Mammographic Masses, Asymmetries, and Distortion

Breast Masses

A mass occupies three-dimensional space with partially or completely convex borders, which bulges into the surrounding tissues. A mass should be identifiable on two orthogonal projections unless obscured by adjacent dense tissue. The radiologist’s goal is to distinguish benign from malignant masses in order to appropriately manage the patient. Masses may be recognized at time of screening or may present as a palpable finding by the patient or referring provider in the diagnostic setting.

Once a mass has been identified, Breast Imaging Reporting and Data System (BI-RADS) lexicon descriptors are used for lesion characterization. Reporting also includes mass location by determining the laterality, quadrant or clockface, depth, and distance from the nipple to the mass. BI-RADS mammography descriptors for mass lesions are summarized in Table 3.1 and are illustrated with diagrams and image examples in Figs. 3.1–3.3 for mass shape, margin, and density. Adhering to BI-RADS terminology allows appropriate characterization of masses, which guides the next step in management. For example, a benign breast mass is assessed as BI-RADS 2 with a recommendation to return to annual screening. A suspicious breast mass is assessed as BI-RADS 4 with a recommendation for tissue diagnosis, usually using image-guided biopsy. Occasionally, a mass is assessed as BI-RADS 3 “probably benign” (with less than 2% probability of malignancy), and recommendation is for short-term imaging surveillance instead of immediate tissue sampling. When multiple suspicious mammographic findings are present suggesting a greater than 95% probability of malignancy ( Box 3.1 ; Fig. 3.4 ) a BI-RADS 5 “highly suggestive of malignancy” assessment is appropriate.

Breast Mass Descriptors Specific to Ultrasound

Ultrasound is frequently performed in conjunction with mammography for further characterization of masses. Breast ultrasound is covered in more detail in Chapter 5: Breast Ultrasound Indications and Interpretation . Similar to mammography, mass shape on ultrasound is described as oval, round, and irregular. Ultrasound terminology for mass margin includes all of the mammographic descriptors, with the exception of “obscured” and an additional term specific to ultrasound: angular ( Fig. 3.5 ). An angular margin indicates an area of a mass margin, which is sharply demarcated away from the mass. Other ultrasound specific descriptors include mass orientation, echo pattern, and posterior features ( Fig. 3.6 ). Table 3.2 summarizes the ACR BI-RADS ultrasound descriptors.

Table 3.2

American College of Radiology (ACR) Breast Imaging Reporting and Data System (BI-RADS) Ultrasound Lexicon Descriptors

Shape	Margins	Echo Pattern	Posterior Acoustic Features	Orientation	Associated Features	Calcifications
■ Oval ■ Round ■ Irregular	■ Circumscribed ■ Not circumscribed: ■ Angular ■ Indistinct ■ Microlobulated ■ Spiculated	■ Anechoic ■ Hyperechoic ■ Complex cystic and solid ■ Isoechoic ■ Hypoechoic	■ None ■ Enhancement ■ Shadowing ■ Combined	■ Parallel ■ Not parallel	■ Architectural distortion ■ Duct changes ■ Skin changes ■ Edema ■ Vascularity: ■ Absent ■ Internal ■ Rim	■ Inside of mass ■ Outside of mass ■ Intraductal

Orientation is an ultrasound-specific descriptor. An antiparallel (older term: taller than wide) orientation refers to a mass with its long axis perpendicular to the skin line (or chest wall), indicating it may be growing against tissue planes, which is a suspicious feature.

Posterior features is an ultrasound-specific term that refers to the sound wave attenuation by tissue. This attribute of a mass may be characterized as having no posterior features, posterior enhancement, shadowing, or a combined appearance. The presence of shadowing is suspicious. Note, however, that not all cancers shadow. Highly cellular tumors such as mucinous, medullary, papillary, or cancers with necrosis can have increased through transmission.

Sonography is useful for distinguishing benign solid masses from indeterminate and malignant solid masses. In a prospective study of 750 sonographically identified breast masses, a negative predictive value of 99.5% was reached. Table 3.3 summarizes the individual sonographic characteristics used in this study. By excluding any mass with at least one malignant feature, sensitivity for cancer was 98.4%.

Table 3.3

Sonographic Appearance of Malignant and Benign Masses

Malignant	Benign
Margin Indistinct Microlobulated Angular Spiculated Marked hypoechogenicity Shadowing Ductal extension	Absent malignant findings Intense hyperechogenicity Ellipsoid shape With no more than 2–3 gentle lobulations Thin capsule

When imaging a patient, the American College of Radiology requires specific labeling of saved ultrasound imaging. Breast ultrasound is covered in detail in Chapter 5: Breast Ultrasound Indications and Interpretation .

Specific pathologic entities presenting as breast masses are covered in detail in Chapter 9: Breast Pathology and Radiologic-Pathologic Correlation . Briefly, in addition to breast cancers, masses on imaging may result from a wide variety of pathologies, including fibroadenoma, hamartoma, pseudoangiomatous hyperplasia, papilloma, and phyllodes tumor. Please refer to Chapter 9 for an overview of the characteristic appearance and management of these lesions.

Asymmetries

An asymmetry is a noncalcified finding seen on one breast and not the other when comparing right and left mammograms. There are four types of asymmetries detailed further below: asymmetry, global asymmetry, focal asymmetry, and developing asymmetry. Asymmetries do not conform to the mammographic definition of a mass and may have the appearance of normal fibroglandular tissue. Slight differences between the two breasts are normal and may be best detected by examining the bilateral breasts back to back to look for differences in symmetry. Asymmetry is a term used only in mammography and is not in the ultrasound or magnetic resonance imaging (MRI) BI-RADS lexicon.

The category of asymmetries refers to a space-occupying lesion that is discernible from the surrounding parenchyma with concave outward borders and usually interspersed with fat. It may be visualized on one or both orthogonal projections, which determines its subcategorization. In some cases, what initially appears as an asymmetry is revealed to be a mass on further workup. In such cases the mass may have been apparent on only one view and obscured by dense tissue on the orthogonal projection and categorized as an asymmetry until its three dimensionality is confirmed.

The next few sections will review the four types of asymmetries in the BI-RADS lexicon (see Box 3.2 ), their imaging evaluation and management including expected outcomes.