Magnetic resonance colonography identified asymptomatic adults with adenomas of 6 mm or larger and advanced adenomas with sensitivities of 78.4% and 75%, respectively.
"If primary screening by colonoscopy is not performed, MR colonography appears to be a better option than a one-time fecal occult blood test" for detecting high-risk lesions, without the radiation associated with computed tomography, reported Dr. Anno Graser and his colleagues in the April 1 issue of Gastroenterology (doi: 10.1053/j.gastro.2012.12.041).
Dr. Graser of the University of Munich and his colleagues looked at 286 asymptomatic adults aged 50 years or older with an average risk of colorectal cancer and asymptomatic adults aged 40 years or older with a family history of colorectal cancer (175 men; mean age, 59 years).
Patients were excluded if they had any prior colonoscopy, symptoms or history of bowel disease, significant weight loss, body weight greater than 150 kg, relevant cardiovascular or pulmonary comorbidity, or contraindications to MR scanning.
All patients underwent fecal occult blood testing prior to bowel preparation, and then underwent both colonoscopy and MR colonography on the same day.
Overall, colonoscopy detected 281 luminal lesions, including one adenocarcinoma of the rectum, one squamous cell carcinoma of the anal canal, and 133 adenomas in 85 patients, including 20 advanced adenomas in 17 patients. There were also 129 hyperplastic polyps detected on colonoscopy, as well as 17 other benign lesions.
MR colonography, on the other hand, detected the two cancers, as well as 43 (32.3%) adenomas, including 29 (78.4%) adenomas of 6 mm or greater.
MR colonography also detected 15 (75%) advanced adenomas and 11 (8.5%) hyperplastic polyps.
"There were no complications in either the MR colonographies or the colonoscopies," wrote the authors.
In contrast, fecal occult blood testing found just 3 of 30 patients (10%) with adenomas of 6 mm or greater and 3 of 17 patients (17.6%) with advanced neoplasia.
MR colonography also identified several "potentially important extracolonic findings" in eight (2.8%) patients: three patients with renal masses; two with bulky retroperitoneal lymphadenopathy "representing manifestations of a newly diagnosed diffuse large-cell lymphoma and a chronic lymphatic leukemia, respectively"; one with a serous cystadenoma of the pancreas; and two with aortic aneurysms greater than 5 cm, the authors reported.
In terms of specificity, for adenomas 6 mm or larger, the specificity was 96.9% for colonoscopy, 95.3% for MR colonography, and 91.8% for fecal occult blood testing.
Similarly, for advanced neoplasia the figures were 48.5%, 81.0%, and 92.2% for colonoscopy, MR colonography, and fecal occult blood testing, respectively.
The authors also compared MR colonography in their study to previous studies of CT colonography, which has been shown to have a sensitivity for advanced neoplasia of 96% (Gut 2009;58:241-8).
"Still, the major advantage of MR colonography over CT colonography is that it does not apply ionizing radiation," wrote the authors.
There are several limitations to the technique, the authors said. For one, MR colonography requires gadolinium-based intravenous contrast. However, except for patients with impaired renal function, this is usually well tolerated.
MR colonography has a limited sensitivity for lesions of 5 mm or less, because of the technique’s limited spatial resolution and lack of significant enhancement of diminutive polyps.
However, "as these lesions only carry a low risk of malignancy, this limitation of MR colonography may not impair its potential use as a screening tool."
Finally, "in the light of cost-effectiveness discussions, MR colonography as a relatively expensive test has to be weighed carefully against the cost of colonoscopy," wrote the researchers.
The authors declared that they had no relevant financial conflicts and that the study had no outside funding.