1. Patient history to consider when evaluating and considering differentials for a breast mass
2. Evaluation (imaging) algorithm for clinically or mammographically detected breast masses
3. Features of masses to consider and appropriate use of descriptors
4. Differential considerations for round (expansile) masses
5. Differential consideration for masses with spiculated, margins
6. Differential considerations for multiple masses in the breast with similar features
7. Differential considerations for fat containing masses
We place much emphasis on detecting microcalcifications and anguish over their characterization and management, but it is important to recognize that most invasive ductal carcinomas, and virtually all invasive lobular carcinomas, present as a mass. In contrast, when associated with malignancy, microcalcifications usually reflect intraductal, noninvasive breast cancer. Our primary goal with screening mammography is the recognition or perception of a possible mass or distortion related to an underlying mass. Our characterization of masses and management recommendations for patients are predicated on physical examination, spot compression, spot rolled, spot tangential, or spot compression magnification views and breast ultrasound. In some women, what appears to be a mass on screening images is shown to be superimposition of normal glandular tissue and what appears as an innocuous asymmetry is identified as likely malignant with further workup. By integrating patient history, clinical, mammographic, and ultrasound findings, and an understanding of breast histopathology, it is possible to approximate a diagnosis and have significant confidence in the appropriate management recommendations.
Relevant history is reviewed in evaluating and managing women with a breast mass. Women with a personal history of breast cancer or a history of breast cancer involving a first-degree relative (mother, father, sister, brother, daughter, or son) are at increased risk for developing breast cancer. This risk is increased if the relative developed breast cancer premenopausally or had bilateral breast cancer. The age and menopausal status of the patient, use of hormone replacement therapy, and physical findings should be known and factored in the formulation of a differential (Table 7.1).
Personal history of breast (or other malignancies, e.g., ovarian cancer)
Family history of breast cancer
Patient age (incidence of breast cancer increases with advancing age, and differential considerations change depending on age)
Menopausal status (tumor sojourn time is shorter in premenopausal women)
Hormone replacement therapy
Spontaneous nipple discharge
History of cyclical change in primary finding
History of surgical procedures involving the breast
Prior breast biopsy with diagnosis of high-risk marker lesion
Lobular neoplasia (LCIS)
In women over the age of 30 presenting with a focal finding (e.g., “lump,” dimpling, focal tenderness), a metallic BB is used to mark the area of concern, and mediolateral oblique (MLO) and craniocaudal (CC) views are obtained bilaterally (1). A spot tangential view of the focal finding is also obtained. Correlative physical examination and ultrasound are usually done. Ultrasound is not absolutely indicated if fatty tissue is imaged corresponding to the site of concern to the patient, and there is no chance that the area of concern has been excluded from the field of view (e.g., if the metallic BB is at the edge of the film, correlative physical examination and ultrasound are always done; see Figs. 3.1 and 3.2).
Physical examination and ultrasound are done in women who are pregnant, lactating, or under 30 years of age and present with a “lump” (see Figs. 4.45 and 4.47). If any concerns persist following this initial evaluation, an MLO may be done to exclude calcifications associated with an intraductal carcinoma that may not be apparent on ultrasound. If an underlying malignancy is suspected, mammographic images are obtained bilaterally to fully evaluate the patient.
As defined by the American College of Radiology Breast Imaging and Reporting Data System (ACR BI-RADS®), a mass is a “space-occupying lesion seen in two different projections.” This is to be distinguished from asymmetry, a term used for “an area of fibroglandular-density tissue that is visible on only one mammographic projection, frequently representing superimposition of normal breast structures” (2). Masses are three-dimensional, have a bulging or convex contour and an abrupt density change at the margin. They may produce architectural distortion and have associated calcifications, skin or nipple changes. Depending on location, size, internal matrix, and surrounding tissue, the mass may be palpable. Asymmetric tissue is planar with a different appearance between projections, scalloped and inhomogeneous with a gradual change in density at the margins. It is usually not palpable (3); palpable asymmetry should be evaluated carefully (see Chapter 9).
