Breast Chapter 3: Breast Anatomy and Development

Sonographic Appearance of the Costal Cartilages:

less attenuative than the ribs on sagittal scans, appear as regularly-spaced, oval, hypoechoic structures care must be taken to not mistake a rib cartilage for a breast mass

Retromammary Space:

lies between the deep layer of the superficial fascia and the deep pectoral fascia. This space allows the breast to move freely over the muscle layer.

Dense Extralobular (interlobular) Stroma:

lies between the lobes and lobules and supports the larger ductal structures

Subcutaneous Fat Layer

lies between the skin and mammary layer is primarily composed of fat lobules enclosed by connective tissue septa blood vessels, lymphatics, and nerves also reside within this superficial layer. Subcutaneous fat does not extend beneath the nipple. Cooper's ligaments are best seen in the subcutaneous layer and appear as thin, hyperechoic, curvilinear bands that extend around the fat lobules toward the skin. Critical angle shadowing can occur from oblique sound incidence to these connective bands.

Axillary Lymph Nodes Anatomic Subgroup:

nodes along the lateral part of the axillary vessels

External Mammary Axillary Lymph Nodes:

nodes along the lateral thoracic vessels

Central Axillary Lymph Nodes:

nodes along the medial part of the axillary vessels embedded in the fat in the center of the axilla

Subclavicular Axillary Lymph Nodes:

nodes along the subclavian vessels medial to the origin of the thoracoacromial artery

SubscapularAxillary Lymph Nodes:

nodes along the subscapular vessels

Lymph Nodes Locations and Sizes

normal lymph nodes can be seen within the mammary zone and the subcutaneous fat layers most intramammary lymph nodes are located in the posterior, upper outer quadrant. intramammary lymph nodes typically measure less than 1 cm normal lymph nodes seen in the axillary regions and often exceed 1 cm in size. internal mammary lymph nodes are not usually detected on a sonogram unless enlarged

Loose Intralobular Stroma:

surrounds the small ductal structures within the lobule gives the lobule its shape and definition the extensive capillary network of the intralobular stroma contains lymphocytes, histiocytes, plasma cells, and mast cells

Characteristics of the Breast With Ovulation:

progesterone levels rise progesterone stimulates growth of the lobules and the terminal ductules following ovulation these changes, along with increased blood flow and interstitial fluid retention, causes physical symptoms of premenstrual breast tenderness, fullness, and nodularity

Changes in the Breast After Having Birth:

prolactin levels increase acini undergo secretory changes milk is produced

Sonography allows what kind of evaluation of the breast?

sectional evaluation of the breast, one "slice" at a time, from the skin to the chest wall.

Retromammary Fat Layer:

separates the mammary layer from the pectoralis muscle and contains adipose tissue and connective fascia

Normal Breast Tissues Described as Hyperechoic:

skin cooper's ligaments dense interlobular stromal fibrous tissue

Levels of the Breast:

skin layer - nipple / areola subcutaneous fat layer mammary layer - parenchyma; fibroglandular tissue retromammary fat layer pectoralis muscle layers - deep to the breast ribs / intercostal muscles pleura - lung

Normal Sonographic Appearance of the Prepubertal Breast:

small and fatty a small, hypoechoic-to-echogenic region of glandular tissue beneath the nipple represents early development of the parenchyma

Prolactin

stimulates acini to produce milk produced by the anterior pituitary gland

Estrogen During Pregnancy:

stimulates growth and division of the ducts produced by the ovary

Progesterone During Pregnancy:

stimulates increase in size and number of the lobules and maturation of the acini produced by the ovary and placenta

What is amazia?

the absence of development of breast tissue can occur secondary to excessive radiation exposure or from surgical excision

Functional Glandular Tissue:

the adult female breast is composed of 15-20 lobes that contain functional, epithelial elements of the breast. the overlapping lobes are arranged in a radial fashion around the nipple. The greatest amount of glandular tissue resides within the UOQ. Each lobe contains numerous lobules, which are drained by small branching ducts that unite to form a main lactiferous duct. The main lactiferous duct widens just below the nipple at the lactiferous sinus - a reservoir for milk or secretions that accumulate beneath the areola. if some of the main ducts join beneath the areola, a lesser number of excretory ducts will exit through the nipple.

