Sonography of the Breast Part II Module Three Anatomy and Physiology Holdorf PhD, MPA, RDMS (Ob/Gyn, Ab, BR), RVT, LRT(AS,) CCP

Module Three: Anatomy and Physiology

Anatomic Layers From Anterior to Posterior Skin Subcutaneous (premammary) layer Mammary Layer Retromammary Space Muscle Layers (pectoralis Major m. and Pectoralis minor m.) Chest wall (ribs and intercostal muscles)

Skin The skin is composed of the epidermis and dermis layers The thickness is 0.5 to 2 mm It is slightly thicker in young females and thins with age. NIPPLE Consists of dense connective tissue and erectile muscle. It contains many sensory nerve endings. 15 to 20 collecting (lactiferous) duct openings may be seen (each of which arise from a breast lobe) AREOLA Circular area of dark pigmentation seen around the nipple. Consists of smooth muscle. Slightly thicker than surrounding skin. Contains Montgomery glands- sebaceous glands seen as small bumps in the areola.

1. Subcutaneous (Premammary Layer) 2. Superficial layer 3. Deep layer 4. Superficial fascia 5. Mammary Layer

Layers of the breast

Subcutaneous (Premammary ) Layer Lies just beneath the skin extending to the mammary layer Consists primarily of fat It is not seen posterior to the nipple Amount of fat increases with age, pregnancy, and obesity Cooper’s ligaments appear as prominent structures within the subcutaneous layer.

Superficial Fascia The breast tissue is completely contained between the layers of the superficial fascia. At the breast, the superficial fascia divides into the superficial and deep layers The superficial layer of the superficial fascia is simply known as the superficial fascia. The superficial fascia is contained within the subcutaneous layer anterior to the mammary layer.

Mammary Layer The mammary layer is also known as the parenchymal or Glandular layer. A portion of glandular tissue extends into the axilla. This is known as the axillary Tail of Spence. The mammary layer is composed of two types of tissue: Stroma- is the supportive tissue of the breast Consists of interlobular fat and connective tissue (Cooper’s ligaments, loose and dense connective tissue) Epithelium – is the functional tissue Consist of acini, lobules, TDLU’s, lobes and lactiferous ducts.

Mammary layer- continued Cooper’s Ligaments (Suspensory Ligaments)- Part of the stoma and supportive tissue of he Mammary layer Provide the architectural “framework” of the breast Run between the superficial and deep layers of the superficial fascia. Acini Also called Acinus or Acinar cell Smallest functional unit of the breast Milk-producing gland Hundreds of acini in each breast Each acini gives rise to a ductule or terminal duct

Lobule Is composed of approximately 30 acini, intralobular terminal ducts, and intralobular stromal tissue (loose connective tissue). TDLU Terminal Duct Lobular Unit TLDU is made up of: Lobule, intralobular terminal ducts, extralobular terminal duct Usually measures 2.0 mm or less Nearly all breast pathology originates in the TDLU. Lobe Several lobules (TDLUs) make up a breast lobe 15 to 20 lobes in each breast One lactiferous duct emerges from each lobe and travels toward the nipple.

Mammary Layer (continued) Lactiferous Ducts- Transport milk from the acini to the nipple Begin with the Ductule of Terminal Duct which arises from the acinar cell Intralobular terminal Duct-within the lobule Extralobular Terminal Duct- outside the lobule Interlobular ducts travel between the lobes The duct enlarges slightly beneath the areola forming the Lactiferous Sinus. Collecting Duct empties milk from the nipple.

Layers of the breast

Cross section of Breast Duct lumen

Lactiferous ducts are lined with a double layer of epithelial cells Epithelium (inner layer) Myoepithelium The epithelial cells are supported by a basement membrane (adventitia) which is the outer fibrous portion of the duct The function of the my0epithelium is to produce milk within the ducts toward the nipple. Deep Fascia The deep layer of the superficial fascia is often referred to as the deep fascia. Located within the retromammary space posterior to the mammary layer. Maintaining integrity of the deep fascia is important in deterring the spread of cancer to the chest wall.

Retromammary Space Space between the posterior margin of the mammary layer and the pectoral muscles Contains thin layer of fat Amount of fat increases with age, pregnancy, and obesity. Also contains the deep layer of the superficial fascia. This layer allows movement of the breast over the chest wall.

Muscles Pectoralis Major arises from the clavicle and costal cartilage of the sternum, attaching to the proximal humerus. Pectoralis Minor arises from the 3rd, 4th, and 5th ribs attaching to the scapula. The pectoral (muscular) fascia encloses the chest muscles and may appear deep to the retromammary layer. Pectoralis Major muscle is located anterior to pectoralis minor muscle. Both are found immediately posterior to the breast tissue.

Chest Wall Ribs are located posterior to the pectoral muscles. In small breasted females, it is important not to confuse a rib with an intra-mammary tumor on a physical or sonographic examination. Intercostal muscles are located between the ribs. Deep to the chest wall layer is the lung.

Deltoid, Pectoralis Major M.

Standard Anatomic Reference Quadrant Method Each breast can be divided into quadrants (4): UO – Upper Outer UI – Upper Inner LO- Lower Outer LI – Lower Inner Glandular tissue is usually thicker in the Upper-Outer quadrant of both breasts Therefore, a larger percentage of cancers are found there.

Clock method Regions of the breast are correlated with positions of a clock. This method allows a more precise location to be documented. Correlating clock locations from right to left side is important in evaluating the breast for symmetry. For example, the 10:00 position in the right breast correlates with the 2:00 position on the left.

Embryologic Development The Early mammary gland begins development during the 4th week of embryologic life. The glandular tissue of the breast begins to evolve into epithelial buds that eventually form approximately 20 epithelial cords (lobes). At 15 weeks gestation, testosterone in the male fetus prohibits further breast development and estrogen in the female fetus continues to stimulate early development. Once the fetus is born, the breast tissues are dormant until puberty.

