The breast is a modified sudoriferous gland of the apocrine variety which is found in both males and females as a paired gland. In males and immature females the breast is rudimentary but during puberty in females the breast undergoes developmental changes but it attains its final development in the final stages of pregnancy and during lactation.
DEVELOPMENT OF THE BREAST
The breast development commences at the sixth week of intrauterine life as two vertical ridges extending from the area of the future axilla and to the inguinal region. This line is referred to as the mammary ridge or the milk line. In human the caudal 2/3rd of the milk line degenerates while the cranial 1/3rd is destined to form the rudiments of the mammary gland. At birth only the lactiferous ducts are present but in females during puberty branching of the lactiferous duct occurs and growth of adipose tissue and fibrous tissue occur thereby increasing the size of the breast, this continues in the nulliferous but during pregnancy the final development of the breast commences whereby the alveoli is formed so as to produce milk immediately after birth.
The female breast is a rounded eminence which is found situated at the superficial fascia of the anterior thoracic wall overlying the pectoralis major muscle, serratus anterior muscle and the aponeurosis of the external oblique abdominus muscle. Its upper lateral quadrant further extend into the axilla as the axillary tail of Spence which pierces the pectoralis fascia at the level of the third intercostal space creating an opening known as the foramen of Langer.
EXTENT OF THE BREAST
The breast has a nipple which corresponds to the apex and a base which is fairly constant in most females. The base extends vertically from the 2nd to the 6th rib taking orientation from the midclavicular line. Horizontally it extends from the lateral border of the sternum to almost close to the mid axillary line.
SIZES AND SHAPE OF THE BREAST
The size and shape of the breast varies among races and among individuals based on functional activities, it also varies with age. It is also anatomically common to find one breast larger than the other in the same individual The shape of the breast varies from hemispherical (globular), conical, various kinds of pendulum, piriform and flattened.. The size of the breast is determined by the fatty content but the size of the breast does not interfere with its milk producing capacity.
RELATIONS OF THE BREAST
The base of the breast is related to the pectoral fascia, the pectoralis major, the serratus anterior muscle, the aponeurosis of the external oblique abolominis muscle. It is separated from the pectoral fascia and the pectoralis major by an areolar space which is referred to as the submammary space or retromammary space. This space allows for an independent movement of breast over the pectoral fascia and the pectoralis major.
STRUCTURE OF THE BREAST
The structure of the breast is quite remarkable and complex, it is consfigured or designed to produce milk. The structure of the breast comprise of:
1. The skin
3. The Stroma
The skin just like in other part of the body enclose the breast but it present the following features:
1. The Nipple or Mammary Papilla: This is a cylindrical or conical projection which lies a little below the center of the breast. It forms the apex of the breast and sometimes in nulliferous females it over lies the 4th intercoastal space. It is traversed by 15-20 lactiferous duct through which milk is discharged to the surface. It also comprises of non-striated myocytes (smooth muscle cells), which are arranged circularly and longitudinally. The circular smooth muscle cells on stimulation either by sucking or by tactile stimulation contracts thereby causing erection of the nipple this serve the purpose of opening up that lactiferous duct in lactating mothers.
The longitudinal smooth muscle cells on contraction causes flattening of the nipple this also serve the function of closing up the lactiferous ducts thereby preventing the outflow of milk in lactating mother.
2. The Areolar: It is the highly pigmented area of the skin that surrounds the base of the nipple it is rose pink in Caucasian females while in blacks and other melanized races it is darker and highly pigmented. During the 2nd months of pregnancy the pigmentation increases thereby giving a darker colour of which after pregnancy it never returns to its original colour. This has a medicolegal importance among the Caucasians. In the areolar are found peripherally arranged, modified sebaceous gland referred to as the glands of Montgomery. At the onset of pregnancy the nipple and areolar become slightly swollen and also the glands of Montgomery form cyst like structures referred to as the tubercle of Montgomery. The secretions from this gland help to lubricate the areolar and the nipple preventing them from cracking in lactating mothers. The nipple and areolar are devoid of hair and there are no fat beneath them.
The parenchyma is the milk producing tissue or the glandular tissue of the breast that is composed of about 15-20 lobes, each lobe is made up of clusters of lobules and each lobule is comprised of clusters of alveoli. The lobes are drained by lactiferous ducts which open into the rough ended tip of the nipple. At the base of the areolar the lactiferous ducts expand forming the lactiferous sinus which acts as a reservoir for milk during lactation.