The sonographic appearance of the normal female breast varies depending on:

the amount of fat, connective tissue, and glandular tissues in the scanning plane

What is unilateral early ripening; premature thelarche?

when the glandular tissue of one breast may start to develop before the other occurs between the ages of 6-8 years usually by age 9 or by puberty, both breasts are of similar size

Where are intramammary lymph nodes located?

within the breast, especially in the UOQ

Where are the nerves of the breast found?

within the skin and the glandular tissue of the breast

Normal Breast Tissue Described as Hypoechoic:

Nipple blood milk in duct

Congenital Nipple Flattening or Inversion

can be congenital, especially if bilateral new findings are suspicious for pathology

Why is the TDLU such an important anatomic structure?

it is the site of origin of most breath pathologies

When do the mammary glands begin to develop?

4th week of embryonic life; 6th week of gestation

The 2 Most Prominent Hormones Active in Breast Physiology:

Estrogen - responsible for ductal proliferation Progesterone - responsible for lobular proliferation and growth Prolactin is another important hormone that is present during late pregnancy and lactation

How does the subcutaneous fat appear sonographically?

Gain settings should be adjusted so fat displays a medium level gray shade Fat lobules appear as oval in one plane and elongated in the orthogonal plane.

Level III Axillary Lymph Nodes:

High axilla nodes medial to the pectoralis minor muscle apical, subclavicular nodes

Interpectoral Axillary Lymph Nodes:

Rotter's lymph nodes nodes between the pectoral major and minor muscles along the pectoral branch of the thoracoacromial artery

Sonographic Appearance of the Pleura:

Since sound does not penetrate the air-filled lung, the pleural interface is the deepest structure identified on a breast sonogram the highly reflective lung interface produces a hyperechogenic band of echoes

Scanning Tips for Evaluating the Skin Layer:

Use of an acoustic standoff allows better focusing at the skin level and better demonstration of the skin contour. When scanning through a standoff pad, the skin appears as two thin, hyperechoic lines encasing a medium-level band of echoes - the dermis. The two highly reflective lines are from the offset/epidermis and the dermis/fat interfaces. extra scan gel also serves as an acoustic standoff. transducer compression can affect skin thickness

The Areola:

a region of smooth, circular, pigmented skin that encircles the nipple contains numerous sebaceous glands - Montgomery's glands - that appear as small nodules under the skin these glands release a fatty substance that protects the nipple during lactation

The Nipple:

a round, fibromuscular papilla projecting from the center of the breast small excretory ducts exit the surface of the nipple and drain the lactiferous ducts

What is amastia?

absence of development of breast and nipple

What is athelia?

absence of the nipple

Lateral Thoracic Artery:

arises from the axillary artery distal to the thoracoacromial artery. passes inferiorly along the lateral border of the breast and gives off branches that supply the lateral breast

Internal Mammary Artery:

arises from the subclavian artery and descends behind the costal cartilage of the upper ribs near the sternum perforating branches supply the medial breast

Sonographic Appearance of the Ribs:

attenuate the sound beam causing acoustic shadowing

What causes acoustic shadowing when scanning the nipple - areola complex?

attenuative connective tissues within the nipple irregular skin contour causing poor skin contact or air gaps between the transducer and the skin/areola/nipple

Where is breast fat found within the breast?

beneath the skin beneath the glandular tissue fills the spaces between the lobes subcutaneous does not extend beneath the nipple

How is the breast innervated?

branches of the intercostal - thoracic - nerves primarily innervate the breast branches of the supraclavicular nerve also innervate the superior and lateral aspect of the breast

What provides the main arterial supply to the breast?

branches of the lateral thoracic artery [external mammary artery] perforating branches of the internal mammary artery [internal thoracic artery]

How is venous drainage of the breast performed?

by superficial and deep venous systems venous anastomoses occur in a circular pattern beneath the areola superficial and deep veins communicate throughout the mammary tissue

What causes bilateral breast development?

can be associated with precocious puberty estrogen-secreting ovarian or adrenal tumor changes within the hypothalamus or pituitary glands

Changes In The Breast During Pregnancy:

changes are seen within several weeks of conception epithelial cells and ducts proliferate, increasing the size and number of the TDLUs. the acini become fully formed within the lobules in anticipation for milk production

The Skin:

composed of epidermis and dermis thickest at the base of the breast pores along the surface indicate the location of sweat glands, sebaceous - oil - glands, and hair follicles

What is the breast parenchyma?

contains the functional glandular elements of the breast and their support systems

Where are the superficial veins of the breast located?

course beneath the superficial fascia communication can exist between the superficial veins of both breasts

