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Gastrointestinal Imaging |
1 From the Departments of Radiological Sciences (R.I., C.C., F.M., D.M., R.P.), Surgery "Pietro Valdoni," Endoscopic Unit (A.L., E.F., A.S.), and Experimental Medicine and Pathology-Medical Biostatistics (I.N.), University of Rome-La Sapienza, Rome, Italy; and Department of Radiology, Osaka University Graduate School of Medicine, Osaka, Japan (T.M., M.H.). Received October 11, 2004; revision requested December 21; revision received March 3, 2005; accepted March 16. Address correspondence to R.I., Via Arturo Graf 40, 00137 Rome, Italy (e-mail: r_iannaccone{at}yahoo.it).
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ABSTRACT |
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 TOP ABSTRACT INTRODUCTIONMATERIALS AND METHODSRESULTSDISCUSSIONReferences |
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MATERIALS AND METHODS: The study was local ethics committee approved, and all patients gave written informed consent. Colonographic images were acquired by using a low-dose multi–detector row CT protocol (effective milliampere-second setting, 10 mAs). Three observers interpreted the CT colonographic data separately and independently by using a two-dimensional technique. Initial conventional colonoscopy was performed by an endoscopist unaware of the CT colonographic findings. Second colonoscopy performed within 2 weeks by a colonoscopist aware of both the CT colonographic and the initial colonoscopic findings served as the reference standard. The sensitivities of CT colonography and initial colonoscopy were calculated on a per-polyp and a per-patient basis. Specificities and positive and negative predictive values also were calculated on a per-patient basis.
RESULTS: Eighty-eight patients underwent CT colonography and initial conventional colonoscopy on the same day. Per-polyp sensitivities were 62% and 83% for CT colonography and initial colonoscopy, respectively. Sensitivities for detection of polyps 6 mm in diameter or larger were 86% and 84% for CT colonography and initial colonoscopy, respectively. Initial colonoscopy failed to depict 16 polyps, six of which were correctly detected with CT colonography. For identification of patients with polyps 6 mm in diameter or larger, CT colonography and initial colonoscopy, respectively, had sensitivities of 84% and 90%, specificities of 82% and 100%, positive predictive values of 70% and 100%, and negative predictive values of 91% and 95%.
CONCLUSION: Low-dose CT colonography compares favorably with colonoscopy for detection of colorectal polyps 6 mm in diameter or larger, with markedly decreased performance for detection of polyps 5 mm in diameter or smaller.
© RSNA, 2005
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INTRODUCTION |
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TOPABSTRACTINTRODUCTIONMATERIALS AND METHODSRESULTSDISCUSSIONReferences |
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In addition, some small polyps may be difficult to identify because of their size, flat morphologic features, and/or lack of color contrast with the surrounding mucosa (14). Although several techniques to reduce the miss rate of colonoscopy (ie, high-magnification chromoscopy with dye spraying [15,16], cap-fitted colonoscopy [17], and wide-angle colonoscopy [12]) have been proposed, to our knowledge none has reached widespread use thus far.
Owing to the use of an imperfect reference standard in studies reported in the CT colonographic literature, the diagnostic performance of CT colonography possibly is underestimated. Specifically, it has been recently demonstrated that, in several instances, CT colonography depicts polyps that have been missed at conventional colonoscopy (13). Thus, some of the false-positive findings at CT colonography could be false-negative findings at conventional colonoscopy (8,18).
The ideal validation of a test for the identification of colorectal polyps, either CT colonography or conventional colonoscopy, would involve direct comparison with the findings at pathologic examination of the entire large bowel—a study that is impossible to perform (11). A method to create an enhanced reference-standard examination—a so-called segmental unblinding—was proposed by Pineau et al (18) and subsequently adopted in two recent studies (5,6). This method involves the incremental revealing of the CT colonographic findings to the endoscopist during colonoscopy as the colonoscope is withdrawn segment by segment, after the endoscopist has recorded his or her own independent observations (19). Therefore, if a polyp is identified in a given segment at CT colonography and is not seen at the "first-look" colonoscopy, the endoscopist has to reexamine the segment to resolve the discrepancy. However, if the CT colonographic result is negative, no further colonoscopic evaluation is performed (18).
To our knowledge, no study to investigate the performance of CT colonography with use of two sequential colonoscopies had been performed before the current investigation. With this approach, after complete initial colonoscopic and CT colonographic examinations, a complete second colonoscopy is performed and serves as the reference standard. Thus, the purpose of our study was to prospectively evaluate the diagnostic accuracy of low-radiation-dose multi–detector row helical CT colonography for the detection of colorectal polyps by using two sequential colonoscopies, with the second colonoscopy as the reference standard.
