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Gastrointestinal Imaging |
1 From the Department of Radiology, Veterans Affairs Medical Center (114), 4150 Clement St, San Francisco, CA 94121 (J.Y., N.N.K., S.G., G.G., D.L.); and the Department of Radiology, University of California School of Medicine, San Francisco (J.Y., N.N.K., J.A.C., R.H., G.G., P.D.). Received January 28; revision requested April 6; revision received September 24; accepted December 29. Address correspondence to J.Y. (e-mail: judy.yee{at}radiology.ucsf.edu).
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ABSTRACT |
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 TOP ABSTRACT INTRODUCTIONMATERIALS AND METHODSRESULTSDISCUSSIONReferences |
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MATERIALS AND METHODS: This study was approved by the institutional review board, and informed consent was obtained from all patients. The study was compliant with requirements of the Health Insurance Portability and Accountability Act. CT colonography was performed in 500 men (mean age, 62.5 years). Of these patients, 194 (38.8%) were at average risk for colorectal cancer and presented for routine screening. The other 306 (61.2%) were at high risk for colorectal cancer. Extracolonic findings were recorded and categorized as either clinically important or clinically unimportant. Clinically important findings were defined as those that necessitated further diagnostic studies or medical or surgical follow-up. The cost of additional imaging required to further characterize important lesions was estimated. Chart review was performed (mean length of follow-up, 3.6 years) to determine whether any important findings were missed at CT colonography. The Fisher exact test was used to determine whether there was a difference between the percentages of average- and high-risk patients with extracolonic findings.
RESULTS: Of the 500 patients in the study, 315 (63.0%) had extracolonic findings, and 45 (9.0%) had clinically important extracolonic findings. Of the 596 extracolonic findings identified, 50 (8.4%) were thought to be clinically important. The mean additional cost to work up important findings was $28.12 per CT colonographic examination. There were no significant differences between average-risk and high-risk patients in the percentages of extracolonic findings (P = .25) or clinically important extracolonic findings (P = .11).
CONCLUSION: A substantial number of both average- and high-risk patients undergoing CT colonography will be found to have clinically important extracolonic findings. There was no increased morbidity or mortality associated with the additional evaluation of extracolonic findings. The cost of evaluating these lesions is low, given the potential for positive effects on patient care.
© RSNA, 2005
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INTRODUCTION |
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TOPABSTRACTINTRODUCTIONMATERIALS AND METHODSRESULTSDISCUSSIONReferences |
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To date, three studies regarding extracolonic findings at CT colonography have been reported (6–8). Two of them involved the performance of cost analyses and the examination of patients at high risk of colorectal cancer who had a personal or family history of colorectal cancer or polyps or a new onset of anemia (7,8). The purpose of our study was to evaluate prospectively the prevalence of incidental extracolonic findings at CT colonography and estimate the cost of imaging work-up in both high- and average-risk male patients.
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MATERIALS AND METHODS |
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TOPABSTRACTINTRODUCTIONMATERIALS AND METHODSRESULTSDISCUSSIONReferences |
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CT Scanning and Interpretation
All patients received a standard colonic preparation that included either magnesium citrate and polyethylene glycol (Colyte; Schwarz Pharma, Jersey City, NJ) or only magnesium citrate (E-Z-Em, Lake Success, NY). A rectal tube was inserted, and either manual insufflation of room air or electronic insufflation with carbon dioxide was used to distend the colon to maximum patient tolerance. After our institution acquired an electronic carbon dioxide insufflator (E-Z-Em), we began using carbon dioxide instead of manual room air for colonic distention. The first 336 patients in the study underwent insufflation with room air; the carbon dioxide insufflator was used for the subsequent 164 patients. Of the average-risk patients, 110 underwent room air insufflation and 84 underwent carbon dioxide insufflation. Of the high-risk patients, 226 underwent room air insufflation and 80 underwent carbon dioxide insufflation. A CT scout scan was used to determine the adequacy of distention before each examination, and additional insufflation was performed if required.
