There are a number of diagnostic criteria used to delineate the benign versus malignant characteristics of focal lesions. These criteria include margins, echogenicity, internal echo pattern, retrotumoral acoustic features, compressibility, and lateral to anterior-posterior dimension ratio [11, 20]. Margins that are smooth and well defined are used to contrast a probable benign lesion with a malignancy having jagged, indistinct margins. A solid lesion is usually hypoechoic to the surrounding glandular tissue with a homogeneous or uniform internal echo pattern more consistent with a benign abnormality [11].

When a lesion is without ultrasound echoes, it is referred to as anechoic. Though an anechoic interior is most commonly associated with a smooth-walled cyst, many malignancies are almost anechoic, but usually have a mixture of echogenicities to give a heterogeneous internal echo pattern. The internal echo pattern is one of the least specific characteristics delineating benign and malignant lesions. Complex cysts, abscesses, and other benign conditions may also have a nonhomogeneous internal echo pattern [1]. Homogeneity limits the amount of sound reflection within a focal abnormality and therefore allows greater sound transmission creating posterior enhancement, another criteria favoring a benign condition [19].

In contrast, the heterogeneity associated with malignant lesions will usually cause dense, irregular, posterior shadowing because of limited sound penetration and sound refraction. A more uniform refraction of sound, however, occurs in association with a smooth (probably benign) lesion. This type of refraction at the edges of smooth-walled lesions creates a symmetric pattern of shadowing known as bilateral edge shadowing [19]. The lateral to anterior-posterior ratio reflects the relationship of a lesion to the surrounding architecture. A malignant lesion is more likely to disrupt adjacent tissue planes growing perpendicular to the skin and muscle and therefore have an anterior-posterior dimension that is greater that the lateral dimension [1, 19]. A benign lesion grows in parallel with the tissue planes and has a lateral dimension greater that the anterior-posterior dimension.

Ultrasound characteristics of focal breast abnormalities help to place them within several categories including simple cysts, fibroadenomas (or benign fibrous nodules), indeterminate, and suspicious. Simple cysts are anechoic, well circumscribed, and thinly encapsulated, typically with posterior enhancement and often with thin edge shadows [11, 20, 22]. Fibroadenomas and benign fibrous nodules are hypoechoic, well-circumscribed lesions with a homogeneous, internal echo pattern; with a lateral to anterior-posterior dimension ratio greater than one; and with both posterior enhancement and bilateral edge shadowing [10, 11, 23]. The larger the fibroadenoma, the more likely it is to be associated with lobulations. Indeterminate lesions are usually hypoechoic with often sharp, smooth margins that may be somewhat indistinct [3, 20]. The internal echo pattern is variable and makes it difficult to distinguish the solid versus cystic nature of such lesions.

Complex cysts frequently fall into the indeterminate category. They have diffuse, low-level echoes as a result of blood, pus, or floating crystalline material and may require aspiration to distinguish them from solid lesions [3]. Movement of echoes within the lesion and compressibility may be demonstrated with real-time ultrasound imaging and, if cystic, may have posterior enhancement [1]. Suspicious breast lesions have indistinct, jagged margins; are almost anechoic; and have a heterogeneous interior, irregular posterior shadowing, and an anterior-posterior dimension greater than the lateral dimension [11, 20]. In a review of 662 consecutive patients undergoing 1,028 diagnostic breast ultrasounds, Staren et al. demonstrated an overall accuracy of greater than 90 % [17]. However, the decision to biopsy, or not biopsy, solid nodules cannot be based strictly on sonographic criteria because of these overlapping features.

The American College of Radiology developed the BI-RADS® classification of mammographic abnormalities to improve the assessment of microcalcifications and masses. Management decisions based upon the BI-RADS® assessment have resulted in standardization of care after being incorporated into the Mammography Quality Standards Act of 1992. An ultrasound BI-RADS® classification has also been developed to better characterize sonographic breast abnormalities, including those with mammographic correlates. The need for standardization of lesion descriptors led the development of lexicons that have been incorporated into these reporting systems (Table 2.1). It is imperative to utilize this list of standard terms when describing ultrasound findings, to reduce variability among imagers and reports [24]. The ASBS has adopted the requirement for BI-RADS classification for ultrasound submissions to the ultrasound certification application.

