Virtual colonoscopy preferred for surveillance follow-up

Jul 9, 2009

Patients referred for polyp surveillance after virtual colonoscopy (also known as CT colonography or CTC) are more likely to opt for another VC exam at follow-up, Italian researchers report. But patients want their follow-up scans sooner rather than later.

Polyp surveillance is the practice of allowing patients with clinically insignificant lesions at CTC to forego immediate polypectomy in favor of waiting two to three years to see if the lesions have grown. If they have not, then the risk and inconvenience of colonoscopy and polypectomy can potentially be avoided.

Data on the natural history of polyps suggest that surveillance is safe because so few diminutive lesions progress to advanced adenomas by the time patients are re-examined. However, the practice remains controversial due to a small risk that a diminutive lesion could harbor advanced pathology.

The CT Colonography Reporting and Data System (C-RADS) (Radiology, July 2005, Vol. 236:1, pp. 3-9) proposes surveillance for so-called category 2 cases, defined as the presence of one or two diminutive polyps 6-9 mm in size.

According to the proposed method, C1 means no significant polyp; C2 means one or two 6- to 9-mm polyps; C3 denotes one or two polyps > 10 mm or more than three 6- to 9-mm polyps; and C4 means a mass.

"Usually a follow-up of three years is suggested in these category 2 cases ... based on the well-known pathogenesis of colorectal cancers which arise from adenomatous polyps within up to 10 years," said Dr. Francesca Turini at the 2009 European Congress of Radiology (ECR).

"The prevalence of high-grade dysplasia or villous histology in different-size polyps in the 6- to 9-mm category is quite low," she said, referring to a study by Kim, Pickhardt, and colleagues (American Journal of Roentgenology, April 2007, Vol. 188:4, pp. 940-944).

Surveillance of C-RADS 2 cases appears safe in early results, but its value is disputed by some CTC critics, who see inadequate evidence supporting the methodology.

"Repeating CT colonography every three years to monitor a 6- to 9-mm polyp seems disingenuous and risky with regard to colorectal cancer development (one third of T1 cancers are ≤ 1 cm) and patients lost to follow-up, not to mention the cost and radiation exposure," wrote gastroenterologist Dr. Douglas Rex in 2007. "Radiologists should ask whether this policy is driven by the economic need of restricting polypectomy referrals to keep CT colonography viable from a cost perspective. Radiologists might also remember the enormous medicolegal risk of delaying the diagnosis of [colorectal cancer] when reviewing this policy," (Mayo Clinic Proceedings, June 2008, Vol. 82:6, pp. 662-664).

VC advocates have countered that accumulating data on the natural history of polyps shows the practice to be safe, as well as cost-effective. On the latter point, a 2008 study by Pickhardt and colleagues analyzed the cost-effectiveness of clinical management of 6- to 9-mm polyps (AJR, November 2008, Vol. 191:5, pp. 1509-1516).

"Comparing three-year CTC surveillance versus immediate colonoscopy, the costs are much higher in cases of immediate colonoscopy," Turini said of the 2008 Pickhardt study. Nevertheless, follow-up of less than three years would be expected to reduce the cost-effectiveness in the model.

What about patient preference?

While researchers offer different perspectives, the Italian researchers decided to assess patient preference in the study they presented at the ECR meeting. The also wanted to investigate the optimal timing interval for follow-up with C-RADS 2 cases, Turini said.

Turini, along with Dr. Emanuele Neri and colleagues at the University of Pisa in Italy, retrospectively reviewed 673 patients who underwent CTC between 2005 and 2008. Twenty percent of the cases (n = 133) revealed fewer than three polyps 6-9 mm, and were therefore classified as C-RADS 2.

In all C-RADS 1 cases, a five-year follow-up interval was suggested. In the C-RADS 2 cases, the investigators recommended follow-up of one to three years by CTC or colonoscopy, while C-RADS 3 and 4 patients were immediately referred to colonoscopy. The researchers estimated the number of C-RADS 2 patients followed up with CTC or colonoscopy, and the patient's preferred follow-up time interval.

Five patients were lost to follow-up over the three-year period and couldn't be contacted, Turini said.

Of the remaining 133 C-RADS 2 patients referred for surveillance, 114 (86%) accepted follow-up and 74 (56%) chose CTC for their repeat exam, at a maximum 18 months after the original scan. Forty-four percent (n = 58) decided on colonoscopy, 13% of whom (n = 17) wanted it immediately, and again with colonoscopy, no patient opted to wait more than 18 months until the next exam.

One asymptomatic woman, in whom CTC revealed a 7-mm polyp in the cecum and an 8-mm polyp in the ascending colon, was intolerant to colonoscopy but nevertheless opted for invasive colonoscopy at 12 months. At histology, one polyp was found to have low-grade dysplasia, Turini said.

A 62-year-old asymptomatic man with a single sessile polyp measuring 6.9 mm in the cecum followed a more complicated diagnostic pathway. He chose CTC follow-up at 18 months, which measured the polyp at 7 mm. He decided to return 10 months later for CTC, which measured the lesion at 7.4 mm, at which point he opted for colonoscopy to remove the lesion, which was shown to have high-grade dysplasia at histology.

Most patients classified as C-RADS 2 preferred to repeat the colon test by means of CTC, but all patients accepted a maximum 18 months of follow-up, even when follow-up at three years was proposed, Turini said.

Turini said that all patients were carefully instructed about the potential risks and benefits of CTC surveillance versus immediate polypectomy, and about the prevalence of cancers, adenomas, and high-grade dysplasia that allow safe surveillance for C-RADS 2 cases.

"We tried to explain that the three-year follow-up can prevent the risk of having cancer, but probably the real reason patients did not accept a 36-month follow-up but preferred follow-up within 18 months [was] because they are afraid of ... an invasive cancer or high-grade dysplasia hiding in the lesion."

By Eric Barnes
AuntMinnie.com staff writer
July 10, 2009

Study warns VC could leave high-risk polyps unresected, January 14, 2009

Model finds small polyp surveillance safe, cost-effective, November 4, 2008

Model finds polyp surveillance effective for cancer prevention, January 21, 2008

VC holds up against back-to-back colonoscopies, July 19, 2005