Fibroadenoma

Dynamic contrast-enhanced magnetic resonance imaging (DCE-MRI) of the breast is being used increasingly in the detection and diagnosis of breast cancer as a complementary modality to mammography and sonography.  The potential diagnostic value of kinetic curves in DCE-MRI is established although the method for generating kinetic curves is not standardized because  curve identification depends on uptake of contrast agent in a breast lesion, which is often heterogeneous, especially in malignant lesions.Breast MRI has high sensitivity but only moderate specificity independent of breast density, tumor type, and menopausal status. Although the positive predictive value of MRI is greater than mammography, MRI does not obviate the need for subsequent tissue sampling. 

Fibrous breast lesions are commonly seen in clinical practice. These lesions are composed of prominent stromal elements and varying amounts of glandular epithelium. The most common of these lesions is the fibroadenoma. Fibroadenomas most frequently occur as palpable masses in women of childbearing age, although 44% of fibroadenomas manifest in postmenopausal women .A lesion that is similar to fibroadenoma both in its clinical manifestations and its imaging features is sclerosing lobular hyperplasia. 

Fibroadenomas are benign fibroepithelial tumors that develop in the lobules at the ends of mammary gland ducts, which are the basic units of analysis at histopathologic assessment. Fibroadenomas are composed of epithelium and stroma, and they are the breast tumors most commonly found in adolescent girls and young women at clinical examination and histopathologic analysis. When palpable,fibroadenomas are smooth, mobile and firm or rubbery. In 15% of cases, multiple fibroadenomas are present .Fibroadenomasoccasionally develop into very large masses, particularly in adolescent girls and young women; such masses are called juvenile giant fibroadenomas . 

At mammography, fibroadenomas appear as well-defined round, oval, or lobulated masses .The masses may be calcified, with the most common pattern of calcification being initial small peripheral dots that coalesce over time into coarser popcorn-shaped features .In the presence of a calcified fibroadenoma, which is characteristically benign, further work-up, including US imaging or biopsy, is not needed. If a non-calcified isodense circumscribed mass is depicted at mammography, imaging with US is the next step toward characterization of the lesion. On US images, fibroadenoma appears as a well-circumscribed elliptic mass that is either hypoechoic or isoechoic and has uniform echogenicity. The lesion is typically larger in the transverse than in the anteroposterior direction and has very well-demarcated margins. A fibroadenoma may have no effect on ultrasound transmission, or acoustic enhancement or shadow may be observed on US images . 

Histopathologic features of fibroadenomas include the concurrent proliferation of stromal and glandular elements. Two histologiccategories of fibroadenomas are described: intracanalicular and pericanalicular. In intracanalicular fibroadenomas, the stroma is dense and compresses the duct into a slitlike space. In pericanalicular lesions, there is no compression of the duct .Occasionally, small punctate, dystrophic, or pleomorphic calcifications may form in a fibroadenoma, and the mass may no longer be visible at mammography. In these cases, biopsy may be necessary because of the equivocal mammographic findings.

In keeping with their histologic variability, fibroadenomas have been noted to vary widely in MR appearance.Fibroadenomas can have low, moderate, or high T2 signal intensity. Three distinct patterns of fibroadenomas (types I-Ill) are usually seen on MR imaging.Decrease of  T2 signal intensity correlates with increasing collagenization i.e.sclerosis-of the stroma. The high- T2-signal-intensity fibroadenomas tends to be more myxomatous; the low-T2-signal-intensity fibnoadenomas tend to be more sclerotic. Cellularity tends to be higher in lesions that are myxomatous. Lesions that are bright on T2-weighted images enhance profusely, while most lesions that are dark on T2-weighted images enhance minimally on not all. There are also a smaller subset of fibroadenomas that are dark on T2-weighted images but do not enhance as profusely as the lesions that are bright on T2-weighted images. It is not explainable  why some sclerotic fibroadenomas enhance and others do not. The presence of enhancement reflects a complex combination of factors, which includes the density of the vessels, the permeability of vessels, and the extent and composition of the intemstitium. The patient’s age may play a role, other factors (eg, microenvironment, hormonal influences) may also contribute to appearence on MRI. Two fibroadenomas in the same breast may exhibit markedly different imaging characteristics. Mixed fibmoadenomas-single fibmoadenomas cornposed of some subunits that are sclenotic and others that are myxomatoushave are also seen. Histopathologic architecture appears to give rise to two MR-detectable featunes in fibroadenomas: internal septations and lobular external contours. Lobular fibroadenoma shape reflects the underlying lobubated-albeit distorted-normal architecture of the breast. Internal septalions appear to represent the dense collagenous bands that surround penductal subunits. Internal septations are dark on T-2 weighted images. T2-weighted images, as expected for a collagenous structure.  The presence of internal septations or lobular shape is found to be highly predictive of benignity. While some forms of carcinoma may occasionally appear as well-defined or lobulated masses, they are not characterized by the kinds of nonenhancing internal septations seen in fibmoadenomas. Rim-enhancing tumour nodules clustered together may give the appearance of contrast-enhancing septations in invasive carcinoma,however these are different in appearance from the internal septations in fibmoadenomas, which most often do not enhance or rarely blend imperceptibly into the sorrounding tissue on postcontnast images.Some of the false-positive findings on MR mammography are caused by hypervascularized fibroadenomas which show carcinomalike enhancement.