Correlating Palpable and Nonpalpable Masses on Mammography and Ultrasound

A common problem is correlating palpable masses with ultrasound findings. To do this, the radiologist or technologist places an examining finger or a cotton-tipped swab directly on the palpable mass. The sonographer scans over the finger or cotton-tipped swab on the mass to generate a ring-down shadow. Subsequent removal of the finger or cotton-tipped swab from under the probe produces a scan of the palpable finding. Then the radiologist, technologist, and patient have no doubt that the palpable finding has been scanned because this technique ensures that the transducer is placed directly on the palpable finding.

Sometimes a palpable mass on the mammogram has to be correlated to the ultrasound and physical finding. Specifically, the radiologist has to show that the palpable mass, from the ultrasound and from the mammogram, are one and the same. To do this correlation, the radiologist or technologist finds the palpable mass, scans over it, and sees if an ultrasound mass is present. If a mass is present, the sonographer scans the mass and places a finger or cotton-tipped swab on the mass. The sonographer puts an indelible ink mark on the skin over the mass and places a skin marker over the palpable finding, then repeats the mammogram. If the marker is at or near the mammographic finding, the palpable, mammographic, and ultrasound findings all correlate with each other.

To correlate nonpalpable ultrasound findings with mammographic findings, the sonographer identifies the ultrasound finding and places a finger, cotton-tipped swab, or large unwound paper clip under the transducer so that a ring-down shadow is superimposed over the finding. The sonographer removes the transducer and marks this location on the skin with an indelible ink marker. A technologist places a metallic skin marker, such as a BB, on the ink spot and takes orthogonal mammographic views. The skin marker over the ultrasound finding should be in the same location as the mammographic finding on the films. It should be expected that even if the mammogram and ultrasound findings are the same, the mammographic finding might be 1 cm or more away from the skin marker on the films because the skin marker will be compressed away from the mass on the mammogram by the compression paddle.

Sometimes it is still uncertain whether an ultrasound and mammographic finding are one and the same. If the patient agrees to a biopsy of the ultrasound finding, the radiologist places a metallic marker into the mass using an ultrasound-guided, percutaneously placed needle after the biopsy (Fig. 4-3). Repeat mammograms should show the marker in the mass if the two findings are the same. Alternatively, a retractable hookwire may be placed in the mass. A mammogram with the wire in place will show that the ultrasound finding and the mammographic finding represent the same mass. The radiologist can subsequently remove the retractable hookwire.

Figure 4-3 Ultrasound-guided marker placement to correlate ultrasound and mammography findings. A, A patient with a mass seen only on the mediolateral oblique (MLO) view underwent ultrasound, showing an ill-defined round mass with an echogenic rim and acoustic shadowing. B, Under ultrasound guidance the patient underwent a core biopsy; a marker was placed in the mass and a BB skin marker was placed over the position where ultrasound detected the mass. C, An MLO view shows the marker in the mass and the BB over the mass, thus proving that the ultrasound-detected finding represents the abnormality on mammography. This mass proved to be invasive ductal cancer. Note the metallic linear scar marker on the skin over a previous biopsy.

The mammography and ultrasound report for a breast mass should describe if the mass is palpable; the size, shape, margin, and density of the mass; its location and associated findings; and any change from previous examinations, if known. The report should also include ultrasound finding descriptors and whether it correlates with the mammographic finding. Finally, each report that includes a mammogram should be assigned an ACR BI-RADS® final assessment code indicating the level of suspicion for cancer and follow-up management recommendations (Box 4-5).

Cancer

Invasive Ductal Cancer

Invasive ductal carcinoma is the most common breast cancer and accounts for approximately 90% of all cancers. Also known as invasive ductal carcinoma not otherwise specified (NOS), invasive ductal cancer usually grows as a hard irregular mass in the breast (Fig. 4-4). The classic appearance of invasive ductal cancer is a dense irregular or spiculated mass, occasionally containing pleomorphic calcifications or having adjacent pleomorphic calcifications representing DCIS. On the mammogram, the mass should be about the same size and density on two orthogonal mammographic views. Spot compression magnification views may show unsuspected calcifications in or around the mass or unsuspected irregular borders.

Box 4-6 Differential Diagnosis of Spiculated Masses

Invasive ductal carcinoma

Invasive lobular carcinoma

Tubular cancer

Postbiopsy scar

Radial scar

Fat necrosis (atypical)

Sclerosing adenosis

Figure 4-4 A to D, Spiculated invasive ductal cancers. A, A screening craniocaudal (CC) mammogram with a scar marker and mole marker shows a possible spiculated mass in the outer breast at the edge of the film (arrow). A spiculated mass is seen in the axilla on B, the mediolateral oblique (MLO) view, and the patient is recalled for a spot view, a lateral view, exaggerated CC, and ultrasound. C, On the exaggerated outer right CC view the mass is seen to greater advantage. D, In another patient, a spiculated retroareolar invasive ductal cancer (arrow) has caused nipple retraction (double arrow). A radiopaque marker has been placed on the nipple. In another patient, two spiculated masses are seen on CC (E) and MLO (F) views. Ultrasound of the spiculated masses shows an irregular mass (G) and a round mass (H) without sonographic spiculation. I, Spiculated invasive ductal cancer on magnification view has two benign-appearing calcifications within it. Note that even though the calcifications look benign, the spiculated borders of the mass are so worrisome for cancer that the worst finding overrides the benign look of the calcifications. Biopsy showed invasive ductal cancer. One should judge a mass with calcifications based on the worst characteristics of either the mass or the calcifications. J to L, Typical invasive ductal cancer findings on magnetic resonance imaging (MRI). J, The MRI shows a large enhancing mass growing through the pectoralis muscle with associated skin thickening. K, The ROI over the enhancing portion of the cancer on MRI selects the area in which a kinetic curve will be drawn. L, The kinetic curve shows rapid initial enhancement with a late-phase washout. The kinetic curve showing a rapid initial uptake and washout of contrast is very typical of cancer.

On ultrasound, spiculated masses shown on mammograms may be round, irregular, or spiculated. Spiculated masses commonly produce acoustic shadowing as a result of either productive fibrosis or tumor extension. When present, acoustic spiculation looks like thin radiating lines extending from the tumor into surrounding breast structures. In a dense white breast, the ultrasound spicules are dark against the white glandular tissue. In a fatty breast, the spicules are white against the dark fatty background. On magnetic resonance imaging (MRI), the usual appearance of invasive ductal cancer is a brightly enhancing irregular mass with or without spiculation; enhancement is initially rapid, with a late-phase plateau or washout curve. Rim enhancement, central enhancement, or enhancing internal septations are other worrisome signs for invasive ductal cancer on MRI.

Invasive Lobular Carcinoma

Invasive lobular carcinoma (ILC) is most commonly seen as an equal- or high-density noncalcified mass, occasionally showing spiculations or ill-defined borders. ILC has a higher rate of bilaterality and multifocality than does invasive ductal cancer. ILC accounts for less than 10% of all invasive cancers, but historically is the most difficult breast cancer to see on mammograms (Box 4-7). ILC is the cancer that gives radiologists a bad name because it can be missed by mammography, at a rate reported by Brem and colleagues to be as high as 21%. This failure can be partly explained by the growth pattern of the carcinoma. Classically, ILC grows in single lines of tumor cells infiltrating the surrounding glandular tissue and may not produce a mass, making it difficult to see by mammography and difficult to feel by physical examination. ILC usually does not contain microcalcifications. It infiltrates the breast, is often seen on only one view, and may cause subtle distortion of the surrounding glandular tissue. When actually seen on the mammogram, ILC masses are often of equal or higher density than fibroglandular tissue and are seen because of the mass itself or its effect on surrounding tissue, such as architectural distortion and straightening of Cooper ligaments. As with any mass, distortion and tenting of glandular tissue caused by ILC are most easily seen in locations where Cooper ligaments extend out into surrounding fat, such as in the retroglandular fat or along the edge of the normal, scalloped fibroglandular tissue (Fig. 4-5).