The stroma of the breast is the supporting tissue of the breast. It comprises of fibrous and adipose tissues, the stroma is enclosed by the subcutaneous tissue and from there septa emerge attaching the skin and the lobes to the pectoral fascia thereby forming the suspensory ligament of Cooper. The adipose tissue are the main determinants of the size of the breast and their presence gives the breast its smooth contour.
BLOOD SUPPLY OF THE BREAST
· The breast is supplied by the perforating branches of the internal thoracic artery.
· Pectoral branch of the thoracoacromial artery.
· Lateral branches of the posterior intercostal artery.
· Lateral thoracic artery.
The breast is drained by veins that bear similar name with the corresponding artery. They first form anastomotic cycle around the base of the nipple this is referred to as circulus venosus. From the anastomotic cycle sets of vein emerge. The superficial varies drain into the internal thoracic vein and into some of the superficial veins of the lower part of the neck. The deep veins drain into the following veins: axillary vein, the anterior intercostal veins and posterior intercostal veins. In the resting state of the breast there is an avascular zone of fibroblast which is referred to as epitheliostromal junction which separates the epithelium of the glandular tissue and the stroma.
The knowledge of the pathway of the breast is of utmost importance for the perfect understanding of the spread of carcinoma of the breast. The lymphatic drainage of the breast runs in two sets.
1. Superficial set of lymphatic vessel drains the skins of the breast except the nipple and areolar.
2. Deep set of the lymphatic vessels drains the parenchyma, stroma the nipple and areolar of the breast.
About 75% of the lymph of the breast drains to the axillary group of lymph nodes, 20% drains into the parasternal group of lymph nodes while 5% drains into posterior intercostal nodes. The lymph of one breast can also drain to the opposite breast passing through the intermammary cleft.
The lymphatic vessels of the breast also form plexuses:
1. Subareolar plexus of Sarpy which main drains into axillary group of lymph nodes, it follows the axillary tail of Spence. The subareolar plexus of Sarpy lies beneath the areolar.
2. Submammary lymphatic plexus lies within the submammary space, though it is not involved with the normal lymphatic drainage of the breast unless there is obstruction of the normal pathway.
It is supplied by the lateral and anterior cutaneous branches of the 4th – 6th intercostal nerves.
Cancer of the breast because of the excessive communication of the breast lymphatic vessels with other parts of the body, cancer of the breast can easily spread into regions like the brain through the posterior intercostal veins which communicates with the vertebral veins that drains the brain. Cancer of the breast can spread to the abdominal region affecting organs like liver through the parasternal group of lymph nodes which communicates with the subperitoneal group of lymph nodes. It can also spread to the pelvis affecting the uterus through a pathway which is referred to as the pathway of Gerota which is not well defined. It can spread from one breast to the other through the inter communicating lymphatic vessels. Cancer cells can infiltrate the lactiferous duct which later results to the inversion of the nipple. When it infiltrates the fibrous tissues (Suspensory ligament of Cooper) it causes retraction of the skin which results to pitting of the skin of the breast. Cancerous cells can also block superficial vessels draining the skin of the breast; this will lead to edema of the skin. As a result of this the skin will have the appearance of an orange skin or peel of orange a condition known as peau d orange. Cancer of the breast could also infiltrate the pectoralis major causing adhesion of the breast to the pectoralis major.
It can lead to abscess formation in the breast which can be drained by incision which could be done in a radial manner so as to avoid laceration of the lactiferous duct. In severe cases of cancer of the breast a radical mastectomy is carried out where the breast is completely removed including the pectoralis major and pectoralis minor. The axillary lymph nodes that are involved are also removed.
CONGENITAL MALFORMATION AND ABNORMALITIES OF THE BREAST
1. Polythelia: A condition where there is more than two nipples.
2. Athelia: A condition where there is absence of one or both nipples.
3. Polymastia: A condition where there is presence of more than 2 breasts.
4. Amastia: A condition where there is absence of one or both breast.
5. Gynaecomastia: A condition where there is development of breast in male
6. Inversion of the nipple: Is where the nipples fail to evect.