Breast Changes That Occur With The Menstrual Cycle:

cyclic changes occur in the breast with each menstrual cycle that causes an increase in glandular tissue

Breast Structures, Least Echogenic to Most Echogenic:

cyst fluid blood muscle fat glandular tissue fibrous tissue cooper's ligaments calcifications

Intercostal Muscles:

demonstrated between the ribs and beneath the pectoralis muscle

Cooper's Ligaments:

dense connective tissue septa suspensory ligaments that extend from the deep layer of the superficial fascia to the skin and separate fat lobules and lobes

Normal Breast Tissue Described as Anechoic:

duct secretion blood in vessel milk in duct

Why might a newborn male or female show mild physiologic prominence of the breast tissue - ducts?

due to the residual effects of maternal hormones these effects subside as hormonal levels return to normal

Skin Layer:

echogenic relative to the subcutaneous fat composed of epidermis and dermis usually less than or equal to 2mm can be thicker in the inferior breast and the areolar region

Location of Glandular Tissue:

enclosed between the superficial and deep layers of the superficial fascia

Characteristics of the Breast During The First Part of the Menstrual Cycle:

estrogen stimulates epithelial proliferation and enlargement of the larger ductal structures within the breast

Axillary Tail of Spence

extension of glandular tissue into the axilla

Normal Breast Tissues Described as Isoechoic / Nearly Isoechoic:

fat epithelium - TDLU loose stromal fibrous tissue - surrounding ducts and lobules; periductal

Normal Sonographic Appearance of the Adolescent Breast:

following puberty, the adolescent becomes increasingly glandular and the amount of fat decreases sonographically, this parenchyma has a very fine, uniform, weakly-echogenic texture - similar to fat. The surrounding fat layers may be too thin to be visualized on the sonogram.

How do the acini change within the breast?

fully form during pregnancy and lactation involute to a variable degree following cessation of lactation

What is a Terminal Duct Lobar Unit (TDLU)?

functional unit of the breast composed of an extralobular terminal duct and a lobule the lobule contains an intralobular terminal duct that drains multiple - 30-50 - tiny blind-ended ductules these ductules correspond to tiny, saccular, milk-producing glands of the breast called acini.

Normal Sonographic Appearance of the Adult Breast:

has the greastest ranges of appearances the young nulliparous female breast is densely glandular with little internal or surrounding fat with an increase in stromal tissue, the fibroglandular tissue becomes more hyperechoic with advancing age and parity, more fat is deposited in the fat layers, as well as in the mammary zone

Sonographic Appearance of the Muscles:

hypoechoic and contain hyperechoic linear striations along the long axis of the muscle

Where do the lymphatic channels of the breast originate?

in the interlobular connective tissue and the walls of the lactiferous ducts

Where are the supraclavicular lymph nodes located?

in the supraclavicular fossa near the internal jugular and subclavian veins lymph must pass through the deep jugular or subclavian nodal chains to reach the supraclavicular nodes

Chest Wall:

includes the serratus anterior muscle, ribs, and intercostal muscles

Scanning Tips to Reduce Cooper's Ligaments Shadowing:

increase transducer pressure to flatten the ligaments angle transducer so scan plane is more perpendicular to ligament

Oxytocin:

initiates contraction of ducts for flow of milk during lactation produced by the posterior pituitary gland

Changes in the Breast With Menopause:

involution of glandular tissues occurs following cessation of lactation, ovarian ablation - by surgical removal, radiation therapy, or chemotherapy - or with natural menopause very few mature lobules normally persist past menopause the sharp decline in hormone production leads to atrophic changes of the lobules, which may be replaced by fat or sclerosis use of hormone replacement therapy can retard involutional changes combined estrogen-progesterone HRT may even cause postmenopausal persistence or development of mature lobules

Mammary Layer:

lies between the subcutaneous and retromammary fat layers contains the fibroglandular tissue of the breast; although the TDLUs are primarily located within the mammary layer, there are instances when a TDLU may extend into either fat layer)

Serratus Anterior Muscle:

lies posterior to the lower outer quadrant of the breast

Pectoralis Minor Muscle:

located beneath the upper, outer portion of the pectoralis major muscle is an important landmark for determining the surgical levels of the axillary lymph nodes

Level 1 Axillary Lymph Nodes:

low axilla nodes lateral to the pectoralis minor muscle

Where does lymph flow when leaving the breast?