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MATERIALS AND METHODS |
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TOPABSTRACTINTRODUCTIONMATERIALS AND METHODSRESULTSDISCUSSIONReferences |
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Patient inclusion criteria included the following: average-risk colorectal cancer screening performed, family history of colorectal carcinoma, personal or family history of colorectal polyps, follow-up of an abnormal screening test result (ie, positive guaiac-based stool test, barium enema examination, or sigmoidoscopy result) performed, evaluation of hematochezia performed, change in bowel movement habits, weight loss, abdominal pain, and/or iron deficiency–related anemia. Exclusion criteria included the following: history of familial adenomatous polyposis or hereditary nonpolyposis cancer syndromes, prior colorectal surgery, suspected inflammatory bowel disease, acute diverticulitis or bowel obstruction, rejection for conventional colonoscopy or CT colonography for any reason, medical condition that precluded the use of bowel preparation, inability to give informed consent, and/or pregnancy. Each patient included in the study underwent CT colonography followed by initial colonoscopy on the same day and second colonoscopy 7–14 days (average, 9.2 days) later.
CT Colonographic Technique
The study participants underwent colonic cleansing by drinking 2 L of polyethylene glycol electrolyte solution (Isocolan; Bracco, Milan, Italy) and 10 mg of bisacodyl (Dulcolax; Boehringer Ingelheim, Florence, Italy) the day before the scheduled examinations. Bisacodyl was used to reduce the amount of fluid ingested by the patient and thus improve patient compliance (21).
The CT colonographic examinations were performed with a multi–detector row helical CT scanner (Somatom Plus 4 Volume Zoom; Siemens Medical Systems, Forchheim, Germany) 3–6 hours before initial colonoscopy. CT colonography was performed with the patient in the prone and supine positions after intravenous administration of 20 mg of hyoscine-N-butylbromide (Buscopan; Boehringer Ingelheim). With the patient in the left lateral decubitus position, the colon was gently insufflated with room air, with a rubber catheter placed in the rectum according to patient tolerance. To prevent air leakage from the anus, the rectal tube was subsequently clamped and left in situ during imaging.
First, with the patient in the prone position, a scout CT image was obtained to estimate the adequacy of colonic distention. Further air insufflation was performed when collapsed bowel segments were observed. Before supine imaging, the colon was insufflated with additional air, again according to maximal patient tolerance, and colonic distention was verified on a second scout CT image. Air insufflation was performed in all patients by the same nurse.
The CT examinations were performed by using the following low-dose protocol, which was previously optimized for the CT scanner used in the present study by Iannaccone et al (22): 4 x 2.5-mm section collimation (effective section thickness, 3.0 mm), 1.0-mm reconstruction interval, 17.5 mm/sec table speed, gantry rotation time of 0.5 seconds, 140 kV, and effective milliampere-second setting of 10 mAs. The ensuing total weighted CT dose index for the combined prone and supine image acquisitions was 2.74 mGy (22). The acquisition time ranged from 14 to 20 seconds. A resident who was not involved in CT colonographic data evaluation documented any complication associated with CT colonography.
CT Colonographic Image Analysis
Three gastrointestinal radiologists (R.I., C.C., F.M.), who were unaware of both the specific indications for CT colonography and the results of the initial colonoscopic examination, separately and independently reviewed each case directly on a dedicated workstation by using a software package with volume-rendering capabilities (Vitrea; Vital Images, Plymouth, Minn). These observers had previously interpreted approximately 400 (R.I.), 200 (C.C.), and 100 (F.M.) CT colonographic cases with endoscopic correlation. The findings in each patient were prospectively recorded by the three observers before second colonoscopy was performed.
For image analysis, the observers were asked to use a previously validated time-efficient technique (23,24). In brief, the initial analysis entailed reviewing magnified two-dimensional transverse CT images. When a suspected polyp was detected on the two-dimensional transverse CT images, coronal and sagittal CT images and three-dimensional endoluminal views were evaluated to confirm the finding. If no suspected polyp was identified at review of the transverse images, no further image analysis was performed. The presence, location, size, and morphologic features of all suspected polyps were documented. Polyps were measured on the transverse CT images by using an electronic ruler.
