Breast disease and mammography

In UK practice, breast abnormalities are evaluated as part of a ‘triple assessment’ process: clinical examination, imaging and subsequent image-guided tissue diagnosis. All breast-imaging tests are assigned a numerical score from 1 to 5 with a prefix for each score: P for clinical examination findings, M for mammography, U for ultrasound and MRI for findings on MRI studies. Subsequent histology/cytology results are similarly described.

The UK classification system for imaging is:

1 = normal
2 = benign findings, no further evaluation required
3 = indeterminate/probably benign findings, small risk of malignancy, requires further evaluation
4 = suspicious findings with a moderate risk of malignancy, requires further evaluation
5 = highly suspicious findings with a high risk of malignancy, requires further evaluation

Further evaluation typically means image-guided core biopsy, and increasingly vacuum biopsy for microcalcification (FNA is not recommended as first line).

These UK categories broadly align with the widely used American College of Radiology breast imaging data and reporting system (BIRADS) classification.

Mammographic, sonographic and MRI features of breast abnormalities

This table describes the classical appearances of benign and malignant abnormalities on mammography, US and MRI, but note that there is significant overlap between the categories. Breast cancers may be occult on imaging, and sensitivity decreases as mammographic breast density increases.

Lesion characteristics	Typically benign	Typically malignant
Mass	Smooth margin, up to three gentle lobulations	Indistinct, spiculated or microlobulated margins
	Low density on mammogram	High density on mammogram
	Wider than tall on US	Taller than wide on US
Echogenicity on US	Variable depending on lesion	Markedly hypoechoic, often with echogenic halo
Enhancement characteristics on MRI	Slow and prolonged moderate enhancement ^a	Rapid marked enhancement with early washout
Calcification	See Section 11.2
Surrounding parenchyma	Normal ^b	Disrupted/distorted ^c
Nipple/areola	Normal	Retracted
Skin	Normal	Thickened ^d
Ducts	See Section 11.11
Subcutaneous/retromammary space on mammogram	Normal	Obliterated

a Lobular carcinoma can also have these characteristics.

b Except in infection where the surrounding breast can be oedematous.

c This may also be seen due to postsurgical/radiotherapy change.

d This may also be seen due to postsurgical/radiotherapy change, inflammation, heart failure or lymphoedema.

Calcification

Microcalcification is defined as individual calcific densities measuring <0.5 mm in diameter. Microcalcification is not specific to carcinoma, whereas coarse calcification may also be found in carcinoma. This table describes the classical mammographic features. Please note that skin/subcutaneous calcification is covered in Chapter 4 .

Definitely benign (see figure)	Probably benign	Suspicious of malignancy
Arterial: tortuous, tramline (1) Widely separated, radiolucent centre (2) Plasma cell mastitis: linear, thick, rod-like ± radiolucent centre (3) Egg-shell or curvilinear margin of cyst/fat necrosis (4) Popcorn within fibroadenoma (5) Large individual >2 mm (6) Floating or layering on lateral mammogram: ‘milk of calcium’ in microcysts (7) Coarse irregular dystrophic calcification after radiotherapy or trauma Suture calcification (curvilinear, looped, calcified knots)	Widespread in both breasts or symmetrical Macrocalcification of uniform size Superficial distribution (i.e. within skin)	Linear (ductal) or segmental distribution ^a Pleomorphic, linear branching shape ^a Increasing on serial mammography

a See figure.

Examples of definitely benign calcification.

Benign lesions with typical imaging appearances

1.
Fibroadenoma —involuting fibroadenomas may contain typical ‘popcorn’ calcification on mammography, which precludes the need for further imaging or biopsy. In the UK national guidance recommends that biopsy in women <25 years is not necessary for confirmation if typical features of a fibroadenoma are present (well-defined, ovoid/round, up to three gentle lobulations). Other countries follow BIRADS recommendations, which advocate US follow-up.
2.
Intramammary lymph node —most often in the upper outer quadrant. A fatty hilum is a characteristic feature, typically seen in normal and reactive lymph nodes, but may also be present in pathological nodes—this is seen as a focal radiolucency within the node on mammography (may be difficult to appreciate), fat signal on MRI or hyperechoic on US. Normal or reactive nodes often have ‘suspicious’ enhancement characteristics on MRI.
3.
Lipoma —well-defined, rounded, exclusively fat-containing.
4.
Oil cyst —well-defined, lucent on mammography ± ‘egg-shell’ peripheral calcification. The presence of multiple subcutaneous oil cysts is characteristic for steatocystoma multiplex (many other subcutaneous oil cysts will also be present on the trunk).
5.
Hamartoma —‘breast tissue within breast tissue’ or ‘salami-slice’ appearance on imaging due to variable mix of fatty and glandular tissue.

