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Technical Developments |
1 From the Department of Radiology, Division of Abdominal Imaging (M.M., M.L., I.P., A.J.M.); the Department of Medicine, Division of Gastroenterology (A.M., M.D.); and the Department of Environmental Medicine, Division of Biostatistics and Epidemiology (X.X.), New York University Medical Center, Tisch Hospital, 560 First Ave, Suite HW 207, New York, NY 10016. Received February 15, 2000; revision requested April 5; revision received April 27; accepted May 22. Address correspondence to M.M. (e-mail: michael.macari@med.nyu.edu).
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ABSTRACT |
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 TOP ABSTRACT INTRODUCTIONMaterials and MethodsResultsDiscussionREFERENCES |
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Index terms: Colon, CT, 75.12115 • Colon neoplasms, 75.30
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INTRODUCTION |
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TOPABSTRACTINTRODUCTIONMaterials and MethodsResultsDiscussionREFERENCES |
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Optimizing patient preparation is an important consideration when performing CT colonography. Too much residual fecal material or fluid in the colon can seriously compromise the results of an individual examination. Residual colonic fluid is generally not an impediment to fiberoptic colonoscopy because the fluid can be aspirated out with the colonoscope. During CT colonography, if too much fluid is present, clinically important lesions, be they polyps or neoplasms, could potentially be obscured despite scanning with the patient in the supine and prone positions. Therefore, every effort should be made to ensure a clean and dry colon during CT colonographic evaluation.
Two commonly used bowel cleansing regimens are polyethylene glycol electrolyte solution and phospho-soda, both available in commercial preparations (8). The phospho-soda preparation kit contains four bisacodyl tablets and one bisacodyl suppository in addition to the phospho-soda. It has been suggested that the phospho-soda preparation kit may provide a "drier" colon at the time of evaluation. In this study, we evaluated the effect of these two different bowel preparations (polyethylene glycol electrolyte solution and phospho-soda) on the degree of residual fluid present within the colon at the time of CT colonography.
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Materials and Methods |
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TOPABSTRACTINTRODUCTIONMaterials and MethodsResultsDiscussionREFERENCES |
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The patients included two different groups. The first group (n = 11) were patients undergoing routine screening colonoscopy; as part of a study approved by the institutional review board, they were also being examined with CT colonography. Informed consent was obtained prior to the procedure. In this group of patients, CT colonography was performed immediately prior to conventional colonoscopy. Choice of bowel preparation in this group was based on gastroenterologist preference; these patients were referred from a variety of gastroenterologists affiliated with our institution. Electrolyte solution was used in all of these patients.
The second group of patients (n = 31) were those who were referred for CT colonography after an incomplete colonoscopic examination. This group of patients underwent CT colonography at least 1 week after conventional colonoscopy. In this group of patients, the phospho-soda preparation was used, which is the preferred regimen in our department of radiology and is recommended for use before double-contrast barium enema examination.
All patients in this study were otherwise healthy. All patients were referred from private practice gastroenterologists, and all patients were given instructions on the proper use of the bowel preparation prior to its use.
Immediately prior to CT colonography, the patient evacuated any residual fluid or fecal material from the rectum. The patient was placed supine on the CT table, and 1 mg of glucagon hydrochloride (Eli Lilly, Indianapolis, Ind) was administered intravenously in an attempt to decrease bowel peristalsis and spasm and to facilitate hypotonia. A flexible rubber catheter was inserted into the rectum, and the colon was insufflated with room air to patient tolerance. The catheter was left in the rectum. A single, low-dose, scout CT image was obtained to verify adequate bowel distention. If adequate bowel distention was present, the CT examination was performed. If bowel distention was not achieved, additional air was insufflated into the rectum. In all patients, the degree of bowel distention at CT colonography was adequate for interpretation.
All CT examinations were performed with a helical CT imaging unit (HiSpeed Advantage; GE Medical Systems, Milwaukee, Wis) by using 5-mm collimation, a pitch of 2.0, and a 2.5-mm reconstruction interval. Additional parameters used were 120 kV and 150 mA. Two sets of images, one obtained with the patient supine and the other with the patient prone, were generated. Each CT examination (supine and prone) was performed in one breath hold of approximately 25 seconds. CT images were transferred to a remote workstation (Advantage; GE Medical Systems).
Three reviewers (M.M., M.L., I.P.), without knowledge of the bowel preparation, retrospectively and independently evaluated colonographic data for residual fluid. For purposes of data recording, the colon was divided into six segments (cecum, ascending colon, transverse colon, descending colon, sigmoid, and rectum). Residual fluid in a colonic segment was measured relative to the maximum anteroposterior diameter of the segment. Residual fluid was ranked on a four-point scale: 1, no residual fluid within a colonic segment; 2, largest air-fluid level less than 25% of the maximum anteroposterior diameter of the segment; 3, largest air-fluid level between 25% and 50% of the maximum anteroposterior diameter of the segment; and 4, an air-fluid level more than 50% of the maximum anteroposterior diameter of the segment (Figs 1, 2).
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Results |
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TOPABSTRACTINTRODUCTIONMaterials and MethodsResultsDiscussionREFERENCES |
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Of the patients who received the phospho-soda preparation, 55% (17 of 31) had a mean score of 15.0 or less. There was some overlap in the scores between the two groups. Twenty-two percent (seven of 31) of the patients in the phospho-soda group had a score higher than 20.0, with a maximum score of 23.3. In the electrolyte solution group, there were two patients with scores less than 23.3. These patients’ mean scores were 20.0 and 21.6.
