Embryology and Anatomy of Breast

Breast

Describe applied anatomy and appropriate investigations for breast disease.

Breast Embryology

• The breast is a modified sweat gland and it is derived from a downward growth of ectoderm into the underlying mesenchyme.
• At 5th or 6th week of intrauterine life, two ventral bands of thickened ectoderm, called mammary ridge/milk line or line of Schultz, appear.

Read And Learn More: General Surgery Notes

• The line extends from axilla to the groin. Thus, accessory nipples can appear along the milk line from axilla to groin.
• Persistent part of mammary ridge is converted into a pit. Placental sex hormones enter fetal circulation during 3rd trimester of pregnancy.
• They induce canalizations of branched epithelial tissues.
• Secondary buds develop, divide and form more lobes.The nipple is everted at the site of original position.

Oestrogens cause enlargement of mammary glands at puberty and progesterone stimulates the development of secondary alveoli.

 

 

Surgical Anatomy Of Breast

• Breast, a modified sweat gland, occupies the pectoral region from the 2nd to the 6th rib vertically, and from the lateral border of sternum to the midaxillary line, horizontally.
• It is hemispherical, and lies in the superficial fascial planes.
• It is composed of fatty tissue and does the function of secreting milk.
• The axillary tail of Spence is the part of the breast which is in the axilla and is deeper to the deep fascia, whereas the entire breast is a subcutaneous structure.
• The opening in the axillary fascia, through which outer quadrant breast tissue enters into axilla is called foramen of Langer.

Structure Of The Breast

1. Nipple and areola complex: The nipple is located in the 4th intercostal space, in the midclavicular line. It is the erectile structure of the breast, and is directed forwards and laterally for the convenience of feeding the child. Areola has modified sweat glands and sebaceous glands. These enlarge during pregnancy and are called glands of Montgomery. Both nipple and areola are pigmented due to melanin deposition which increases during pregnancy. Hair is absent in the areola of women (present in males).

2. Parenchyma of breast.

3. Stroma gives support to the glandular structure. Therein lie ligaments of Cooper which are coneshaped fibrous bands. Their apex is attached to overlying skin, and base to the fascia over pectoralis major. Puckering of the skin is due to infiltration of the ligaments of Cooper.

4. Lobule is the chief functional and structural unit of breast. Many lobules join to form a lobe. There are 15–20 lobes and each lobe is drained by a lactiferous duct. They are 15–20 in number arranged radially, lined by myoepithelial cells, which converge into the nipple. Diameter of a lactiferous duct is 2–4 mm.
5. Skin: The skin of the breast is thin and contains hair follicles, sebaceous glands and eccrine sweat glands.

Lymphatic Drainage

They can be divided into lymph nodes and lymphatics.

1. Lymph Nodes

1. Anterior or pectoral: They are under the pectoralis major which forms anterior fold of axilla.

2. Central group: These lymph nodes are present in the centre of axilla (armpit). One has to dip the examining fingers slightly deeper into axilla to detect the enlargement.

Anterior and central group of nodes are commonly involved in carcinoma breast.

3. Lateral group are felt against humerus. They are also called brachial group.

4. Apical: They are found at apex of the axilla. It is the space between pectoralis minor and clavicle. They are also called infraclavicular nodes, situated very high in the axilla. They are difficult to feel clinically.

5. Posterior: They are also called subscapular group of lymph nodes. They are felt along the posterior fold of the axilla. These five groups together form the axillary group of lymph nodes.

6. Internal mammary lymph nodes: Also called parasternal nodes. They lie along internal mammary vessels. They are located in the 2nd, 3rd and 4th space.

7. Supraclavicular lymph nodes: Spread to supraclavicular lymph nodes indicates advanced stage of the disease. It indicates poor prognosis.

Miscellaneous Lymph Nodes/Plexus

1. Cephalic nodes—deltopectoral nodes
2. Interpectoral nodes—Rotter’s nodes
3. Posterior intercostal nodes—in front of heads of ribs
4. Intra-abdominal—subdiaphragmatic/retroperitoneal.

2. Lymphatic Vessels:

1. Superficial lymphatics: Drain skin over the breast except nipple and areola. Superficial lymphatics of one breast communicate with the contralateral breast across midline.

2. Deep lymphatics: Drain parenchyma of the breast. They also drain nipple and areola.

Important Key Points About Lymphatics And Spread

• The first lymph nodes draining the tumour-bearing area is called sentinel node.
• 75% of the lymph from the breast drains into axillary nodes.
• 20% drains into the internal mammary nodes.
• 5% of lymph drains into posterior intercostal lymph nodes.
• Most of the lymphatics eventually drains into central to apical and then to supraclavicular lymph nodes.
• Internal mammary nodes receive lymphatics not only from inner quadrant but also from outer quadrant.
• Lymphatics from inner quadrant of the breast penetrate rectus sheath and thus spread into coelomic cavity. It results in ascites, rectovesical deposits and Krukenberg tumours.
• Krukenberg tumours are bilateral bulky ovarian metastasis in premenopausal women.
• During ovulation, raw surface develops over the ovary into which malignant cells drop and develop into large tumours (transcoelomic spread).

Blood Supply of the Breast (Branches of Axillary Artery)

Breast Arterial Supply:

1. Lateral thoracic artery gives many branches which penetrate through the pectoralis major and supply the breast.
2. Internal mammary artery gives branches which perforate intercostal spaces.
3. Pectoral branches of thoracoacromial artery supply upper part of the breast.
4. Lateral branches of posterior intercostal arteries.

Venous Return:

• Breast is drained by perforating branches of internal mammary veins, tributaries of axillary veins and perforating branches of posterior intercostal veins.
• Venous return follows the arteries but drain into large veins that also receive blood from vertebrae and thoracic cage, e.g. posterior intercostal veins joining paravertebral plexus of veins (Batson’s venous plexus).
• This explains the occurrence of metastasis in the vertebrae and pelvic bones from carcinoma of the breast.

Breast Physiology: 

• Oestrogen: Initiates ductal development.
• Progesterone: Differentiation of epithelium and lobular development (glandular development)
• Prolactin: Lactogenesis in late pregnancy and postpartum period. It also upregulates hormone receptors and stimulates epithelial development.

Benign Breast Disease Including Infections Of The Breast