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 epithe- lium, and are often seen in the subareolar region or in subareo- lar 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 symp- tom of DCIS, causing patients to seek advice. Clinically, papil- lomas 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, and equal-density masses that occasionally contain calcifications, They are usually located in the subareolar region, but they can be located in the breast periphery (Fig. 4.41). In papillomatosis, papillomas can be multiple and peripherally located. Occasion- ally, papillomas are not seen on mammography or US despite the
symptom of bloody or clear nipple discharge. On US, papillomas are solid round, oval, or microlobulated hypoechoic masses. Small internal cystic spaces are seen occasionally in juvenile papilloma- tosis. In patients with nipple discharge, US may show papilloma as a solid mass in a fluid-filled subareolar duct. On galactogra- phy, the papilloma produces an intraductal filling defect (see Fig.
10.23).
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 (Fig. 4.42). 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 diag- nosed by core biopsy is controversial. However, surgical exci- sional 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 rec- ommend excision, particularly if the patient is at high risk for breast cancer, or if any atypia or other high-risk lesions found at surgery will prompt chemoprevention therapy and change patient management.
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FIG. 4.40 Fibroadenoma on magnetic resonance imaging (MRI) and elastography. (A) T2-weighted sagittal noncontrast MRI image shows a slightly high signal intensity (arrow) lobulated mass in the lower breast and fluid in benign breast ducts (double arrows). Precontrast (B) and postcontrast (C) sagittal 3D spectral-spatial excitation magnetization transfer MRIs show an oval enhancing mass with dark septations and circumscribed margins (arrow). Enhancement kinetics showed a slow uptake and late persistent curve, suggesting fibroad- enoma. (D) MRI-directed ultrasound (US) shows an oval circumscribed homogeneous mass (arrow) in the area of the MRI-detected mass. (E) B-mode (left image) and elastography (right image) US images show that the mass (arrows) is about the same size on the strain view, suggesting a benign finding. Biopsy showed fibroadenoma.
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Cancer
Invasive Ductal Cancer. Invasive ductal cancer is the most common round breast cancer (Fig. 4.43). The “round” invasive ductal carcinoma is an uncommon form of the most common cancer, invasive ductal carcinoma. Invasive ductal carcinoma rep- resents approximately 90% of all invasive breast cancers. Even though invasive ductal carcinomas are not often round, there are so many invasive ductal carcinomas that the most common round cancer is ductal carcinoma (uncommon round form of the most common breast cancer; Box 4.11).
The classic invasive ductal carcinoma is a dense spiculated or irregular mass on mammography. The much less common round invasive ductal carcinoma may grow so rapidly that it does not produce spiculated margins; instead, it has smooth or pushing borders (Fig. 4.44). This is especially true of triple negative (ER, PR, HER2 receptor negative) breast cancers, which are often round (M.Y. Kim, 2013). On screening mammography, round inva- sive ductal carcinoma may appear to have a circumscribed bor- der. However, the mass borders may be obscured by surround- ing breast tissue, or the standard mammogram may not have the resolution to reveal abnormal margins. 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 carcinoma mimics benign cysts or fibroadenomas, and the radi- ologist can mistakenly think the round mass is benign until the mass undergoes magnification.
On US, the round invasive cancer may be circumscribed, or may show suspicious indistinct or angular margins, and not-parallel orientation (taller than wide) or may have a thick echogenic rim. The not parallel or taller than wide orienta- tion is an important ultrasonographic sign in the diagnosis
of breast cancer. Taller than wide is a US term described by Stavros et al. (1995) for masses invading through the normal horizontal tissue. It means that the cancer grows up toward the skin and violates normal tissue planes rather than grow- ing horizontally between Cooper’s ligaments (like benign tumors). The corresponding BI-RADS term is not parallel.
Benign masses growing between Cooper’s ligaments are called parallel in orientation in BI-RADS (parallel to Cooper’s ligaments, or wider than tall).