Box 4-7 Features of Invasive Lobular Carcinoma

10% of all breast cancers

Grows in single-cell files

Hardest tumor to see on mammography

Often seen on one view

Causes mass or architectural distortion

Calcifications not a feature

Figure 4-5 A to C, Invasive lobular cancer seen on only one view. Screening mediolateral oblique (MLO) (A) and craniocaudal (CC) (B) views; the suggestion of a spiculated mass behind the nipple is seen on the left CC view only. C, A spot compression CC view shows persistent spiculation and distortion caused by the invasive lobular carcinoma (ILC) behind the nipple on the left. The straight lines extending from the tumor into subcutaneous tissue are indicative of its presence. D, In another patient with ILC, a spiculated mass is seen at the edge of the film in the lower right breast on the right MLO view (arrow). The cancer looks very similar to the rest of the breast tissue and is seen only because of the spiculations extending into the fat and because it is a density where there is usually only fat. E, The MLO view in this patient shows a density behind the nipple, possibly a mass, but the nipple is not in profile. F, The right CC view with the nipple in profile now shows skin thickening and widespread architectural distortion throughout the entire breast tissue. G and H, On ultrasound, there is an extensive ILC with marked shadowing throughout the entire upper breast, with cancer in the entire breast on mastectomy. I and L, ILC presenting as a focal asymmetry. I, MLO paired mammograms show a focal asymmetry near the chest wall of the right breast. J, The CC mammogram shows a focal asymmetry in the medial right breast (arrow) roughly corresponding to the mass seen in the MLO view. K, Magnification cropped mammogram of the medial right CC study shows the mass that has caused the architectural distortion (arrow). L, Photographic magnification of the asymmetry shows not only a spiculated mass, but also tiny calcifications. This is invasive lobular cancer. Note that the mass is initially seen only because it is asymmetrically white on the initial mammograms.

On ultrasound, ILC is a hypoechoic, irregular, spiculated, or ill-defined mass that may or may not have acoustic shadowing. When ILC becomes very large, only the acoustic shadowing may be apparent; the mass itself can be difficult to see because of its large size. On MRI, invasive lobular cancer looks like a spiculated mass, with some limitations. Unfortunately, ILC has variable enhancing patterns; it can look like a mass, like a distortion of tissue, or like nodular regions connected by strands of tissue. Its enhancement kinetics can be similar to those of normal breast tissue and can thus be a cause of false-negative MRI examinations.

Postbiopsy Scar

On mammograms, an old postbiopsy scar looks like a spiculated mass that is impossible to distinguish from cancer. Postbiopsy scars show air and fluid at the biopsy site in the immediate postoperative period. Later, the air and fluid are absorbed and the surrounding glandular tissue is drawn to a central dense nidus of scar tissue. As a result, the mammogram shows a centrally dense spiculated mass (the scar) with straightening of the surrounding Cooper ligaments and indrawing of normal glandular tissue, simulating breast cancer. In some patients, no dense central nidus occurs, and the scar appears as a focal architectural distortion. On ultrasound, a postbiopsy scar is a hypoechoic mass with acoustic spiculation and shadowing, similar to cancer. There should be distortion of subcutaneous tissue extending from the scar on the patient’s skin down the plane of the incision to the spiculated postbiopsy scar.

The scar is not of concern for cancer if it occupies a surgical site (Box 4-8). To distinguish postbiopsy scars from cancer, the radiologist looks at the previous biopsy locations on the breast history form and reviews older films to see if the “scar” is at the same location. Some facilities place a radiopaque linear metallic scar marker on the patient’s skin scar to show the location on the mammogram (Fig. 4-7A to D). The metallic linear scar marker should be on top of the “scar” (see Fig. 4-7E and F). If the “scar” does not correspond to a postbiopsy site, it is not a scar. Because spiculated masses may represent cancer, they should be considered suspicious and should undergo biopsy.

Figure 4-7 A to D, Postbiopsy scar versus cancer simulating a scar. Left (A) and right (B) mediolateral oblique (MLO) and left (C) and right (D) craniocaudal (CC) views; architectural distortion is seen in the right upper outer quadrant only on the MLO view and not on the CC view in a patient with a history of previous benign surgical biopsy findings. A metallic linear scar marker placed on the patient’s scar in the MLO projection (B) shows that the distortion lies directly below the skin scar and represents a postbiopsy scar. E, In another patient, the linear metallic biopsy scar marker lies far from a spiculated mass on the CC view. F, A lateral view shows the spiculated mass in the midportion of the breast, above the top of the biopsy scar marker in the lower part of the breast; it is better seen on the MLO view (G). Because the spiculated mass was far from the biopsy site, the mass could not represent a postbiopsy scar and was sampled; grade II invasive ductal cancer was diagnosed.

Fat Necrosis, Sclerosing Adenosis, and Other Benign Breast Disease

Fat necrosis is due to saponification of fat from previous trauma, usually from surgery or blunt trauma due to an injury, such as from a steering wheel or seat belt in an automobile accident. On mammography, fat necrosis typically contains a fatty lipid center and is round, but it occasionally has a spiculated appearance. Other appearances include asymmetric opacity, round opacity, and dystrophic or pleomorphic calcifications. The diagnosis may be established by eliciting a history of blunt trauma or previous surgery. On occasion, fat necrosis contains a dense or equal-density central nidus with radiating folds extending from its center, similar to cancer, prompting biopsy. On ultrasound fat necrosis can appear cystic with or without posterior acoustic enhancement or internal echoes in about 30%, showing increased echogenicity in 27% and solid in approximately 14%, as reported by Bilgen and colleagues. With true fat necrosis, follow-up should show a decrease in size of masses; the occasional increasing fat necrosis lesion should undergo biopsy, leading to the diagnosis.

Sclerosing adenosis is a proliferative benign lesion resulting from mammary lobular hyperplasia. It is characterized by the formation of fibrous tissue that distorts and envelops the glandular tissue. The resulting process produces sclerosis of the surrounding tissue. The small duct lumens can contain microcalcifications. This results in spiculations and calcifications that, in mammography, can be difficult to distinguish from invasive cancer, resulting in biopsy.

Both sclerosing adenosis and proliferative fibrocystic change may have a slightly spiculated appearance on mammography; they occasionally also contain calcifications and can simulate cancer. When spiculated and associated with calcifications, fat necrosis, sclerosing adenosis and proliferative fibrocystic disease undergo biopsy and are a cause of false-positive biopsies (Fig. 4-8).

Figure 4-8 Proliferative fibrocystic change appearing as architectural distortion. A, A magnification exaggerated craniocaudal view shows architectural distortion. B, The distortion is very hard to see on the corresponding magnification mediolateral view in the upper outer quadrant of the left breast. Excisional biopsy showed proliferative fibrocystic change and calcifications in benign ducts—a very unusual appearance of proliferative fibrocystic change.

Radial Scar

A radial scar is a benign proliferative breast lesion that has nothing to do with a postbiopsy scar but looks like a spiculated mass or postbiopsy scar. Both radial scars and their larger variants, called complex sclerosing lesions, may include adenosis and hyperplasia. In autopsy series, small radial scars are common but often may not be apparent on mammography. The central part of a radial scar undergoes atrophy, thereby resulting in a scarlike formation, with pulling in of the surrounding glandular tissue that produces a spiculated mass. On occasion, because of entrapment of breast ductules, the radial scar may be difficult for pathologists to distinguish from infiltrating ductal carcinoma. However, both epithelial and myoepithelial cells in benign radial scars distinguish them from breast cancer. Radial scars may contain or be associated with atypical ductal hyperplasia, atypical lobular hyperplasia, lobular carcinoma in situ, or cancer. This is one of the rationales for surgical excision. Some pathologists believe that a radial scar may be a precursor to tubular carcinoma and should be excised, although this position is controversial.

