Breast Development:
  • Mammary gland begin to develop at 6wks LMP
  • Multiple paired areas of ectodermal thickening occur along the mammary ridges, 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 connective tissue to elongate and grow, vascularity increases and fat deposition increases
  • Progesterone stimulates TDLU growth
  • Thelarche: rapid breast tissue development at puberty
  • Premature Thelarche: unilateral early ripening of the breast; usually occurs at 6-8yrs of age
  • Precocious Puberty: Bilateral breast enlargement before age 8; Causes include adrenal gland tumor, primary hypothyroidism or ovarian cyst
  • 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
Three Layers of Breast Tissue:

1.  Mammary Layer:
  • AKA glandular or parenchymal layer
  • 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, separated by fatty tissues
  • Lobes consist of multiple lobules, each with an associated intralobular duct
  • Lobules are composed of glandular tissues made of the functional epithelial cells (acini cells) that produce milk
  • Intralobular Ducts from the smaller lobules drain milk into the ductal system, once the milk exits the lobule it enters the  Extralobular duct
  • Extralobular ducts converge into the main Interlobular duct which drains all the milk from that cluster of lobules; ends at the Main Extralobar Duct
  • Main extralobar ducts drain the milk from each breast lobe (15-20 ducts); ducts form a pyramid shape, focused to an apex at the areola/nipple
  • Ampulla is a widening of the distal end of each of the main ducts; serves as a reservoir for milk just prior to it leaving the breast through the excretory duct
  • Cooper’s ligaments course between lobes from the chest wall/axilla toward the nipple, support parenchyma
  • Upper outer quadrant of each breast contains the most glandular tissue

2.  Subcutaneous Layer:
  • Contains fat, amount varies with age, obesity and pregnancy

3.  Retromammary Layer:
  • Contains fat, varies with age, obesity and pregnancy

Superficial Fascia:
  • Surrounds all mammary tissues
  • Two layers, superficial and deep
  • Superficial layer within the premammary layer
  • Deep layer posterior portion of the retromammary space
Terminal Duct Lobular Unit (TDLU):
  • Considered the "functional unit" of the breast
  • Refers to 30-50 acinar cells grouped together in a lobule and their associated ducts
  • Acini cells are the smallest functional unit of the breast
  • # and size of TDLUs vary with age and hormone levels
  • Proliferation of the TDLUs normally occurs during reproductive years and pregnancy/lactation
  • Atrophy of the breast lobules normally occurs with cessation of breast feeding and in post menopausal women
  • Almost ALL breast pathology originates in the TDLU

Ductal System:
  • Lined with epithelial cells to reduce friction for milk flow
  • Middle layer of myoepithelial cells aids in movement of milk
  • Basement membrane forms the outer layer of the duct which is in contact with the intralobular stroma
  1. Intralobular terminal duct
  2. Extralobular terminal duct
  3. Interlobular terminal duct
  4. Main Terminal Duct/Lactiferous Sinus or Ampulla
  5. Collection duct or Excretory duct
  6. Nipple
Vasculature:

Arterial Supply:
  • Lateral thoracic artery originates from the axillary artery and supplies lateral breast tissues
  • Internal thoracic artery (AKA internal mammary artery) originates at the subclavian artery and supplies medial breast tissues
  • Thoracoacromial artery supplies superior breast tissue
  • Intercostal artery supplies the inferior breast tissue
  • ***the right and left intercostal nerves innervate each breast
Venous Drainage:
  • Superficial system lines superficial layer of superficial fascia
  • Deep system travels with arterial system and communicates with the axillary vein, subclavian vein and SVC
  • Includes lateral thoracic, axillary, subclavian and intercostal veins

Lymphatic System:
  • Intramammary nodes within breast parenchyma, most concentrated in the upper outer quadrants
  • Flow is from the deep nodes to the superficial system
  • Majority of flow out of the breast is through the axillary, internal mammary and intercostal lymphatic chains

Lymphatic Chains Draining the Breast:
  1. External Mammary: follow lateral thoracic vessels
  2. Scapular: follow the subscapular vessels
  3. Axillary: follow the lateral axillary vessels; 30-40 lymph nodes, 75% lymph drainage; #1 site for lymphnode metastasis
  4. Subclavicular: follow the subclavian vessels
  5. Central: within fatty tissues medial to the axillary vessels
  6. Rotter’s (interpectoral): between the pectoral major and minor muscles

