Pediatric CT colonography sheds light on screening

Researchers have generally discarded the notion of virtual colonoscopy screening in children because colonic pathology in pediatric patients is rare and radiation exposure is a concern. A study from Argentina, however, has found that pediatric patients with suspected polypoid lesions of the colon can safely undergo diagnostic low-dose CT colonography. The low-dose protocol could have implications for adult colon cancer screening as well.

"Although our standard protocol for adults entails 100 mAs or more, we think that in the proper clinical context we could utilize doses of 50 mAs or less," said principal investigator Dr. Carlos Maria Capunay, a radiologist at the Diagnostico Maipu center in Buenos Aires.

Capunay and colleagues enrolled 100 pediatric patients presenting with rectal bleeding. The researchers sought to detect elevated lesions of the colon using both virtual and optical colonoscopy. They found that CT colonography could accurately detect those lesions with a radiation dose between 15 mAs and 30 mAs and in less time than optical colonoscopy.

The group published their findings on the Web site of the European Journal of Radiology in July. Their study validates a similar report on eight pediatric patients performed by Boston researchers and published a few months earlier (Pediatr Radiol 2005;35[5]:518-524).

The majority of children in the Capunay study had benign polyps, which limits virtual colonoscopy's utility in this setting. Comparable CT colonography screening in adults requires additional optical colonoscopy for polypectomy in less than 10% of cases, said Dr. Perry J. Pickhardt, an associate professor of radiology at the University of Wisconsin, Madison.

The choice between virtual and standard colonoscopy as a diagnostic test is complicated. However, the study supports the notion that CT colonography could replace barium enema for colorectal lesions, and, unlike colonoscopy, it does not need sedation, said Dr. Joel G. Fletcher, an assistant professor of radiology at the Mayo Clinic in Rochester, MN.

Lower doses may be possible, as the MSCT protocol described in Capunay's study proves. But a lower dose must be weighed against the possibility of degrading the quality of the 3D endoluminal images and the overall exam performance, said Dr. C. Daniel Johnson, principal investigator for the ongoing American College of Radiology Imaging Network trial on virtual colonoscopy. Such studies could probably be performed most efficiently with automated dose techniques available on new CT scanners.

"A specific study in an adult population would be needed," he said.