On mammography, a radial scar appears as a spiculated mass with either a dark or white central area that may or may not have associated microcalcifications (Fig. 4-9). It is a myth that radial scars have dark centers in the mass on mammography (Fig. 4-10) and can be distinguished from breast cancers, which have white-centered masses. Scientific studies have shown that radial scars and breast cancer can both have either white or dark centers on mammograms. This means that all spiculated masses not representing a postbiopsy scar should be sampled histologically (Box 4-9). On ultrasound, a radial scar is a hypoechoic mass, with or without acoustic shadowing.

Figure 4-9 Radial scar simulating cancer. Mediolateral oblique (MLO) (A) and craniocaudal (CC) (B) views show the suggestion of a spiculated mass in the upper outer portion of the breast. The presence of a spiculated mass is confirmed on spot magnification MLO (C) and CC (D) views. Note that a spiculated radial scar is indistinguishable from spiculated cancer. E, Another radial scar is seen as a vague spiculated mass with a dense white center in the upper part of the breast, and on ultrasound (F) it has characteristics similar to those of cancer, thus showing that radial scars can be indistinguishable from cancer on imaging. G, A radial scar in a third patient appears as a spiculated mass with associated calcifications and on biopsy contained high-grade ductal carcinoma in situ, fibrocystic change, and calcifications.

Figure 4-10 Radial scar. A craniocaudal mammogram shows a dense spiculated mass suggestive of cancer. Spot compression magnification shows that the central dense portion of the mass is less dense but the architectural distortion remains. Cancer can look exactly the same.

Malignant Tumors

Invasive Ductal Cancer

Invasive ductal cancer is the most common round breast cancer (Fig. 4-11). The “round” invasive ductal cancer is an uncommon form of the most common cancer. Invasive ductal cancer represents approximately 90% of all invasive breast cancers. So even though invasive ductal cancers are not often “round,” there are so many invasive ductal cancers that the uncommon round form of the most frequent breast cancer is the most common histologic type (Box 4-11).

Box 4-10 Differential Diagnosis of Round Masses

Cyst

Fibroadenoma

Invasive ductal cancer not otherwise specified (most common round cancer)

Medullary cancer

Mucinous (colloid) carcinoma

Papillary carcinoma

Intracystic carcinoma

Metastasis

Phyllodes tumor

Papilloma

Lactating adenoma

Adenoid cystic carcinoma

Sebaceous cyst (near skin)

Epidermal inclusion cyst (near skin or in breast after biopsy)

Figure 4-11 A to E, Round invasive ductal carcinomas (not otherwise specified). A, A mediolateral oblique (MLO) mammogram shows a round dense mass with associated pleomorphic calcifications and a suggestion of smaller round masses adjacent to it. Ultrasound shows an oval hypoechoic irregular mass (B) and a multilobulated mass (C), both representing invasive ductal cancer. In another patient, a slightly lobulated, circumscribed, round equal-density mass on mammography (D) simulates a fibroadenoma; on ultrasound it has a benign circumscribed oval shape (E). Biopsy showed invasive ductal cancer. Palpable round mass in left breast representing invasive ductal cancer on MLO (F) and craniocaudal (CC) (G) views with a marker on the finding. Note that the mass could easily be mistaken for a fibroadenoma or a cyst because of its benign appearance. H, CC mammogram shows a vague round mass in the medial left breast, seen because it is against a fatty background and is in a medial location (arrow). The differential is a focal area of glandular tissue, a cyst or a solic mass. I, Magnification mammogram shows the mass has indistinct borders rather than circumscribed borders (arrow). This shows the importance of getting additional views and of being suspicious of medial breast masses. Usually residual fibroglandular tissue is in the upper outer (not inner) quadrants. A biopsy showed invasive ductal cancer.

Box 4-11 Round Breast Cancers

Although medullary and mucinous cancers are often round in form, they are uncommon. The most common round breast cancer is invasive ductal cancer, an uncommon form of the most common cancer.

The classic invasive ductal cancer is a dense spiculated or irregular mass on mammography. The much less common “round” invasive ductal cancer may grow so rapidly that it does not produce spiculated margins. On screening mammography, round invasive ductal cancer may appear to have a smooth border. However, the borders of the mass may be obscured by surrounding breast tissue, or the standard mammogram may not have the resolution required to reveal abnormal borders. Magnification views may show irregular, microlobulated, or indistinct borders, suggesting invasion of surrounding tissue and the true diagnosis. This is why new round masses on screening mammography are tricky and should be recalled from screening. A new round invasive ductal cancer mimicks benign cysts or fibroadenomas, and the radiologist can mistakenly think the “round” mass is benign until the mass undergoes magnification.

On ultrasound, the round invasive cancer may be smooth-bordered, may show suspicious abnormal findings such as “taller than wide” shape, or may be characterized by a thick echogenic rim. Taller than wide, as described by Stavros and colleagues, means a mass that has invaded through the normal horizontal tissue planes as defined by the thin echogenic Cooper ligaments. Taller means that the cancer grows up toward the skin and violates normal tissue planes rather than growing horizontally between Cooper ligaments (like benign tumors). The “taller than wide” ultrasonographic sign is important in the diagnosis of breast cancer.

Medullary Cancer

Medullary cancer is an invasive breast cancer that commonly has a round or pushing border. Medullary cancers occasionally have a surrounding lymphoid infiltrate and have a better prognosis than infiltrating ductal cancer (NOS). They are common in BRCA1-associated carcinomas. Atypical medullary cancers have the same prognosis as infiltrating ductal cancer. On screening mammography, medullary cancer is a high- or equal-density round mass whose margins may appear well circumscribed, suggestive of a cyst or fibroadenoma (Fig. 4-12). On ultrasound, medullary cancers are round, solid, and homogeneous. Because they are homogeneous, medullary cancers occasionally cause posterior acoustic enhancement. Because medullary cancers can simulate a breast cyst by their homogeneous nature and posterior acoustic shadowing, it is important to pay careful attention to technical details during scanning to show that the internal features are hypoechoic rather than anechoic. Color or power Doppler ultrasound may show internal vascularity, unlike an anechoic simple cyst. The pushing expansile growth of medullary cancer may produce well-circumscribed mass borders, similar to fibroadenoma, and is a cause for misdiagnosis. This means that a new round solid mass should be biopsied even if it is well-circumscribed.

Figure 4-12 Medullary cancer. The mammogram shows a round cancer with apparent circumscribed borders when they are not obscured by adjacent dense glandular tissue in the inner portion of the breast on craniocaudal (A) and mediolateral oblique (B) mammograms. C, On ultrasound, the medullary cancer is a round mass with microlobulated and occasionally irregular borders and acoustic enhancement.

Mucinous (Colloid) Carcinoma

This rare, round or oval cancer contains malignant tumor cells that float in mucin within a solid tumor rim. The mucinous portion can have fibrovascular bands segregating the mucinous compartments that comprise the tumor and give it its name. On mammography, mucinous cancers with a large volume of mucin show a well-circumscribed low-density round mass that can suggest a cyst or fibroadenoma and can occasionally have lobulated margins. Mixed type mucinous carcinomas may have poorly defined or spiculated margins. On ultrasound, the tumor mass is round and may be isoechoic to fat, occasionally contains fluid-filled hypoechoic spaces, and may have posterior acoustic enhancement (Fig. 4-13). The mass can simulate a cyst on ultrasound, but unlike the cyst it will not be entirely anechoic. Thus, new round masses on a mammogram that have solid components or do not meet all the specific criteria for a simple cyst on ultrasound should be considered for biopsy.

