Breast hamartoma

Last revised by Mohammad Taghi Niknejad on 6 Mar 2024

Breast hamartomas, also known as fibroadenolipomas, are benign breast lesions. They are typified by a "breast within a breast" appearance on mammogram.

They typically occur in women older than 35 years of age. 

Breast hamartomas most commonly are asymptomatic or present as a painless soft breast lump. They may also present as unilateral breast enlargement without a palpable localized mass 4.

Hamartomas represent benign proliferation of fibrous, glandular, and fatty tissue (hence fibro-adeno-lipoma) surrounded by a thin capsule of connective tissue. All components are found in normal breast tissue, which is why the lesions are considered hamartomatous.

Macroscopically, hamartomas are slightly larger and softer than common adenofibromas and are well-defined, whitish, pinkish and fleshy, with islands of yellow fat tissue.

Histologically, they exhibit pushing borders with a pseudo-encapsulation, and consist of a combination of variable amounts of stromal and epithelial components.

Lesions can be any size but are typically large at presentation.

  • well-circumscribed, round or oval mass surrounded by a thin capsule
  • comprising of both fat and soft-tissue internal densities
    • i.e. fat component appears radiolucent, soft tissue component appears radiodense
  • classic description:  "breast within a breast"  or a "slice of sausage" appearance

Because it resembles normal breast tissue, the margins are often difficult to delineate. It may be seen as a well-circumscribed, solid lesion without any intralesional microcalcification. Internal echotexture is most often mixed with both hyperechoic and hypoechoic components 3. Lesions are soft and easy to compress.

Although previously reported as "fibrolipoma" or "fibroadenolipoma", they were initially termed "hamartomas" by M G Arrigoni et al. in 1971 2.

The diagnosis of hamartoma is normally straightforward, due to an extremely characteristic imaging appearance. In rare cases, a differential diagnosis may include other well-defined lesions:

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