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Discussion |
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TOPABSTRACTINTRODUCTIONMaterials and MethodsResultsDiscussionREFERENCES |
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As CT colonography continues to be evaluated as a screening technique, the mechanics of performing the study are beginning to be clarified with an attempt toward standardization. There is considerable interest in positioning, optimal choice of insufflating agent (room air or carbon dioxide), and use of hypotonia. Regardless, bowel preparation is essential for confident detection of clinically important lesions because residual fecal material may be indistinguishable from polyps or neoplasms. The choice of the bowel preparation for colon cleansing has been at the discretion of the radiologist and/or gastroenterologist. We routinely use the phospho-soda preparation for double-contrast barium enema examinations. We have found that this preparation provides a clean colon with little residual fluid and good barium coating of the colonic mucosa. Electrolyte solution, the phospho-soda preparation used in this study, and other phospho-soda preparations are routinely prescribed by gastroenterologists before colonoscopy. Many gastroenterologists favor electrolyte solution because it provides a clean but wet mucosal surface.
Although these preparations are adequate for colonoscopy, the potential limitation of large amounts of residual fluid at CT colonography is important. At colonoscopy, residual fluid can be aspirated out of the colon. During barium enema examination, imaging can be performed in multiple different projections to allow the fluid to redistribute. With CT colonography, the examination is limited by the possibility of imaging in only two projections—supine and prone. In this setting, the preparation that provides the least amount of residual fluid theoretically would provide the greatest opportunity to detect polyps by enabling evaluation of the entire mucosal surface of the colon.
Uncertainty exists regarding the optimal bowel preparation for CT colonography (11). There is currently interest in developing orally ingested agents that would tag residual fecal material with barium and allow differentiation of stool from polyps and neoplasms (5). If this proves reliable, it would offer an advantage over other preparations in that differentiating residual fecal material from polyp is a major limitation of CT colonography.
Most of the data in the current literature regarding CT colonography have been obtained in patients by using either a phospho-soda preparation or electrolyte solution preparation (8,11). There has been no formal assessment as to which preparation may be preferable for CT colonography. The phospho-soda preparation may offer an advantage when compared with the electrolyte solution preparation in that it may provide a drier mucosal surface (11). Our results confirm this observation by demonstrating that there was, on average, significantly less residual fluid with use of the phospho-soda preparation when compared with use of the electrolyte solution preparation. In our study, both preparations resulted in colons that were free of residual fecal material.
Ingestion of electrolyte solution, which contains 236 grams of polyethylene glycol and an electrolyte solution reconstituted in 4 L of water, results in virtually no internal fluid shifts during administration. This is an advantage of the electrolyte solution preparation over the phospho-soda preparation in that it can be administered in patients with renal failure and in patients with congestive heart failure. The electrolyte solution preparation induces an osmotic diarrhea, which rapidly cleanses the colon (12). For routine studies, electrolyte solution is usually ingested orally the evening before the scheduled gastrointestinal examination. The recommended dose produces a satisfactory bowel preparation in more than 95% of individuals for barium enema examination and colonoscopy (12).
The phospho-soda preparation kit contains 45 mL of monobasic sodium phosphate, four bisacodyl laxative tablets, and one bisacodyl suppository (12). Like electrolyte solution, it is used to cleanse the bowel before evaluation. Because this preparation may result in acute elevation of serum sodium concentration, it is contraindicated in patients with congestive heart failure or renal failure (12). The sodium phosphate acts as an osmotic cathartic and the bisacodyl as a colonic stimulant. This combination, as well as the decreased total volume that needs to be ingested with this preparation, may account for the decreased colonic fluid noted with use of the phospho-soda preparation in our study.
As stated in the introduction, the complete phospho-soda preparation is different from a simple phospho-soda preparation that is often administered by gastroenterologists prior to colonoscopy. With a simple phospho-soda preparation, two 45-mL doses of phospho-soda are administered, one the day prior to the examination and one on the morning of the examination. Bisacodyl is not included in this preparation. We did not assess residual fluid in this group of patients. It is possible that without the bisacodyl component more residual fluid may be present in these patients than in those who have received the complete phospho-soda preparation.
There are several limitations of this study. We were not able to determine the exact volume of residual fluid present within the colon at the time of CT colonography. However, we think that our method for quantifying residual fluid provided a reasonable representation of relative amounts. This is evident in the similarity of the scores of the three reviewers for each patient.
Another limitation is that the patient populations were different. In the first group were patients in whom CT and conventional colonoscopy were compared, and in the second were patients being examined with CT colonography after an incomplete colonoscopic examination. This could conceivably lead to patient bias. It is possible that one group may have been more motivated in the use of one of the preparations. A larger group of patients ideally could have been placed randomly into one of two categories for preparation: phospho-soda or electrolyte solution. However, as stated earlier, all patients in this study were referred from private gastroenterology group practices, and all patients were given instructions on the proper use of the bowel preparation. Finally, some gastroenterologists may opt to use bisacodyl with the electrolyte solution. When this is done, the results of the electrolyte solution preparation could improve.
In conclusion, optimal patient preparation prior to CT colonography is necessary to maximize the inherent sensitivity and specificity of the technique. This includes obtaining a well-distended, clean, and dry colon. We have found that preparation with phospho-soda leaves less residual fluid than does preparation with electrolyte solution at CT colonography. For patients without heart failure or renal insufficiency, CT colonography should be performed with this phospho-soda preparation to allow optimal mucosal depiction.
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FOOTNOTES |
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