lympathic drainage closely follows the path of the veins and empties into the axillary, internal mammary, and intercostal chains of lymph nodes a small amount of lymph can drain from channels that cross the mid chest to the contralateral breast some drainage can extend to the supraclavicular nodes or to the diaphragmatic nodes

How does lymph drain into the internal mammary lymph nodes

lymph drains to the internal mammary nodes via channels that penetrate through the chest wall into the intercostal spaces medially located cancers may metastasize to the internal mammary nodes. these nodes also provide collateral drainage for lateral tumors when axillary nodes are obstructed

How does lymph drain flow the breast?

lymph flow begins deep within the breast the direction of lymph flow is toward the subareolar plexus where the intramammary and subdermal lymphatics anastomose under the areola. flow through the superficial channels is directed outward toward the lymphatic chains that drain the breast

Normal Sonographic Appearance of the Postmenopausal Breast:

menopausal changes cause atrophy of the parenchymal structures and a relative increased deposition of breast fat residual fibroglandular tissue may persist mainbly beneath the nipple and outer breast quadrant on a sonogram, the hyperechoi Cooper's ligaments are easily seen encasing the fat lobules. older nulliparous women, or those on replacement therapy, may retain greater amounts of glandular tissue

Level II Axillary Lymph Nodes:

mid axilla nodes deep to the pectoralis minor muscle nodes located between the medial and lateral borders of the pectoralis minor muscle includes Rotter's lymph nodes

Changes in skin contour and thickness may indicate:

neoplastic, traumatic, post irradiation, or inflammatory changes at or below the skin level

Sonographic Appearance of The Nipple Areola Complex:

nipple is displayed as a homogeneous texture of low-to-medium level internal echoes the areola is thicker than the surrounding skin of the breast acoustic shadowing is often generated

What controls the number of lobules within the breast?

number and size vary with patient's age and hormonal status rapid proliferation occurs during early reproductive life, during the postovulatory phase of the menstrual cycle, and during pregnancy and lactation. regression or atrophy of the lobules is more pronounced following pregnancy and lactation.

Characteristics of the Breast With The Onset of Menses:

occurs with declining progesterone levels changes within the lobular units begin to regress and involute some changes persist

Sonographic Features of Normal Lymph Nodes:

oval or reniform shape with smooth margins hypoechoic outer cortex hyperechoic fatty hilum - with Doppler flow

Axillary Lymph Nodes:

over 75% of the lymph from the breast drains into the axillary lymph nodes there are 30-40 lymph nodes along the axillary chain, which are subdivided into anatomic groups The most common site for lymphatic metastasis from breast cancer. for surgical and staging purposes, the axillary lymph nodes are divided into three levels relative to the pectoralis minor muscle.

Sonographic Appearance of the Pectoral Fascia:

overlies the pectoralis major muscle produces a thin, hyperechoic band of echoes

How do the breasts form?

paired regions of ectodermal thickening occur at intervals along bilateral mammary ridges or "milk lines" these milk lines extend from the axilla to the inguinal region one pair along the upper one-third of the milk lines, persists to eventually form the breasts during the remainder of fetal life, epithelial cells proliferate and gradually form buds and cords of cells that project into the subcutaneous tissues during the last 3 months of gestation, secondary buds eventually canalize to form rudimentary lactiferous ducts. by birth, little more than the main ducts have developed in both males and females the breasts of males and females are generally similar until puberty, when estrogen and other hormones initiate breast development in the female during adolescence the breast lobules form within the female, the male breast remains in an underdeveloped state with each menstrual cycle, the female breast undergoes proliferative and involutional changes further maturation of the breast occurs with pregnancy and lactation

What are the external characteristics of the female breast?

paired, dome-shaped, modified apocrine sweat glands located anterior to the muscles overlying the 2nd-6th ribs extend from the sternal ridge to the mid axillary line

Internal Mammary Lymph Nodes:

parasternal nodes follow the path of the internal mammary arteries and veins lie within the 2nd-4th intercostal spaces just lateral to each side of the sternum

Smaller amounts of blood are supplied to the breast by:

perforating branches of the intercostal artery help perfuse the lower breast pectoral branch of the thoracoacromial artery help perfuse the upper breast

Other hormones That Influence The Breast During Pregnancy and Lactation:

placental lactogen HCG produced by the placenta

What is the most common breast developmental anomaly?

polythelia

What are the clinical findings of unilateral early ripening?

presents as a tender discoid lump beneath the areola

Prolactin-Inhibiting Factor

prevents the release of prolactin until milk production is needed after childbirth produced by the hypothalamus

