Extracolonic findings from CT colonography can uncover serious disease

A lifesaver for some and source of wasted diagnostic effort for others, incidental findings from CT colonography present opportunities and risks for patients and imaging practitioners.

The Centers for Medicare and Medicaid Services pointed to unaddressed questions about extracolonic findings when it ruled May 12 against expanding Medicare coverage to pay for virtual CT colon screening. Dr. Perry Pickhardt, an associate professor of radiology at the University of Wisconsin, supplied answers during a Wednesday morning session at the 2009 International Symposium on Multidetector-Row CT.

"Extracolonic evaluations at CTC are unavoidable, but they are also diagnostically limited," Pickhardt said.

Findings outside of the colon during a screening exam appear in about 10% of the procedures. The lack of incidental findings should be reassuring for the nine of 10 patients issued a clean bill of health, he said.

Early detection can have major medical implications for a few individuals with unsuspected cancers or vascular disease, but they can also stir unnecessary anxiety for patients and waste time and money for providers and payers. Some physicians are concerned enough about extracolonic findings to refuse to refer patients for CT colonography, Pickhardt said.

"They fear this workup cascade," he said. "That's what we are trying to avoid constantly."

Potentially significant extracolonic findings appeared in 8.6% of the first 2195 colonography screenings performed at the University of Wisconsin Medical Center in Madison. Further workups were recommended for 7.2% of the cases overall, and more studies, usually involving CT or ultrasound, were performed in 6.1% of the cases overall.

Relevant new diagnoses were rendered for 2.6% of those who received screening. The cost of the additional imaging workup for the screened population broke down to $31.02 per case, he said.

Additional data have been compiled from 10,286 asymptomatic adults who received CT colonography in a collaboration between Bethesda Naval Hospital in Bethesda, MD, and the University of Wisconsin. From this experience, 38 proven cancers were diagnosed from extracolonic findings. Such serious disease appeared once in about every 300 procedures, Pickhardt said.

Renal cell carcinoma represents the cancer diagnosed most often from the incidental findings. Lung cancer and lymphoma also figure prominently. In combination, they outnumbered the 21 unsuspected invasive colorectal cancers identified during colonography.

Follow-up studies have led to the discovery of asympotomatic abdominal aortic aneurysms requiring urgent workup and repair, obstructing urethral calculus with hydronephrosis, polycystic renal disease, and hemochromatosis.

"In the end, if we handle these responsibly, I truly believe there is a net gain—if we don't try to overwork the things that don't matter in the end." Pickhardt said.