Ultrasound of the breast is the most common adjunct modality used for breast evaluation. It employs no ionizing radiation, does not require intravenous contrast material, and is well tolerated and widely available. The breast is an ideal subject for ultrasound imaging because it is superficially located and easily accessible (without overlying structures) for interventional procedures. In addition, the sensitivity of ultrasound is not affected by the type of breast tissue. Optimal results depend on having adequate equipment with high frequency transducers and are highly operator-dependent. Reliability varies according to the operator’s expertise which determines the reproducibility of images and rates of false-negative and false-positive results.
The indications for breast ultrasound include:
(1) evaluation of a palpable or mammographically visualized mass;
(2) guidance for interventional procedures, for radiation planning, the initial imaging technique for the young (under 30 years of age), in pregnant, or lactating women;
(3) for the evaluation of implants, especially silicone.
Additionally, ultrasound has been very useful for the second-look targeted ultrasound after a suspicious lesion is seen on the MRI or breast-specific gamma imaging for guidance of the biopsy. Screening is not an indication for breast ultrasound, however, various studies have shown that the addition of ultrasound to mammography in high-risk women with dense breast tissue will increase detection of breast cancer. The ACRIN 6666 study found that in this group of women, the addition of ultrasound to mammography yielded an additional 7.2 cancers per 1,000 women. The sensitivity of combined mammography and ultrasound was 77.5% compared to 49% with mammography alone. In this multicentered study, 29% of the cancers were only visualized by ultrasound. However, it is important to realize that the positive predictive value of screening ultrasound is low, that is to say that only 8.6% of the biopsies performed are positive for breast cancer compared to 14.7% with mammography. The increased number of false positives resulted in additional biopsies and cost, and created unnecessary anxiety in patients.