The patient was then scanned in both the supine and the prone position. Helical CT scans were obtained through the entire abdomen and pelvis during a single breath hold with a single– or multi–detector row CT scanner. Single–detector row CT was performed with a HiSpeed CT/i scanner (GE Medical Systems, Milwaukee, Wis) at the following settings: collimation, 3.0 mm; reconstruction interval, 1.5 mm; pitch, 1.5–2.0; 120 kVp; and 150 mA. After our institution acquired an eight–detector row CT scanner (Lightspeed Plus/Ultra; GE Medical Systems) the following protocol was used: collimation, 2.5 mm; reconstruction interval, 1.25 mm; pitch, 0.875; 120 kVp; and 120 mA. Of the average-risk patients, 161 underwent single–detector row CT and 33 underwent multi–detector row CT. Of the high-risk patients, 257 underwent single–detector row CT and 49 underwent multi–detector row CT. The radiation dose to each patient was not specifically recorded because that was not considered the main purpose of this study.
The data were sent to one of two workstations (Advantage Workstation [GE Medical Systems] or Innerview GI [E-Z-Em]) that were equipped with specialized three-dimensional software. One abdominal radiologist (J.Y., with 12 years of experience) assessed transverse data sets (obtained with patients supine and prone) for both colonic lesions (using primary two-dimensional reading with three-dimensional problem solving) and extracolonic findings (using bone, soft-tissue, and lung windows). The reader was blinded to the fiberoptic colonoscopic findings and patient history. The time spent evaluating the colon and the extracolonic findings was not documented, but the time ranges were estimated and depended on the complexity and number of findings in each case.
Extracolonic findings were categorized as either clinically important or clinically unimportant. Important findings were defined as lesions that necessitated further diagnostic studies or medical or surgical intervention. The patient's primary care physician was notified by telephone of clinically important findings. The CT colonographic examinations performed in this study were for research purposes only; therefore, no official report was generated. Patients' physicians were not notified of the clinically unimportant extracolonic findings. Although other investigators have classified extracolonic findings into those of high, medium, or low importance, we decided on a simpler scheme that is more clinically relevant to the ordering provider for short-term management. For example, lesions such as renal masses or abdominal aortic aneurysms were classified as important, while those such as cysts or hiatal hernias were classified as unimportant.
Chart Review
Through June of 2003, chart review was performed (by all authors) for all patients to stratify them as either at average or at high risk for colorectal cancer. Chart review was also performed for patients with important findings to determine whether these findings were new or old and which additional imaging examinations or treatments were performed for new important extracolonic lesions. The mean follow-up for all patients in the study was 3.6 years (range, 8 months to 5.3 years). The costs of diagnostic imaging examinations performed to work up clinically important extracolonic lesions were estimated by using the national average 2003 Medicare reimbursement rates for technical and professional fees (9).
In a separate analysis, all patients' charts were reviewed through June 2003 (J.Y., N.N.K., S.G., J.A.C., R.H.) to identify extracolonic lesions that were found by means of examinations other than CT colonography performed up to 2 years before and any time after CT colonography. If important lesions were found with these other imaging examinations, the CT colonography data sets were reexamined by a radiologist (J.Y.) to determine whether these findings were missed during the initial CT colonographic interpretation.
Statistical Analysis
To determine the significance of differences between the percentages of extracolonic findings in average-risk patients and those in high-risk patients, P values were obtained with the Fisher exact test. To determine whether there was a difference in mean age between the average- and the high-risk patients, a Mann-Whitney nonparametric rank test was performed. Differences were considered significant if the P value was less than .05. Inferential statistical analysis employed a "by patient" method; therefore, analyses at the patient level did not involve data clustering. All statistical analyses were performed by a statistician.
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RESULTS |
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TOPABSTRACTINTRODUCTIONMATERIALS AND METHODSRESULTSDISCUSSIONReferences |
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Findings in Average- versus Those in High-Risk Patients
Our study included 194 patients stratified as having average risk for colorectal cancer who presented for screening. Of these patients, 116 (59.8%) had extracolonic findings at CT colonography, and 12 (6.2%) had clinically important extracolonic findings. Of the 306 high-risk patients, 199 (65.0%) had extracolonic findings at CT colonography, and 33 (10.8%) had clinically important extracolonic findings. There were no significant differences between these two groups in the percentages of patients with extracolonic findings (P = .25; odds ratio, 1.25; 95% confidence interval: 0.85, 1.84) or clinically important extracolonic findings (P = .11; odds ratio, 1.83, 95% confidence interval: 0.89, 4.0). There was also no significant difference in mean age between patients in the high-risk and patients in the average-risk group (P = .26).