To specify the location of each polyp, the colon was divided into six segments: cecum, ascending colon and hepatic flexure, transverse colon and splenic flexure, descending colon, sigmoid colon, and rectum. With regard to morphologic features, all polyps were classified as pedunculated, sessile, or flat. Flat polyps were defined as those with a base at least twice as long as the height. Sessile polyps were those that did not meet the criteria to be classified as flat and did not have a stalk. Pedunculated polyps had an identifiable stalk. All polyps seen at CT colonography were photographed, and the colonographic images were stored in digital format. The image interpretation time for each CT colonographic examination was recorded with a stopwatch.
Initial Conventional Colonoscopy
All colonoscopies were performed by one of two staff endoscopists (A.L., E.F.) with extensive and comparable colonoscopic experience (each having interpreted more than 5000 cases prior to this study). Both endoscopists were unaware of the CT colonographic findings. Two endoscopists participated in the study because the sensitivity of colonoscopy has been shown to vary between examiners (25) and because variation in examination technique is potentially responsible for the nondetection of polyps (26). To avoid bias, the two endoscopists alternated between performing the first and second examinations. All examinations were performed while the patients were sedated. Sedation was induced with intravenous administration of midazolam hydrochloride (Versed; Hoffmann-La Roche, Nutley, NJ).
The endoscopist performed conventional colonoscopy with a standard videocolonoscope (model C240 or CV-1; Olympus Optical, Tokyo, Japan). The endoscopist was asked to pass the instrument tip to the cecum and withdraw the endoscope segment by segment for the detection of polyps. Cecal intubation was verified on the basis of the identification of the appendiceal orifice, triradiate cecal fold, and ileocecal valve and the findings at biopsy of the small bowel after intubation of the terminal ileum. The presence, location, size, and morphologic features of all colorectal polyps were documented. All polyps were photographed. The width of each lesion was estimated to the nearest millimeter by means of visual comparison with the known diameter (4 mm) of an opened biopsy forceps that was pushed against the polyp; the height was estimated by placing the closed forceps tip (2.1 mm) adjacent to the lesion. This allowed subsequent calculation of the height-to-width ratio for each polyp, which is important in assessing the flat morphologic features of polyps.
The location of each polyp was mapped within the same six colonic segments used in CT colonographic analysis. The morphologic criteria for polyps at colonoscopy were the same as those at CT colonography. During the initial conventional colonoscopic examination performed on the same day as but after CT colonography, no polyp was sampled at biopsy or resected. In addition, a resident who was not involved in CT colonographic data evaluation was present to document any complication associated with initial colonoscopy.
Second Conventional Colonoscopy
Each second colonoscopic procedure was performed by the endoscopist who did not perform the first examination. The bowel preparation before colonoscopy and the technique used were the same as those described for the first colonoscopic examination. The location, size, and morphologic criteria used for polyp assessment also were the same as those used for the first colonoscopy. The endoscopist who performed the second colonoscopic examination was aware of the findings of both initial colonoscopy and CT colonography. Specifically, to facilitate polyp-to-polyp matching with the lesions depicted at second colonoscopy, the initial colonoscopic images and the CT colonographic images—together with the reference images of the identified polyps—were reviewed before the second colonoscopy. To solve any potential discrepancy in the polyp-to-polyp matching, the endoscopist who performed the first colonoscopic examination and one radiology resident who was aware of the results derived by the three CT observers also were present. The complications associated with the second colonoscopic procedure also were recorded.
Histologic Features of Polyps
All polyps were sampled at biopsy or resected during the second colonoscopy. The histologic appearances of all polyp specimens were evaluated by the same pathologist, who had 11 years of experience. Histologically, polyps were classified as nonneoplastic (including hyperplastic, inflammatory, and juvenile polyps) or neoplastic (including tubular, villous, tubulovillous, serrated, and microtubular adenomas; carcinomas in situ; and invasive carcinomas) (27).
Data Analyses
Results were calculated in two ways: by using individual polyp detection—that is, per-polyp analysis—and by using patient detection—that is, per-patient analysis. For per-polyp analysis, the results of the second colonoscopy—in terms of the location, size, and morphologic features of the depicted polyps—were considered the reference standard against which the findings at initial colonoscopy and CT colonography were compared. For a given polyp to be considered a true-positive match between second colonoscopy and either CT colonography or initial colonoscopy, the location, size, and morphologic features of the polyp had to be considered.
