Breast (Left)

Structure/Morphology

The breast is a modified cutaneous, glandular structure located on the anterior aspect of thorax. Although both men and women have breasts, there are normally well developed in females.

On the anterior surface of the breast, there is a prominent cylindrical projection, the nipple, which is surrounded by the highly pigmented areola. The mammary glands are located within the breasts and are considered specialized accessory glands of the skin. During puberty in females, the breasts enlarge, mainly due to the deposition of fat, but in part due to the development of the glandular tissue. Mammary glands are functionless in the male breast and normally do not develop.

In non-lactating breasts, the amount of adipose tissue (fat) surrounding the glandular elements of the breast determines their size.

Anatomical Relations

The body of the breast lies within the superficial fascia of the anterior thoracic wall. It sits on a bed, extending horizontally from the lateral border of the sternum to the midaxillary line, and vertically from the second to the sixth ribs. The medial two-thirds of the bed of the breast is formed by the pectoral fascia, while the lateral third of the bed is formed by the deep fascia overlying the serratus anterior muscle (Standring, 2016).

The breast extends along the lateral edge of the pectoralis major muscle towards the axilla, thus forming an axillary process, or axillary tail of Spence.

The retromammary space is a small potential space that lies between the breast and the pectoral fascia and is filled with fat. It allows for a limited degree of movement of the breast on the pectoral fascia.

Function

The breasts are accessory glands to the reproductive system and are responsible for the production of milk for the nourishment of infants.

Arterial Supply

The breasts receive arterial supply primarily from lateral and medial mammary branches that arise from the lateral thoracic and internal thoracic arteries, respectively. It may also receive branches from the superior thoracic, thoracoacromial, intercostal, and subscapular arteries.

Venous Drainage

Blood is drained from the glandular tissue of the breast and from an areolar venous plexus via the internal thoracic, lateral thoracic, and intercostal veins.

Innervation

The breast receives sensory and sympathetic innervation from the lateral and anterior cutaneous branches of the fourth to sixth anterior rami of the thoracic spinal nerves (fourth to sixth intercostal nerves). The nipple is supplied by the fourth lateral cutaneous branch (see dermatomes). The nipple receives extensive innervation, via free nerve endings, Meissner corpuscles, and Merkel disc endings.

Lymphatic Drainage

75% of lymphatic drainage of the breast is received by the axillary lymph nodes. Deep lymph vessels terminate in the subclavicular lymph nodes.

Ultimately, lymph of the left breast terminates in the thoracic duct, which drains into the left subclavian vein. Lymph of the right breast drains into the right subclavian vein via the right lymphatic duct. The medial right side of the breast may drain towards the parasternal lymph nodes, which in turn, may drain inferiorly at the groin, via the superior and inferior epigastric routes.

Additionally, lymphatic drainage may cross the midline, such that lymph may reach axillary lymph nodes on the opposite side (Standring, 2016).

List of Clinical Correlates

- Breast cancer

- Gynecomastia

Reference

Standring, S. (2016) Gray's Anatomy: The Anatomical Basis of Clinical Practice. Gray's Anatomy Series: Elsevier Limited.