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Original Research |
1 Department of Radiology, University of Wisconsin, 600 Highland Ave., Madison,
WI 53792-3252.
2 Present address: X-Ray Associates of New Mexico, Albuquerque, NM 87110.
Received June 22, 2005;
accepted after revision September 18, 2005.
Address correspondence to A. J. Taylor.
Abstract
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SUBJECTS AND METHODS. Eighty adult emergency department patients who underwent abdominal CT to evaluate for appendicitis were studied. Forty patients received the department's standard dose of 1,600 mL of a water-iodinated contrast mixture (ratio of 2 mL of iodinated contrast material to 100 mL of water) with a standard delay time of 2-2.5 hours from the beginning of contrast medium ingestion. Forty patients were given a new oral contrast mixture of 1,000 mL of polyethylene glycol (PEG) mixed with 30 mL of iodinated contrast agent, and the examination was conducted only 1 hour from inception of contrast administration. Examinations were reviewed for the presence of contrast medium in the cecum and the presence of appendicitis or other abdominal abnormality.
RESULTS. Thirty-eight of 40 patients in the PEG group had contrast medium in the colon at 1 hour after contrast administration, 20 of whom had surgically confirmed cases of appendicitis. In five other patients in that group, another cause to explain the patient's complaints was identified on imaging. Only 18 of the 40 patients who received the standard oral preparation had contrast material present in the cecum. Eleven patients in that group had confirmed appendicitis, and four others had another abnormal finding detected at CT. There was a significant difference in the success of contrast medium transit to the colon with these two agents (p < 0.0001).
CONCLUSION. The use of an oral contrast agent composed of PEG and iodinated contrast material provided a marked improvement in oral agent transit to the colon even in patients with intraabdominal inflammation.
Keywords: appendicitis • contrast media • emergency radiology • polyethylene glycol
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At our institution, clinicians were frustrated with the length of time between their request for CT of suspected appendicitis and the adequate oral preparation of the patient for opacification of the terminal ileum and cecum. In this study, we report our findings with the use of a new oral contrast solution that was evaluated for its ability to opacify the terminal ileum and cecum in this patient population. The oral preparation that was used for the study consisted of a combination of polyethylene glycol (PEG) and an iodinated contrast agent. We compared that mixture with our institution's prior standard dose of iodinated contrast agent diluted in water that typically is used for abdominal CT examinations.
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The control group patients ingested one dose of our institution's previous standard preparation—a mixture of 200 mL of water combined with 4 mL of MD-Gastroview—in 20 minutes, at which time another dose of that solution was given to the patient. Patients ingested a total of eight doses over a 2- to 2.5-hour period, immediately after which CT scans of the abdomen and pelvis were obtained. Overall, the patient received 1,600 mL of solution having a ratio of 20 mL of iodinated contrast material to 1,000 mL of water.
CT Protocol
Both groups of patients, the study group and control group, underwent
single breath-hold 8- or 16-MDCT of the abdomen and pelvis from the diaphragm
to the pubic symphysis using a 5-mm collimation and reconstruction (LightSpeed
Series, GE Healthcare). IV contrast material was given using 100 mL of 300
mg/dL of nonionic contrast agent at a rate of 3-4 mL/s followed by a 50-mL
bolus of normal saline.
The images were evaluated on a PACS workstation. The initial interpretation was performed by the resident and faculty physician on the service at the time of the examination. A retrospective evaluation was subsequently performed in consensus by two of the authors to assess whether ingested oral contrast material was in the colon and whether appendicitis or other significant findings were present. Although an evaluation as to the absence or presence of appendicitis was done retrospectively by two authors, the initial interpretation at the time of the examination was used for all data evaluation because that was the information relayed to the clinical service. The CT diagnosis of appendicitis followed previously published criteria [2] and was correlated with surgical and pathologic findings for diagnosis confirmation. The other CT diagnoses were correlated with clinical follow-up of the patient and the patient's response to treatment.
Statistical Analysis
Statistics were tabulated and analysis was performed, including calculation
of sensitivity, specificity, positive predictive value (PPV), and negative
predictive value (NPV). Fisher's exact test was used in lieu of the more
widely known but less accurate chi-square test to compare differences in
successful colonic transit between the two groups. A two-sided p
value was calculated.
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The ingested contrast agent reached the cecum in 18 (45%) of 40 patients in the control group after the 2- to 2.5-hour preparation time with 1,600 mL of the standard mix (Table 1). Eleven patients in this group had radiologic and surgical confirmation of appendicitis with three false-positives (PPV = 79%). In two of the three patients with false-positive findings, the dilute iodinated contrast material failed to reach the cecum. In seven of the 11 patients, contrast medium traversed to the colon during the preparation time. All 29 patients with negative CT studies for appendicitis either improved clinically or were treated for an alternative diagnosis (NPV = 100%), with four having another radiologic diagnosis identified as the cause of abdominal pain: ureterovesical junction calculus, diverticulitis, Crohn's disease, and pancreatitis. Of this latter group, only the patient with pancreatitis had the ingested contrast agent travel to the colon.
