To evaluate the rates of inter- and intraobserver agreement of the BI-RADS US lexicon.

Two radiologists reviewed 60 sonograms of solid breast masses to evaluate interobserver agreement. After four weeks, the radiologists reinterpreted the series to evaluate the intraobserver agreement. The radiologists described shape, orientation, margin, lesion boundary, echo pattern, posterior acoustic features and microcalcifications. Final assessment categories and management plans were suggested for each case. The rates of inter- and intraobserver agreements were measured by the use of kappa statistics.

Interobserver agreement ranged from the highest for orientation (κ=0.65) and shape (κ=0.61) to the lowest for posterior acoustic features (κ=0.42). For the final assessment categories (κ=0.46) and management (κ=0.49), interobserver agreements were moderate. Intraobserver agreement ranged from the highest for microcalcifications in mass (κ=0.90, 0.82) and orientation (κ=0.87, 0.83) and the lowest for echo patterns (κ=0.62, 0.57) and posterior acoustic features (κ=0.59, 0.65). In the final assessment category and management, intraobserver agreements were substantial or nearly complete (κ=0.65-0.83).

There were variable ranged inter- and intraobserver agreements in the description of the BI-RADS US lexicon of solid breast masses. Among them, margin and lesion boundary showed lower agreements. A modification of the BI-RADS US lexicon with more detailed guidelines, followed by continuous education, are suggested.