Breast tissue is a type of modified sweat gland, hemispherical in shape, located in the superficial fascia of the pectoral region. In males the breasts are rudimentary whereas in females they are well developed starting at puberty.
The axillary tail of Spence is a small extension in the superolateral aspect.
The breast is divided into 4 quadrants.
It extends vertically from 2nd to 6th rib, and horizontally from lateral border of sternum to mid axillary line. Position of nipple lies in 4th intercostal space, shifts downwards with age.
Breast lies over the deep fascia.
Deep fascia gives rise to Coopers ligaments which maybe infiltrated during CA breast, causing puckering of the skin.
The breast is separated from the deep fascia by a space called retromammary space, which is filled with loose areolar tissue, due to which the breast is free to move side to side and up and down.
The muscles underlying the breast are pectoralis major, serratus anterior and external oblique.
Internal Structure of the Breast
Breasts consists of three structures- skin, stroma and parenchyma(glandular tissue/mammary gland proper).
Skin– Skin covers the breast and has the following-
Nipple– Conical projection, usually at 4th Intercostal space.
It consists of smooth muscle fibres which can flatten or make the nipple stiff.
It is richly innervated by sensory nerve endings.
Areola– The pigmented area surrounding the nipple, contains modified sebaceous glands which lubricates the nipple, preventing them from drying and cracking.
Stroma– Consists of connective tissue, which condenses to form fibrous strands/septa, called ligaments of cooper, arranged in a radial fashion.
The ligaments of cooper connect the deep fascia to the dermis and give the breasts its shape. With age these ligaments atrophy, making the breasts pendulous.
Parenchyma-The breast parenchyma is made of glandular tissue, and consists of about 15-20 lobes arranged in radial fashion. These lobes produce milk for feeding the newborn baby.
Each lobe is made up of lobules. These lobes are drained by a lactiferous duct, which open into a lactiferous sinus, that stores the milk during breast feeding.
Breast blood supply
Breast is supplied medially and laterally by 5 arteries-
Medial aspect- of the breast is supplied by internal thoracic artery which is a branch of internal thoracic artery.
- Lateral thoracic and thoracoacromial branches- from axillary artery.
- Lateral mammary branches- Originate from posterior intercostal arteries(derived from the aorta).
They supply the lateral aspect of the breast in the 2nd, 3rd and 4th intercostal spaces.
- Mammary branch- originates from anterior intercostal artery.
Venous drainage of the breast
- Axillary vein
- Internal thoracic vein
- Posterior intercostal veins
These veins follow the arteries mentioned above.
These veins form an anastomotic venous circle at the base of the nipple, where they run into superficial and deep plexuses.
The superficial veins drain into internal thoracic vein. The deep veins drain into the internal thoracic, axillary and posterior intercostal veins.
Mets to brain occur via the following route-
Posterior intercostal veins—>vertebral venous plexus—>intracranial dural venous sinuses—>brain.
Nerve supply of breast
Anterior and lateral cutaneous branch of 4th -6th intercostal nerve.
Sensory fibres go to skin of breast.
Autonomic fibres- to smooth muscle and blood vessel.
Can be subdivided into lymph nodes and vessels.
- Internal mammary- Lying along the internal mammary vessels
- Supraclavicular nodes- Lying above the clavicle
- Posterior intercostal nodes- Lying in posterior intercostal spaces in front of the head of ribs.
- Cephalic(deltopectoral nodes)- lying in the deltopectoral groove.
The breast also drains into the diaphragmatic and subperitoneal lymphatic plexuses.
75% of lymph from the breast is drained by axillary lymph nodes.
Levels of Lymph Nodes
Lymph Nodes can be further divided based on their relation to the pectoralis minor muscle.
Lateral to the Pectoralis minor is level I lymph nodes, behind the Pectoralis minor is level II lymph nodes and medial to the Pectoralis minor is level III.
These three levels of lymph nodes are divided into five groups–
Level I group– Includes Lateral group, Posterior group and Anterior group.
- Anterior or pectoral group- They lie along the lateral thoracic vein at lower border of Pectoralis minor.
