The evaluation of abnormal findings on a screening mammogram in an asymptomatic woman has been well characterized and usually begins with diagnostic mammography to confirm the presence of a persistent, abnormal finding and to characterize the degree of suspicion for carcinoma. As outlined in Chapter 12, the majority of abnormalities identified on a screening mammogram are resolved with a diagnostic work-up and only about 10% will require a tissue diagnosis. Ultrasound of the lesion is an essential part of the evaluation as it reliably allows the identification of simple cysts that require no further intervention. Even in the case of calcifications, ultrasonography is useful to determine if there is an associated mass lesion. Visualization of the calcifications with ultrasound allows an ultrasound-guided biopsy to be performed, avoiding exposure to ionizing radiation and the need for breast compression during the biopsy procedure.

Although the characteristics of benign and malignant lesions differ on both mammography and ultrasonography, the currently accepted threshold for considering a biopsy in the United States is a probability of malignancy of 3% to 4% or more (1). It was initially hoped that magnetic resonance imaging (MRI) would reliably differentiate benign and malignant abnormalities, reducing the number of biopsies generated by screening programs. Studies have demonstrated that MRI lacks the sensitivity and specificity to substitute for a histologic diagnosis and should not be obtained for this purpose. In a multicenter trial of 821 women with clinical, mammographic, or ultrasound findings suspicious enough to warrant biopsy, Bluemke ...