The breast or the mammary gland is the most important structure in the pectoral region. Both men and women have breasts; but they are well developed only in women. It is rudimentary in men. It is well developed in the female after puberty. The breast is a modified sweat gland. It forms an important accessory organ of the female reproductive system, and it provides nutrition to the new born in the form of milk.
Situation: It lies in the superficial fascia of the pectoral region. Axillary tail (of Spence) pierces the deep fascia and lies in the axilla. Some women discover this- especially when it may enlarge during a menstrual cycle- and become concerned that it may be a ‘lump’ or enlarged lymph nodes.
- Vertically, it extends from the second to the sixth rib.
- Horizontally, it extends from the lateral border of the sternum to the mid-axillary line.
- The deep surface of the breast is related to the following structures in the following order:
- The breast lies on the deep fascia (pectoral fascia) covering the pectoralis major.
- Still deeper are the parts of three muscles, namely the pectoralis major, the serratus anterior, and the external oblique muscle of the abdomen.
- The breast is separated from the pectoral fascia by the loose areolar tissue (sometimes called as the retromammary space or bursa). Because of the presence of this loose areolar tissue the normal breast can be moved over the pectoralis major.
Structure of the breast: The structure of the breast can be studied by dividing the breast into the skin, the parenchyma, and the srtroma.
The skin: It covers the gland and presents the following features.
1. A conical projection called the nipple is present just below the centre of the breast at the level of the fourth intercostals space. However the position varies in multiparous women and therefore is not a reliable guide to fourth intercostals space in adult females. The nipple is pierced by 15-20 lactiferous ducts. It contains circular and longitudinal smooth muscle fibres which can make the nipple stiff or flatten it. It has few modified sweat and sebaceous glands. It is rich in its nerve supply and has many sensory end organs at the terminations of nerve fibres.
2. The skin surrounding the base of the nipple is pigmented and forms a circular area called areola. This region is rich in modified sebaceous glands, particularly in its outer margin. These become enlarged during pregnancy and lactation to form raised tubercles (of Montgomery). Oily secretions of these glands lubricate the nipple and prevents them from cracking during lactation. Apart from sebaceous glands the areola also contains some sweat glands and accessory mammary glands. The skin of areola and nipple is devoid of hair, and there is no fat subjacent to it.
The parenchyma: It is made up of glandular tissue which secretes milk. The gland consists of 15 to 20 lobes. Each lobe is a cluster of alveoli, and is drained by a lactiferous duct. The lactiferous ducts converge towards the nipple and open on it. Near its termination each duct has a dilatation called a lactiferous sinus.
- A ducts
- B lobules
- C dilated section of duct to hold milk
- D nipple
- E fat
- F pectoralis major muscle
- G chest wall/rib cage
- A normal duct cells
- B basement membrane
- C lumen (center of duct)
It forms the supporting framework of the gland it is partly fibrous and partly fatty. The fibrous stroma forms septa, known as the suspensory ligaments of cooper, which anchor the skin and gland to the pectoral fascia. The fatty stroma forms the main bulk of the gland. It is distributed all over the breasts, except beneath the areola and nipple.
During puberty,(8-15 years of age), the breasts normally grow because of glandular development and increased fat deposition. The areola and nipples also enlarge. Breast size and shape results from genetic, racial, and dietary factors. In a nursing mother milk accumulates in the lactiferous sinus. As the infant begins to suckle, compression of the areola (and the lactiferous sinus beneath it) expresses the accumulated droplets and encourages the infant to continue nursing as the hormonally mediated ‘let down reflex’ ensues and the mothers milk is secreted into – not sucked from the gland by- the baby’s mouth.
Blood supply: The mammary gland is extremely vascular. It is supplied by branches of the following arteries:
- Internal thoracic artery (a branch of sub-clavian artery)
- The lateral thoracic, superior thoracic and acromiothoracic branches of the axillary artery.
- Lateral branches of the posterior intercostals artery.
Venous drainage: The venous drainage is mainly to the axillary vein but there is some drainage to the internal thoracic vein.
Lymphatic drainage: The lymphatic drainage of the breast is important because of its role in the metastasis of cancer cells. Lymph passes from the nipple, areola and lobules of the gland to the subareolar lymphatic plexus, and from it:
Most lymph (more than 75%), especially from the lateral quadrants of the breast, drains to the axillary lymph nodes, initially to the pectoral nodes for the most part; however, some lymph may drain directly to the otheraxillary nodes or even to the interpectoral, deltopectoral,supraclavicular, or inferior deeo cervical nodes.
Most of the remaining lymph, particularly from the medial quadrants, drains to the parasternal nodes or to the opposite breast, while lymph from the lower quadrants passes deeply to the inferior phrenic (abdominal) nodes.
Lymphatic vessels in the skin of the breast, except the nipple and areola, drain into the axillary, inferior deep cervical, and inferior clavicular nodes, and also into the parasternal nodes of both sides.
Lymph from the axillary nodes drains into infraclavicular and supraclavicular nodes and from them into the subclavian lymphatic trunk, which also drains lymph from upper limb. Lymph from parasternal nodes enters the bronchomediastinal trunk, which drains lymph from the thoracic viscera. These trunks open independently into the junction of the internal jugular and subclavian veins to form the brachiocephalic veins.
Nerve supply: The breast is supplied by the anterior and lateral cutaneous branches of the 4th to 6th intercostals nerves. The nerves convey sensory fibres to the skin, and autonomic fibres to smooth muscle and to the blood vessels. The nerves do not control the secretion of milk. Secretion is controlled by the hormone prolactin, sedreted by the pars anterior of the hypophysis cerebri.
