Female Breast Anatomy

• Mammary glands begin to develop at 6wks LMP
• Multiple paired areas of ectodermal thickening occur along the mammary ridges but only one pair remains to form the breasts
• Mammary ridges are also known as milk lines
• At birth only the main lactiferous ducts have developed
• Ripening of the breast normally occurs between 9-16yrs
• Estrogen causes stromal (connective) tissue to elongate and grow, vascularity increases and fat deposition increases
• Progesterone stimulates TDLU growth
• Thelarche refers to rapid breast tissue development at puberty
• Premature Thelarche
  • Refers to breast enlargement, onset of menses, underarm/pubic hair, and acne that occurs before age 8
  • Most common cause is ovarian hyperstimulation due to early release of gonadotropins (luteinizing hormone and follicle stimulating hormone)
  • The pituitary gland produces LH and FSH, which stimulate the ovaries
  • Other causes include pituitary tumor, adrenal gland tumor and primary hypothyroidism
• Breast tissue is not considered completely mature or ripened until pregnancy and lactation occurs
• If there is no "immediate" pregnancy, the breast tissue fully matures 2 years post menarche
• Breasts are normally asymmetric in size; usually L>R

1. Nipple Inversion:
   • Usually bilateral if congenital
   • Associated with ductal ectasia and periductal mastitis
   • Associated pathology can be present if the nipple change is a new finding and/or occurs unilaterally
2. Athelia: absence of the nipple
3. Polythelia:
   • Accessory nipples, can develop anywhere along the milk line
   • Most commonly seen just inferior to the normal nipple
   • #1 congenital anomaly of the breast in females and males
4. Amastia: failure of the breast and nipple to develop
5. Polymastia:
   • Accessory breast tissue resulting from incomplete involution of mammary ridge
   • Most commonly forms without a nipple
   • Usually found in the axilla
   • More common in men
6. Amazia: absence of development of the functional breast tissue beneath a normal nipple/areola
7. Poland syndrome
• Missing or underdeveloped muscles on one side of the body
• Unilateral hypoplasia of breast, hemithorax, and pectoral muscle
• Upper extremity abnormalities are usually seen on the affected side

• Classification developed in 1915 by Dr. Kajava
• Polymastia and/or polythelia
• Polythelia most common

Original image licensed by CC BY 2.0

• AKA Mammary glands
• Milk Lines: refers to the areas between the axilla and inguinal region where breast tissue may be formed
• Sonographically there are 6 layers of tissue identified:
  • Skin
  • Premammary layer
  • Mammary layer
  • Retromammary layer
  • Muscle layer
  • Chest wall
• Skin layer:
  • Usually between 0.5 – 2mm thick
  • Composed of epidermal cells
  • Contains sebaceous glands and hair follicles
  • Covers the subcutaneous layer of breast tissue
  • Thickest at the base of the breast (inferior crease line)
  • Thicker in younger patients and thins as the patient ages
• Nipple: composed of erectile tissue and contains 15-20 small excretory ducts to drain milk
• Areola: small area of pigmented skin that encircles the nipple and is composed of smooth muscle tissue
• Montgomery glands: small sebaceous glands on the surface of the areola that secrete "protective" oily substance during lactation
• Morgagni tubercles: raised areas or bumps on the areolar region that are formed by the Montgomery gland ductal openings
• Axillary Tail of Spence: refers to the part of the mammary tissue that extends into the upper outer quadrant and axilla area
• Pectoralis muscles: lie posterior to retromammary layer and line the chest wall from the 2nd - 6th rib from sternum to axilla
• The pectoralis minor muscle lies posterior to the pectoralis major muscle
• The breast lies superior to the 7th rib and inferior to the 1st or 2nd rib
• Ribs lie posterior to the pectoralis muscles (***a rib is the most common palpable finding that is mistaken for a mass)
• Right and left intercostal nerves innervate each breast

Axilla:

• Pyramidal space directly inferior to the shoulder joint that is between the upper lateral chest and medial arm
• Contains the axillary artery and vein, brachial plexus, axillary lymph nodes and fat
• There is also possible vestigial breast glandular tissue present
• The axilla is a primary route for the spread of breast cancer
• Axilla evaluation is an important component of nodal staging
• Axillary metastases highly correlates with poor outcomes for breast cancer patients

