Fibroadenomas are benign fibroepithelial tumours. They are most common in adolescent girls and young women [3]. Fibroadenomas typically present as smooth, mobile, firm masses but may also be impalpable and detected via mammographic imaging. It is not uncommon for individuals to have multiple fibroadenomata.

On mammography fibroadenomas appear as well-defined round, ovoid, or lobulated masses (Fig. 4.2). The masses may calcify over time and develop a typical popcorn-shaped pattern (Figs. 4.3 and 4.4). A typical benign calcified fibroadenoma requires no further work-up. If non-calcified, ultrasound is required to characterise the lesion and dependent upon the age of the patient histological sampling (needle core biopsy) may be performed.

There are also special types of fibroadenoma to include: lactating adenomas, tubular adenomas and juvenile fibroadenomas. Occasionally in adolescent girls and young women these masses grow to a large size and are termed juvenile giant fibroadenomas.

Phyllodes tumours are also fibroepithelial tumours of the breast which have some similarities to a fibroadenoma, but are rare in comparison accounting for less than 1 % of all breast tumours [4]. They most commonly occur between the ages of 40 and 60. Clinically they commonly present as a large rapidly growing lump.

Mammographically, most phyllodes tumours are large, circumscribed masses that are round, oval, or lobulated [5] (Fig. 4.5).

Phyllodes tumours are classified as benign (non-cancerous), malignant (cancerous), or borderline. Benign Phyllodes tumours require excision with a good clear histological margin as they have a likelihood of local recurrence after excision.

Borderline or malignant tumours and those of a large size are considered significant risk factors for local recurrence. For these lesions mastectomy and immediate breast reconstruction may be advocated as the role of adjuvant treatments remain unproven [6].

Breast haemangiomas are benign vascular tumours, which fall into two categories (capillary and cavernous) dependent upon vessel size [7]. Clinical manifestation is a palpable lump but they are often incidental findings on screening mammography.

Haemangiomas appear as well-defined, ovoid or lobulated masses located within the superficial tissues of the breast (Figs. 4.6 and 4.7), and based on mammography alone can also be difficult to distinguish from fibroadenomas.

Gynaecomastia is the commonest benign male breast condition, peaking in adolescence and over 50 years of age. Breast enlargement occurs due to benign ductal and stromal proliferation. There are a wide range of causes including endogenous hormonal imbalance, systemic disease, hormone producing tumours, obesity and an action of some drugs. Gynaecomastia usually presents as a firm, palpable subareolar mass which may be tender and can be unilateral or bilateral.

On mammography, gynaecomastia has three typical patterns [8]: nodular, dendritic, and diffuse.

The early florid phase of gynaecomastia (nodular) is associated with shorter duration of symptoms and is identified on mammography as a large, poorly defined, subareolar density (Fig. 4.8).

The dendritic growth pattern is observed when symptoms are persistent over a longer time period and mammographically manifests as a smaller, spiculated, subareolar density (Fig. 4.9).

The third pattern, diffuse gynaecomastia, is frequently related to oestrogen exposure. Mammographically this mimics a heterogeneously dense female breast (Fig. 4.10).

Pseudogynaecomastia relates to purely fatty enlargement of the breasts simulating gynaecomastia but there is no glandular tissue (Fig. 4.11).

The majority of primary tumours of the breast have an epithelial origin. Non-epithelial tumours in the breast are rare [9]. A Schwannoma (Fig. 4.12) develops from ‘Schwann’ cells of the peripheral nerve sheath, and may also be referred to as a neurilemmoma, or peripheral nerve sheath tumour.

For unknown reasons, Schwann cells can occasionally grow in a neoplastic fashion resulting in a benign tumour. However, there is a remote likelihood of a Schwannoma developing malignant cellular characteristics [10].

A breast hamartoma is a benign breast lesion resulting from proliferation of fibrous, glandular, and fatty tissue surrounded by a thin capsule of connective tissue [12].

Lesions can be variable in size, and present as painless soft lumps, unilateral breast enlargement without a palpable mass or can be asymptomatic and an incidental finding on mammography.

Multiple hamartomas are associated with Cowden’s syndrome (a rare autosomal dominant inherited disorder), which also carries an associated increased risk of breast carcinoma [13].

Mammographically hamartomas are typically seen as a well circumscribed, round or ovoid masses comprising of both fat and soft-tissue densities (both radiolucent and dense components). Sometimes this is described as a “breast within a breast” appearance [14] (Figs. 4.13 and 4.14).