The difference between the two orally administered preparations in terms of successful transit to the cecum was statistically significant: p < 0.0001; odds ratio, 23.222; 95% CI, 4.915-109.71 (using the approximation of Woolf).
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Although the sensitivities and specificities for all the techniques are greater than 90%, results may be slightly improved with a nonfocused examination using both IV and oral contrast material [2], given the value of visualizing enhancement characteristics of the appendiceal wall and the visualization of oral contrast material entering or filling the appendix. One potential down-side to high-attenuation enteric contrast material is the concern about possibly obscuring an appendicolith, but we did not find that to be an issue.
Especially in the thin patient without mesenteric, retroperitoneal, or omental adipose tissue helping define the periappendiceal area, gastrointestinal contrast agent in the terminal ileum and cecum in addition to IV contrast material plays an important role in definition of this area. From our previous research and that of others, a full-strength PEG solution has been shown to provide excellent gastrointestinal tract distention and reliable transit to the colon [1, 8, 9]. After modifications to that solution were made, subsequent studies found that 1,000 mL of PEG mixed with 30 mL of full-strength water-soluble iodinated contrast agent gave excellent gastrointestinal tract distention and opacification with a reliable transit time in the general patient population undergoing abdominopelvic CT. Therefore, it seemed reasonable to study this mixture in the patient population with a possible inflammatory process such as appendicitis. Our previous standard preparation of 1,600 mL of dilute water-soluble contrast material given over 2-2.5 hours was not reliable for opacification of the terminal ileum and cecum.
The formulation used in the PEG solution is an isotonic solution that causes neither fluid absorption nor secretion and is less dependent on the stimulation of bowel contraction to move the fluid with the dilute water-soluble contrast agent. The presence of peritonitis from an abdominal inflammatory process such as appendicitis can cause a reflex ileus and therefore negate the contractions elicited by the dilute water-soluble contrast agent. The ability to "wash" fluid down the gastrointestinal tract without a dominant component of contraction would make the PEG solution more effective in this circumstance. However, the addition of the water-soluble contrast agent to the PEG solution to help luminal opacification probably contributes to propagation of this mixture through the gastrointestinal tract.
The present study shows a marked improvement of the PEG solution over the same iodinated contrast agent diluted with water. The patient ingests significantly less fluid when the PEG solution is used, 1,000 versus 1,600 mL, and the preparation time is half as long. Only 18 of 40 patients ingesting the standard oral mixture had contrast material reach the colon 2-2.5 hours after ingestion, whereas 38 of 40 patients had contrast material reach the colon 1 hour after contrast administration in the PEG group (p < 0.0001).
Although no formal feedback was obtained, the patients receiving the new oral agent did not complain about this contrast agent to the CT technologist or emergency department personnel.
One of the two patients in the PEG group who did not have contrast material enter the colon had an uncomplicated appendicitis. The reason for this delay is not known. In the second case, however, the patient had a complicated, perforated appendix with abscess formation. At surgery, there were adhesions to the terminal ileum because this segment of bowel had been recruited to wall off the abscess (Fig. 4). Therefore, when the combination of peritonitis and small-bowel obstruction was present, even the PEG solution was not effective.
However, 18 of the 20 patients with surgically proven appendicitis in the PEG group did have contrast transit to the colon. There were five other significant findings on CT in this group, and the PEG solution was able to reach the colon with these intraabdominal processes as well.
The cost of the PEG solution is greater than that of the standard oral contrast mixture. One dose of PEG plus the water-soluble contrast material was $6.65. One dose of the 1,600-mL mixture of the water and iodinated contrast material costs $1.75. However, the significant decrease in time that the patient spent in the emergency department may make use of the PEG solution cost-effective. More important, the diagnosis and subsequent management of these patients are processed more rapidly than is possible with the standard contrast solution.
This study has some design limitations. The first relates to the selection of the PEG group of patients. These patients were initially entered into the study consecutively because of the dedicated reporting of the radiology residents and faculty who were using the new contrast agent for examinations in the population being studied. However, as the department became more familiar with the "PEG appendicitis" protocol, they often reported only the positive appendicitis cases. This lack of accurate patient reporting in the later part of the project resulted in a lack of purely consecutive cases for this study. This fact may also account for the different ratio of appendicitis cases between the two groups.
Another limitation is that the evaluation of colonic transit was performed retrospectively by the authors, who were not masked to which oral contrast agent had been used. This unblinded review may have created interpretation bias in the results, but we do not think this occurred because visualization of contrast material in the cecum is a fairly straightforward and objective criterion. The interpretation about the presence of appendicitis used for this study was the initial result given to the clinical service.
Also, there is no definite diagnosis of the patients in both groups who did not have either appendicitis or some other CT diagnosis as a cause for abdominal pain. Thus, a certain unknown or group of unknown diagnoses may have caused the difference in contrast transit success between the PEG and standard oral agents groups; however, we believe that this is highly unlikely.
In conclusion, the oral contrast solution composed of 1,000 mL of PEG mixed with 30 mL of an iodinated contrast agent provides relatively rapid and dependable opacification of the terminal ileum and cecum even in cases of appendicitis or certain other abdominal inflammatory processes. This solution has now become our standard CT preparation for all patients being evaluated for suspected appendicitis.
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