Breast physiology:

the design and function of the breast is to produce milk the breast does not produce hormones, but the breast tissues respond to a variety of hormones produced by the ovaries, hypothalamus, pituitary glands, placenta, thyroid, and pancreas

How does unilateral early ripening appear sonographically?

the developing glandular tissue appears as a hypoechoic, subareolar nodular region this should not be mistaken for a mass and does not require biopsy. excision will remove vital glandular tissue and prevent further breast development

Characteristics of the Ducts Within the Breast:

the ducts are lined by specialized cells and are bounded by the basement membrane the inner lining of the ducts is composed of epithelial cells. beneath the epithelium is a layer of more widely-spaced myoepithelial cells that lie by the basement membrane of the duct. the myoepithelial cells contain contractile fibers that aid in the transport of milk from the acini and ducts. in the nonlactational breast, the lumen of the ducts may contain variable amounts of fluid, protein, and cellular debris.

Normal Sonographic Appearance of the Breast during Pregnancy and Lactation:

the glandular tissue dramatically extends and compresses the surrounding fat the glandular tissue is reflective than fibrous tissue and appears isoechoic or mildly hyperechoic relative to fat giving the breast a fine, "ground-glass" appearance with milk production, the ducts dilate and contain anechoic or hypoechoic fluid

Sonographic Appearance of the Ducts in the Mammary Layer:

the main lobar ducts are best seen on radial scans ducts increase in size as they approach the nipple generally ducts measure less than or equal to 2 mm but can be larger at the lactiferous sinus and during pregnancy and lactation Doppler differentiates fluid-filled ducts from arteries or veins

What is polythelia?

the presence of accessory - supernumary - nipples affects both males and females an accessory nipple is most often located just inferior to the breast, but can develop anywhere along the milk lines

What is polymastia?

the presence of accessory - supernumerary - breasts a fully formed accessory breast with nipple / areolar tissue is rare accessory mammary tissue - without the nipple / areola is more common and often forms in the axillary region

Stromal Tissue of the Breast:

the supportive elements of the breast consist of fat - adipose - tissue and fibrous connective tissues consists of loose intralobular stroma and dense extralobular stroma

What is the importance of the venous drainage of the breast?

the veins are routes of hematogenous metastases from carcinomas intercostal veins anastomose with vertebral veins and can provide a pathway for bone metastases

Why is ultrasound helpful in assessing the internal mammary lymph nodes?

these nodes are not detectable on a mammogram or by clinical palpation

Changes in the Breast After Lactation Ends:

these structures begin to involute and regress to a variable degree

Sonographic Appearance of the Retromammary Fat Layer:

this layer is thinner and contains smaller fat lobules than the subcutaneous fat layer TGC and overall gain settings should be adjusted so both fat layers are of similar echogenicity

What is the main function of the breast?

to produce milk during lactation

Where are the deep veins of the breast located?

travel alongside the arteries and drain into the internal mammary, axillary, subclavian, and the intercostal veins

Pectoralis Major Muscle:

two-thirds of the breast tissue lies anterior to the pectoralis major muscle runs obliquely from the mid sternum and medial half of the clavicle to the greater tubercle of the humerus sonographic visualization is important since it verifies that the sound beam has fully penetrated the breast tissue

What are some scanning tips for evaluating the nipple/areola complex?

use of ample acoustic gel and transducer pressure to compress the nipple and to eliminate trapped air pockets placement of the transducer along side of the areola and angling under the nipple performance of specialty maneuvers: 2-handed peripheral compression; rolled-nipple technique spatial compound imaging use of acoustic offset -standoff pad, extra gel - to evaluate the nipple

Sonographic Appearance of the Mammary Layer:

varies between individuals and significantly changes with regards to the female's age and hormonal status - pregnancy, lactation, menopause fibroglandular tissue is typically hyperechoic when compared to fat, primarily due to the dense fibrous stromal elements. When sonographically visible, glandular tissues - TDLUs; ductal structures - along with loose stromal fibrous tissue tend to be more isoechoic to fat. fluid-filled lactiferous ducts can be visualized within this breast layer The superficial and deep layers of the superficial fascia - premammary and retromammary fascia - encase the mammary layer and are occasionally seen as thin, hyperechoic lines when the sound beam is directed perpendicular to the fascial planes

The mature female breast is composed internally of:

varying mixtures of fat glandular tissue fibrous connective tissue blood vessels lymphatics nerves