https://orcid.org/0000-0003-2833-2149
History
A 64-year-old woman with a remote history of right mastectomy presented to our institution for a second opinion for a finding in the left breast detected on screening mammogram, assessed as Breast Imaging Reporting and Data System (BI-RADS) 2 at an outside facility.
Imaging findings
A diagnostic left mammogram showed a 6-mm oval mass at the 12 o’clock position, posterior depth (Figure 1), new from a screening mammogram performed 1 year prior (not shown). Subsequent targeted left breast US at the 12 o’clock position, 5 cm from the nipple (Figure 2) demonstrated a 5-mm hypoechoic, oval, nonparallel mass with circumscribed and inferior indistinct margins (Figure 2A), without internal vascularity (Figure 2B), and intermediate on elastography (Figure 2C). Given that the finding was new mammographically and with suspicious sonographic features, an US core biopsy was performed.
Sixty-four-year-old woman with a screening mammogram–detected oval mass. Tomosynthesis slices of left mediolateral oblique (MLO) and cradiocaudal (CC) views show a 6-mm oval mass with microlobulated margins at the 12 o’clock position, posterior depth that was new from screening mammogram performed 1 year prior.
Sixty-four-year-old woman with a screening mammogram-detected oval mass. Left breast US at the 12 o’clock position, 5 cm from the nipple demonstrates a 5-mm hypoechoic, oval, nonparallel mass with mostly circumscribed and inferior indistinct margins (A), without internal vascularity (B), and intermediate stiffness on elastography (C).
Differential diagnosis
Given the small 5-mm size of the lesion and far posterior depth, a complicated cyst or focal duct ectasia is high in the differential diagnosis and suggested by overlying soft elastography features of this deep mass. However, keeping in mind that some margins are indistinct and no posterior features are confidently identified, breast carcinoma (the mass form of ductal carcinoma in situ and/or invasive carcinoma) is possible, as are a small fibroadenoma or peripheral papilloma.
Diagnosis:
Histology revealed multiple cholesterol clefts arranged in irregular arrays surrounded by histiocytes and giant cells seen along with the areas of chronic inflammation and fibrosis, thus rendering the diagnosis of cholesterol granuloma (Figure 3)
Sixty-four-year-old woman with a screening-detected oval mass. (A) Low-power view (×40 magnification) showing collection of cholesterol clefts, fibrosis, chronic inflammation, and foreign body giant cells. (B) Higher-power view (×100 magnification). Blue arrow indicates cholesterol clefts. Red arrow indicates foreign body–type giant cells. Yellow arrowheads indicates background of fibrosis, chronic inflammation, and hemosiderin deposition.
Discussion
Cholesterol granuloma or cholesteroloma of the breast is a rare benign condition representing an inflammatory/reactive process with unclear etiology. It mimics breast cancer on imaging. It most commonly presents as a painless, palpable mass or is discovered incidentally on screening mammography, as in our case. It is thought to be an unusual development in the advanced stage of mammary duct ectasia. It frequently is seen in various sites in the human body such as ear, gallbladder, kidney, testis, peritoneum, parotid gland, liver, and spleen but is rare in the breast, with only a few case reports (1,2). Mammogram and US features are nonspecific, emphasizing the role of tissue biopsy and histology in the correct diagnosis (3). Histologically, the characteristic appearance of cholesterol crystals, lipid-laden macrophages, and foreign body giant cells confirmed the diagnosis of cholesterol granuloma (1).
The pathogenesis of cholesterol granuloma formation is not fully elucidated, with more insight needed into the pathomechanism; however, it is thought to result from sequela of chronic inflammation in mammary duct ectasia. The primary lesion may be mammary duct ectasia or periductal inflammation, and a history of trauma or prior breast biopsy may be the culprit (1,2).
In areas of chronic inflammation, the macrophage and lymphocyte populations increase. Lipid accumulates in the form of cholesterol crystals and globules of neutral fat derived from degenerated cell. As the relatively nonlysable cholesterol crystals leak from the ectatic duct lumen into the periductal parenchyma, they incite a foreign-body giant cell reaction that leads to the formation of cholesterol granuloma in the breast (1). The lesion is most frequently seen in middle-aged and older women with elevated blood cholesterol levels (4,5); however, underlying lipid biochemistry has not been explored.
On imaging, cholesterol granuloma typically presents as a mass (due to the cholesterol aggregates), frequently associated with calcifications. The majority of reported masses are solid, with about 20% of the masses cystic. A 10-year retrospective review from Nam et al described the most common associated histological findings as macrocysts, followed by fibrocystic changes and dilated ducts. About 9% of the masses have been reported to persist on follow-up imaging (5).
While imaging appearance overlaps with breast malignancy, the histological appearance of cholesterol granuloma is distinctive. The histological elements of chronic inflammation, cholesterol crystals, and scattered multinucleated giant cells are pathognomonic and are all evident in our case. Due to the benign nature of the diagnosis, imaging follow-up is not warranted. Our patient returned to routine screening.
Conflict of interest statement
None declared.