Figure 4-13 Mucinous cancer. A, A mediolateral oblique (MLO) mammogram shows dense tissue and a metallic scar marker over a previous benign biopsy site; the palpable mass is not seen. B, Ultrasound shows an oval solid heterogeneous mass representing the mucinous cancer. C, Ultrasound of another patient with mucinous cancer shows an oval heterogeneous mass containing fluid-filled spaces. Left MLO (D) and craniocaudal (E) mammograms show an equal-density lobulated mass near the nipple with the marker on it. On ultrasound, a microlobulated heterogeneous mass containing cystic structures is seen on transverse (F) and longitudinal (G) views, worrisome for cancer or a heterogeneous fibroadenoma. Note that the mucinous cancers often contain “cystic” spaces due to the mucin within the tumors. On magnetic resonance imaging (MRI) the axial T1-weighted noncontrast localizer (H) shows a low signal intensity mass against the bright fat near the nipple, corresponding to the mass seen on the mammogram and ultrasound. I, The unenhanced T2-weighted sagittal MRI shows a high signal intensity mass with dark septations within the mass, suggesting either fibroadenoma or mucinous cancer. J, The contrast-enhanced 3-D spectral-spatial excitation magnetization transfer (SSMT) sagittal image shows an irregular round mass with either dark septations or central necrosis. The irregular mass margin and thick irregular internal dark septations suggest cancer instead of fibroadenoma (in fibroadenoma the septations are thinner and regular, and the mass border is usually smooth). Core biopsy showed mucinous cancer.

Papillary Carcinoma

This rare tumor accounts for only 1% to 2% of all cancers and is the malignant form of benign intraductal papilloma. Papillary cancers may be single or multiple (Box 4-12), and DCIS is sometimes seen in surrounding breast tissue. Classically, these masses are round, oval, or lobulated on mammography, sometimes containing calcifications, and are solid on ultrasound. If associated with nipple discharge and detected by ultrasound, papillary cancers are solid intraductal masses outlined by a fluid-filled structure and are difficult to distinguish from a benign intraductal papilloma (Fig. 4-14).

Box 4-12 Differential Diagnosis of Multiple Round Masses

Cysts

Fibroadenomas

Multiple round invasive breast cancers

Metastases; vary in size, nonductal growth pattern

Papillomas; may grow in a ductal pattern

False masses: skin lesions

Figure 4-14 Papillary carcinoma. Ultrasound of a papillary cancer shows a fluid-filled dilated duct with a solid oval intraductal mass that cannot be distinguished from a benign intraductal papilloma on the scan.

Intracystic Carcinoma

This extremely rare tumor produces a solid mass in a cyst wall, and the mass looks like a cyst on mammography. Because the tumor is mostly mucin, the mammographic mass is low density unless it has a denser solid component or has bled into the cystic portion to produce a dense mass (Fig. 4-15A). On ultrasound, an intracystic carcinoma is a solid mural mass surrounded by cystic fluid that yields fresh or old blood on aspiration (see Fig. 4-15B). On pneumocystography, the air inside the cyst wall will outline a solid mass along the border of the wall. Intracystic carcinomas must be excised, just as all other cancers are excised. The differential diagnosis for a solid intracystic mass includes intracystic carcinoma, intracystic papilloma, and a cyst with debris adherent to the cyst wall.

Figure 4-15 Intracystic carcinoma. A, A mammogram shows a dense oval mass. B, Ultrasound shows a fluid-filled cyst with an irregular mural mass. Although this mass was an intracystic carcinoma, the differential diagnosis includes papilloma or debris in a benign cyst.

Breast Metastasis

Axillary or intramammary lymph node metastasis from breast cancer, lymphoma, or other malignancy makes the normal benign lymph node change its appearance from a well-defined oval or lobular mass with a central radiolucency to a rounder, bigger, and denser mass with loss of the fatty hilum (Fig. 4-16). This results in a round, dense mass. Metastases can occur from breast cancer, lymphoma, leukemia, melanoma, other adenocarcinomas, and even mesothelioma.

Figure 4-16 A to D, Breast metastases. Bilateral right (A) and left (B) mediolateral oblique (MLO) views in a patient with colon cancer show a palpable round dense mass in the right axilla with a marker on it (A) and a palpable round mass in the lower left breast (arrow) (B). Ultrasound on the left (C) and right (D) masses shows round echogenic but heterogeneous masses. The differential diagnosis is metastasis, primary breast cancer, or fibroadenoma. Biopsy showed metastatic colon carcinoma. Bilateral right (E) and left (F) MLO views in a patient with neuroendocrine cervical cancer show multiple dense masses in the retroareolar regions. The masses are also seen on the right (G) and left (H) craniocaudal views. The differential diagnosis includes multiple cysts, fibroadenomas, cancers, papillomas, and metastases. On breast ultrasound, the masses are solid; some are round or oval (I), but others have at least one microlobulated border (arrow) (J) or irregular borders (K), excluding the diagnosis of cysts or fibroadenomas. Core biopsy showed bilateral breast metastases.

Hematologically spread metastases are single or multiple, round, usually circumscribed, and very dense masses in one or both breasts (see Fig. 4-16). The masses vary in size as a result of the various lengths of time that the metastases have had to grow in breast tissue. Typically, the appearance of multiple new solid masses all over the breast in a nonductal pattern is worrisome for hematogenous spread of cancer from a nonbreast site, similar to pulmonary metastases. Melanoma and renal cell carcinoma were reported to metastasize to the breast in this manner. The differential diagnosis of multiple solid breast masses includes multiple fibroadenomas or papillomas, or metastases when there are no old films for comparison.

Benign Tumors

Fibroadenoma

This most common solid benign tumor in young women is thought to arise from the terminal ductal lobular unit via localized hypertrophy. Fibroadenomas can be single or multiple. A fibroadenoma contains structures suggesting breast ductules and also has stromal tissue, which can be quite cellular in young women. Fibroadenomas may also undergo adenosis or hyperplasia and proliferation and may contain fibrous bands or septations. DuPont and colleagues described fibroadenomas containing such proliferation or cysts with the nomenclature complex fibroadenomas. Giant fibroadenomas are 8 cm or larger. Juvenile fibroadenomas occur in adolescents and can grow rapidly, stretch the skin, and become huge. Because juvenile fibroadenomas may grow to such a large size, they may be called giant fibroadenomas, but not all giant fibroadenomas are juvenile fibroadenomas.

On mammograms, the classic fibroadenoma is an oval or lobular equal-density mass with smooth margins. In young patients, fibroadenomas are very cellular. As the fibroadenoma ages, it may become sclerotic and less cellular. Popcorn-like calcifications subsequently develop at the periphery of the mass. Eventually, the entire mass may be replaced by dense calcification and look like a “breast rock.”

On ultrasound, fibroadenomas are oval, well-circumscribed homogeneous masses, usually wider than tall, with up to four gentle lobulations. They are hypoechoic but may occasionally contain cystic spaces. Posterior acoustic enhancement is increased, equal, or shadowing (Fig. 4-17). Fibroadenomas occasionally display irregular borders or heterogeneous internal characteristics, so biopsy is necessary to distinguish these atypical-appearing fibroadenomas from cancer.

