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 excellent equipment with high frequency transducers and experienced technologists.
The indications for breast ultrasound include:
(1) evaluation of a palpable or mammographically visualized mass;
(2) guidance for interventional procedures or radiation planning;
(3) initial imaging technique for young (under 30 years of age), pregnant, or lactating women;
(4) evaluation of implants, especially silicone;
(5) additional assessment after a suspicious lesion is seen on breast MRI or breast-specific gamma imaging.
Screening for breast cancer is not an indication for breast ultrasound in the general population. However, various studies have shown that the addition of ultrasound to mammography in high-risk women with dense breast tissue increases detection of breast cancer. The ACRIN 6666 study found that an additional 7.2 cancers per 1,000 women were found with ultrasound compared with mammography alone. The sensitivity of combined mammography and ultrasound was 77.5% versus 49% with mammography alone. In this multi-center (including Weinstein Imaging) study, 29% of the cancers were only visualized by ultrasound. However, it is important to note 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, which is why ultrasound is not advocated an a screening tool for lower risk women.