Breast Anatomy Explained In Depth

Women are at a higher risk for developing breast cancer. It is estimated that around 61,000 people are diagnosed with breast cancer every year in the United States. But only around 30,000 people will survive the disease.

Certain risk factors raise the probability of developing breast cancer. Having a family history of the condition, hormonal changes, being overweight, and being of a certain ethnicity are all risk factors. Breast cancer is more likely to occur in people aged 40 and above. Pakistani women in the 45-55 age range are the most susceptible to developing breast cancer.

There are five main stages of breast cancer as per the TNM staging system. These stages are based on the extent and size of cancer. Breast cancer is a heterogeneous disease, which is further determined by the type of cells involved and the number of hormones produced by the breast. This may explain its high incidence among women of reproductive age.

ANATOMY OF FEMALE BREAST:

The breast is a symmetrical organ that sits on the anterior thoracic wall, in the pectoral region. The mammary glands are present in both males and females, but the female glands are more prominent and different due to milk ducts. The breasts extend horizontally from the lateral border of the sternum to the mid-axillary line.

The bottom edge is around 2 inches below your armpits, and it spans between costal cartilages 2 and 6 on each side. The breast is located superficial to the serratus anterior and pectoralis major muscles. The superficial structures of the breast are thought to consist of two different regions:

Axillary Tail

It is the small part of the breast that lies along the bottom edge of the pectoralis major and runs towards the axillary fossa.

Circular Body

The circular body is made up of adipose tissue, and the axillary tail extending from the circular body. An interlacing network of blood vessels, nerves, and lymphatics surround the adipose tissue in the breast, forming lactiferous ducts. The lactiferous ducts meet at a nipple known as the areola and drain into a network of lymph nodes called the axillary lymph nodes. Anatomy of the breast has been displayed well in Figure.

The most prominent and largest part of the breast. The circular body of the breast can be divided into the:

• Lobes
• Mammary Gland (Lobules)
• Lactiferous Ducts
• Connective Tissue Stroma
• Pectoral Fascia & Retro-mammary Space
• Nipples and Areola

Lobes

There are 15 to 20 sections surrounding the nipple in a spiral wheel shape in each breast.

Mammary Gland (Lobules)

These are known as the modified form of sweat glands. Mammary glands consist of a network of secretory glands.³¹The mammary glands are composed of two types of tissue:

-Endocrine tissue–is responsible for making hormones that stimulate breast development and maturation.

–Exocrine tissue–is responsible for the production of milk.

Lactiferous Ducts

Small tubes carry milk from the exocrine tissue of the mammary gland to the nipples, which are also known as milk ducts.

Connective Tissue Stroma

The connective tissue in the breasts is known as the stroma. The stroma strengthens the breast, separates the mammary gland tissue, and contains nerves and blood vessels.

Pectoral Fascia & Retro-Mammary Space

The pectoral fascia is a superficial layer of connective tissue. It covers the chest wall and extends across the nipple³¹. The pectoral fascia can be pulled apart to reveal the nipple. The pectoralis major muscle extends from the sternal border to the mid-axillary line in a horizontal manner. It is found in the front portion of the thoracic wall. It extends horizontally from the lateral border of the sternum to the mid-axillary line.

The Retromammary space is composed of a thin layer of loose connective tissue separating the pectoral fascia from the breast. Muscles and ligaments in the chest wall helps to expand the space when we breathe in. The breast contains extra nerves and blood vessels that make up this space.

Nipples and Areola

The central prominence on the circular region of the breast is known as the nipple. Each nipple consists of 9-10 milk ducts.³²

The nipple is surrounded by an annulus of skin that is darker in color. Montgomery’s glands secrete lubricating oil to protect the nipple and skin from chafing during breastfeeding.

VASCULATURE OF BREAST:

The female breast is a highly vascular organ, providing a rich blood supply to each of the lobes and the blood supply to the nipple is also very rich in blood vessels. The breast is comprised of lobes and ducts.

The lobes and ducts are connected by blood vessels. The blood supply to the lobes is mostly by lateral branches that come off the lateral thoracoacromial arteries and end in the lobes. The blood supply to the ducts is mostly by mammary branches that come off the lateral mammary arteries and end in the ducts.

• Branches of Axillary Artery

The axillary artery gives off branches that supply the lateral thoracic, superior thoracic, subscapular, and thoracoacromial regions. They travel through the Brachial plexus and then branch off the lateral thoracoacromial arteries and end in the lobes.

• Internal Thoracic Branches

These branches are located on the front of the neck just below the clavicle. These branches supply the medial part of the breast.

• Branches of Intercostal Arteries:

The pectoral branches of the 2^nd, 3^rd, and 4^th intercostal arteries supply the complete breast³⁶.

• Venous Drainage of Breast

There are many breast veins that follow the corresponding arteries in order to drain into the axillary, internal thoracic, and second-fourth intercostal veins.

BREAST LYMPHATIC DRAINAGE:

The metastasis of cancer cells is of great clinical significance, as lymphatic drainage of the female breast plays a vital role.

Breast tissue is drained by lymph nodes; there are three sets of lymph nodes;

• Axillary Lymph Nodes of Breast

It drains 75 % of the lymph from breast tissue. The lymph vessels in the breast lobes, nipple and areola areas (lateral quadrants mostly) are collected into the subareolar lymphatic plexus.³⁷From here the lymph is poured into pectoral lymph nodes which drain into the axillary lymph nodes.

• Parasternal Nodes

These drain about 20 % of the lymph from the rest of the breast tissue.³⁸The parasternal lymph nodes drain in to the lymphatic trunks.

• Posterior Intercostal Nodes

Besides axillary and parasternal lymph nodes some drainage occurs through the posterior intercostal lymph nodes.