Compression, rolled and magnification views done with the round spot compression paddle (see Fig. 3.4A, B) are used to establish the shape, margins, and density of breast masses. Round, oval, and irregular (if “shape cannot be characterized”) are the terms in BI-RADS® to describe the shape of a mass. Circumscribed, microlobulated, obscured (margins “hidden by superimposed or adjacent normal tissue”), indistinct, and spiculated are the terms used to describe the margins of a mass. The x-ray attenuation or density of a mass is described as high, equal, or low (but not fat-containing) relative to an equal volume of fibroglandular tissue (Table 7.2) (2). Please see Appendix A for the ACR BI-RADS® mammography, US and MRI lexicons. Every rule has an exception; but in general, benign masses have circumscribed or partially circumscribed margins and are low to equal in density. In contrast, malignant lesions have indistinct or spiculated margins, and the expansile (round, oval, lobulated) masses are usually high in density.
Density (Water Density)
Low (but not fat-containing)
Sickles EA, D’Orse CJ, Bassett LW, et al. ACR-BIRADS®
Density (low, equal or high density; no fat)
Features of associated calcifications
Effects on surrounding tissue
Stability (previous films)
Additional features to consider when evaluating masses are listed in Table 7.3. Establishing the presence of associated calcifications and their morphology is helpful in assessing the etiology of a mass. Benign calcifications are usually associated with benign masses (Fig. 7.1). If malignant-appearing calcifications are associated with a mass, invasive ductal carcinoma with an intraductal component is the most likely diagnosis (Figs. 7.2 and 7.3). Likewise, establishing the presence of satellite lesions is helpful (Fig. 7.3). Although maligned, the halo sign is a good indicator of benignity (4–6). The halo sign is narrowly defined as a 1-mm sharp lucency, partially or completely surrounding a mass (Fig. 7.4). Not all masses with a true halo are benign but many are (4,5). The halo sign is probably as good a sign of benignity as spiculation is of malignancy. The halo sign may reflect active changes in the size of the mass (4).
The presence of multiple masses with similar mammographic features (Fig. 7.5) is suggestive of benignity. However, do not be lulled into a false sense of security by multiplicity. Women with multiple masses can develop breast cancer. It has been reported that since the frequency of cancer development among women not recalled for evaluation of multiple masses and the stage of the cancers diagnosed in these women is no different than that seen in the general screening population, evaluation of multiple masses appears not to be justified (7). Others advocate ultrasound evaluation in these patients (8). Although controversial, our approach to the patient presenting for the first time with multiple masses is to evaluate each mass as though it were a single finding. Our decisions are based on physical examination and the mammographic and ultrasound features of the masses evaluated. On subsequent mammograms in these patients we only evaluate new, developing masses. Also, don’t let yourself be mesmerized with multiple benign findings, but actively focus your brain away from the obviously benign findings and evaluate the surrounding tissue. Differential considerations for patients presenting with multiple masses is provided in Table 7.4.
Previous films are useful in the evaluation of masses. Although stability is not an absolute sign of benignity, if a mass with benign features (e.g., circumscribed margins, low to isodense) has been present for several years with no change, the likelihood of malignancy is low and recommending a 6-month follow-up is not appropriate. If the mass has features of malignancy (e.g., spiculation, distortion) that are not explained easily (e.g., prior trauma or surgery correlating with the site of the mass) it may represent a low-grade invasive lesion and biopsy is indicated (Fig. 7.6). In selecting prior films for comparison, try to use films from at least 2 years previously if available and, when evaluating a possible finding, look at multiple prior studies to establish slow progression or fluctuation in the finding. Subtle changes may not be apparent from 1 year to the next but may be striking when comparison is made with studies from 2 or 3 years previously (see Fig. 11.9).
Skin lesions (neurofibromas)
Invasive ductal carcinoma (multifocal or -centric)
Peripheral papillary carcinomas
Masses on the skin include moles, seborrheic keratosis, accessory nipples, skin tags, sebaceous cysts (epidermoid inclusion cysts), and neurofibromas (9). Keloids may also be noted projecting on the breast parenchyma. Unlike parenchymal masses, a thin lucency (air) may be noted surrounding the margins of the mass that protrude beyond the skin; the lucency is lost where the lesion attaches to the skin (Fig. 7.7). In some women, talc, calcifications, or air outlines the crevices of moles (Fig. 7.8A, B; also see Fig. 6.10). We mark skin lesions with a metallic BB prior to taking films so that we do not call a patient back unnecessarily for a skin lesion.
