Carcinomas have a range of ultrasound appearances, but the most typical is a mass with an echo-poor central nidus (less reflective than fat), often somewhat heterogeneous, with distal shadowing that is often intense and characteristically variable across the lesion.24,37 The nidus tends to lie with its long axis anteroposteriorly, reflecting its invasive behavior as it grows through the layers of the gland and, for the same reason, it tends to disrupt the adjacent fibroglandular structures, though these features are less obvious with subcentimeter lesions (Figure 42-5). They have poorly defined outer margins, which have a microlobulated contour, perhaps the single most reliable sign of malignancy.
Breast carcinomas. A: This subcentimeter carcinoma shows the typical features, with a poorly defined echogenic halo surrounding the echo-poor nidus, which casts an acoustic shadow. The tissue planes are broken (arrowheads) B: On power Doppler the lesion is markedly vascular. C: A larger tumor also shows these features, and there is thickening of Cooper's ligaments (arrowhead), producing a stellate pattern converging on the lesion. D: Multicentric cancers are not uncommon and should be carefully sought—2 foci are seen in this case.
Around the nidus, an echogenic "halo" representing the infiltrating edge of the malignancy may be seen. Typically, it is more obvious at the sides of the lesion than anteriorly, probably because of the different orientation of the invading columns with respect to the direction of the ultrasound beam. The halo is more difficult to detect when the surrounding tissue is itself echogenic, as occurs in premenopausal women. It is often easier to appreciate with real-time scanning because it moves with the nidus on probe or finger palpation. Measurements that include the halo are closer to histological measurements of tumor size but are more difficult to make than those of the nidus because the halo merges gradually into surrounding tissue.38
Cancers are generally hard and so do not distort under probe pressure and, when invasive, they may be fixed to the adjacent breast tissue, which is dragged or rotated when the tumor is pushed by the finger. Invasion into the pectoralis muscle can be demonstrated in this way. The stiffness (coefficient of elasticity) of cancers is higher than normal tissues and benign lesions. Tissue stiffness increases with increasing probe pressure so the biggest difference of stiffness between benign and malignant tissue is seen with minimal precompression free-hand elasticity imaging.39 Typically, cancers have a larger strain (elasticity) image than the gray-scale image (Figure 42-6), while benign lesions often have a smaller strain image than the gray-scale image.40,41 Using the Ueno/Tsukuba scoring method, cancers are stiff with high scores.21,22,42 The extent of the strain image of cancers seems to be a more accurate measurement of tumor size than the gray-scale image.43 Even in situ and mucinous cancers cause increased stiffness compared with the surrounding normal tissues. Mucinous cancers and cancers with internal necrosis may exhibit a more heterogeneous strain pattern than solid tumors.
Elastograms. A: This small (c 5-mm) echo-poor lesion, which is deeper than wide, has the features of a carcinoma. It was impalpable. B: On elastography, it is stiffer than the surrounding tissue and is larger than on the B-mode image. Histology revealed an intraduct carcinoma. C: A typical fibroadenoma is depicted on B-mode with (D) its elastogram, which shows the stiff region to be smaller than the B-mode—a typical benign feature.
The neovascularization that is always present in carcinomas larger than a few millimeters in diameter may be demonstrable on color Doppler. Often the increased vascularity with numerous, tortuous vessels is very obvious and forms a useful additional sign of malignancy, especially where the typical anatomical features are not seen, for example, in inflammatory or non–mass-forming carcinomas. The degree of vascularization of a breast cancer correlates with its invasive potential.44 The vascularity surrounding the lesion may be more visible than that within the lesion because of necrosis or loss of signal caused by the complex, chaotic nature of the tissues. The external and surface vessels frequently have a radial alignment, penetrating into the mas.6 Benign masses may also have Doppler signals, but the vessels usually track around the lesion rather than penetrating into it and are usually sparse and lack the chaotic pattern of malignant neovascularization.45
There are often characteristic changes in the breast around a cancer. Thickening of Cooper's ligaments, caused by invasion or desmoplastic reaction, gives a typical stellate pattern when they retract. This is often much more clearly seen on three-dimensional scans that have been reformatted to show the coronal plane (C-scan).43 Skin thickening results from invasion or edema and is most obvious in inflammatory cancers. Dilated ducts may result from obstruction or invasion, so that both the upstream and downstream portions may be dilated. Involved nodes are often obvious in the axilla and parasternal regions, and can be distinguished from reactive nodes by their spherical shape and effacement of the normal echogenic hilum.45 Like the primary tumor, involved nodes may be vascular with peripheral vessels penetrating the capsule—a sign of neovascularization.