With regard to location and morphologic features, a polyp detected at CT colonography or first colonoscopy was considered to be concordant with one seen at second colonoscopy if it was located in the same or an adjacent colonic segment (with the exception of polyps in the cecum, for which no margin of error was allowed) and had the same morphologic features, compared with the polyp seen at second colonoscopy. Precise matching of polyps according to size criteria was rarely possible because of the known measurement error with conventional colonoscopy and the unknown measurement error with CT colonography (5,18). Thus, for a given polyp to meet the size criteria, the size measured at CT colonography or initial colonoscopy had to be within a 50% margin of error of the size determined at second colonoscopy (5,6,18).
Each polyp that was seen at second colonoscopy but not documented at CT colonography or initial colonoscopy was classified as a false-negative finding of CT colonography or initial colonoscopy, respectively. In cases in which additional polyps that were not seen at first colonoscopy were identified at second colonoscopy, the two endoscopists jointly discussed the possible reason(s) for the initial nonvisualization (ie, a polyp situated behind a colonic fold, an area of interest that was difficult to assess for anatomic reasons, or perceptual error). If a polyp was depicted at CT colonography or initial colonoscopy but not confirmed at second colonoscopy, it was deemed to be a false-positive finding of CT colonography or initial colonoscopy, respectively.
After the comparisons, a retrospective review of all false-negative and false-positive CT colonographic findings was jointly performed by the three observers and a study supervisor (R.P.) to determine the reasons for the diagnostic errors. In addition, because of the potential range of size measurements for a given polyp among the three observers, a consensus reading was performed to determine the CT colonographic size of each polyp. Therefore, the average results given throughout this report refer to the polyp sizes estimated during this consensus reading.
For per-patient analysis, the overall results of CT colonography or initial colonoscopy were compared with the overall results of second colonoscopy for each patient. A patient was considered to have true-positive findings at CT colonography or initial colonoscopy if the given examination depicted at least one polyp that was seen at second colonoscopy on the basis of the location, size, and morphologic criteria described earlier.
Statistical Analyses
All statistical analyses were conducted by using commercially available software (SPSS for Windows, version 11.0.0; SPSS, Chicago, Ill). For per-polyp analysis, the sensitivity and corresponding 95% confidence interval (CI) of both CT colonography and initial colonoscopy were calculated on the basis of the total number of polyps (ie, neoplastic and nonneoplastic polyps combined) and on the basis of the number of neoplastic polyps only. The specificity of the examinations for the detection of individual polyps could not be calculated because the total number of true-negative polyps could not be assessed (5).
For per-patient analysis, the sensitivity, specificity, positive predictive value, and negative predictive value of both CT colonography and initial colonoscopy, with corresponding 95% CIs, were calculated.
In this study, per-polyp and per-patient analysis data were calculated according to size thresholds (6,19), with separate evaluations for polyps 5 mm in diameter or smaller, 6 mm in diameter or larger, 7 mm in diameter or larger, 8 mm in diameter or larger, 9 mm in diameter or larger, and 10 mm in diameter or larger.
Interobserver reliability for both the detection of individual polyps and the detection of patients with polyps at CT colonography was evaluated by calculating 
statistics for multiple observers with use of nonweighted binary statistic values. A value of 0.01–0.20 was considered to indicate minor agreement; 0.21–0.40, fair agreement; 0.41–0.60, moderate agreement; 0.61–0.80, high agreement; and 0.81–1.00, excellent agreement.
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RESULTS |
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TOPABSTRACTINTRODUCTIONMATERIALS AND METHODSRESULTSDISCUSSIONReferences |
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Initial Conventional Colonoscopy
No complications were associated with the initial colonoscopic examination. Overall, initial colonoscopy (Table 3) yielded a per-polyp sensitivity of 83%, with a sensitivity of 87% for the detection of neoplastic polyps. Initial colonoscopy "missed" 16 polyps (diameter range, 4–14 mm) that were depicted at second colonoscopy, for a total miss rate of 17%. Five (four tubular adenomas and one tubulovillous adenoma; diameter range, 5–14 mm) of these 16 missed polyps were neoplastic. Thus, the neoplastic polyp miss rate of initial colonoscopy was 13% (five of 39 polyps). The reasons for missed polyps at initial colonoscopy were a blind spot (ie, the polyp was located behind a colonic fold) in 12 cases and perceptual error in the remaining four cases. All polyps found at initial colonoscopy were confirmed and resected at second colonoscopy—that is, there were no false-positive findings at initial colonoscopy.
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The values for agreement among the three observers indicated moderate to high agreement on a per-polyp basis and high to excellent agreement on a per-patient basis (Table 5).