Sebaceous cysts and epidermoid inclusion cysts are common, often palpable, intradermal masses that may undergo changes in size from one year to the next. They commonly develop in the axilla (Fig. 7.9) or in the lower inner quadrants at the medial most extent of the inframammary fold (Fig. 7.10). On physical examination, sebaceous cysts may cause a smooth skin bulge and the orifice of the gland may be visible as a punctum (“black head”). On palpation, the mass moves with the skin such that you cannot glide skin over the mass. If squeezed, a white, thick, cheesy material that may be malodorous can be expressed from the punctum. When inflamed, localized erythema may be noted and tenderness elicited clinically; incision and drainage may be needed for treatment. However, complete removal of the cyst wall is required, otherwise, these lesions recur. On the mammogram, these masses have circumscribed margins or, when inflamed, indistinct (Fig. 7.11A) or spiculated (Fig. 7.12A) margins; associated calcifications may be present (Fig. 7.13; also see Fig. 6.9). On spot tangential views, they are localized to the skin (Figs. 7.9B and 7.12B). On ultrasound, an anechoic, hypoechoic, or echogenic mass often with posterior acoustic enhancement may be seen separating the dermal layers (Fig. 7.11C). As the patient is scanned and the transducer is manipulated, the skin track can be identified in some patients (Fig. 7.12B; also see Fig. 4.11). As the mass enlarges, the deep dermal layer may not be readily apparent (Fig. 7.10B). With inflammation or associated calcifications, the echotexture may be heterogeneous. These lesions can attain significant sizes such that patients present with discomfort particularly when the sebaceous cyst is in the axilla or along the inframammary fold (e.g., along the bra line). On magnetic resonance imaging (MRI), sebaceous cysts are masses localized to the skin that demonstrate a high T2 signal with no significant enhancement (Fig. 7.14), unless there is associated inflammation.
Keloids are clinically apparent, developing at prior surgical sites. They occur with a higher incidence among Black and Hispanic patients and reflect abnormal wound healing. They are irregular, serpiginous, tubular, or mass-like structures noted at, and extending away from, the surgery site. The portion that projects beyond the skin is outlined by air such that a thin radiolucency is apparent mammographically (Fig. 7.15A). On MRI, they can be localized to the dermis and do not usually demonstrate significant enhancement (Fig. 7.15B). Treatment options are variable and include injections (steroids, 5 fluorouracil, interferon, retinoids, and calcium channel blockers) directly into the keloid, surgery, radiation therapy, topical applications of silicone gel, laser, pressure therapy, and cryosurgery. Mixed results are reported for each, and appropriate treatment remains controversial.
Clinically, neurofibromas are readily apparent in patients with neurofibromatosis. There is wide variation in the number, size, and distribution of the lesions on the breasts; however, there is a predilection for the periareolar areas in many patients. Although patients can develop new lesions, and preexisting lesions can increase in size, the rapid growth of a single lesion is of concern and biopsy may be indicated since malignant peripheral nerve sheath tumors may develop in preexisting neurofibromas (Fig. 7.16A). Neurofibromas are noted mammographically as masses that may be lobulated with circumscribed margins and partially or completely outlined by air. Depending on the number of lesions, evaluation of the underlying breast parenchyma may be difficult. Extra care should be used to actively disregard the obvious benign findings in search of a possible unsuspected malignancy in these patients. On ultrasound, a hypoechoic mass with gently lobulated, circumscribed margins and posterior acoustic enhancement is imaged in the dermis or in a subcutaneous location (Fig. 7.16B). On MRI, the lesions can be seen extending beyond the borders of the breast and usually demonstrate no significant enhancement (Fig. 7.16C).
