Benign Findings in Breast MRI

Duct Ectasia

Duct ectasia is a nonspecific dilation of the major subareolar ducts, with occasional involvement of smaller ducts. It has been found in women of all ages, and its etiology is unknown. Some consider all inflammatory processes as the initiating event, leading to destruction of the elastic network of the duct with subsequent duct ectasia and periductal fibrosis. Others suggest that duct dilation is the primary event, caused by obstruction of the ducts leading to secondary inflammation owing to leakage of duct contents.

Most patients are asymptomatic. Some may present with spontaneous and intermittent clear to yellow nipple discharge. Mammographically, the calcified proteinaceous secretions within dilated ducts appear as bilateral symmetric rodlike “secretory calcifications.” Ultrasonography will demonstrate dilated ducts filled with anechoic fluid, without or with debris.

On MRI, ectatic ducts are usually incidental findings. They appear as non-enhancing, fluid-filled, often branching, tubular structures converging toward the nipple. The contents of the ducts may show signal intensities similar to that of water, hypointense on T1-weighted images and hyperintense on T2-weighted sequences. More often, the fluid is hyperintense in signal on T1-weighted images because of proteinaceous or hemorrhagic contents ( Figure 7.1 , A ). Because of such signal hyperintensity on precontrast images, postcontrast subtraction images are usually needed to confirm absence of contrast enhancement ( Figure 7.1 , B ). Focal enhancement within the duct lumen would raise concern for intraductal papilloma or carcinoma.

Fibrocystic Changes

Fibrocystic change (FCC) refers to a constellation of benign breast changes that represent normal but exaggerated, hormonally mediated breast tissue response. The histologic findings include cyst formation, apocrine metaplasia, mild epithelial hyperplasia, stromal fibrosis, and mild adenosis. It is common in younger women, affecting one third of females 20 to 45 years of age. There is no increased risk for the subsequent development of breast carcinoma in women with non-proliferative FCC. The risk of developing carcinoma is increased to 1.5 to 2 times when FCC is associated with moderate or florid ductal hyperplasia and increased 5 times with the presence of atypia.

FCCs do not have specific mammographic or sonographic findings other than cyst formation. FCC has a wide spectrum of morphologic and kinetic features on MRI. It may appear as prominent nonmasslike enhancement in regional, focal, or segmental distribution ( Figures 7-2 and 7-3 ). A focal (nodular) form of FCC may appear as a mass with spiculated or smooth margins ( Figures 7-4 and 7-5 ). The degree of initial enhancement ranges from slow to rapid, and the kinetic curves may vary between washout, plateau, or persistent enhancement during the delayed phase. In a small series of 11 cases studied by Chen and colleagues, 62% of FCC showed early rapid enhancement with delayed washout, mimicking carcinoma.

Simple and Inflammatory Cysts

Cysts may be an isolated finding or may be seen as a component of FCCs on breast imaging. Simple cysts appear as circumscribed round or oval structures that are signal hyperintense on T2-weighted images and without contrast enhancement on postcontrast T1-weighted sequences ( Figure 7.6 ). Cysts associated with inflammation will show a thickened enhancing wall on postcontrast images ( Figure 7.7 ).

Sclerosing Adenosis

Sclerosing adenosis is a benign proliferative lesion composed of distorted epithelial, myoepithelial, and stromal elements in a lobulocentric pattern. It may form a distinct nodule, hence the term nodular sclerosing adenosis or adenosis tumor .

Sclerosing adenosis is usually asymptomatic and is often an incidental microscopic finding in breast tissue removed for another indication. The nodular form may cause a palpable mass. Mammographically, sclerosing adenosis may present as clustered, round, or punctate microcalcifications; a focal asymmetry; architectural distortion; or a spiculated mass. The combination of these features may mimic carcinoma. Its sonographic appearance is also nonspecific, including masses with circumscribed, indistinct, or microlobulated margins.

On MRI, sclerosing adenosis may present as ductal enhancement or as homogeneously enhancing masses that are oval or round with lobulated or angular margins. According to Oztekin and coworkers , it shows intermediate signal intensity on T1- and T2- weighted images, with rapid initial enhancement and delayed persistent or wash-out kinetics. At our institution, both plateau and washout kinetics have been observed in biopsy-proved sclerosing adenosis. Figure 7.8 illustrates an example of nodular sclerosing adenosis showing as a mass.

Radial Sclerosing Lesion

Radial scar is a benign sclerosing breast lesion of unknown cause, characterized by a central fibroelastotic core with radiating ducts and lobules exhibiting various proliferative changes. The term complex sclerosing lesion is used in cases in which the lesion is larger than 1 cm or composed of several closely contiguous fibroelastotic areas. Rosen prefers the term radial sclerosing lesions for both entities. Radial sclerosing lesions are considered high-risk lesions because of their association with carcinomas. This entity will be covered in Chapter 8 .

Usual Ductal Hyperplasia

Ductal hyperplasia of usual type, or usual ductal hyperplasia (UDH), is a benign epithelial proliferation in a duct or lobule beyond the usual double cell layer, but no more than three to four cell layers above the basement membrane. It is a response to hormonal stimulation and imbalance. The term can be misleading, because this lesion usually occurs within the terminal ductal lobular unit (TDLU).