- Posterior group- lies along the subscapular vein and drains the axillary tail of spence.
- Lateral group- Lie along the upper part of the humerus and drain lymph from the upper limb, in relation to the axillary vein.
Level II group– Central lymph nodes
- Central group- These groups are situated in the upper part of axilla and receive lymph from other axillary groups.
The intercostobrachial nerve passes through them. Hence enlargement of these nodes compresses the nerve and causes pain along the medial side of the arm.
Level III group– Apical lymph nodes
- Apical group- They are located deep to the clavipectoral fascia at the apex of the axilla and receive lymph from the upper part of the breast and other axillary nodal groups.They drain i
Ultimately all these lymph nodes drain into the subclavian veins.
Level 1 drains in level 2 which drains in level 3 . They drain into the subclavian trunk on the right side and thoracic duct on the left side.
Superficial lymphatics– drain the skin of the breast except nipple and areola.
Deep lymphatics– drain the parenchyma of the breast and skin of nipple and areola. The subareolar plexus is also called ‘subareolar plexus of Sappey’. Most of the lymph drains into the anterior group of lymph nodes.
Superficial lymphatics of both breasts communicate with each other.
Lymphatic Quadrants of the breast
Lateral quadrants of the breast drains into the axillary group of nodes.
Medial quadrants of the breast drain into the internal mammary lymph nodes and may also drain into the internal mammary lymph nodes of the opposite side.
The lymph vessels from the lower lateral quadrants may drain into the posterior intercostal vessels into the posterior intercostal nodes.
Sometimes the lymphatics from the lower medial quadrant pierce the anterior anterior abdominal wall and reach the subdiaphragmatic and subperitoneal plexus(responsible for ovarian metastasis also called Krukenberg tumour). Vessels from the deep surface may pierce the Pectoralis major and the clavipectoral fascia to drain into apical group of lymph nodes.
Normal breast histology
The breast is composed of epithelial and stromal components.
The mammary gland is a modified sweat gland, made up of secretory lobes. Each of these lobes are made up of lobules that are compound tubular acinar glands.
Breasts normally have 15-20 lobes.
A compound gland has a branching duct. These ducts arrange themselves into tubules which comprise secretory acini.
The acini are lined by cuboidal cells and are surrounded by myoepithelial cells. These cuboidal cells are responsible for milk secretion.
Basement membrane– Contains type IV collagen and laminin, and separates the ductal system from the surrounding stroma. Invasive carcinoma invades the basement membrane.
Stroma– can be divided into
- Interlobular stroma– Surrounds large ducts and terminal ductal lobar units, and is more denser and collagenous than intralobular connective tissue. This component is responsible for mammographic density. This component becomes fatty after puberty and makes up for most of the volume of the breast.
- Intralobular stroma- Loose connective tissue, surrounding the acini. It contains lymphocytes, plasma cells, macrophages and vessels. It is hormonally responsive. Contains no elastic fibres.
- Multinucleated giant cells– no known clinical significance.
- Intramammary lymph nodes– Appear as densities on the mammogram and are considered as axillary lymph nodes in TNM staging.
What are terminal ductal lobar units?
These are the functional units of the breast. These consist of extralobular terminal ducts and extralobular terminal ducts. The intralobular terminal ducts is what forms the central space of the lobule and have multiple outpouchings and acini.
ITD-interlobular terminal ductule
ETD-extralobular terminal ductule
How does normal breast tissue change with age?
When a girl approaches her teens, due to release of estrogen fat begins to collect in the connective tissue. The duct system also tends to grow. With rising estrogen levels, development of glandular tissue takes place.
With age, especially after menopause, less estrogen is produced in the body. Without estrogen the gland tissue tends to shrink, making the breasts smaller and less full. Fibrous tissue within the breasts stroma tends to increase. The ligaments of Cooper lose their elasticity causing the breasts to sag.
In the nipple-areolar complex, with increasing age,the nipple becomes smaller in size and may even disappear.
The nipple may also turn in slightly.