Most people -- even those at average risk for colorectal cancer -- have extracolonic findings at virtual colonoscopy, including significant numbers with clinically important conditions, according to a new study from the Veterans Affairs Medical Center in San Francisco.
One of the largest peer-reviewed efforts of its kind to date, the Radiology study sheds new light on VC's ability to find such abnormalities while there is often still time to treat them successfully.
"Detection of potentially serious asymptomatic lesions at an early and curable stage can prompt meaningful medical follow-up or surgical intervention, ultimately leading to decreased morbidity and mortality," wrote Dr. Judy Yee and colleagues from the departments of radiology at the VA Medical Center and the University of California School of Medicine in San Francisco. "Many incidental lesions are benign, however, and efforts to characterize them further may lead to additional costs, patient anxiety, and iatrogenic injury. It is therefore important to examine the nature of extracolonic findings in terms of their clinical importance, follow-up cost, and effect on subsequent patient care"(Radiology, August 1, 2005, Vol. 236:2, pp. 519-526).
The study population of male military veterans (mean age 62.5 years) included those at average risk (n = 194, 38.8%) and high risk (n = 306, 61.2%) of colorectal cancer. Subjects deemed to be at high risk presented with hematochezia, heme-positive stools, iron-deficiency anemia, and/or a family or personal history of colorectal polyps or cancer, the researchers wrote.
Three peer-reviewed studies of extracolonic abnormalities have been published previously, including two that analyzed the cost of examining patients at high risk of colorectal cancer due to personal or family history of colorectal cancer or polyps, or new onset of anemia, the authors wrote. "The purpose of our study was to evaluate prospectively the prevalence of incidental extracolonic findings at CT colonography and estimate the cost of imaging workup in both high- and average-risk male patients, the team explained.
Following a standard bowel-cleansing regimen that included a magnesium citrate and/or polyethylene glycol solution, a rectal tube was inserted and either manual insufflation (the first 336 patients) or automated CO2 insufflation (PROTOCO2L, E-Z-EM, Lake Success, NY) in the subsequent 164 patients was used to insufflate the colon to maximum patient tolerance. Scout CT images were acquired to assess the adequacy of distension, and additional insufflation was performed if necessary, the authors wrote.
All patients underwent prone and supine scanning on either a single-detector HiSpeed CT/i scanner (GE Healthcare, Chalfont St. Giles, U.K.) or an eight-detector scanner (GE LightSpeed Plus/Ultra). Single-detector scans (n = 418) were acquired at 3-mm collimation, 1.5-mm reconstruction interval, pitch 1.5-2.0, 120 kVp, and 150 mAs. Eight-detector scans (n = 82) were acquired at 2.5-mm collimation, 1.25-mm reconstruction interval, pitch 0.875, 120 kVp, and 120 mAs, according to the authors.
The data were sent to either a GE Advantage Workstation or an E-Z-EM Innerview workstation, and examined by radiologists who were blinded to the same-day colonoscopy results used as a reference standard.
All findings were categorized as clinically important or clinically unimportant, and the patients stratified at average or high risk for colorectal cancer following a chart review.
In all, 315/500 patients (63%) were found to have extracolonic abnormalities at virtual colonoscopy, including clinically important findings in 45/500 (14.3%). Of these 45 patients, 35 (78%) had important findings that had not been previously identified, Yee and colleagues wrote.
Interestingly, there was no significant difference in the incidence of extracolonic findings between subjects at average and high risk. Extracolonic findings were seen in 116/194 (59.8%) of patients at average risk, including 12 (6.2%) clinically important findings. Among the 306 high-risk patients, 199 (65%) had extracolonic findings, 33 (10.8%) of which were clinically important.
Only the 50 clinically important findings were followed up, including 14 (28%) that had been diagnosed previously. That left 36 important findings in 35 patients that were considered new, including eight renal masses, seven pulmonary nodules, four abdominal aortic aneurysms (mean size 3.7 cm, range 3.0-4.4 cm), four iliac artery aneurysms, three indeterminate adrenal masses, three suspicious liver lesions, two cases of hydronephrosis, two indeterminate retroperitoneal masses, a suspicious bone lesion, and single cases of cirrhosis, gallbladder wall thickening, and lymphadenopathy.
After follow-up imaging of these 35 patients, 13/35 findings were confirmed to be important, and five patients underwent surgical treatment (for renal cell carcinoma, a liver abscess, an abdominal aortic aneurysm, a common bile duct stone, and a left internal iliac artery aneurysm).
The most common unimportant findings (545 in 306 patients) were renal cysts, hepatic cysts or hemangiomas hiatal hernias, granulomatous disease, cholelithiasis, and renal calculi, according to the report. Findings were missed at VC in 15/500 patients but found subsequently, including eight clinically important lesions, the authors noted.
According to 2003 Medicare reimbursement rates, a total of $14,058 was spent following up findings deemed important, an additional cost of $28.12 per virtual colonoscopy exam.
Considering the relatively small additional cost per patient, and the fact that additional workup was reserved for lesions deemed truly important, the cost seems economically feasible, the group stated. (The average additional cost per VC study was $34.33 for Gleucker et al, and $28 for Hara et al.)
Moreover, "The percentage of patients with extracolonic findings in our study (63.0% [315 of 500 patients]) is similar to that reported by Gleucker et al (69% [469 of 681 patients])," the team noted. "Two smaller studies of extracolonic findings -- one by Hara et al and the other by Edwards et al -- yielded lower percentages: 41% (109 of 264 patients) and 15% (15 of 100 patients), respectively. 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 mAs and 120 kVp, whereas we used a slightly higher dose (120-150 mAs and 120 kVp)."
The published data in virtual colonoscopy are comparable to those found in other nonenhanced CT studies such as those performed to evaluate renal colic, they stated.
The use of lower-dose protocols may compromise detection of extracolonic abnormalities, as it increases image noise. However, they cautioned, this potential effect has not been proved conclusively, and requires further investigation. They noted that a small pilot study by Kalra et al found that the use of noise reduction filters can compensate for the higher noise levels (Radiology, July 2003, Vol. 228:1, pp. 251-256).
Further study is needed to determine whether the use of intravenous contrast agents would aid in detecting extracolonic abnormalities, the team wrote.
The principal limitation of the present study was its lack of female patients, which eliminated the ability to evaluate common findings in women such as ovarian neoplasms, uterine masses, and breast cancer metastases, the researchers noted. In addition, 10/35 patients with findings deemed important were lost to follow-up.
"We have demonstrated in our large series that a substantial number of both average and high-risk patients presenting for CT colonography (virtual colonoscopy) have clinically important extracolonic findings that affect patient care," the authors concluded. Considering the low cost of imaging follow-up, they added, "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."
By Eric Barnes
AuntMinnie.com staff writer
July 28, 2005
Related Reading
VC with contrast finds more extracolonic trouble, April 11, 2005
Panoply of VC studies yields significant extracolonic findings, March 23, 2005
Diagnostic, screening VC comparable in extracolonic disease detection, December 6, 2004
Even low-dose VC yields extracolonic findings, September 21, 2004
In VC, extracolonic findings offer valuable information at little extra cost, June 3, 2002
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