A lipoma is a benign lesion composed of fat. Generally breast lipomas present as painless, soft, mobile lumps, which are variable in size (ranging from <1 cm to >6 cm) [15].

Mammographically lipomas (Figs. 4.15 and 4.16) are identified as radiolucent masses and are often easier to detect in denser breasts.

Pseudoangiomatous stromal hyperplasia is a benign, uncommon form of stromal (mesenchymal) overgrowth within breast tissue [16].

PASH is typically found in premenopausal women but can be a common incidental finding at breast biopsy. If forming a mass lesion, the presentation is commonly a solitary, circumscribed, firm palpable mass. There is a wide variance of size of PASH mass lesions with diameters ranging from 1 to 12 cm. PASH is not associated with malignancies and is not considered a premalignant lesion [16].

Most frequently they appear on mammography as a circumscribed mass, but variable appearances have also been reported [17].

A galactocele is a benign breast lesion that typically occurs in lactating women or more commonly on cessation of lactation [18]. They occur as a result of ductal obstruction and inspissation of the milk

Galactoceles have differing proportions of water, proteins, fat, and lactose and this is reflected as variable mammographic appearances [19]. Based on this galactoceles could appear radiolucent, have a fat/fluid level or appear of mixed density.

Typical presentation is that of a painless breast lump that may be solitary and unilateral, but multiple and bilateral nodules have also been reported.

Spontaneous resolution occurs in the majority of cases, but if there is diagnostic uncertainty aspiration can be performed which will classically yield milky fluid of variable viscosity dependent on how old the liquid is.

A haematoma is a collection of blood, which usually results from a preceding direct trauma, surgery, or biopsy but can spontaneously occur in those on anticoagulants. Clinical correlation is essential to avoid misinterpretation with breast malignancy.

Dependent on the stage of haematoma formation they have variable mammographic appearances; the most common being an area of diffusely increased glandular density [20]. If more localised a relatively well-defined mass may also be seen (Fig. 4.17).

The majority of haematomas resolve within 2–4 weeks and no further evaluation is required. Some haematomas may liquefy and develop into a breast seroma or over time may evolve into fat necrosis.

An intraductal papilloma is a benign tumour that grows within the breast ducts. They are wart-like growths of glandular tissue with fibrous tissue and blood vessels.

Intra ductal papillomas are classified into two categories. Central – are typically solitary lesions within a large duct in the subareolar region. These may be felt as a small lump and are typically associated with a clear or bloody nipple discharge. Peripheral papillomas are likely to be multiple and located within smaller ducts.

Mammograms are often normal particularly if the papillomas are small. When imaging findings are present, they are identified as a circumscribed subareolar mass or a solitary dilated retroareolar duct [21] (Fig. 4.18).

Papillomas are considered heterogeneous lesions with variable pathological features and therefore large volume core sampling (Vacuum Assisted Biopsy) or surgical excision is required to exclude atypia.

Multiple papillomatosis is defined as an abnormal overgrowth of cells within the ducts and is more frequently associated with hyperplasia, atypia, DCIS, sclerosing adenosis, and radial scar [22]. Mammographic findings of multiple papillomatosis are variable from well-defined masses with or without calcification, foci of microcalcification, clusters of nodules, and asymmetric densities.

Amyloidosis results from the abnormal deposition of a protein, called amyloid, in various tissues of the body. Breast amyloidosis is rare and can be part of a systemic disease or it may be localised to the breast [23] (Fig. 4.19). The typical clinical presentation is a unilateral, painless, solitary breast mass, which may have associated microcalcifications.

Mastitis refers to inflammation of breast tissue. Early stages of mastitis typically present as localised pain, redness, swelling, and warmth with a fairly rapid onset.

Metastases to the breast are rare. The most frequent source of a metastatic breast lesion is the contralateral breast but may also arise from:

Lymphoma/leukaemia, melanoma, sarcomas, prostate cancer, lung cancer, gastric cancer, ovarian cancer and renal cell cancer [25].

Metastases to the breast tend to be rounded, well defined and located in the subcutaneous fat and are much more likely to be multiple and/or bilateral.

Breast lymphomas are comprised of lymphoid tissue and breast tissue. They can be primary or secondary lesions, but both are uncommon [26].

Presentation may be as a palpable mass or as diffuse thickening of the breast, with enlarged axillary lymph nodes.