The resected specimen consisted of a 770 g, 20.0 × 14.0 × 4.0 cm nodular and relatively well-circumscribed mass. The cut surface was tan-white, firm, and homogenous with a few scattered slit-like spaces. No areas of necrosis or hemorrhage were seen. Microscopically, the mass was not encapsulated but was well-circumscribed with an abrupt transition between the mass and the surrounding adipose tissue (Figure ​(Figure4).4). Low power magnification showed multiple large lobules displaying a proliferation of ductules and acini (Figures ​(Figures44 and ​and5).5). A few ducts were dilated and elongated. There was lobular epithelial hyperplasia with rare mitotic figures and without cellular atypia. The intralobular and interlobular connective tissue consisted of dense collagenous fibrosis that was predominantly bland and relatively acellular (Figure ​(Figure5).5). In many areas, however, there was prominent fibroblastic and myofibroblastic proliferation in a background of dense keloid-like collagenous fibrosis. In these areas, the proliferating fibroblasts and myofibroblasts formed pseudo-vascular slit-like spaces giving the appearance of pseudoangiomatous stromal hyperplasia (Figure ​(Figure6).6). The stromal cells did not show any atypia and no mitotic figures were identified. A diagnosis of sclerosing lobular hyperplasia was rendered.

Sclerosing lobular hyperplasia is an infrequently encountered benign proliferative lesion of the breast. It was first described in 1984 by Kovi et al. and is diagnosed in 3–7% of benign breast biopsies [1]. Sclerosing lobular hyperplasia most commonly occurs between the ages of 14 and 46 years [1]. It usually presents as a discrete, palpable, and painless mass in the upper outer quadrant of the breast. Mammography usually reveals a lobular or oval, well-circumscribed mass with echogenic septa that correspond to interlobular sclerosis. Microcalcifications may be seen occasionally, especially in older women. These calcifications may be present in irregular clusters and as granular suspicious lesions. However, distinguishing sclerosing lobular hyperplasia from fibroadenoma on radiologic investigations is difficult in most cases and probably not warranted either, as both lesions are benign and require similar clinical management [5-7].

Fine-needle aspiration cytology findings have been previously reported in two cases of sclerosing lobular hyperplasia [3,4]. Both reports emphasized the presence of ductal epithelial cells in monolayered sheets and of round acinar clusters in a clean background devoid of stromal fragments and with only a few bare nuclei. The cytology findings in our case were similar to those described previously, in the lack of elongated and branched tubular fragments. However, unlike the previously described cases, we saw a few scattered stromal fragments and a fair number of bare nuclei. The sclerosed stroma may make fine-needle aspiration a difficult task and also account for the relative paucity of stromal fragments. However, a complete absence of stromal fragments and rarity of bare nuclei are not consistent features of sclerosing lobular hyperplasia and may not be relied upon to distinguish it from fibroadenoma; a reliable distinction requires histologic examination of the architecture of the two lesions.

Grossly, sclerosing lobular hyperplasia is composed of firm, nodular, tan-white tissue. Histologically, there are enlarged lobules with increased numbers of acini. The intralobular stroma is collagenized with loss of stromal mucopolysaccharides, and there is variable sclerosis of the interlobular stroma [1,2]. Focally, there may be pseudoangiomatous changes in the sclerosed stroma [8]. The lobular acini and ducts have distinct single-layered epithelial and myoepithelial components. Secretory activity is not prominent.

Other palpable breast masses in adolescents include fibroadenoma, juvenile papillomatosis, juvenile hypertrophy, and tubular adenoma. Like sclerosing lobular hyperplasia, fibroadenoma is usually a well-defined, firm to rubbery mass. Histologically, sclerosing lobular hyperplasia is distinguished from fibroadenoma by preservation of the acinar architecture, despite the hyperplastic appearance caused by an increased number of acini per lobule and increased collagenized intralobular and interlobular stroma.

Fibroadenomas, on the other hand, clearly differ from normal acinar architecture with their irregular proliferating elongated and distorted ducts and loose cellular stroma [2]. Sclerosing lobular hyperplasia does appear to be closely related to fibroadenoma. Microscopic fibroadenomas have been described in some sections from sclerosing lobular hyperplasia and sclerosing lobular hyperplasia may occur in the breast tissue surrounding fibroadenomas [1]. The natural course of sclerosing lobular hyperplasia is not known. However, till date no association with or natural progression towards malignancy has been reported. Excision of the lesion is considered adequate therapy. Recurrences have not been documented [6].

DR participated in the diagnosis of the case, took pictures for the manuscript, and participated in revising and finalizing the manuscript.

DC performed and read the fine-needle aspiration cytology, and participated in revising the manuscript.

SJW read the surgical pathology sections, and participated in revising and finalizing the manuscript.