• AKA subcutaneous fat layer
• Lies between the skin and the superficial layer of the superficial fascia
• Contains varied levels of fat related to age, obesity and pregnancy
• After every pregnancy, there is a reduction in breast parenchyma quantity and an increase in quantity of fat and connective tissue
• Present across the breast EXCEPT immediately posterior to the nipple
• Sebaceous cysts and lipomas occur in this layer

• AKA glandular or parenchymal layer
• Between the superficial and deep layers of the superficial fascia
• Only layer that contains glandular tissues (functional tissues)
• Most breast pathology originates in this layer
• Contains epithelial and stromal tissues
• Epithelial tissue is considered the functional tissue of the breast; includes TDLU, lobules, lobes, lactiferous ducts
• Stromal tissue is the structural tissue of the breast; includes fat and connective tissue
• Each breast is composed of 15-20 lobes of glandular tissue arranged in a radial fashion around the nipple and separated by fatty tissues
• Lobes consist of multiple lobules, each with an associated intralobular terminal duct
• Lobules are composed of glandular tissues which contain the functional epithelial cells (acini cells) that produce milk
• Intralobular terminal ducts from the smaller lobules drain milk into the ductal system, once the milk exits the lobule it enters the extralobular duct
• Extralobular terminal ducts converge into the main interlobular duct which drains all the milk from that cluster of lobules; end at the main extralobar duct
• Main/Extralobar ducts/Segmental ducts drain the milk from each breast lobe (15-20 ducts); ducts form a pyramid shape, focused to an apex at the areola/nipple
• Widening of the distal end of each of the main ducts is referred to as the ampulla; serves as a reservoir for milk just prior to it leaving the breast
• Interlobular/anterior suspensory/Cooper ligaments course between lobes from the deep fascia of the chest wall/axilla toward the nipple to attach to the anterior fascia of the skin
• The interlobular ligaments support the breast parenchyma
• Intralobular connective tissue is a less dense form of connective tissue that surrounds each individual lobule of breast tissue
• Upper outer quadrant of each breast contains the most glandular tissue
• The amount of glandular tissue in the mammary layer varies with age and menopause

• Located posterior to the mammary layer
• Contains varied levels of fat related to age, obesity and prior pregnancy
• After every pregnancy, there is a reduction in breast parenchyma quantity and an increase in quantity of fat and connective tissue
• Deep layer of the superficial fascia is also within the retromammary space
• This layer of tissue allows breast motion over the chest wall

• Surrounds all mammary tissues and separates the breast into superficial and deep tissues
• Composed of two layers; superficial and deep
• Superficial layer (superficial fascia) within the premammary layer
• The superficial layer is also called the anterior mammary fascia
• The Cooper ligaments are contiguous with the anterior mammary fascia
• Deep layer (superficial fascia) lies posterior to the mammary layer within the retromammary space
• The deep layer is also called the posterior mammary fascia
• Deep fascia lines the anterior pectoralis major muscle
• Irregularities of the deep fascia posterior to a malignancy can indicate metastasis to the chest wall

• Acini cells are the smallest functional unit of the breast
• Several hundred acini cells are in the breast
• TDLU refers to 30-50 acinar cells grouped together in a lobule and their associated terminal duct
• TDLUs are usually less than 2mm in size
• Patients with fibrocystic disease or adenosis may have up to 5mm TDLUs
• Simple cysts originate in the TDLU
• # and size of TDLUs vary with age and hormone levels
• Proliferation of the TDLUs normally occurs during reproductive years and pregnancy/lactation, also with oral contraceptives and hormone replacement therapy
• Atrophy of the breast lobules normally occurs with cessation of breast feeding and in postmenopausal women
• Nearly all breast pathology originates in the TDLU
• Most malignancies arise from the terminal duct near the junction of the intralobular and extralobular segments
• Most TDLUs are in the anterior breast, therefore most breast pathology arises in the superficial half of the mammary zone, just deep to the superficial layer of the superficial fascia

• Lined with a double layer of epithelial cells to reduce friction for easier milk flow
• Middle layer composed of myoepithelial cells which aid in the movement of milk
• Basement membrane forms the outer layer of the duct which is in contact with the intralobular stroma
• Each breast lobe has one ductal system
• Normal ducts in a non-lactating female should measure <2mm diameter and increase in size closer to the nipple
• Normal ducts in a lactating female should measure <8mm diameter
• Each terminal duct begins within the lobule and extends to the nipple