An increasing number of patients are being referred to us for the evaluation of cellulitis. In most patients, no underlying etiology is identified; in some, radiation therapy may precede the presentation. Clinically, localized or diffuse erythema is the primary finding, and depending on the amount of inflammation, peau d’orange changes or localized areas of necrosis may be apparent (Fig. 7.17A); significant tenderness is elicited and often precludes a mammogram. The main differential consideration in many of these patients is inflammatory breast carcinoma (IBC). Patients with cellulitis are more likely to have localized findings, be more tender, and respond to antibiotics with no progression or recurrence of symptoms. At presentation, ultrasound is often the starting point because some of these patients do not tolerate the compression required for a mammogram. Ultrasound is helpful in localizing the process to the skin (Fig. 7.17B), excluding the presence of an underlying abscess requiring drainage or other focal parenchymal finding. Axillary lymph nodes may be prominent in patients with cellulitis; however, the lymph nodes retain normal morphologic features in contrast to the grossly abnormal lymph nodes that are seen in many patients with IBC at the time of presentation.
Fat-containing masses in the breast are almost always benign (1–3,5). These masses can be completely fatty (Table 7.5) or mixed in density (Table 7.6). Although ultrasound findings are described for completeness, the diagnosis is established reliably when lucent or mixed-density masses are seen on the mammogram (with some of these lesions, the features on ultrasound may raise concerns inappropriately). It is important to note that, although many of the entities described are commonly fatty or mixed in density, they may also present as water density masses. So you will find an overlap in the differentials provided for each. For example, lymph nodes and fat necrosis are typically considered mixed-density masses, but each may present as a water density mass. Rarely, entities typically presenting as water density masses (including malignancy) may be noted to have lucent areas.
Intramammary lymph nodes
Fat necrosis, oil cysts
Postoperative/traumatic fluid collections (hematomas, seromas)
Patients with a lipoma can be asymptomatic or present with a soft or hard, mobile mass. A radiolucent mass with an expansile circumscribed margin and a thin fibrous capsule are detected in the breast (Fig. 7.18A), or less commonly in the pectoral muscle (Fig. 7.18B), on the mammogram. Although the diagnosis is reliably made on mammographic findings, a mass with circumscribed margins and a homogeneously hypo-, iso-, or hyperechoic echotexture is imaged on ultrasound (see Fig. 4.40A) (10); in some patients, short, curvilinear hyperechoic internal septations may be apparent (Fig. 7.19A). Gentle mass effect can be seen on surrounding structures (Fig. 7.19B). Uncommonly, hemorrhage may occur in preexisting lipomas so that on the mammogram a mixed-density mass (Fig. 7.20A, B) is seen at the site of a preexisting lucent mass. As the hemorrhage resolves, the lucent nature of the mass becomes more apparent on follow-up mammograms; the mass is complex on ultrasound and fluid–fluid levels may be seen (Fig. 7.20C). A mass with the signal characteristics of fat (high T1 and T2 signal, suppressed on fat-suppression images) and no enhancement is incidentally noted on MRIs performed as screening studies in high-risk women or those being evaluated for other breast-related issues (Fig. 7.21). Histologically, these lesions are characterized by the presence of mature lipocytes surrounded by a thin capsule (11,12). If otherwise asymptomatic, no intervention or short-term follow-up is indicated. Rarely, liposarcomatous lesions can present in the breast typically as a rapidly growing mass. The size, age of the patient, and growth pattern should suggest a malignant process. On the mammogram, internal septations may be seen in an otherwise lucent mass and the typically homogenous echotexture on ultrasound may be more heterogeneous (see Fig. 8.50).