Figure 4-17 A to F, Biopsy-proven fibroadenomas. Magnification craniocaudal (A) and mediolateral oblique (B) views in a young woman show an equal-density, circumscribed oval mass that is hard to see against the dense tissue. Ultrasound shows an oval, lobulated, well-circumscribed homogeneous mass on transverse (C) and longitudinal (D) scans. E, In another patient, the mammogram shows a lobular well-circumscribed mass whose borders are partly obscured. F, Ultrasound shows an oval well-circumscribed homogeneous mass. Another patient has a round equal-density mass on mammogram (G), but on ultrasound (H) the mass is multilobulated and very hypoechoic, similar to cancer. I and J, Ultrasound of another atypical biopsy-proven fibroadenoma shows a taller than wide multilobulated mass with internal speckles. Another atypical palpable biopsy-proven microlobulated fibroadenoma, seen on the mammogram in the lower part of the breast (K) and on ultrasound (L). M and N, Other atypical appearances of biopsy-proven fibroadenoma on ultrasound. O to Q, Ultrasound of a typical fibroadenoma. O, Ultrasound of a palpable mass in a young woman shows a typical well-circumscribed homogeneous mass suggestive of fibroadenoma. P, Doppler ultrasound shows vascularity within the fibroadenoma. Q, Image of the needle during ultrasound-guided core biopsy. Pathology showed fibroadenoma. R to T, Ultrasound of a complex fibroadenoma. Ultrasound of a palpable mass in a young patient shows a well-circumscribed oval solid mass with bright linear septa and a slightly hypoechoic central area in transverse (R) and longitudinal (S) images. The mass has five gentle lobulations on the longitudinal scan and an area of central hypoechogenicity. T, Color Doppler ultrasound shows flow within the mass. Biopsy was done because of the central hypoechogenicity and five lobulations. Biopsy showed fibroadenoma.

Because fibroadenomas contain ductal elements, ductal or lobular carcinoma in situ occurs in fibroadenomas rarely. Any suspicious change in a fibroadenoma should prompt biopsy for this reason.

On MRI, fibroadenomas have the classic appearance of an enhancing oval or lobulated mass with well-circumscribed borders. In 20% they contain dark internal septations. Kinetic data shows a gradual initial enhancement rate and a late persistent enhancement curve. The initial enhancement rate in fibroadenomas can change from slow to rapid, depending on the phase of the woman’s menstrual cycle. In premenopausal women, the initial enhancement changes from slow to rapid, as rapid as cancer, just before menses. But unlike cancer, which shows late plateau or washout curves, the late enhancement curve of a fibroadenoma is persistent. In the week or two after the onset of menses, the initial enhancement curves in fibroadenoma revert back to a gradual initial enhancement curve.

Phyllodes Tumor

Phyllodes tumors used to be called cystosarcoma phyllodes, which is a misnomer because most of these uncommon tumors are benign. Classically, the phyllodes tumor occurs in women in their fifth decade, with a median age of 45 years, and can be quite large, up to 5 cm in size when first detected. In the clinic, most often women with a phyllodes tumor seek advice for a rapidly growing palpable mass. Because the phyllodes tumor can have a biphasic growth pattern, some women report growth of a mass that has been stable for many years. A phyllodes tumor has both stromal and epithelial elements, in contrast to fibroadenoma. The phyllodes tumor also has fluidlike spaces containing solid growth of cellular stroma and epithelium in a leaflike configuration, from which the tumor gets its name. The preferred treatment is wide surgical excision. Incomplete excision of either benign or malignant phyllodes tumors may result in local recurrence in 15% of cases, and they may be excised again and again, only to grow back. About 25% of phyllodes tumors are malignant; 20% of the malignant subtype may metastasize. No distinguishing imaging features can be used to differentiate malignant phyllodes tumors from the more common benign form.

On mammography, a phyllodes tumor is a dense round, oval, or lobulated noncalcified mass with smooth borders. On ultrasound, a phyllodes tumor is a smoothly marginated inhomogeneous mass that occasionally contains cystic spaces producing acoustic posterior enhancement, and it can be mistaken for a fibroadenoma or circumscribed cancer (Fig. 4-18). The goal of imaging is to identify the tumor for wide excision and to search for recurrence in the biopsy bed after surgery when the patient returns for routine follow-up.

Figure 4-18 Phyllodes tumors. A to C, Ultrasound of three separate phyllodes tumors in a young woman shows palpable solid lobulated masses, two of which are circumscribed and lobulated. One is heterogeneous and slightly suggestive of cancer. In another patient with a phyllodes tumor, lateral (D) and craniocaudal (E) mammograms show a dense circumscribed mass and a separate cluster of pleomorphic calcifications. Note metallic scar markers showing a previous biopsy site. F, Ultrasound reveals a lobulated circumscribed hypoechoic mass that was removed by excisional biopsy; examination of the specimen showed a phyllodes tumor and calcifications in benign ducts.

Papilloma

Papillomas are either solitary or multiple. In young patients, papillomas are called juvenile papillomas. Solitary papillomas are either central or peripheral, originate in the ductal epithelium, and are often seen in the subareolar region or in subareolar ducts. Tumors starting in the terminal ducts further from the nipple are called peripheral papillomas and are considered a risk factor for breast cancer. Multiple papillomas are usually in a more peripheral location in younger women. Juvenile papillomatosis occurs in young women, but multiple papillomas can also be seen in much older women. Papillomas grow on fibrovascular stalks, which can twist and lead to ischemia, necrosis, and blood extending into the duct. The bleeding papilloma results in the classic symptom of bloody nipple discharge, similar to a symptom of DCIS, causing patients to seek advice. Clinically, papillomas can also cause new, spontaneous clear or serous nipple discharge. Papillomas are usually excised to exclude DCIS or papillary cancer.

On mammography, papillomas are round, well-circumscribed, equal-density masses that occasionally contain calcifications. They are usually located in the subareolar region. In papillomatosis, papillomas can be multiple and peripherally located (Fig. 4-19). Occasionally, papillomas are not seen on mammography or ultrasound at all despite the symptom of bloody or clear nipple discharge. On ultrasound, papillomas are solid round, oval, or microlobulated hypoechoic masses. Small internal cystic spaces are seen occasionally in juvenile papillomatosis. In patients with nipple discharge, ultrasound may show papilloma as a solid mass in a fluid-filled subareolar duct. On galactography, the papilloma produces an intraductal filling defect.

Figure 4-19 Papillomas. Craniocaudal (CC) (A) and mediolateral (B) magnification views of a galactogram show an irregular microlobulated filling defect from a papilloma. C, A galactogram in another patient shows a papilloma as a smooth filling defect obstructing a dilated duct. D, A mammogram in another patient shows a palpable round irregular mass with calcifications. E, Ultrasound shows a circumscribed oval homogeneous mass. Biopsy revealed intraductal papilloma with apocrine atypia. F, In another patient with nipple discharge and a marker on the nipple, CC spot mammogram shows dilated ducts, a possible mass in the retroareolar region, and scattered benign-appearing calcifications. Ultrasound shows an intraductal mass in a fluid-filled duct in transverse (G) and longitudinal (H) images (arrows). The differential diagnosis includes papilloma, papillary cancer, and ductal carcinoma in situ. Biopsy showed papilloma. I to L, Papilloma on magnetic resonance imaging (MRI). I, Noncontrast T1-weighted fat-suppressed sagittal MRI of the mass seen in parts F to H shows high precontrast signal intensity in a dot in the retroareolar region on the right, which may represent debris in the fluid-filled duct. J, Postcontrast 3-D spectral-spatial excitation magnetization transfer (SSMT) sagittal MRI shows an enhancing mass in the retroareolar region. K, Spiral dynamic sagittal MRI with an ROI over the enhancing mass; the corresponding kinetic curve (L) shows that the mass has a rapid initial enhancement curve and washout. The MRI findings are compatible with either invasive ductal cancer or a papilloma. Biopsy showed papilloma.

On MRI, papillomas are round enhancing masses, with a rapid initial rise and a late plateau as washout on kinetic curves, indistinguishable from invasive ductal cancers. Bright T2-weighted signal in ducts on precontrast studies, when seen, represents fluid-filled ducts. If a papilloma is present, the high signal in the duct may obscure an enhancing papilloma within it.