Single well-defined mammographic soft-tissue opacity

As a general guide any well-defined opacity >1.0 cm in diameter is usually subjected to US and, if solid, biopsy is performed.

Benign

1.
Cyst —round/oval, low-density mass. In the case of an oil cyst: rounded, fat density mass ± peripheral calcification.
2.
Fibroadenoma —round/oval mass, similar density to glandular breast parenchyma. Cysts and fibroadenomas can have similar appearances on mammography.
3.
Intramammary lymph node —common in normal breasts. Pathological causes are the same as those in Section 11.12 .
4.
Skin lesion — e.g. irregular ‘warty’ skin papillomas. The air/soft-tissue interface creates a characteristic hypodense halo around skin lesions. Skin markers may be used to confirm.
5.
Nipple not in profile — may resemble a soft-tissue opacity on the mediolateral oblique (MLO) view.
6.
Hamartoma — variable appearance depending on composition—if mostly glandular tissue it can present as a well-defined mass with density identical to surrounding glandular parenchyma. If mostly fatty, it can present as a well-defined lucent mass.
7.
Galactocoele — round/oval mass in a lactating woman. Appearance depends on proportion of fat, water and milk content. May mimic lipoma (if high fat content), hamartoma (if mixed viscous contents) or cyst. May contain characteristic fat-fluid level if contains fresh liquid milk. Can become infected.
8.
Sebaceous cyst— opacity related to the dermis.
9.
Lactating adenoma —occurs during lactation or in the third trimester of pregnancy. Imaging features are similar to fibroadenoma. Regresses spontaneously after cessation of breast feeding.
10.
Pseudoangiomatous stromal hyperplasia (PASH) —the rare tumoural form presents as a well-defined, noncalcified mass in a premenopausal woman. Can mimic fibroadenoma on US.
11.
Myofibroblastoma —rare benign spindle cell tumour usually found in postmenopausal women and older men. Well-defined, round/oval, noncalcified mass, hypoechoic on US, mimicking fibroadenoma (patient age can be a useful discriminator).
12.
Other rare soft-tissue masses not specific to the breast —e.g. haemangioma (± phleboliths), leiomyoma (often near areola), schwannoma, neurofibroma, solitary fibrous tumour. These are typically well-defined and hypoechoic on US (mimicking fibroadenoma), although haemangiomas may be microlobulated and have variable echogenicity.

Malignant

1.
Carcinoma —a small number of carcinomas can look ‘benign’ on mammography: high-grade invasive ductal carcinoma, mucinous carcinoma (often mixed solid-cystic), medullary carcinoma, papillary carcinoma (often within a cyst or dilated duct) and adenoid cystic carcinoma.
2.
Phyllodes tumour —indistinguishable from a fibroadenoma on mammography, but characterized by its rapid growth and often large by time of presentation. Usually present in an older age group than fibroadenomas. Most are benign, but borderline and malignant varieties exist. Calcification is rare. Malignant lesions metastasize to lung and bone, and may invade the chest wall.
3.
Metastasis to the breast —can be solitary, see Section 11.5 .
4.
Lymphoma *—can appear as a single, well-defined, noncalcified mass. Spiculations and architectural distortion are usually absent. May be primary (rare) or secondary.

Multiple well-defined mammographic soft-tissue opacities

1.
Cysts — most common cause.
2.
Fibroadenomas —10-20% are multiple.
3.
Skin lesions —e.g. cutaneous papillomas, neurofibromas (NF1).
4.
Intramammary lymph nodes .
5.
Metastases —lymphoma, leukaemia (especially acute myeloid leukaemia), melanoma, lung and ovaries are the most common sources. Often involve the subcutaneous fat. Calcification is rare (except in ovarian cancer). Metastases elsewhere are usually also present.
6.
Silicone or paraffin injections —usually very dense and widely distributed in the breast, accompanied by dense striated appearing fibrosis (sclerosing lipogranulomatosis) ± dense calcification.
7.
Cowden syndrome —may present with multiple fibroadenomas, fatty hamartomas and/or tubular adenomas. Increased risk of breast cancer.

Large (>5 cm) well-defined mammographic abnormality

1.
Giant cyst — radiopaque, usually low density.
2.
Giant fibroadenoma — radiopaque.
3.
Lipoma — radiolucent.
4.
Phyllodes tumour — radiopaque, indistinguishable from fibroadenoma.
5.
Hamartoma —mixed density, depending on composition of fatty and glandular tissue.
6.
PASH —see Section 11.4 .

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