Though a surgeon traditionally has relied on the clinical breast examination to evaluate non-discrete palpable “lumps” or regions of nodularity, in the patient with a negative or nonspecific mammogram because of tissue density, breast ultrasound can often assist the surgeon in ruling out the presence of a focal suspicious lesion [25, 26]. By palpating the “lump” or clinical region of concern while scanning, a corresponding ridge of fibroglandular tissue can often be visualized as a homogeneous, isoechoic tissue pattern following the same contour found on physical exam [1]. When the physical examination reveals a discrete palpable abnormality, ultrasound is complementary to both the clinical and mammographic evaluation and helpful in determining the cystic versus solid nature of the lesion and directing further workup [3].

A diagnostic workup that includes breast ultrasound is very useful in evaluating mammographically indeterminate, non-palpable lesions presenting as discrete nodules, focal asymmetries, and areas of architectural distortion. Ultrasound is the primary imaging modality to establish if a discrete focal lesion on mammogram is a cystic or solid abnormality [6–8]. The determination of the fluid-filled nature of cysts as small as 2–3 mm, reaching an accuracy of 96–100 %, is easily accomplished with today’s improved ultrasound technology [4, 6, 8]. With such lesions presenting as discrete nodules, ultrasound is the imaging modality of choice to differentiate cystic from solid abnormalities and also to distinguish a solid lesion’s benign versus malignant nature. Areas of persistent asymmetry or architectural distortion after appropriate diagnostic focal compression mammography can be evaluated with ultrasound [4, 20, 21]. An area of asymmetry may only represent prominent fibroglandular tissue, but an underlying cystic or solid lesion may be further evaluated with ultrasound-guided intervention, depending on symptoms related to a simple cyst or the benign versus suspicious characteristics in the case of a solid lesion [1, 3, 20].

Diagnostic breast ultrasound is performed in the evaluation of younger patients [15] when mammography is less helpful and will assist the clinician in evaluating the patient who is pregnant or lactating when mammography is contraindicated [27]. The increase in water tissue density provides a favorable acoustic condition. Ultrasound may assist in the evaluation of mastitis and detection of underlying abscess formation where mammography is difficult secondary to pain and edema and may not demonstrate an abscess due to inflammation [28]. Ultrasound may guide aspiration or drainage techniques to provide nonoperative management of those ultrasound-identified breast abscesses [1, 29].

Postoperative oncologic follow-up for both mastectomy and breast conservation may be aided by evaluation with ultrasound. A palpable nodule of the chest wall may be visualized and assessed for depth of penetration, and then ultrasound may be used to guide a fine-needle aspiration or core needle biopsy for diagnosis [30]. After breast conservation surgery, there is a loss of the typical breast anatomy with an increase in tissue density that allows for evaluation and/or intervention of the lumpectomy site for evidence of recurrent disease [1]. Ultrasound is useful for postoperative follow-up for both benign and malignant diseases, including monitoring and management of seromas and hematomas [20, 30, 31].

The accuracy of intervention and tracking the pathway of a needle under real-time imaging may allow for the safe biopsy of a suspicious lesion in a patient who has undergone elective augmentation mammoplasty [32]. The axilla may be scanned for preoperative staging of the patient with a known or obvious breast cancer [1, 30]. Assessment of the axillary region for recurrent disease is aided by the enhanced imaging condition created by a decrease in fatty tissue postaxillary surgery. Ultrasound is also useful in guiding a biopsy of a pathologic-appearing lymph node in a patient with an unremarkable breast evaluation [1].

Ultrasound may assist in the workup of the patient with a pathologic nipple discharge. Considered by many radiologists to be the method of choice for evaluating nipple discharge, performing a ductogram is limited by the necessity of reproducing the discharge from a duct so that it can be successfully cannulated. Ultrasound evaluation of the ducts may be accomplished with the technique of duct echography, performed in a radial fashion, maintaining the ultrasound transducer in alignment with the ducts. By identifying a dilated, fluid-filled duct and in some cases an intraluminal filling defect or lesion responsible for the discharge, localization can be successfully performed to direct mammary duct evaluation and management [3, 20, 21]. In terms of overall cost, ultrasound is a much less expensive alternative to breast MRI in evaluating silicone breast implants for rupture or leak. Though MRI is considered by many as the standard diagnostic study of choice for identifying subtle leaks, ultrasound can often detect obvious rupture or leakage with improved cost-effective efficiency [33].