Changes in the breasts:
Changes, such as branching of the lactiferous ducts, occur in the breast tissues during the menstrual cycles and pregnancy. Although mammary glands are prepared for milk secretion by mid pregnancy, they do not produce milk until shortly after the baby is born. Colostrum, a creamy white to yellowish premilk fluid, may secrete from the nipples during the last trimester of pregnancy and during initial episodes of nursing. Colostrums is believed to be especially rich in protein, immune agents, and a growth factor affecting the infant’s intestines.
In multiparous women the breasts often become large and pendulous. The breasts in elderly women are small and wrinkled because of the decrease in fat and atrophy of glandular tissue.
Breast quadrants: For the anatomical location and description of tumors, the surface of the breast is divided into 4 quadrants, upper outer, lower outer, upper inner and lower inner. For e.g. a physician’s record might state:
A hard irregular mass was felt in the upper inner quadrant of the breast at 2’o clock position, approximately 2.5 cm from the margin of the areola.
Incisions: Incisions into the breast are usually made radially to avoid cutting the lactiferous ducts.
Cancer of the breast:
Understanding the lymphatic drainage of the breasts is of practical importance in predicting the metastasis of carcinoma of the breast- breast cancer. Carcinomas of the breast are almost all adenocarcinomas derived from the glandular epithelium of the terminal ducts in the mammary gland lobules. Cancer cells that enter a lymphatic vessel usually pass through two or three group of lymph nodes before entering the venous system.
Interference with the lymphatic drainage of the breast by cancer cells may cause deviation of the nipple and produce a leatherlike, thickened appearance of the skin. The skin is thickened or ‘puffy’with prominent pores that give it an orange peel appearance (peau d’orange sign), because of the edema (excess fluid in the subcutaneous tissue) resulting from the blocked lymphatic drainage. The larger dimples result from cancer invasion of the glandular tissue and fibrosis that causes shortening of the suspensory ligaments. Subareolar breast cancer may cause inversion of the nipple by the same mechanism.
The posterior intercostals veins drain into the azygous /hemiazygous system of veins along side the bodies of vertebrae, which empties in the superior vena cava. Through this route cancer cells can spreads from breast to the vertebrae and from there to the skull and the brain.
When cancer cells invade the retromammary space, attach to or invade the deep pectoral fascia overlying the pectoralis mojor or metastasize to the inter pectoral nodes, the breast elevates when the muscle contracts. This movement is a clinical sign of advanced cancer of breast. To observe this upward movement, the physician should ask the patient place her hands on her hips and press to tense her pectoral muscles.
Lymphatic vessels carry cancer cells from the breast to lymph nodes, chiefly those in the axilla. The cells lodge in the nodes, producing nests of tumor cells (metastasis). Abundant communications between lymphatic pathways and between the axillary, cervical, and parasternal nodes may cause metastases from the breast to develop in the supraclavicular lymph nodes, the opposite breast, or the abdomen. Because the axillary lymph nodes are the most common site of metastases from a breast cancer, enlargement of these palpable nodes in a woman suggests the possibility of breast cancer and may be the key to detection.
Because of communications of the lymph vessels with those in the abdomen, breast cancer may spread to the liver and cancer cells may ‘drop’ into the pelvis producing secondaries there.
- Excision of the breast is called mastectomy. It is not as common as it once was as a treatment for breast cancer.
- In simple mastectomy, the breast is removed down to the retromammary space.
- Radical mastectomy, a more extensive surgical procedure, involves removal of the breast, pectoral muscles, fat, fascia, and all lymph nodes in the axilla and pectoral region.
- In current practice, often only the tumor and surrounding tissues are removed; this is lumpectomy, or a wide local excision.
It is the radiographic excision of the breasts. It is one of the techniques to detect breast masses. The carcinoma appears as a large, jagged density in the mammogram. Mammography is also used by the surgeons to guide them when removing breast tumors, cysts, and abscesses.
Polymastia, polythelia, and amastia: Supernumary breasts (exceeding the normal number) – polymastia- or nipples (polythelia) may occur superior or inferior to the normal breasts, occasionally developing in the axilla or anterior abdominal wall.
Usually supernumary breasts consist only of a rudimentary nipple and areola, which may be mistaken for a mole (nevus) until they change pigmentation with the normal nipples during pregnancy. However, glandular tissue may also occur and further develop with lactation. Extra breasts may appear anywhere along a line extending from the axilla to the groin, the location of the embryonic mammary ridge (milk line) from which the breasts develop and along which breasts develop in animals with multiple breasts.
In either sex, there may be no breast development (amastia) or there may be a nipple but no granulation tissue.
Breast cancer in men:
Approximately 1.5% of breast cancer occurs in men. As in women, breast cancer in men usually metastasises to lymph nodes, bone, pleura, lung, liver, and skin. A visible and/or palpable subareolar mass or secretion from a nipple may indicate a malignant tumor. Although breast cancer is uncommon in males, the consequences are serious because they are frequently not detected until extensive metastases have occurred, as in bones.
Enlargement of the breast in males is called gynaecomastia. It commonly occurs at puberty but may also accompany ageing or be drug related (after treatment with diethyl stilbestrol for cancer of prostate. It may also result from a change in the metabolism of sex hormones by the liver. About 40% of post pubertal males with Klinefelter syndrome (xxy trisomy) have gynaecomastia.