Last revised by Dr Daniel J Bell on 25 Aug 2022

The breast is an apocrine gland seen in both males and females. However, in females it has a specific function which is the production of milk for neonatal nutrition and immune function.

The breast has an inhomogeneous structure which is predominantly composed of adipose tissue and glandular tissue. In addition, there are also suspensory Cooper's ligaments and connective tissue such as collagen and elastin. The adult breast has nearly 14-18 lactiferous lobes which drain into lactiferous ducts which further converge to drain at the nipple-areola complex

The glandular parenchyma is estrogen dependent, thus on attaining menopause the glandular parenchyma atrophies. 

The breasts are seen to overlie on the pectoralis major muscles and extend from the level of the second-to-sixth ribs:

  • superior: clavicle
  • inferior: middle of sternum
  • lateral: midaxillary line
  • medial: sternum

There is often an extension of breast tissue into the axilla called the axillary tail

The drainage of lymph from the breast has significant impact on spread of malignancy and as such has a separate article: lymphatic drainage of the breast

During embryological development, breast tissue first appears as ectoderm ridges during the 6th week of gestation. This ridge grows thicker and leads to mesodermal compression. With further proliferation of the ectodermal cells, there is a growth of the same into the mesodermal layer leading to a formation of clusters which further form lobules. In the fifth month of gestation some cords of ectodermal cells sprout from each of these lobules with the central parts undergoing apoptosis leading to formation of ducts. Similarly on the surface apoptosis occurs leading to formation of pits which protrude through the nipples after connecting with the formed ducts. 

  • a wide variation of homogeneously dense, milky structures (representing glandular tissue) interrupted by areas of curved or round radiolucent fat 
  • Cooper's ligaments appear as curved, linear radiopacities
  • duct system is not normally visualized except near the nipple 2

See articles: mammography views; breast density

  • glandular tissue appears variably hyperechoic and fat appears hypoechoic
  • ducts appear as regular interspersed tubular, hypoechoic structures
  • Cooper's ligaments appear as hyperechoic, linear structures and may cause acoustic shadowing 2-3
  • nipple can also cause acoustic shadowing, sometimes creating a pseudomass 3

See article: breast ultrasound.

  • T1: fat has moderate high signal; glandular, ductal and connective tissue has low signal 
  • T1C+: normal breast tissue is typically non-enhancing 2

See article: breast MRI.

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Cases and figures

  • Figure 1: breast (Gray's illustration)
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  • Figure 2: lymphatics of the breast (Gray's illustration)
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  • Figure 3: normal annotated mammogram
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  • Figure 4: normal annotated mammogram
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  • Case 1: normal RMLO mammogram
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  • Case 1: normal RCC mammogram
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  • Case 1: normal breast ultrasound
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  • Case 1: normal RMLO tomosynthesis
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  • Case 1: normal RCC tomosynthesis
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  • Case 2: normal breast MRI (fatty breasts)
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