Oil cysts are radiolucent, solitary (Fig. 7.22), or multiple (see Fig. 6.26B), uni- or bilateral masses. They vary in size, can progressively decrease, and resolve completely on subsequent mammograms. They are idiopathic or develop in areas of prior trauma or surgery and, in this setting, probably represent an end stage of fat necrosis. Some develop mural calcifications resulting in lucent-centered (or rim) calcifications (see Figs. 6.26B and 6.29A), while in others, the mural calcifications are seen “en-phase” having a coarse, irregular, curvilinear appearance (see Fig. 6.28). In most women, oil cysts are noted incidentally on screening mammography. Some patients may present for diagnostic mammography describing a discrete, hard mass that is correlated with one or multiple oil cysts mammographically. In this situation it is important to assure the patient and referring physician that the palpable finding is an oil cyst requiring no intervention or follow-up. The diagnosis is established on the mammogram (Figs. 7.23 and 7.24) such that ultrasound is rarely indicated. Given the variability in the appearance of oil cysts on ultrasound, the ultrasound features may raise concerns over the benign diagnosis (see Fig. 4.34). They may be anechoic with through-transmission indistinguishable from fluid-containing cysts (Fig. 7.23B). Internal echoes, fluid–fluid levels, septations, and complex cystic masses either predominantly cystic with intracystic or mural solid-appearing components (Fig. 7.24B) or solid with cystic components or they may appear solid (13). On MRI, oil cysts are characterized by circumscribed margins and demonstrate decreased signal on T2-weighted, fat-suppressed images (Fig. 7.25A) and a high signal on T2- and T1-weighted, non–fat-suppressed images. Most oil cysts demonstrate no enhancement (Fig. 7.25B); however, a thin enhancing rim may be apparent in some patients.
In some women, oil cysts may be more appropriately characterized as mixed-density masses (Fig. 7.26) because of thickened, ill-defined, or spiculated margins, or the presence of a round or oval intracystic mass. With a history of trauma or surgery, and if fat (radiolucency) is associated with these masses in orthogonal projections, no intervention or short-term follow-up is warranted regardless of the spiculated margins or associated nodules (see below, fat necrosis).
Steatocystoma multiplex is a rare condition with an autosomal dominant mode of inheritance associated with multiple intradermal oil cysts scattered over the body but with a predilection for the trunk and upper extremities (14,15). Although more commonly seen in males, women with this condition may be found to have multiple oil cysts in the breasts bilaterally.
Intramammary and axillary lymph nodes are common and variable in number, size, density, shape, and location (Fig. 7.27). They can fluctuate in size, and in some women can disappear only to reappear on subsequent studies. Keep in mind that on the basis of the positioning of the woman for the MLO views, you may see variable amounts of axillary tissue, and with that, a variation in our ability to evaluate axillary lymph nodes mammographically. Typically, they are round or oval masses of mixed density with circumscribed and sometimes lobulated margins located in the upper outer quadrants posteriorly and in the axillae; however, they can be found anywhere, including, less commonly, the medial quadrants of the breast. The presence of a variably sized fatty hilum either centrally or peripherally is required prior to assuming that a mass in the upper outer quadrant of the breast is a lymph node. Size alone is not used to determine the need for evaluation. We rely on density, margins, contour (bulging) alterations, absence of a fatty hilum, and changes compared with prior studies to determine appropriate management.
On ultrasound, lymph nodes are round or oval hypoechoic masses with circumscribed margins and an area of hyperechogenicity either centrally or peripherally (Fig. 7.28; also see Fig. 4.21). Reactive lymph nodes may demonstrate a symmetric increase in the size and density of the cortex and may or may not retain a fatty hilum. If the fatty hilum is not readily apparent on the mammogram, it may be seen on ultrasound (Fig. 7.28); however, if a fatty hilum is not identified with either modality and the mass is new or enlarging, biopsy is indicated (Fig. 7.29). Although in evaluating lymph nodes it is important to factor in all features including cortical thickening and bulging (16), the echogenicity of the cortex on ultrasound can be a helpful guide. The cortex in patients with an underlying inflammatory process is often iso to slightly hyperechoic, whereas in patients with metastatic breast cancer or lymphoma, the cortex is often markedly hypoechoic (almost anechoic), the fatty hilum is either attenuated or not present, and there may be posterior acoustic enhancement (see Figs. 4.22, 8.59, through 8.61).
The oval shape and circumscribed margins of lymph nodes described mammographically and on ultrasound are also noted on MRI (see Fig. 5.18). The distribution and relationship to vasculature is readily appreciated on MRI. The extension of lymph nodes from the axilla inferiorly along the midaxillary line is also readily apparent on MRI in some patients (see Fig. 8.61A). The enhancement pattern of lymph nodes is variable but normal lymph nodes commonly demonstrate rapid washin and washout kinetics on the dynamic T1 sequences. Unlike most malignancies, lymph nodes demonstrate an intermediate to high T2 signal. The fatty hilum may have a high signal on T1 non–fat-suppressed sequences and low signal on the fat-suppressed sequences.