The finding of a round solid mass suspected to be papilloma requires a histologic diagnosis. Follow-up for papillomas diagnosed by core biopsy is controversial. However, surgical excisional biopsy is universally advised for papillomas with papillary carcinoma, atypia, or nonconcordant imaging findings. Surgical excisional biopsy for papillomas without atypia or malignancy diagnosed by core biopsy is variable, but many investigators recommend excision.

Lactating Adenoma

Occurring in young pregnant patients in the second or third trimester, lactating adenomas are solid well-circumscribed masses that can enlarge rapidly during pregnancy. Patients seek clinical evaluation because of a growing palpable mass not previously felt. On ultrasound, a lactating adenoma is oval or lobular, smoothly marginated, and can contain cystic or necrotic spaces; biopsy by either fine-needle aspiration or core needle biopsy is used to evaluate it (Fig. 4-20). The mass may regress in size in the postpartum period.

Figure 4-20 Lactating adenoma. A, A periareolar, well-circumscribed mass containing one calcification in a 7-month-pregnant woman grew in the previous few weeks and was confirmed to be a lactating adenoma on biopsy. B, A 4.8-cm heterogeneous lobulated oval mass in another pregnant patient. C, It is seen to contain blood vessels within the lactating adenoma on Doppler ultrasonography.

Invasive Ductal Cancer

On mammography, the indistinct margins of invasive ductal cancer are due to infiltration of the surrounding glandular tissue by tumor. The mass margin can appear unsharp or smudged, similar to a line partially erased by a pencil eraser. The indistinct margin is best seen on spot magnification views against a fatty background. On ultrasound, the indistinct tumor mass occasionally has an echogenic rim or halo that suggests the diagnosis (Fig. 4-21).

Figure 4-21 A and B, Indistinct invasive ductal cancer. A, Mammography shows a round mass with indistinct margins and an upper partly spiculated border displayed against a fatty background. B, Ultrasound shows a round, irregular mass with a thick echogenic halo. C to E, Indistinct invasive ductal cancer. C, Craniocaudal (CC) paired mammograms show a focal asymmetry in the medial right breast (arrow). D, Paired mediolateral oblique mammograms show a focal asymmetry in the upper right breast corresponding to the finding on the CC mammogram (arrow). E, Photographic magnification shows an indistinct mass representing invasive ductal cancer (arrow).

Invasive Lobular Carcinoma

Often seen on only one view, lobular carcinoma may appear as an indistinct mass without microcalcifications. A more typical appearance of invasive lobular carcinoma is a spiculated mass or architectural distortion without calcifications.

Sarcoma

Breast sarcomas are rare. Typically, they contain malignant stromal elements but, on occasion, may contain fibrous elements, seen in the rare fibrosarcoma. Even more rarely, a breast sarcoma contains osseous elements and bone. As in invasive ductal cancer, these tumors are usually solid masses with ill-defined margins on both mammography and ultrasound.

Lymphoma

Lymphoma can involve breast lymph nodes or can occur as a primary or secondary site in the breast parenchyma. Lymphadenopathy is the most common appearance of lymphoma involving the breast and is seen on the mammogram as large dense lymph nodes in the axilla that have lost their fatty hila and become bigger and rounder (Fig. 4-22A). Primary or secondary breast lymphoma is usually caused by non-Hodgkin lymphomatous infiltration into breast tissue and not into a lymph node. It is a rare cause of an ill-defined mass that looks just like invasive ductal cancer on mammography (see Fig. 4-22B to F). The borders of the mass are indistinct because of lymphomatous infiltration into the surrounding glandular tissue, but it can occasionally be well-circumscribed or lobulated. On ultrasound, primary or secondary breast lymphomas in the breast tissue appear as hypoechoic masses.

Figure 4-22 Breast lymphoma involving the axillary lymph nodes. A, Bilateral mediolateral oblique mammograms show large dense masses in each axilla representing lymphadenopathy from lymphoma. Bilateral lymphadenopathy suggests systemic disease, such as lymphoma, leukemia, metastatic disease, systemic infection, or collagen vascular disease. Primary breast lymphoma in another patient appears as an equal-density, ill-defined mass in the lower part of the breast on lateral medial (B) and craniocaudal (CC) (C) mammograms in breast tissue that is indistinguishable from breast cancer. Note the linear scar marker showing a previous biopsy site.D, Craniocaudal spot compression shows that the mass persists. E, Ultrasound reveals a hypoechoic mass. Primary breast lymphoma in another patient appearing as an ill-defined mass near the chest wall on craniocaudal (F) and mediolateral (G) mammograms is less distinct and less dense than the lymphoma that appears more mas7slike in parts B to D.

Without a diagnosis of lymphoma elsewhere in the body, the diagnosis of primary breast lymphoma is often unsuspected until percutaneous biopsy is performed on the breast mass prompting the investigation. Primary breast lymphoma is treated by chemotherapy and radiation therapy, not by surgical excisional biopsy, thus distinguishing its treatment from that of breast cancer. If a patient has a primary diagnosis of lymphoma elsewhere in the body and presents with a new ill-defined breast mass, the first and foremost diagnosis for the breast mass should be primary breast cancer, with a secondary but important differential diagnosis of breast lymphoma. Because breast cancer and lymphoma of the breast are treated differently, fine-needle or core biopsy should be done to establish a diagnosis and determine patient management.

Pseudoangiomatous Stromal Hyperplasia

Pseudoangiomatous stromal hyperplasia (PASH) is a rare benign cause of a growing ill-defined noncalcified round or oval mass. It occurs in premenopausal women or in postmenopausal women receiving exogenous hormone therapy (Fig. 4-23). Occasionally, the mass may be well-circumscribed. This entity is of unknown etiology and is composed of stromal and epithelial proliferation; it occasionally shows rapid growth on mammography and requires biopsy. On ultrasound, PASH is a mixed or hypoechoic mass with ill-defined borders in 62%, as reported by Wieman and colleagues. It is thought that there is a hormonal influence on its development, and PASH is more often seen in premenopausal women or postmenopausal women receiving hormone therapy. Fine-needle aspiration can be inconclusive, as can core needle biopsy. Because low-grade angiosarcoma can mimic PASH on core biopsy, excisional biopsy is recommended if the mass grows.

Figure 4-23 Pseudoangiomatous stromal hyperplasia (PASH). A, This solid oval mass on ultrasound in an older woman looks like fibroadenoma or cancer but proved to be PASH on biopsy. B, In another patient, biopsy-proven PASH was discovered on the mammogram as a dense, partly obscured mass in the midportion of the breast, and a biopsy of the mass was performed.

Squamous Cell Carcinoma

Squamous cell tumors are even rarer than adenoid cystic carcinoma and produce a large, round, noncalcified, ill-defined mass. Other reports describe well-defined masses. On ultrasound, the masses are hypoechoic, with some reports describing central cystic spaces. They are located in breast tissue and are not found near the skin. The diagnosis of a primary squamous cell carcinoma should be established after the exclusion of the possibility of metastasis from another site, such as either a primary skin cancer or cancer at a distant site such as cervical carcinoma.

Lymph Nodes

The lymph nodes are typically seen in the axilla. They are round or oval and contain a radiolucent fatty center. Benign lymph nodes may be of any size, have a smooth solid cortex, and contain a fatty hilum (Fig. 4-24). An intramammary lymph node has the same appearance as lymph nodes in the axilla; it is often located in the upper outer quadrant of the breast along blood vessels and should not be mistaken for a malignancy. In questionable cases, spot magnification views demonstrate a well-circumscribed oval or lobulated mass and, importantly, its fatty hilum. On breast ultrasound, the lymph node is hypoechoic and bean-shaped and contains a fatty center. On color Doppler ultrasound, the lymph node hilum or fatty center will contain a pulsating blood vessel (see Fig. 4-24D). On MRI, the lymph node kinetics show rapid initial enhancement with late washout, similar to cancer, due to its central blood vessel. However, its typical appearance on MRI, which shows a solid mass with the fatty hilum and high signal on T2-weighted images, should distinguish it from cancer, which has no fatty hilum and commonly has low signal on T2-weighted images.