Medullary Carcinoma. Medullary carcinoma is an invasive breast cancer that commonly has a round or pushing border.
It occasionally has a surrounding lymphoid infiltrate and has a better prognosis than infiltrating ductal cancer (NOS). They are common in BRCA1-associated carcinomas. Atypical medul- lary carcinomas have the same prognosis as infiltrating ductal cancer. On screening mammography, medullary carcinoma is a high-density or equal-density round mass whose margins may appear well circumscribed, suggestive of a cyst or fibroadenoma (Fig. 4.45). On US, medullary carcinomas are round, solid, and ho- mogeneous. Because they are homogeneous, medullary carcino- mas occasionally cause posterior acoustic enhancement and it is important pay attention to scanning parameters to not mistake the solid medullary carcinoma for a cyst. Color or power Dop- pler US may show internal vascularity, unlike an anechoic simple cyst. The pushing expansile growth of medullary carcinoma may produce 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 circumscribed.
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. The amount of mucin versus solid A
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FIG. 4.41 Papilloma. (A) Left mediolateral oblique mammogram shows a small round mass (arrow) with indis- tinct margins in the posterior upper breast. (B and C) Corresponding ultrasound shows an oval hypoechoic mass containing a cystic space at its periphery (B; arrow), with no apparent increased vascularity (C). Biopsy showed a peripheral papilloma with focal atypia.
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FIG. 4.42 Papilloma in fluid-filled ducts. (A) In a patient with nipple discharge, craniocaudal spot mammogram with nipple marker shows dilated ducts (arrowheads) and a possible retroareolar mass (arrow). (B and C) Ul- trasound shows an intraductal mass in a fluid-filled duct in transverse (B) and longitudinal (C) images (arrows) suggesting papilloma, papillary cancer, or ductal carcinoma in situ. (D–F) Dynamic contrast magnetic resonance imaging (MRI) was performed. On precontrast T1-weighted fat-suppressed sagittal MRI (D), there is a precontrast high signal intensity retroareolar dot (arrow), which may represent debris in a fluid-filled duct. Postcontrast 3D spectral-spatial excitation magnetization transfer sagittal MRI (E) shows an enhancing mass in the retroareolar region (arrowhead). The kinetic curve of the mass (F) shows rapid initial enhancement and delayed washout, sug- gesting invasive ductal cancer or a papilloma. Biopsy showed papilloma.
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tumor components vary from tumor to tumor, and account for the variable appearance of mucinous carcinoma on mammogra- phy and US. On mammography, mucinous carcinomas contain- ing mostly mucin show a well-circumscribed low-density round mass that can suggest a cyst or fibroadenoma and can occasional- ly have lobulated margins (Fig. 4.46). Mixed-type mucinous carci- nomas may be of higher density and have ill-defined or spiculated margins. On US, the tumor mass is round and may be isoechoic to fat, occasionally contains fluid-filled hypoechoic spaces, and may have posterior acoustic enhancement (see Fig. 4.46). The mass can simulate a cyst on US, but unlike the cyst it will not be en- tirely 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 US should be considered for biopsy.
Papillary Carcinoma. This rare tumor accounts for only 1%
to 2% of all cancers and is the malignant form of benign intra- ductal papilloma. Papillary cancers may be single or multiple, 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 US. If associ- ated with nipple discharge and detected by US, papillary cancers are solid intraductal masses outlined by a fluid-filled structure and are difficult to distinguish from a benign intraductal papil- loma (Fig. 4.47).
Adenoid Cystic Carcinoma. A very rare tumor that clinically manifests as a palpable firm mass, the adenoid cystic carcinoma, has a mixture of glandular and stromal elements that infiltrate the normal fibroglandular tissue in approximately 50% of cases.
The tumor has a good prognosis if completely resected; however, recurrence is possible if the mass is not entirely excised. Imag- ing characteristics vary because of the rarity of reported cases and range from a well-circumscribed lobulated mass to ill-defined masses or focal asymmetries.