New versus Existing Clinically Important Findings
One hundred seventy-eight patients had more than one extracolonic finding. Of 596 extracolonic findings identified in the 500 patients, 50 (8.4%) were deemed clinically important, warranting further diagnostic evaluation. The remaining 546 findings were considered clinically unimportant, and no clinical follow-up was recommended for these findings. Of the 50 clinically important lesions, 14 (28%) had been diagnosed before CT colonography (Fig 1). These included four abdominal aortic aneurysms (mean size, 3.7 cm; range, 3.0–4.4 cm), three iliac artery aneurysms, an adrenal mass, three pulmonary nodules, one case of cirrhosis, and two cases of hydronephrosis, one of which was caused by metastatic bladder cancer.
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The patient with the liver abscess was asymptomatic at the time of CT colonography but soon thereafter developed abdominal pain and underwent follow-up CT with contrast enhancement. An interventional procedure was subsequently performed to place a percutaneous drain. Eight patients had lesions (two abdominal aortic aneurysms, two iliac aneurysms, two cases of cirrhosis, and one case of hydronephrosis) that required interval monitoring. The remaining patient with a finding that was confirmed to be important after follow-up studies and that required interval monitoring had a renal mass at CT colonography that was subsequently revealed to be renal cell carcinoma at abdominal and pelvic CT. Radical nephrectomy was planned but not performed because the patient had concurrent metastatic colorectal cancer.
Twelve of 35 patients (34%) had lesions that either were benign (one retroperitoneal cyst, one pulmonary granuloma, one fibrotic liver scar, two adrenal adenomas, two complex renal cysts, one unspecified renal cyst, one pulmonary nodule [Fig 5]) or were not seen at follow-up imaging (one adrenal lesion, two pulmonary nodules). Ten patients did not undergo documented follow-up for their new important lesions (Table 1).
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Estimated Costs of Subsequent Imaging Work-up
Evaluation of the cost of CT colonographic follow-up examinations was based on the national average Medicare reimbursement rates for 2003 (9) (Table 3). The total cost of all additional imaging performed for extracolonic findings at CT colonography was $14 058.43, with an average additional cost of $28.12 per CT colonographic examination. Total per-patient costs ranged from $0 to $1566. Considering only the patients who underwent follow-up, the average additional cost was $562 per CT colonographic examination. The confirmation of 13 important findings occurred at an expense of $4872, averaging $375 per CT colonographic examination (range, $0–$1043); this $4872 accounted for 34.7% of the total cost for follow-up studies. Another $9186 (65.3% of the total cost) was spent on the work-up of 12 lesions that were ultimately found to be benign, with the cost to these patients averaging $766 and ranging from $70 to $1566. There was no documented morbidity or mortality related to these additional imaging examinations.
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DISCUSSION |
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TOPABSTRACTINTRODUCTIONMATERIALS AND METHODSRESULTSDISCUSSIONReferences |
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The percentage of patients with extracolonic findings in our study (63.0% [315 of 500 patients]) is similar to that reported by Gluecker et al (69% [469 of 681 patients]) (8). Two smaller studies of extracolonic findings at CT colonography—one by Hara et al (7) and the other by Edwards et al (6)—yielded lower percentages: 41% (109 of 264 patients) and 15% (15 of 100 patients), respectively. From this literature it appears that the larger the study population, the greater the percentage of extracolonic findings detected. These differences may partially be due to the demographics of the patient cohorts studied, the skill level of the interpreting radiologists, or differences in CT colonographic technique. All three other investigations used doses of 70 mA and 120 kVp, whereas we used a slightly higher dose (120–150 mA and 120 kVp).
The use of a lower-dose technique for CT colonography may compromise the detection of extracolonic abnormalities, although this possibility requires further study and documentation. Decreasing the radiation dose generally results in increased image noise. Results of a recent pilot study (10), however, showed that postprocessing of low-dose images with noise reduction filters can compensate for increased noise. Therefore, it may eventually be possible to preserve image quality in the evaluation of extracolonic tissues at decreased radiation doses. Compromised image quality may occur with new ultra-low-dose CT colonography protocols with 30 mAs (11). We did not specifically evaluate differences in the detection of extracolonic findings between single– and multi–detector row helical CT. The decrease in collimation from 3.0 to 2.5 mm with multi–detector row CT was thought to have a negligible effect in improving the detection of extracolonic findings, but we did not directly address this question.