On screening mammograms, diffuse increases in the size and density of axillary, and less commonly intramammary, lymph nodes may be identified in some patients. Before undertaking extensive workups it is important to review the patient’s history with respect to possible underlying causes of benign lymphadenopathy (Table 7.7) (17). If no underlying etiology is readily identified in the patient’s history, the patient is called back and evaluated with spot compression views, physical examination, and ultrasound. On the basis of this evaluation, a core biopsy may be done (Fig. 7.30) to determine the underlying cause of the adenopathy (18).
Gold particles imaged as high density, punctate particles mimicking microcalcifications can be seen bilaterally in the axillary and intramammary lymph nodes of women treated for rheumatoid arthritis with gold (Fig. 7.31) (19). Coarse calcifications occurring in lymph nodes are often related to granulomatous disease and do not require intervention.
In a retrospective 5-year review, Lee et al. (20) reported unilateral enlargement of axillary or intramammary lymph nodes in 0.2% of their patients with otherwise normal mammograms. In their experience, biopsy is indicated in patients with a history of an underlying malignancy if the lymph node enlarges by more than 100% over baseline. If the woman does not have a history of a malignancy, the lymph node enlargement is small, the node is not palpable, and it maintains a benign appearance, they suggest clinical and mammographic follow-up. In the majority of their patients, lymph node enlargement decreased on follow-up studies. Please see Chapter 8 for a more detailed discussion of the imaging features of potentially abnormal lymph nodes.
Fibroadenolipomas (FAL) or hamartomas are characterized by the presence of a pseudocapsule within which fatty, glandular, and fibrous elements are admixed. This appearance has led some to describe them as a “breast within a breast” (Fig. 7.32A). The overall density of these lesions is variable depending on the proportions of intermingled fat and glandular tissue. In some women, FAL may enlarge and present as a palpable mass (Fig. 7.33A). Since the lesions are made up of breast tissue, breast cancer of any type can arise in hamartomas (21). Development of pleomorphic calcifications (Fig. 7.34), increasing density, particularly if ill-defined or spiculated in a FAL, should prompt further evaluation and, if indicated, an imaging-guided biopsy. If the patient presents with a palpable mass in an FAL, imaging guidance is helpful in targeting the areas of soft tissue in the FAL; otherwise, false-negatives may result if fatty elements are sampled. On ultrasound, these lesions can be distinguished from the surrounding glandular tissue and have a heterogeneous echotexture with admixed areas of hypo- and hyperechogenicity; gentle mass effect may be seen on the surrounding tissue (Fig. 7.33B). On MRI, fatty and glandular elements are isolated within the breast by a thin “pseudocapsule” (Fig. 7.32B). Progressive enhancement of the glandular tissue may be seen on the dynamic sequence (Fig. 7.32C).
Lymphoid hyperplasia (acute or chronic inflammation)
Collagen vascular disorders (rheumatoid arthritis, scleroderma, lupus)
Granulomatous disease (sarcoid, tuberculosis)
Human immunodeficiency virus (HIV)
Dermatopathic (exfoliative or atopic dermatitis, psoriasis, infectious rashes)
Toxoplasmosis (cat scratch)
Trauma or surgery resulting in the release of fatty substances in the stroma of the breast can lead to an inflammatory response commonly characterized, in the acute setting, by an irregular mass with fatty tissue centrally, spiculated margins and architectural distortion; skin thickening and retraction may be present (Fig. 7.35). Alternatively, a round or oval mass with indistinct margins (Fig. 7.36A), an irregular mass with spiculated margins (Fig. 7.37A), a mixed-density mass with indistinct margins, or an irregular area of density (Fig. 7.38A) may be seen. As the inflammatory response subsides, the mammographic and ultrasound features of the lesion usually evolve. In some women, the mixed-density mass with spiculated margins becomes less dense and a fatty center develops; as the ill-defined soft tissue component resolves, a smooth thin walled oil cyst may be all that remains. The progression from dense, mass with spiculated margins to oil cyst is appreciated as films are viewed sequentially (Fig. 7.38B, C). In the intermediate stages, densities or nodules may be seen in the developing oil cyst (Fig. 7.38B, C). As the lesion continues to evolve, dystrophic-type calcifications can develop (Fig. 7.39); however, early in their formation, the calcifications can be linear with irregular margins and pleomorphism indistinguishable from the microcalcifications associated with comedo necrosis in ductal carcinoma in situ (DCIS) (see Figs. 6.43A and 6.46C, D). In other women, fat necrosis resolves completely, with no residual abnormality seen on subsequent studies (22). Less common appearances for fat necrosis include developing parenchymal asymmetry (Fig. 7.40A) or trabecular thickening, forming a fine reticular pattern (Fig. 7.40B).