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5 mm polyps, two 8-mm polyps, and one 14-mm polyp) that were not seen at initial colonoscopy but were confirmed and resected at second colonoscopy. Four of these six polyps were neoplastic (three adenomas, one tubulovillous adenoma) (Fig 2).
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DISCUSSION |
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TOPABSTRACTINTRODUCTIONMATERIALS AND METHODSRESULTSDISCUSSIONReferences |
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In contrast, although the sensitivity of initial colonoscopy remained stable (sensitivity for detection of polyps 5 mm, 82%), the diagnostic performance of CT colonography decreased substantially when polyps 5 mm in diameter or smaller were considered (mean sensitivity, 47% [29 + 27 + 24]/[57 + 57 + 57] for the three observers). This finding is in agreement with several previous reports (1,7,29). In our study, 26, 26, and 28 polyps 5 mm in diameter or smaller could not be detected with CT colonography, even at retrospective analysis. Because a substantial proportion of these small polyps missed at CT colonography were hyperplastic, one possible explanation for the nonvisualization of such lesions could be their soft consistency, which favors the effacement against the colonic mucosa once the colon is distended with air (1,30).
In our study, however, the sensitivities of CT colonography for the detection of all polyps (ie, neoplastic and nonneoplastic polyps combined) and for the detection of neoplastic polyps only were relatively stable. This indicates that diminutive lesions, regardless of their histologic type, are difficult to detect at CT colonography. However, the minority of such small polyps are malignant (31–33), and the adenoma-to-carcinoma transformation is believed to take at least 10 years on average (34,35). Thus, the clinical importance of identifying such small polyps is controversial.
It is perhaps more important that all of the flat polyps in our series were missed at CT colonography. Although only five such lesions were identified, there is increasing evidence that flat adenomas are extremely difficult to detect at CT colonography (7,8,36–38) because they cause only minimal alterations of the colonic mucosa. In this regard, it should be emphasized that even conventional colonoscopy has limited capability to depict flat lesions without the supplementary use of special techniques, such as high-magnification chromoscopy and dye spraying (16). In addition, the clinical importance of flat adenomas is still controversial because their prevalence and malignant potential are unclear (39).
Another important issue that emerged from our research is that false-positive CT colonographic findings are relatively frequent: The three observers had 19, 20, and 24 false-positive findings in our study. In agreement with the findings of two recent studies (40,41), the most frequent cause of the false-positive cases in our study was the presence of residual fecal material. Small fecal residue often adheres to the colonic mucosa and is too small to contain gas bubbles (a finding consistent with fecal material). Thus, such residue is often indistinguishable from polyps and thus has the potential to prompt many unnecessary colonoscopic examinations (42).
Although per-polyp analysis is important for determining which polyps will most likely be identified or missed with CT colonography, from a clinical point of view per-patient analysis is far more important because it enables the use of CT colonography to preselect those patients with polyps who might benefit from colonoscopy (5,8). In this regard, the diagnostic performance of CT colonography was comparable to that of initial colonoscopy in terms of sensitivity, specificity, and positive and negative predictive values for the identification of patients with polyps 10 mm in diameter or larger. Moreover, the negative predictive value of low-dose CT colonography—that is, its effectiveness in the identification of patients who did not need to undergo colonoscopy—was approximately equal to the negative predictive value of initial colonoscopy in the identification of patients with polyps 6 mm in diameter or larger (91% for CT colonography vs 95% for initial colonoscopy). This finding has important clinical implications for CT colonography as a potential screening tool because 46%–85% of screening colonoscopies do not reveal clinically important abnormalities (43,44).
Moreover, our study results demonstrate that low-dose CT colonographic images are interpreted with moderate to high interobserver agreement on a per-polyp basis and with high to excellent agreement on a per-patient basis among observers with different levels of experience. The three observers had previously interpreted approximately 400, 200, and 100 CT colonographic cases with endoscopic correlation in our series. The reproducibility of our results was thus demonstrated. These results correlate with the findings of other authors (6,45) but differ from those reported by Johnson et al (38). It is possible that the interobserver variability in our study was reduced, compared with that in the Johnson et al (38) study, owing to the use of thin-section multi–detector row helical CT image acquisitions.
One of the major strengths of our study was the use of two sequential colonoscopies to evaluate the performance of CT colonography. The performance of a second complete colonoscopic examination by an experienced endoscopist who was aware of the CT colonographic and initial colonoscopic findings yielded a greatly improved reference standard compared with the reference standards used in the majority of studies reported in the CT colonographic literature. It is conceivable that, although second colonoscopy may depict some polyps missed at the first examination, it may fail to depict other missed polyps (10,13). However, it can be assumed that after two colonoscopic procedures performed by two experienced endoscopists and CT colonography, the probability of having missed polyps in our cohort was minimal.