Overall, we found that 9.0% of patients (45 of 500) presenting for CT colonography had clinically important extracolonic findings. Similar results were obtained by Hara et al (11% [30 of 264 patients]) (7) and Gluecker et al (10% [71 of 681 patients]) (8). Edwards et al (6) did not stratify their extracolonic findings according to clinical importance. From their data, however, it appears that 8% of their patients (eight of 100) had findings that we would have considered important according to our imaging criteria. These percentages are impressive, given that a recent large trial in a screening population (2) revealed that the prevalence of polyps 10 mm or larger was 7% (82 of 1233 subjects) and the prevalence of colon cancer was 0.2% (two of 1233 subjects). The results of these studies indicate that there are as many clinically important extracolonic findings detected at CT colonography as there are large colorectal polyps and cancer in specific patient cohorts.
The published data regarding incidental extracolonic findings at CT colonography may be compared with those found for other nonenhanced CT studies, such as those performed to evaluate renal colic. Several investigations have examined the occurrence of incidental findings on CT scans ordered by emergency department physicians for the evaluation of nephrolithiasis. Messersmith et al (12) found that, of 321 patients (mean age, 43 years; 64% men [205 of 321]) in whom nonenhanced CT scans had been ordered by emergency department physicians for the evaluation of renal colic, 215 (67%) had nephrolithiasis, while 159 (49.5%) had either incidental findings or alternate diagnoses for their pain (eg, appendicitis, cholelithiasis, diverticulitis); 23% of patients (74 of 321) had incidental findings that were classified as moderate or severe. In a larger study by Katz et al (13), 10% of patients (101 of 1000) who underwent CT for the evaluation of renal colic received important new alternative diagnoses. The most recent study—that performed by Ahmad et al (14)—yielded similar results, with nonenhanced CT for the evaluation of renal colic revealing new important findings in 12% of patients (28 of 233) (14). Although there are differences between the patient cohorts with renal colic at presentation (these patients are usually younger and have pain and/or hematuria) and those presenting for colon evaluation (these patients are typically older than 50 years and may be symptomatic or asymptomatic), the percentages of patients with incidental findings and patients with important incidental findings appear to be similar in many studies. Incidental findings detected during CT evaluation for renal stones have been found to be useful in determining patient care, and this advantage has likely contributed to the replacement of excretory urography by nonenhanced CT.
Potential drawbacks of using CT colonography for colorectal cancer screening include the possibility of generating unnecessary work-up and increased patient morbidity in the process of evaluating extracolonic findings that are ultimately proved to be benign (15). In our study, however, only 2.4% of patients who underwent CT colonography (12 of 500) underwent follow-up imaging for findings that were later shown to be benign. None of these 12 patients suffered any morbidity or mortality as a direct result of the follow-up imaging.
The cost in our study of $28.12 per patient for additional work-up of extracolonic findings at CT colonography is consistent with the calculated costs from prior studies. Gluecker et al (8) found the average added cost per CT colonographic examination to be $34.33, while Hara et al (7) reported an added cost of $28 per patient for additional imaging studies. These costs were all based on Medicare reimbursement values. Although not all patients presenting for CT colonography qualify for Medicare, these values are a useful benchmark for cost estimation, given that many private insurers base their reimbursements on Medicare levels. Ultimately, 34.7% of the total costs in our study ($4872 of $14 058.43) contributed directly to the diagnosis of 13 clinically important extracolonic lesions that necessitated surgery or routine monitoring. Given the relatively small additional cost of $28.12 per patient and given that a substantial portion of the total cost was directed toward diagnosing lesions that were truly important, the work-up of abnormal extracolonic findings seems economically feasible.
The percentage of important extracolonic findings that were missed in our study was very low (1.6% [eight of 500 findings]). This percentage is comparable to the miss rates reported in the literature for what we would consider important extracolonic findings: 2.3% (six of 264 findings) for Hara et al (7) and 3.4% (23 of 681 findings) for Gluecker et al (8). All of these percentages are within the range of error that has been reported in the literature for general abdominal and pelvic CT with contrast enhancement.