Breast ultrasound screening had historically been used more commonly in several European countries despite the prior lack of any randomized controlled trials to evaluate the impact of screening on breast cancer mortality [1, 20, 21]. Several studies have indicated that whole breast sonography as an adjunct to screening mammography may depict small, non-palpable cancers not seen on mammogram, especially when the breast tissue is dense [34, 35]. In the ACRIN 6666 trial, 2,809 women determined to be at high risk for breast cancer at 21 different site were enrolled to compare mammography screening alone to mammography plus physician-performed screening ultrasound. Berg and colleagues found that adding a single screening ultrasound found 28 % more cancers compared to mammography alone. However, the combined screening strategy led to four times the number of false positives [36]. Patients with a strong family history, a radiographically dense breast tissue, and a difficult clinical breast examination due to extensive nodularity may benefit from whole breast ultrasound [24, 25]. Whole breast ultrasound may also be useful in following the patient with multiple known sonographic lesions and to exclude multicentric malignancy when breast conservation is an option for a known malignancy [1]. Finally, ultrasound is used as the imaging modality to guide minimally invasive percutaneous aspirations, biopsies, localization procedures, and even nonoperative potentially therapeutic modalities [1, 20, 37].

Each year in the United States, women undergo an increasing number of biopsies required for the definitive diagnosis of image-detected abnormalities. Fortunately, a greater proportion of these biopsies are amenable to minimally invasive image-guided needle biopsies. The most recent International Consensus Conference on diagnosis and treatment of image-detected breast cancer once again reconfirmed that minimally invasive image-guided percutaneous breast biopsy should be the first-line intervention for both palpable and non-palpable image-detected abnormalities [38].

Image-guided percutaneous breast biopsy should eliminate the need for open surgical biopsy for diagnosis. Unfortunately, the proportion of open surgical biopsies remains high. Clark-Pearson found the average rate of open biopsy among surgeons at their institution to be 36 % [39]. This finding was disappointing as the integration of the image-guided needle biopsy approach found to be less invasive and more cost effective has been accomplished without sacrificing diagnostic accuracy [1, 37]. If image-guided needle biopsy results are benign, the patient requires no further intervention, monitored with only appropriate imaging and clinical follow-up; however, if diagnosed with breast cancer by image-guided percutaneous biopsy, the patient will proceed to definitive surgical management.

The physician performing the ultrasound-guided percutaneous biopsy must decide on the proper device or instrument that best accomplishes the goal of the procedure. The most important objective for any image-guided biopsy procedure is to obtain the correct diagnosis (benign versus malignant). The tools for specimen acquisition have evolved from fine-needle aspiration cytology to automated Tru-Cut® core needles providing histology. Further advancements of vacuum-assisted and rotational core technology, available with ultrasound guidance, allow for tissue acquisition with either multiple insertions of the device or a single device insertion allowing multiple tissue samples. Either approach provides adequate “sampling” capability for diagnosis for most lesions or therapeutic “removal” (by percutaneous excisional biopsy) capability for selected lesions. Understanding similarities and differences in the current technology enables the surgeon to select the most appropriate device and application.

The minimum requirement for ultrasound-guided biopsy of “indeterminate” or “high-risk” lesions is cytologic or histologic confirmation of a malignancy. Fine-needle aspiration biopsy (FNA) of solid masses has received considerable criticism, especially in the United States, related to the degree of insufficient sampling and the need for expert cytopathology [41]. Despite such criticisms, FNA is a quick and inexpensive technique to delineate benign from malignant solid breast masses. The sensitivity and specificity are affected not only by expert cytopathology evaluation but also by who is performing the FNA technique. It should be noted that many community surgeons that participate in managed care organizations may be limited to only certain choices of technique and pathology labs for specimen evaluation. Despite these limitations, in experienced hands, ultrasound-guided FNA can delineate benign from malignant solid breast masses.

