Radiology: Virtual colonoscopy safe, beneficial for patients with metallic stents

The use of CT colonography is useful—and safe—for a preoperative exam of the proximal colon in patients who have been treated with metallic stents due to colon obstruction caused by colorectal cancer, according to a study published in the March issue of Radiology.

According to Eun-Young Cha, MD, department of radiology at the University of Ulsan College of Medicine, Asan Medical Center in Seoul, and colleagues, a complete preoperative exam of the entire colon of patients with colorectal cancer is important because synchronous cancers are found in 1.5 to 9 percent of these patients. A complete evaluation of the colon is not always feasible because of the problem of advancing a colonoscope past a cancerous lesion.

According to the authors, while the use of metallic stents are widely used in patients with acute severe colonic obstruction caused by cancer, only one previous study has shown that a colonoscopy can be successfully performed in  those patients. Consequently, the authors say, ”colonoscopy involving passage through a metallic colonic stent is probably not routinely performed in many institutions.” Therefore, “evaluating the feasibility of CT colonography as a method to examine the proximal colon after metallic stent placement is a clinically relevant issue.”

Between January 2006 and January 2009, 51 patients who had been successfully treated with self-expandable metallic colonic stents—and had shown no clinical evidence of stent-related complications such as a perforation of the colon—were referred for CT colonography for preoperative evaluation of the proximal colon.

One woman was denied CT colonography because peritoneal free air was detected before colon insufflations. The remaining 50 patients consisted of 34 men (mean age 60) and 16 women (mean age 55). Images were interpreted prospectively by one of two radiologists, both of whom at the beginning of the study period had interpreted at least 100 CT colonography studies.

Exam quality was inadequate for 6 percent for the patients. The researchers found that per-lesion and per-patient sensitivities of CT colonography for lesions 6 mm or larger  in diameter in the colon proximal to the stent were 85.7 percent and 90 percent respectively and CT colonography depicted all synchronous cancers (two lesions) and advanced adenomas (five lesions). Per patient specificity for lesions 6 mm and larger in the proximal colon was 85 percent.

According to the authors, CT colonography did not generate any false diagnoses of synchronous cancers or result in false positive findings that changed any surgical plans for patients. In addition, there were no instances of the procedure resulting in stent dislodgement or displacement or perforation of the colon.

Consequently, the authors concluded that CT colonography can be used safely and effectively to preoperatively examine the proximal colon of patients with metallic stent placements.