1. Intralobular terminal ducts - carry milk from the acini
2. Extralobular terminal ducts - once the milk exits the lobule it enters the Extralobular duct
3. Interlobular terminal ducts - extralobular ducts converge into the main Interlobular duct; travel between the breast lobules to reach the main extralobar duct
4. Main Extralobar Ducts/Main Terminal Ducts/Segmental Ducts - drain the milk from each breast lobe; end at the ampulla
5. Lactiferous Sinus or Ampulla which is an area of ductal enlargement just prior to the opening to the nipple; usually 2-3mm in diameter indicates a normal finding
6. Collection ducts or Excretory ducts - 15-20 openings that excrete the milk from the nipple
7. Nipple 

• Lateral thoracic artery:
• Originates from the axillary artery and courses lateral and inferior along the pectoralis major muscle
• Courses from the axilla to the nipple
• Supplies lateral breast tissues
• Internal thoracic artery (AKA internal mammary artery)
• Originates at the subclavian artery
• Courses lateral to the sternum
• Supplies medial breast tissues
• Used for coronary bypass surgery when other vessels unavailable (great saphenous vein, radial artery)
• Thoracoacromial artery supplies superior breast tissue
• Intercostal artery supplies the inferior breast tissue
• There are 18 intercostal arteries on each side of the spine
• They course between the ribs and branches supply the breast with oxygenated blood

• Lymphatic drainage pathways parallel venous drainage
• Superficial venous system lies within the subcutaneous fat tissue
• There are usually no accompanying arteries for the superficial veins of the breast
• Blood moves from the superficial system into the deep system
• Most distal veins line the superficial fascia and drain blood centrally
• Provides connection between right and left breast with potential for metastasis to occur between breasts
• Deep venous system consists of veins that follow the arterial system
  • These veins typically have an accompanying artery on their course
  • Primary route of venous drainage of the breast
  • Includes internal mammary vein, lateral thoracic, axillary, subclavian and intercostal veins
  • Drain into the axillary vein, subclavian vein and SVC

• Intramammary nodes are found within the breast parenchyma
• They are normally oval or reniform (kidney-shaped) in shape
• Lymph nodes are most concentrated in the upper outer quadrants
• Lymph vessels closely follow the venous drainage system of the breast
• Lymphatic system function is important for assessing possible routes for metastasis
• Superficial lymphatic vessels drain the lymph from the skin layer
• Deep lymphatic vessels drain the lymph from the breast tissue, nipple and areola
• Flow in the deep lymph system travels toward the areola and superficial system
• Most lymphatic drainage moves from deep to superficial, which is opposite of the venous drainage system of the breast where blood moves from the superficial system to the deep system
• Flow in the superficial system moves centrally toward the nipple
• Once the lymph fluid reaches the subareolar plexus, it then moves toward the axilla
• Majority of lymph flow out of the breast occurs through the axillary chain (75%)
• A smaller amount drains through the internal mammary and intercostal lymphatic chains
• Lymphatic vessels contain valves to assist in the flow of lymphatic fluid
• Lymphatic vessels are not usually visible Sonographically
• Lymphatic vessels do not easily dilate when flow abnormalities are present and they are not easily compressible when dilated
• The lymphatic system of the breast is the primary route of spread of breast cancer
• Lymphatic channels may communicate with the contralateral skin and breast

• Used for staging and developing the surgical approach
• Lymph nodes are grouped according to their location relative to the pectoralis minor muscle
• Nodes are assessed for metastasis
• Lymph drainage to the axilla passes through level I, then level II and finally to level III
• The sentinel node is usually a level I node

• Intramammary: within the glandular tissue of the breast
• Internal Mammary or Parasternal:
  • Lymph nodes and vessels that follow the internal mammary (internal thoracic) vessels
  • Drains the medial breast
  • Involved in metastatic drainage most commonly with medial cancer formation
• Intercostal: found along the intercostal arteries as the course between the ribs
• Supraclavicular:
  • Found adjacent to the internal jugular vein and the subclavian vein
  • Only involved in metastasis if level I, II and II nodes are affected
  • Considered distant metastasis and if involved, the prognosis is very poor