support the notion that CT may be
an overutilized resource because 34.9% (231/661) of the CT scans revealed no
evidence of an acute abdominal process. Even when an acute abdominal process was
discovered, only 46% (198/430) of these cases led to a subsequent procedural
intervention. These findings support the necessity of employing alternative diagnostic
tools as a means of minimizing the radiation exposure risks associated with CT.
Despite the fact that contrast agents have been proposed to increase diagnostic
accuracy of CT imaging [3–5], none are without risks or concerns. Oral contrast
allows small bowel opacification and aids in the diagnosis of structural abnormalities
(e.g., ulcers, perforations, obstructions, space-occupying lesions). However,
limitations for the use of oral contrast include patient intolerance due to ileus, the
need for intragastric administration via a tube, risk of vomiting and aspiration, and
time between administration and CT study, which typically is 90 min.
IV contrast is used to diagnose inflammatory-based lesions or for detection of bowel
wall pathology and provides detail regarding arterial supply and venous drainage for
abdominal organs. Situations that limit the use of IV contrast include allergy to iodine
or impaired renal function. The latter is a common clinical finding in urgent and
emergent clinical settings.
Rectal contrast, administered via enema, fills the colon from the rectum proximally,
possibly as far as the ileocecal junction. This allows for visualization of spaceoccupying lesions, obstructions, diverticula, anastomotic leaks, bowel perforation, and
inflammatory bowel diseases affecting the large intestine. Limitations mainly involve
restricted access to the anorectum or concern regarding contrast extravasation.
Multiple studies have been performed in specific disease states involving the
abdomen comparing the use of various combinations of contrast. However, these are
limited to the emergency department setting. Nonetheless, the accuracy of
unenhanced CT imaging has been supported by several of these studies [6–9]. Huyn et
al. found they could shorten time to diagnosis of an acute abdomen an average of
68 min by performing a CT without contrast compared to contrast-enhanced CT [10].
One study found a 79% agreement between noncontrast enhanced and contrast
enhanced CT for abdominal pelvic pain, attributing the discrepancy largely to
interobserver variability [11]. Comparing unenhanced CT to three-view acute
abdominal series, MacKersie et al. reported no change in any diagnosis among a small
group of patients who underwent follow-up contrast-enhanced CT after initial
unenhanced CT [8]. The presence of pericecal and periappendiceal fat inflammatory
changes visible with unenhanced CT aid in the diagnosis of acute abdominal
processes [7]. These changes, particularly in the case of diverticulitis or appendicitis,
allow unenhanced CT imaging to be as effective as an IV contrast enhanced study [7,
9].
However, not all studies conclude that unenhanced CT imaging is as effective as those
where contrast was used. Jacobs et al. concluded that the use of IV contrast
significantly improved the radiologists’ ability to diagnose acute appendicitis or to
establish an alternative diagnosis [12]. When the appendix was normal, an
unenhanced study was as accurate as an IV enhanced study. Lane et al. noted that to
increase the accuracy of unenhanced CT to a level comparable to enhanced CT, there
must be sufficient understanding of abdominal anatomy, increased experience with
unenhanced CT, and greater awareness of the appearance of signs suggestive of
alternative diagnoses [13].
At our hospital, the standard protocol is to administer both oral and rectal contrast in
addition to IV contrast when performing a CT scan for an acute abdominal process.
However, this study reveals that actual implementation of the full protocol is rarely
followed (3/661 cases) and often is influenced by the clinical situation and perceived
risk or delay in imaging. The use of contrast agents in CT imaging is associated with
several concerns. Most importantly, there is the burden of patient discomfort
associated with administration of oral and rectal contrast. In addition, the CT scan is
delayed while the contrast fills the desired portion of the alimentary canal. IV contrast
use is limited to patients with adequate kidney function and has been implicated in
causing severe hypersensitivity reactions. Finally, there is the financial cost associated
with contrast use. Therefore, if contrast is not necessary for accurate diagnosis of an
acute abdominal process, several aspects of patient care may be benefited without its
use.
Our findings suggest that when an acute abdominal process is suspected, the use of
any contrast agent is not necessary to accurately diagnose the pathology. It does seem
that the use of oral and IV contrast can slightly improve the diagnostic capabilities of
CT (Fig. 3), but this difference is not statistically significant. Therefore, we are able to
conclude that performing a CT scan on an inpatient suspected of having an acute
abdominal process does not require contrast to yield an accurate diagnosis. Our
findings from an inpatient setting corroborate the results from similar studies
performed with emergency department patients [6–9]. When considering all aspects
of CT in the inpatient setting (e.g., diagnostic outcomes, patient comfort, financial
cost), eliminating the use of contrast for an acute abdominal process may be
beneficial.
Our study does have limitations. The sample sizes of the IV and oral contrast,
unenhanced, and oral contrast only groups are relatively small compared with the IV
contrast-only group. The study was not powered to assess differences between these
contrast groups in regards to specific CT pathology and need for intervention but
instead only for the accuracy of CT diagnostic capabilities. Additionally, patient
comorbidities, other than age, were not considered in our study. Therefore, we cannot
make conclusions regarding clinical decisions influencing the use of the various
contrast agents. For instance, it is well known that as age increases glomerular
filtration rate (GFR) decreases, putting an elderly patient at increased risk of
developing IV contrast-induced nephropathy. The average patient age was
significantly higher in patients who did not receive IV contrast (unenhanced and oral
contrast only), suggesting that clinical consideration was given to the age-related
decreasing GFR. However, our study did not measure GFR to confirm this.
Comparing actual CT diagnoses and clinical outcomes, including interventions,
between the various contrast groups and consideration of patient comorbidities would
provide a benefit for future research in this area. Despite these limitations, the goal of
the study, which was to assess the ability of CT to evaluate acute abdominal
pathology as actually utilized clinically, was accomplished. The data should give
some pause for greater clinical evaluation to decrease the rate of CT that do not lead
to a specific intervention.
Conclusions
We believe that when evaluating an acute abdominal process from the inpatient
setting, unenhanced CT imaging is reasonable and provides several advantages over
the standard enhanced CT scan. However, as described previously, increased
experience with the unenhanced technique is required before implementation of this
recommendation.
Acknowledgments The authors are grateful for Alan T. Davis, PhD and Tracy
Frieswyk, BA for their guidance and advising throughout this project and their
assistance editing this manuscript.
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