In addition, the use of two sequential colonoscopies yielded important information about the performance of conventional colonoscopy. In agreement with previous study (9,10,12,13) findings, our study results show that conventional colonoscopy has a substantial miss rate in the identification of colorectal polyps. The overall miss rate was 17% in our study: 16 of 94 polyps were not seen prospectively. In our series, 16 polyps (five neoplastic, 11 nonneoplastic) that were missed at initial colonoscopy were identified at second colonoscopy. Six of these polyps, four of which were neoplastic, were seen at CT colonography. Thus, if initial colonoscopy had been the reference standard, these six polyps would have been wrongly classified as false-positive findings at CT colonography. In agreement with the recent findings of Pickhardt et al (13), the most frequent reason for missed polyps at initial colonoscopy in our study was the location of polyps behind colonic folds (in 12 [75%] of 16 cases).
Because both endoscopists in our study had extensive colonoscopic experience (as indicated by cecal intubation rates of 94% and 100% at initial and second colonoscopy, respectively), the miss rate of conventional colonoscopy confirms that colonoscopy is an imperfect reference standard. Therefore, an improved reference standard is needed for accurate assessment of the performance of CT colonography (18,19).
As a possible way to create an improved reference standard, so-called segmental unblinding has been described (18) and adopted (5,6). This method has the important advantage of enabling both initial evaluation and reevaluation of a colonic segment during the same endoscopic session, so only one colonoscopic procedure is needed. However, this approach also has certain limitations: First, if a polyp is not seen at CT colonography and at first-look colonoscopy, a second colonoscopic look is not performed (18). Second, owing to a learning effect, this technique may hamper the comparison of diagnostic performance between colonoscopy and CT colonography, because if the endoscopist misses a polyp in a specific segment, he or she may unintentionally adjust the examination approach during assessment of the remaining segments (8). Third, segmental unblinding with same-day colonoscopy may be difficult to perform at many centers owing to logistic reasons, because the CT colonographic report must be available within a few hours. This can be difficult to achieve in routine clinical practice, especially if three CT observers are needed to prospectively assess interobserver variability.
The limitations of our study require comment. First, similar to what has been reported regarding colonoscopy and the expertise of endoscopists (44), there is increasing evidence that greater observer experience is associated with increased CT colonographic performance (4). In our study, the three observers had greater-than-average experience in CT colonographic data interpretation, having interpreted approximately 400, 200, and 100 cases with endoscopic correlation. Therefore, further studies are needed to confirm the diagnostic performance of low-dose CT colonography when its findings are interpreted by less experienced readers.
In addition, instead of monobasic sodium phosphate monohydrate combined with dibasic sodium phosphate heptahydrate, polyethylene glycol electrolyte solution and bisacodyl were used for cathartic preparation. The monobasic sodium phosphate monohydrate–dibasic sodium phosphate heptahydrate preparation has been demonstrated to leave a drier colonic surface compared with the polyethylene glycol preparation (46). However, in our study, residual fluids were rarely responsible for diagnostic errors at CT colonography.
In conclusion, our study results show that the performance of low-dose multi–detector row helical CT colonography compares favorably with that of conventional colonoscopy in the detection of colorectal polyps 6 mm in diameter or larger and has markedly decreased performance in the detection of polyps 5 mm in diameter or smaller. The high negative predictive value of CT colonography can be used to exclude the presence of clinically important colorectal polyps in the majority of patients and thus potentially to reduce the number of negative-result colonoscopies performed. Further studies are needed to determine which lesion cutoff size is clinically acceptable and the appropriate time interval for repeat CT colonography when lesions smaller than this cutoff size are detected.
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FOOTNOTES |
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Abbreviations: CI = confidence interval
Authors stated no financial relationship to disclose.
Author contributions: Guarantors of integrity of entire study, R.I., R.P.; study concepts/study design or data acquisition or data analysis/interpretation, all authors; manuscript drafting or manuscript revision for important intellectual content, all authors; approval of final version of submitted manuscript, all authors; literature research, R.I., D.M.; clinical studies, R.I., F.M., A.L., E.F.; statistical analysis, R.I., I.N.; and manuscript editing, R.I., C.C., T.M., M.H., R.P.
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