Figure 4-24 Lymph node. A, A mediolateral oblique (MLO) view shows benign fat-containing lymph nodes in the axilla and a round mass in the central portion of the breast. B, A craniocaudal view shows the round mass but without a fatty hilum, not suggestive of an intramammary lymph node. C, Ultrasound of the mass shows an oval hypoechoic mass with an echogenic center, typical of a lymph node. D, Doppler ultrasound shows the typical pulsating blood vessel in the middle of the fatty hilum. E, Ultrasound shows a typical lymph node in the axilla of the same breast. F, Lymphadenopathy and cancer. MLO mammogram with the marker on a round cancer in the upper left breast shows an abnormal round, dense lymph node in the axilla overlying the pectoralis muscle (arrow). Note the abnormal lymph node that has lost most of its fatty hilum, compared to the normal axillary lymph node overlying the pectoralis muscle in the same location in part A.

Hamartoma

This entity, also known as a fibroadenolipoma, is a benign mass that contains fat and other elements found in the breast. On physical examination, a hamartoma may not be felt distinctly if it contains mostly fat and glandular tissue. The classic appearance is that of an oval mass containing fat and fibroglandular tissue with a thin capsule or rim, the “breast within a breast” appearance (Fig. 4-25). Breast hamartomas have a variable appearance, depending on the amount of fat and stromal elements that they contain. On occasion, a hamartoma may have mostly stromal and glandular elements and appear as a dense mass rather than one containing mostly fat and glandular elements (Fig. 4-26). Because cancer can develop in breast elements and ducts, cancer can develop in hamartomas. Biopsy should be performed on hamartomas if suspicious microcalcifications are developing within it. Otherwise, a classic “breast within a breast” hamartoma is benign and should be left alone.

Figure 4-25 Typical hamartoma. A mammogram shows an oval mass containing fat and fibroglandular elements typical of a hamartoma. On breast physical examination, the mass was difficult to feel despite its large size.

Figure 4-26 Typical hamartomas. Hamartomas may have a variable appearance, depending on the amount of fat and glandular elements that they contain. A, A mammogram reveals a lobular, partly circumscribed, partly indistinct mass that may contain fat. B, A spot magnification view shows the mass to better advantage. C, Ultrasound shows a partly echogenic, partly hypoechoic shadowing mass. D, A specimen radiograph confirms that the hamartoma contains fat. Note the localizing hookwire. E, In another patient, the hamartoma is an oval mass containing fat and fibroglandular elements with a thin capsule near the anterior portion of the breast (arrows); it has an oval shape on ultrasound (F).

Oil Cyst

An oil cyst is a sequela of fat necrosis after blunt trauma or surgery. A benign oil cyst is a radiolucent oval or round mass containing fatty fluid with a thin radiodense rim (Fig. 4-27). Oil cysts may subsequently calcify and result in eggshell-type calcifications. On ultrasound, oil cysts are round or oval and contain liquefied fat that is usually hypoechoic or isoechoic. The oil cyst is benign and is one of the “don’t touch” lesions that should be left alone.

Figure 4-27 Oil cyst. A, A spot compression magnification view shows a thin-walled mass with a radiolucent center and faint calcifications along its rim in the area of a previous biopsy. B, In another patient, a palpable oil cyst is marked by a skin marker and is seen as a fat-containing thin-walled mass. C, Ultrasound shows a hypoechoic, oval, well-circumscribed mass.

Lipoma

Breast lipomas are similar to lipomas elsewhere in the body. They produce a soft mass or a mass that may not be felt at all. On mammography, a lipoma is a fatty mass containing a radiolucent center that may have a distinguishable thin discrete rim separating it from the surrounding glandular tissue. Unlike a post-traumatic oil cyst, a lipoma never calcifies. Typically, a lipoma is discovered because the patient feels a mass. If a technologist places a skin marker over the palpable lipoma, a spot compression view of the mass shows only fat (Fig. 4-28). Ultrasound of a lipoma shows only fatty tissue in a well-circumscribed oval or round mass. Lipomas are benign and should be left alone.

Figure 4-28 Lipomas. A, Craniocaudal and B, mediolateral oblique (MLO) mammograms show markers over palpable masses where only fat is present. C, In another patient, the palpable lipoma is not seen high in the breast on the MLO view where only fat is present, but ultrasound (D and E) shows a hypoechoic fatty mass corresponding to the palpable finding that proved to be a lipoma on excisional biopsy. Note that the lipoma blends into the surrounding fat and is seen only with the calipers.

Liposarcoma

Liposarcoma is the only fat-containing malignancy and is extremely rare. A fat-containing, but rapidly growing mass should raise suspicion of the rare liposarcoma.

Steatocystoma Multiplex

This is a rare, autosomal dominantly inherited condition that is characterized by multiple and extensive intradermal oil cysts bilaterally. The oil cysts may be palpable or nonpalpable. Mammography shows extensive bilateral well-circumscribed radiolucent masses with a typical appearance of oil cysts, but unlike post-traumatic intraparenchymal oil cysts, the oil cysts in steatocystoma multiplex are intradermal in location, innumerable, and bilateral without a history of trauma. In 40% of affected patients, a typical family history of steatocystoma multiplex confirms the diagnosis.

Cyst

A simple cyst occurs in 10% of all women and is frequently seen in women receiving exogenous hormone replacement therapy. Caused by obstruction and dilatation of the terminal ducts with fluid trapped within them, a cyst can enlarge with the patient’s menstrual cycle and decrease after the onset of menses. Cysts may be asymptomatic or may become painful and produce a palpable lump. They may be single or multiple, and they can regress or grow spontaneously and rapidly.

Because cysts often produce a palpable mass, they are a frequent cause of symptoms for which patients seek advice. On mammography, cysts are round or oval, well-circumscribed, and are low-density or equal in density to fibroglandular tissue. Spot compression magnification will show an equal-density or low-density mass with a sharply marginated border where they are not obscured by adjacent dense glandular tissue.

Breast ultrasound shows an anechoic mass with imperceptible walls, a sharp back wall, and enhanced posterior transmission of sound (Fig. 4-29). Cysts may have internal echoes as a result of debris. Cysts may be left alone (Box 4-16) or can be aspirated by palpation or under ultrasound guidance if symptomatic, but they have no malignant potential. If a cyst is causing a palpable mass, the palpable finding should resolve after cyst aspiration. On MRI cysts have a high T2-weighted signal and show no enhancement. Occasionally inflamed cysts show rim enhancement and can be a cause of a false-positive MRI. However, the bright T2-weighted signal, no enhancement after contrast injection, and a thin rim should differentiate the inflamed cyst from cancer.

Figure 4-29 Cyst on ultrasound. A, A well-circumscribed anechoic mass with an imperceptible back wall and enhanced transmission of sound is a simple cyst and needs no further follow-up unless it is symptomatic. B, In another patient, a mammogram shows multiple round circumscribed, partly obscured, equal-density masses representing cysts. C, Notice that on the ultrasound this complex cyst had debris within it and could not be distinguished from a solid mass until aspiration.

