Extracolonic findings on CTC represent mixed bag

Indeterminate renal masses detected on CT colonography (CTC) warrant follow-up as they have a one-in-five chance of malignancy, according a review of research of extracolonic findings on CTC published in the June issue of Academic Radiology.

However, indeterminate masses detected on CTC in other organs—the lung, liver, pancreas and ovary—have high false positive rates and warrant more conservative clinical follow-up, according to Karen J. Wernli, PhD, of the Group Health Research Institute in Seattle, and colleagues.

“Indeterminate renal masses were associated with a high [positive predictive value (PPV)] and lowest [false positive rate (FPR)], suggesting that CT colonography might provide useful clinical information about incident renal tumors, particularly in the nonscreening population,” wrote the authors.

Since being developed in 1994, CTC has been an attractive alternative to optical colonoscopy for colon cancer screening. It also allows the opportunity to evaluate the abdomen and pelvis for extracolonic findings, though guidelines for follow-up of these findings are not clear.

Wernli and colleagues searched PubMed for English-language studies that dealt with extracolonic CTC findings in five organs published from Jan. 1, 1994, through Dec. 31, 2010. A total of 24 publications were eventually deemed eligible for review.

According to the literature, indeterminate renal masses on CTC had a 20.5 percent median PPV and a pooled FPR of 1.3 percent. In contrast, indeterminate masses of the liver, pancreas and ovary were associated with PPVs ranging from 0 percent to 3.8 percent, “suggesting that these lesions could be followed clinically with or without further imaging,” wrote the authors. Results were similar in studies of both screening and nonscreening populations.

The probability of a false positive result from an extracolonic finding was 46 per 1,000 for men and 68 per 1,000 for women. FPR was highest for indeterminate masses of the ovary at 2.2 percent. The majority of ovarian lesions that were benign on resection were cystic ovarian lesions corresponding to cysts, benign mucinous or serous cystadenomas, cystadenofibromas, mature teratomas, or abscesses, according to the authors.

“Even very low FPRs can drive multiple subsequent tests that result in relatively few detected cancers,” they wrote. “Patient distress and inconvenience associated with extracolonic findings, the impact of extracolonic findings on the cost-effectiveness of CT colonography, and methods for prioritizing effective follow-up of extracolonic findings all deserve further study.”

The authors also noted that further study and the creation of clear guidelines require more standardized terminology, as the studies in the review used a wide range of definitions. For example, some studies described indeterminate renal masses as including complex cystic masses, while others did not.

In a guest editorial, Jianhua Yao, PhD, from National Institutes of Health, Bethesda, Md., and Joseph E. Burns, MD, PhD, of the University of California, Irvine School of Medicine, wrote that Wernli et al’s analysis suggests an emphasis on follow-up of indeterminate renal masses, while a more conservative approach to cystic ovarian lesions. “The meta-analysis results will help clinicians better understand the likelihood of detecting extracolonic findings on CTC in different patient populations and the chances that the findings may correspond to false-positive diagnoses.”

Yao and Burns noted, however, that CTC scanning protocols do have a number of limitations. They are often performed with low radiation doses and without contrast, making them suboptimal for diagnosing extracolonic lesions compared with standard diagnostic CT of the abdomen and pelvis.

“It is important to stress that CTC at today's level of technological development is by no means a replacement for standard diagnostic CT of the abdomen and pelvis in detecting significant extracolonic pathologies,” wrote Yao and Burns. “Extracolonic findings on CTC at the current level of systems development are typically viewed as inconclusive and usually require further examination for definitive characterization.”