Fornage and colleagues demonstrated a sensitivity of 97 % and a specificity of 91 % after evaluating 355 breast masses with ultrasound-guided FNA biopsy [12]. Gordon et al. confirmed the diagnosis of malignancy with ultrasound-guided FNA biopsy in 213 of 225 cases, yielding a sensitivity of 95 % and specificity of 92 % [44]. The majority of false-negative findings in this series (6 of 12) were lobular carcinoma, known to be difficult to diagnose with FNA due to the paucity of shed cells available for collection by aspiration. In addition to cytologic confirmation of malignancy of a “high-risk” lesion, ultrasound-guided FNA is frequently used to evaluate lesions in areas where more invasive biopsy devices may be difficult or dangerous, such as the axilla or adjacent to a breast implant [1, 32]. The diagnosis of lymph node metastasis by FNA can assist with preoperative staging, such as the consideration of neoadjuvant chemotherapy [45] or eliminating sentinel lymph node biopsy for pathologically involved lymph nodes. An adequately performed FNA provides ample cells in order to perform hormone receptor studies [46].

The limitations of FNA are essentially eliminated with the use of an automated, large-core needle biopsy, especially for “high-risk” lesions [1, 3, 20]. Histologic type and grade of a diagnosed cancer can be adequately determined with core histology, in contrast to FNA cytology which rarely provides sufficient tissue [14, 47]. Staren et al. reduced the initial false-negative rate obtained with ultrasound-guided FNA from 20 to 3.6 % using ultrasound-guided, 14-gauge core biopsies in 210 patients with a non-palpable, mammographically detected lesion [48]. There were no false positives, and no cancers were detected after a median follow-up of 18 months in the patients with a benign diagnosis.

The automated needles used to perform a core biopsy are available in a variety of lengths, gauges (12–16), and forward throw (1–2.3 cm). Some core needle devices are completely disposable, while others utilize disposable needles only within a more permanent, reusable housing device. The mechanism of tissue acquisition is similar with the automated forward movement of an inner cannula with a sampling notch. This is immediately followed by utilization of an outer sheath that cuts and samples the tissue. Two-phase firing action is accomplished under direct ultrasound visualization. The 14-gauge spring-loaded core biopsy needle has been the most common device for ultrasound-guided percutaneous biopsy device of solid lesions. It has been utilized since the mid-1990s and remains the most commonly used device for ultrasound-guided core “sampling,” in particular for the larger, easily targeted suspicious masses requiring diagnosis only.

The accuracy of ultrasound needle core biopsy has been widely documented. Parker et al. found no subsequent cancers in 132 lesions with a benign diagnosis obtained by ultrasound-guided core needle biopsy [14]. Eventually, an updated report of a larger, multicenter, image-guided biopsy series (stereotactic and ultrasound guided) showed 15 false-negative cases out of 280 benign lesions diagnosed by core biopsy, with most representing a biopsy of microcalcifications [49]. The false-negative rate for ultrasound-guided needle core biopsy of solid masses was 1.4 %.

A specific benign diagnosis such as fibroadenoma, which is concordant with the radiologic imaging, does not require further intervention. The patient is placed into an appropriate follow-up protocol, such as a 6-month follow-up with mammogram and/or ultrasound [14]. A diagnosis of cancer provides the information necessary to plan definitive therapy. Once the diagnosis of breast cancer is obtained, the surgeon may alter the lumpectomy technique to improve the chances that clear pathologic margins will be obtained at the initial surgical setting. Whitten et al. achieved a tumor-free margin rate of 71 % when the initial lumpectomy followed an image-guided biopsy diagnosis. This is compared with only 35 % free margins when the initial diagnostic procedure for diagnosis was an open surgical (needle localization) biopsy [50]. Excision is necessary also for cytologic atypia, because of the significant number of cancers that are identified in association with these pathologic changes [16]. Excision of a lesion will also follow an ultrasound-guided needle core biopsy if medical judgment dictates because sample quality is inadequate or poor or there is suspected discordant pathology.

There has been an evolution of biopsy technology over the last decade in order to address both real and perceived problems associated with image-guided needle core breast biopsy tissue acquisition. Despite accurate histology with spring-loaded core needles, specimens that are more substantial, obtained with the larger, vacuum-assisted/rotational core devices, offer advantages. During the 1990s, several publications brought to light the problem of “upgrading” the diagnosis, specifically with regard to the biopsy of microcalcifications [16, 51, 52]. Stereotactically guided 14-gauge needle core biopsy was found to significantly underestimate the diagnosis of cancer. A diagnosis of atypical ductal hyperplasia (ADH) is upgraded to ductal carcinoma in situ (DCIS) on excision in 33–50 % of cases, and DCIS is upgraded to invasive carcinoma in up to 20 % of cases [16, 51, 52].