A study of 694 consecutive abdominal and pelvic CT scans by Bechtold et al (16) revealed an overall error rate of 7.6% (53 of 694 findings) among five faculty radiologists, with an error rate of 2.7% (19 of 694 findings) for clinically important findings. Individual faculty overall error rates ranged from 3.6% to 16.1%. The conclusion of Bechtold et al was that the primary determinant of error rates in body CT is the skill of the radiologist interpreting the study. Although this finding may seem intuitive, recent preliminary work (17) suggests that nonradiologists can be trained to interpret CT colonographic findings for colonic lesions. However, the study by Bechtold et al (16) underscores the need for experienced radiologists to read CT colonographic studies so that important extracolonic findings are not missed.
We believe that a strength of our study was the inclusion of both high-risk and average-risk patients. The study by Gluecker et al (8) was not conducted in a true average-risk patient population and included high-risk patients with anemia, patients with a positive family history, and patients with a personal history of polyps or colorectal cancer. Our findings demonstrate that there is no significant difference in the percentage of extracolonic findings between an average-risk patient cohort and a high-risk group. Therefore, the presence of risk factors for colorectal cancer does not itself appear to lead to an increase in unrelated extracolonic disease that is detected with nonenhanced CT colonography.
Certain limitations were intrinsic to our study. All of the patients were male because they were recruited at a veterans' hospital. The percentages of extracolonic findings we report may not be applicable to a population of both men and women. All of the important findings and almost all of the unimportant findings that we documented, however, can be seen commonly in both men and women. For example, in our study, a sex-neutral lesion such as an incidental adrenal mass was present in 1.0% of patients (five of 500). This prevalence falls within the reported range of 0.5%–2% for incidental adrenal CT findings in the general population and is close to the mean autopsy prevalence of 2.3% for incidental adrenal masses (18). The only male-specific pathologic process found in our study was prostatomegaly. Potentially, however, we should also be able to identify bone metastases or local invasion into the seminal vesicle or bladder due to prostate cancer. Several sex-specific pathologic processes may be identified in women with nonenhanced abdominal CT, such as ovarian neoplasms, uterine masses, and breast cancer metastases. According to results of the three other published studies (6,7,8) of extracolonic findings at CT colonography, the most common female-specific findings were uterine leiomyomas and ovarian cysts. The lack of female patients in our study may account for some differences in the percentages of extracolonic findings; however, these may be offset by the percentages of male-specific pathologic processes, such as those due to prostate disease. The percentage of extracolonic findings in our study (63.0%) was similar to that found by Gluecker et al (69%) (8), whose study included women.
Another limitation of our study was the percentage of patients who were unavailable for follow-up. Ten of the 35 patients with important extracolonic findings at CT colonography underwent no documented follow-up. Some of them may have moved or undergone follow-up at outside institutions. Therefore, it is unknown whether their findings were ultimately proved to be benign or important.
Our CT colonographic technique did not include the use of intravenous contrast material. Intravenous contrast material is used widely in most routine CT scans of the abdomen and pelvis and should increase the detection of abdominal and pelvic disease. To our knowledge, only one small study (19) to date has compared the detection of polyps at CT colonography performed with intravenous contrast material with the detection at CT colonography performed without contrast material, and this study did not address extracolonic findings. Additional investigation is needed to examine the possible benefits of intravenous contrast material at CT colonography in the detection of colonic and extracolonic lesions.
In conclusion, we have demonstrated in our large series that a substantial number of both average- and high-risk patients presenting for CT colonography have clinically important extracolonic findings that affect patient care. The cost for work-up of these findings was low, and no increase in morbidity or mortality resulted from the additional work-up. Therefore, it is important for the ordering physician, the radiologist, and the patient to be aware of the potential benefits of finding extracolonic lesions during CT colonography.
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FOOTNOTES |
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Author contributions: Guarantor of integrity of entire study, J.Y.; study concepts and design, all authors; literature research, all authors; clinical studies, J.Y.; data acquisition, J.Y., N.N.K.; data analysis/interpretation, all authors; statistical analysis, all authors; manuscript preparation and editing, J.Y., N.N.K., R.H.; manuscript definition of intellectual content, J.Y., N.N.K.; manuscript revision/review and final version approval, all authors
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TOPABSTRACTINTRODUCTIONMATERIALS AND METHODSRESULTSDISCUSSIONReferences |
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