Research study validates use of BI-RADS in breast MRI

BI-RADS descriptors for breast MRI can help determine the risk of malignancy for lesions detected only on MRI, according to a study from the University of Washington. The findings offer a scientific model that may predict malignancy in otherwise occult lesions.

Radiologists are already using the American College of Radiology's BI-RADS descriptors for breast MRI, but this study evaluates how well the lexicon correlates with malignancy, said Dr. Chris Comstock, director of breast imaging at the University of California, San Diego.

Until now, researchers knew little about which lesion characteristics on MRI suggested malignancy compared with mammography, according to Dr. Robert L. Gutierrez, an assistant professor of radiology at the University of Washington and lead author of the study. Methods of assessing breast MRI findings vary across practices and have been somewhat intuitive, he said.

Gutierrez and colleagues found that for masses, size, irregular or spiculated margins, and heterogeneous internal enhancement are the BI-RADS lexicon descriptors associated with malignancy (AJR 2009;193:994-1000). Out of 258 suspicious lesions, masses 1 cm or greater with heterogeneous enhancement and irregular margins had a 68% probability of malignancy.

Smaller masses with smooth margins and homogeneous enhancement had the lowest probability of malignancy (3%). BI-RADS descriptors and size were not significant predictors of malignancy for nonmasslike enhancement.

The researchers captured data from consecutive breast MRI exams at their institution for 30 months ending in June 2005.

Radiologists run across masses with smooth margins and homogeneous enhancements frequently, according to Dr. Cherie Kuzmiak, an associate professor of radiology at the Lineberger Comprehensive Cancer Center at the University of North Carolina-Chapel Hill.

"Right now we struggle with if you have a finding that's probably benign, where's the line in the sand to dump it into the category of ‘probably benign'?" she said.

This research lays the groundwork for answering that question but multisite studies are needed to expound on the results, Kuzmiak said.

"Most radiologists have little difficulty identifying and managing clearly suspicious breast MRI findings," Gutierrez said. "It is the lesions that are less suspicious that pose a diagnostic problem."