UDH is clinically silent and almost always detected on screening mammography as microcalcifications or a mass. It does not have specific sonographic presentation. No systematic review of the MRI appearance of UDH is available in the literature. Published images demonstrate either foci or nonmasslike enhancement (stippled or clumped) in a linear, ductal, or regional distribution ( Figure 7.9 ). Some biopsy-proved cases at our institution showed UDH as a sub-centimeter mass ( Figure 7.10 ). Delayed enhancement kinetics may be persistent, plateau, or mixed with some washout.

Columnar Cell Changes/Flat Epithelial Atypia

Columnar cell changes refer to a condition in which the normal epithelial cell layer of the TDLU is replaced by one or two layers of taller columnar epithelial cells that have basal nuclei and apical cytoplasmic snouts. When these columnar cells show cellular stratification with more than two cell layers, the entity is described as columnar cell hyperplasia. Columnar cell change with atypia and columnar cell hyperplasia with atypia are collectively referred to as flat epithelial atypia (FEA). Because of its frequent association with carcinomas, FEA is regarded as a high-risk lesion. This entity will be discussed in detail in Chapter 8 .

Atypical Ductal Hyperplasia

Atypical ductal hyperplasia (ADH) defines a group of proliferative lesions that have some, but not all, of the features of ductal carcinoma in situ (DCIS), either by lack of a major defining cytologic feature of carcinoma or by having the features to lesser extent than true DCIS. ADH is associated with a 4 to 5 times relative risk of development of breast cancer within 10 to 15 years. It will be covered in Chapter 8 .

Lobular Neoplasia

Atypical lobular hyperplasia (ALH) and lobular carcinoma in situ (LCIS) are relatively uncommon lesions, collectively identified as lobular neoplasia. These lesions are considered to be generalized risk factors for subsequent breast cancer, with a relative risk of 4 to 5 times for ALH and 8 to 10 times for LCIS. Lobular neoplasias are high-risk lesions that will be discussed in detail in Chapter 8 .

Fibroadenoma

Fibroadenoma is a benign hyperplastic fibroepithelial tumor characterized by concurrent proliferation of both glandular and stromal elements in varying proportions. It is the most common breast mass encountered in women younger than 35 years of age and the most common solid mass in women of all ages. Juvenile (cellular) fibroadenoma is a variant of fibroadenoma that occasionally occurs in adolescents who present with a rapidly growing, well-defined mass that may reach 20 cm in size. The macroscopic and histologic appearances are similar to fibroadenomas, although the stroma may be more cellular. This makes differentiation from phyllodes tumor challenging in some cases.

A patient with a fibroadenoma usually presents with a mobile, painless, palpable mass. Mammographically, it appears as a circumscribed round, oval, or lobular mass that is iso- or hypodense to the parenchyma. Coarse calcifications, when present, may be diagnostic. Sonographically, it appears as a mass that is iso- or hypoechoic to fat, with a parallel orientation to the skin. Atypical findings include microlobulated or indistinct margins and acoustic shadowing due to internal calcification. In keeping with their histologic heterogeneity, fibroadenomas have been shown to have widely varied MRI appearances. On MRI, a fibroadenoma typically appears as an oval mass with smooth margins. It may have a lobular shape. On T1-weighted images, it is iso- or hypointense to normal parenchyma. On T2-weighted images, its signal intensity varies with the amount of myxoid (high signal) and fibrous (low signal) components. The fibrous component increases with increasing age. The degree of contrast enhancement varies with its degree of sclerosis and cellularity.

Nunes and coworkers described low-signal internal septations that are seen on T2- or enhanced T1- weighted images, representing dense collagen bands, as 89% to 93% specific for the diagnosis of fibroadenoma. The specificity increased slightly when internal septations were seen in combination with features of smooth margins or lobular shape. Figure 7.11 illustrates a fibroadenoma with these classic features. However, such septations are observed in only 40% to 64% of fibroadenomas on MRI. Furthermore, they have recently been described in benign and malignant phyllodes tumors and mucinous carcinoma and may be of limited value for diagnosing fibroadenoma when considered alone.

Fibroadenomas usually enhance homogeneously, with heterogeneous enhancement seen with increasing sclerosis. The most common enhancement kinetics of fibroadenoma is rapid (early phase) and persistent (delayed phase). However, some fibroadenomas are known to show rapid early enhancement with delayed washout kinetics, mimicking malignancy ( Figure 7.12 ).

When a fibroadenoma is suspected on MRI, review of the mammogram and sonogram may help in confirming the diagnosis. However, biopsy should be considered in cases in which a presumed fibroadenoma demonstrates interval growth or atypical features on conventional imaging.

Phyllodes Tumor

Phyllodes tumor is a rare neoplasm with a reported incidence of less than 1% of all female breast tumors. This tumor is similar to fibroadenoma in that it is a fibroepithelial lesion with both epithelial and stromal proliferations. However, phyllodes tumor has a much greater stromal cellularity than a fibroadenoma. Phyllodes tumors are high-risk lesions and will be covered in Chapter 8 .