Soo et al. (23) describe a wide range of ultrasound patterns for fat necrosis. In their experience, a complex mass with echogenic bands that may shift in position as the patient is moved is strongly suggestive of fat necrosis. They also found masses with echogenic mural nodules (Fig. 7.41B) that evolve with time, solid-appearing masses, and anechoic masses with posterior acoustic enhancement or shadowing (Fig. 7.37B) as manifestations of fat necrosis on ultrasound. In our experience, one of the more common ultrasound features of fat necrosis is an area of hyperechogenicity that may be well- to ill-defined, associated with cystic spaces or small round or oval areas of hypoechogenicity (Fig. 7.41C; also see Fig. 4.36) commonly disrupting tissue planes.
The appearance of fat necrosis on MRI is variable and, as seen with mammography and ultrasound, fat necrosis can mimic breast cancer on MRI (24). Low signal is noted on fat-suppressed T1 and T2 images (Figs. 7.36C and 7.42C) correlating with the fatty component seen mammographically, commonly in a subcutaneous location. The edges of these lesions may demonstrate smooth rim enhancement in the predominantly cystic lesions; however, the rim may be thickened, spiculated, or indistinct. If there is no lipid component, these lesions can simulate cancers morphologically with kinetic curves that can range from slow to rapid initial washin and progressive, plateau, and rapid washout delayed kinetics (Figs. 7.36B and 7.42B).
A history of trauma or surgery and the appearance of the lesion on sequential mammograms provide the assurance needed to characterize these lesions as benign in many patients. Ultrasound is usually not needed for the diagnosis. It is critical to recognize that following biopsy or trauma, mammographic findings peak approximately 4 to 6 months following the event, after which the findings stabilize or slowly resolve as described. Rarely, fat necrosis can develop and increase in size and density years after a biopsy or trauma. Since the mammographic, ultrasound (Fig. 7.43A, B), and MRI (Figs. 7.36B and 7.42B) features of fat necrosis overlap those of cancer, biopsy is indicated in those patients without a history of surgery or trauma correlated to the site of the imaging findings or in those in whom it develops years after the surgery with no apparent cause.
Histologically, fat necrosis is characterized by acute changes that evolve with time. Initially, fat cell disruption and hemorrhage is followed by hemosiderin deposition, infiltration by variable numbers of histiocytes, plasma cells, and lymphocytes. Chronic, progressive fibrosis develops peripherally surrounding the necrotic fat cells and calcifications (11,12).
WATER DENSITY MASSES
These masses contain no fat. In addition to the shape and marginal features of these masses, consider their density. The density can be described as low, equal to, or increased, compared with the density of an equal volume of breast tissue. Differential considerations for the more common benign and malignant round or oval masses with circumscribed to indistinct margins are provided in Table 7.8. The differential for some of the more common benign and malignant masses with spiculated margins is provided in Table 7.9. Depending on history, clinical presentation, palpable findings, imaging features (mammography and ultrasound), the lists can be more appropriately focused to a given patient and the clinical and imaging features of the mass. The age of a patient is a particularly critical factor when considering an appropriate differential for an individual patient: a developing, solid mass in a postmenopausal patient raises differential considerations that are different from the considerations for a developing solid mass in a woman in her 30s or early 40s.