Hematoma/Seroma

Breast hematomas and seromas occur after biopsy or trauma, and their diagnosis is established by correlating the hematoma/seroma to the clinical history. On mammography, a hematoma has an irregular or ill-defined border and may be high-density or equal density (Fig. 4-30). In the acute phase, surrounding hemorrhage may obscure hematomas. A hematoma will become smaller with time as the blood resorbs. Initially on ultrasound, a hematoma is a fluid-filled mass. Later, as the hematoma evolves, ultrasound shows that the previously hypoechoic blood-filled mass changes to serous fluid. Subsequently, the seroma may contain thin movable septa that move on real-time ultrasound, or it may contain debris or fluid/fluid levels.

Figure 4-30 Hematoma/seroma. A mammogram shows a density near a linear metallic scar marker 5 months after biopsy of a benign tumor that is hard to see on the craniocaudal mammogram (A) but easier to see on the magnification view (B). C, Ultrasound shows a fluid-filled biopsy cavity with healing hypoechoic breast tissue surrounding it. D, Ultrasound of another biopsy cavity shows a V-shaped fluid-filled cavity, with the upper portion of the V representing fluid tracking along the incision toward the skin.

Necrotic Cancer

Cancers with central necrosis may contain fluid. In general, necrotic tumors usually have a thick, irregular solid rim, thus distinguishing it from a thin-walled simple or complex cyst.

Intracystic Carcinoma

See the section “Solid Masses with Rounded or Expansile Borders” in this chapter.

Intracystic Papilloma

This tumor is also rare and appears as a round mass on mammography. On ultrasound, an intracystic papilloma is a solid mural nodule or mass in a round fluid-filled mass, with a similar appearance to that of the rare intracystic carcinoma.

Abscess

A breast abscess occurs after mastitis. Staphylococcus aureus or Streptococcus is the usual pathogen in abscess. In a nursing mother, the infection develops as a result of bacterial entry through a cracked nipple. In teenagers, infection may occur during sexual contact. In older women, those who are diabetic or immunocompromised are especially at risk for mastitis and abscess. Typically, an abscess is a painful hard mass that is tender to touch, with overlying red, edematous skin and surrounding cellulitis.

On mammography, an abscess is usually subareolar, appears as a dense or equal-density noncalcified irregular mass with focal or diffuse skin thickening, and may be obscured by surrounding breast edema.

On ultrasound, an abscess is an irregular fluid-filled mass occasionally containing debris or septations (Fig. 4-31). The surrounding edema blurs the normal adjacent breast structures, makes the adjacent fat gray, and causes skin thickening. A breast abscess usually does not contain air. Bright echoes or specular reflectors may represent air in the abscess after attempted drainage.

Figure 4-31 A to C, Abscesses. A, Ultrasound shows an irregular heterogeneous mass with extensions of fluid into tissue. Notice the thickened skin and indistinctness of the surrounding breast tissue structures from cellulitis. B, In another patient, two hot retroareolar, painful, round, well-organized fluid-filled abscesses were surrounded by a less well-organized infection. C, In a third patient, the abscess is well-formed and encapsulated and appears as an oval mass with septated fluid collections within it. D and E, Abscess drainage. D, Ultrasound shows a hypoechoic irregular indistinct mass representing a breast abscess. The surrounding fat has turned gray (instead of the normal black color), indicating breast edema, and there are dilated subdermal lymphatics in the upper right corner of the image. There is a needle within the abscess. E, Another view shows solid clumped debris within the fluid-filled abscess and a needle during attempted drainage. Because the pus was too thick to be drained through a needle, a percutaneous drainage catheter was placed in the interventional radiology department.

Treatment involves antibiotic therapy and drainage of the abscess by either percutaneous or surgical methods. Surgery usually involves incision and debridement, leaving the abscess cavity open to heal by granulomatous formation by second intention. Percutaneous needle aspiration without catheter placement is usually unsuccessful as the only method of drainage if the abscess is large (>2.4 to 3 cm) or septated, or if incompletely drained pockets are left in the surrounding breast tissue. In these cases, percutaneous needle drainage without an indwelling catheter may be palliative. Women with a chronic subareolar abscess caused by chronic duct obstruction are in a special category and require duct excision as well as abscess treatment. The chronic subareolar abscess may have an adjacent skin fistula. The abscess requires excision of the fistula as well as incision and debridement of the abscess.

Sebaceous and Epidermal Inclusion Cysts

Sebaceous cysts are not cysts at all, but result from keratin accumulation in plugged ducts. Sebaceous cysts have an epithelial cell lining from the sebaceous gland, whereas epidermal cysts have a true epidermal cell lining and no sebaceous glands. Because they have almost no malignant potential, biopsy is not required unless the patient desires removal.

Clinically, sebaceous cysts can produce a palpable mass, a “blackhead” that when squeezed will yield cheesy yellow or white material. On mammography, sebaceous and epidermal inclusion cysts are identical, with subcutaneous oval or round well-defined masses that are often overexposed because of their location near the skin surface; they occasionally contain calcifications (Fig. 4-32A to C). Ultrasound shows an oval, well-circumscribed, hypoechoic or anechoic mass in a subcutaneous location with a little tail extending into the skin, representing the dilated hair follicle (see Fig. 4-32D to F).

Figure 4-32 Sebaceous cyst. In a patient with gynecomastia and a palpable mass, craniocaudal (A) and mediolateral oblique (B) views show bilateral subareolar breast tissue that is palpable on the left and marked by a skin marker, as well as a separate discrete upper inner quadrant mass that was detected in the skin on physical examination. C, Ultrasound of the sebaceous cyst shows an oval, hypoechoic, well-circumscribed mass in the skin that correlates with the physical finding. D and E, In another patient, ultrasound scans of two sebaceous cysts show oval hypoechoic sebaceous cysts at the junction of the skin surface and subcutaneous fat, with the typical thin tail extending into the skin from the cyst. Note that on the transverse scan (F), the sebaceous cyst in part D is seen as an oval mass without the “tail.” The tail is seen only with careful scanning and attention to the skin surface in masses suspected of being a sebaceous cyst.

Displacement of epidermal fragments from the skin surface to locations deep within the breast parenchyma cause epidermal inclusion cysts after percutaneous biopsy or surgery. The epidermal inclusion cyst produces a round or oval mass located within breast tissue far away from the skin surface. Because epidermal inclusion cysts have an epithelial lining, they can produce a growing mass on the mammogram as a result of accumulating inspissated material within them. Because they cause a growing solid mass, the epidermal inclusion cyst often requires biopsy to exclude cancer.

Galactocele

Typically seen in lactating women, a galactocele represents a focal collection of breast milk that occasionally causes a palpable mass. On mammography, a galactocele is a low- or equal-density, oval or round, well-circumscribed mass (Fig. 4-33A and C), but it can be of higher density, depending on resorption of its fluid contents and the residual solid component. On an upright mammogram, a classic, but rarely seen finding of a fat/fluid level in the mass represents fat rising to the top of the galactocele while the other milk components layer dependently below. On ultrasound, a galactocele may look like a well-defined hypoechoic cystlike mass. Galactoceles containing more solid elements simulate a solid mass that occasionally displays posterior acoustic shadowing (see Fig. 4-33B and D). On aspiration, milky fluid will be obtained. Atypical galactoceles with a round or irregular shape, nonparallel orientation, indistinct or microlobulated noncircumscribed margin, but with a relatively sharp convex anterior or posterior echogenic rim, requiring biopsy, have been reported by Kim and colleagues.

Figure 4-33 Galactocele. A, A mammogram shows a palpable equal-density mass marked by a skin marker that is difficult to see against the dense fibroglandular tissue. B, On ultrasound, the galactocele is oval and hypoechoic and yielded milk on aspiration. C, In another patient, the galactocele is a dense round mass on the mammogram. D, Ultrasound of the galactocele in this patient shows an oval, shadowing mass. Excisional biopsy revealed a galactocele.