Axillary Node Classification:
  • Used for staging and developing the surgical approach
  • Nodes are assessed for metastasis
Level I - found in nodes lateral to pectoralis minor muscle
Level II - found in nodes deep to the pectoralis minor muscle
Level III - found in nodes medial to the pectoralis minor muscle


Accessory Node Chains (25%)
  • Internal Mammary: follow the internal mammary vessels, metstasis seen most commonly with medial cancer formation
  • Intercostal/Parasternal: adjacent to the course of the internal thoracic artery and vein
  • Supraclavicular - adjacent to the internal jugular vein and subclavian vein
Perimemopausal: Hormone levels decrease, glandular tissue shrivels or involutes, Fat levels increase
Postmenopausal: HRT can cause glandular tissue levels to increase
Breast Physiology:
  • Production and secretion of milk
  • Several hundred acini cells in each breast produce milk into a separate duct (terminal duct)
  • Acini cells are the smallest functional unit of the breast
  • Milk funneled into ductal system toward the nipple
  • Estrogen - produced by the ovaries; levels rise during the first half of the menstrual cycle and stimulates ductal proliferation
  • Progesterone - produced by the ovaries; levels rise with ovulation and stimulates lobular proliferation and growth; leads to "PMS" symptoms in breasts
  • Prolactin inhibitors - produced by the hypothalamus; prevents lactation until pregnancy
  • Prolactin - produced by the pituitary gland; stimulates milk production with pregnancy
  • Oxytocin - produced by the pituitary gland; causes ductal contraction with lactation
  • Milk production usually begins within 2-3 days post partum
MALE BREAST

Anatomy:
  • Rudimentary ductal system surrounded by minimal fat and connective tissue
  • Lobules of breast tissue normally do not form, nor does a secondary ductal system exist


Clinical Indications for Breast Sonography for a Male:
  • Pain
  • Palpable lump
  • Nipple discharge
  • Enlarged breast(s)


Abnormalities of the Male Breast:

Gynecomastia:
  • Male breast enlargement due to an abnormal growth of fibroglandular tissue and increased volume of fat
  • Can be idiopathic
  • Causes include hormonal imbalance, cirrhosis, AIDS and chronic renal failure
  • Pubertal form is most common; most often presents around puberty or over age 50
  • Some medications are related to this disorder; anabolic steroids, estrogen therapy for prostate cancer, methotrexate and digitalis
  • Unilateral or bilateral
  • Often painful, palpable firm mass may be felt beneath the nipple
  • Usually will resolve once causative agent identified and "removed"

Sonographic Appearance:
  • Hyopechoic to hyperechoic region in the subareolar portion of the breast
  • Increased subcutaneous fat accumulation
  • May see ductal dilatation
Note: Click any image to enlarge.
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BREAST ANATOMY AND PHYSIOLOGY
Male Breast Cancer:
  • <1% of all breast cancers
  • Occurs in men at an older age than women
  • Risk factors include Cryptochordism, Klinefelter syndrome, Cowden Syndrome, Family history of breast cancer, radiation exposure
  • Most common male breast cancer is Invasive Ductal Carcinoma
  • 30% of male breast malignancies have microcalcifications seen on mammo
  • Clinical symptoms and sonographic characteristics very similar to female breast malignancy
  • Male breast malignancy usually occurs in the subareolar breast tissues (not UOQ)
  • Doppler evaluation normally demonstrates flow within the mass


Male Breast Metastasis:
  • Most commonly occurs with prostate cancer
  • Also seen with melanoma, lymphoma, lung and bladder cancer
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Congenital Anomalies:
  1. Nipple Inversion: usually bilateral if congenital; can be associated pathology if nipple change is a new finding
  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; most commonly forms without a nipple; usually found in the axilla
  6. Amazia: absence of development of the functional breast tissue beneath a normal nipple/areola
Supernumerary Breast Tissue:
  • Classification developed in 1915 by Dr. Kajava
  • polymastia and/or polythelia
  • polythelia most common
Breast Anatomy:
  • AKA Mammary glands
  • Milk Line: AKA mammary ridges; area between the axilla and inguinal region that breast tissue may be formed, EX: Accessory nipples
  • Sonographically there are 6 layers identified, skin, 3 layers breast tissue, muscle layer and the 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
  • Nipple is composed of erectile tissue and contains small excretory ducts to drain milk
  • Areola is a small area of pigmented skin that encircles the nipple
  • Montgomery glands are small sebaceous glands on the surface of the areola; secrete "protective" oily substance during lactation
  • Axillary Tail of Spence refers to the part of the mammary layer 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