In addition to such typical lesions, a variety of other patterns may be encountered, some of which correspond to particular histological types. Where the cancer contains little fibrous tissue, shadowing is less apparent, and very cellular carcinomas may even show increased through-transmission with a confusingly benign appearance (eg, medullary, tubular, and mucinous carcinomas).47 The halo is absent if the tumor does not invade locally. The nidus can be echogenic and blend with the fibroglandular layer or match that of the subcutaneous fat—a feature of colloid carcinomas.48 In these instances, the tumor may be invisible on the static scan, although it can be picked out by its harder consistency than the surrounding tissues on probe palpation or on elastography. Although patchy necrosis may occur with larger lesions, extensive necrosis is rare except after chemotherapy; it produces a partly cystic lesion whose walls are irregular. Coexistence of a cyst or fibroadenoma and a carcinoma is well recognized; the ultrasound features of the malignant component are usually typical.49
Some important types of carcinoma are particular diagnostic problems for ultrasound. Small cancers (<5 mm) sometimes have characteristic appearances that allow their diagnosis but may mimic the appearances of fibroadenomas; therefore, biopsy is required. Elastography is promising in their characterization. Widely infiltrating carcinomas that do not form a discrete mass are difficult to detect on ultrasound; even when extensive (eg, lobular carcinomas), they may not be apparent (ultrasonically occult lesions). Inflammatory cancers may mimic an infective process or developing abscess with increased vascularity, although the hardness of the affected portion of the breast and the associated skin thickening (peau d'orange) may be suspicious (Figure 42-7).50 Smaller infiltrating carcinomas without a mass may be undetectable or may cause only subtle architectural disturbance or shadowing, which should be considered as suspicious if it persists on probe compression. They may be more rigid than the surrounding tissue and show as stiff regions on elastography.
Inflammatory carcinoma. Although the breast was obviously hard on palpation, no discrete mass could be demonstrated on ultrasound. However, the skin is thickened and the breast architecture diffusely effaced. Color Doppler shows the typical generalized hypervascularity, and the spectral trace shows this to be of low impedance with continuous flow through diastole.
Lobular, low-grade, and small high-grade ductal in situ carcinomas (DCIS) cannot be detected reliably by ultrasound; often no abnormality is seen, although occasionally microcalcifications in a portion of dilated duct may be detectable. The higher the grade of DCIS and the greater the extent of disease, the greater the likelihood of their being identified on ultrasound. Classically, DCIS is detected mammographically because of the microcalcifications associated with the comedo necrosis. Prior mammography increases the detection rates of small lesions by indicating the site of abnormality. In women under 35 who present with an area of vague thickening, for whom mammography may be contraindicated, medium- to high-grade DCIS may be detected on ultrasound, particularly if it causes clinical thickening felt by the patient. This change in consistency often shows up as increased stiffness on elasticity imaging. Absence of stiffness in clinical areas of thickening is nearly always indicative of normal tissue. The ducts are usually dilated with echo-poor contents and punctuate bright echoes that are caused by microcalcifications. Diagnosis is often aided by hypervascularity, which is probably caused by increased flow in the adjacent normal tissue induced by cytokines secreted by the tumor.51 Mammography can often help guide the experienced sonographer to recognize smaller areas of DCIS, which otherwise may not have been appreciated on routine ultrasound, and ultrasound can then be used to target core biopsy.
Metastases and lymphoma in the breast tend to be better defined than infiltrating carcinomas and lack an echogenic halo.52 Otherwise, they have similar appearances, with low-level heterogeneous echoes. They are also incompressible and often are vascular.
Intraduct tumors can be diagnosed if they are surrounded by fluid (Figure 42-8).53 However, when there is no surrounding fluid, they appear as well-defined, solid masses and can be confused with small carcinomas or fibroadenomas. They are usually stiff on elasticity imaging. They can be diagnosed with needle core biopsy, but distinction between benign and malignant forms requires excision biopsy.
Intraduct papilloma. This mass (arrowheads) lying within a duct turned out to be a papilloma, but a carcinoma could have the same appearance. (D, duct.)