Breast enlargement in the male or female newborn may be seen due to placental and maternal hormone stimulation. The breasts develop along a line extending from the axilla to the inguinal region known as the MILK LINE. Occasionally, accessory or supernumerary breasts are found along this line.

The milk line

Development Anomalies Amastia- absence of one or both breasts Polymastia – accessory breast or more than two breasts. Athelia- absence of the nipple. Polythelia – accessory nipple (most common breast anomaly). Amazia- absence of the breast tissue with development of the nipple. Nipple flattening or Nipple inversion. Unilateral early ripening – asymmetric growth of the breasts. Polythelia is more common in men than in women.

Arterial Supply Two main arteries supply blood to the breast tissues. These include the Lateral thoracic artery Internal mammary artery The lateral thoracic artery arises from the axillary artery and courses inferior and lateral along the pectoralis major muscle. It gives rise to small perforating branches to supply the lateral regions of the breast. The internal mammary artery (also known as the internal thoracic artery) arises from the subclavian artery. It courses lateral to the sternum and inferiorly behind the upper ribs. Small perforating branches supply the medial region of the breast.

Arteries of the Breast

The internal mammary artery is often used in coronary artery bypass graft (CABG) procedures. Two secondary sources of blood supply to the breast tissues include the Thoracoacrominal artery (supplying a superior region) Intercostal artery (supplying the inferior region) The arteries of the breast 1. Internal mammary artery (IMA) 2. perforating branches of the IMA 3. Intercostal artery 4. perforating branch of intercostal artery 5. Lateral Thoracic Artery 6. Axillary artery 7. Thoracoacromial artery

Venous Return There are two venous systems that drain the breast tissue: Superficial Deep The superficial veins of the breast are located just deep to the superficial fascia. The superficial veins allow venous communication between the right and left breasts. This may be a route for cancer metastasizing to the opposite breast. The Deep veins of the breast include small branches that drain into the internal mammary vein, lateral thoracic vein, axillary vein, subclavian vein, and the intercostal veins.

Breast cancer most frequently spreads by the hematogeneous route. The intercostal veins also communicate with the vertebral veins. This may be a route for bone metastasis from breast cancer. The superficial and deep venous systems communicate within the breast parenchyma. It is also important to note the lymphatic vessels of the breast tissues closely follow the same route as the superficial and deep venous systems. Breast cancer most frequently spreads by the hematogeneous route. Veins of the breast 1. Internal mammary vein 2. perforating branches of IMV 3. intercostal vein 4. perforating branch of intercostal vein 5. lateral thoracic vein 6. axillary vein 7. subclavian vein.

The venous return from the breast

The Lymphatic System The Lymphatic System transports a watery clear fluid called lymph. The lymphatic system aids the immune system in destroying pathogens and filtering waste so that the lymph can be safely returned to the circulatory system. The lymphatic system contains immune cells called lymphocytes, which protect the body against antigens such as harmful bacteria and viruses that invade the body.

Lymphatic System Lymph flow begins deep within the breast tissues through lymphatic vessels that originate in the stroma and lactiferous ducts (deep system). Intramammary Lymph Nodes are seen throughout the breast parenchyma as part of the deep system. Flow direction from the deep system is toward the areola into the periareolar plexus and continues into the subdermal lymphatic vessels (superficial system). From the subdermal vessels, lymph flows outward to the outer lymphatic chains that drain the breast. The outer lymphatic chains are located in multiple areas surrounding the breast.

Intra-mammary Lymph Node

Approximately 75% of lymphatic drainage is to the axilla Approximately 75% of lymphatic drainage is to the axilla. Therefore, the axillary lymph node chain becomes extremely important in predicting the spread of breast cancer. The axillary lymph node chain consists of 6 groups of nodes: 1. External mammary group-located along the lateral thoracic vessels. 2. Scapular group-run with the subscapular vessels. 3. Axillary group- run with the axillary vessels. 4. Central group – run with the axillary vessels 5. Subclavicular group – run with the subclavian vessels. 6.Interpectoral (Rotter’s) nodes – found between pectoralis major and minor muscles.

Lymph nodes of the axillary region

The remaining 25% of lymphatic drainage include: 1. Internal mammary lymph nodes – lie along the internal mammary vessels. 2. Intercostal Lymph nodes 3. Flow to the opposite breast 4. Subclavicular Lymph nodes – Within the subclavicular fossa 5. Diaphragmatic Lymph Nodes – allow drainage to the abdomen.

The lymph node is reniform (kidney – like) in shape The lymph node is reniform (kidney – like) in shape. It has an outer cortex and medial hilum where the small artery, vein, and lymph vessel enter and exit the node. Outer afferent lymphatic vessels carry lymph into the node where it is filtered and released through the hilar vessel.

Nerves A complicated network of nerves serve the breast, chest muscles, an surrounding tissues. These include: 1. Long thoracic nerve 2. thoraco-doral verve 3. Thoracic intercostal nerves 4. 3rd and 4th Branch of the cervical plexus 5. Circumflex nerve (Axillary Nerve) 6. Subcapular nerves 7. Anterior thoracic nerves

Circumflex (Axillary) nerve

The nerves of the axilla region

Physiology and Hormonal Influences Puberty At puberty, breast development occurs due to hormonal stimulation by the ovaries (the larche). The amount of growth of breast size and volume will vary with each individual. Estrogen stimulates changes of stromal tissues: elongation of the mammary ducts, growth of connective tissue, increase in adipose tissue and increased vascularity. Progesterone stimulates growth of the glandular tissue: TDLUs.

Mature female breast The mature female breast is sensitive to the menstrual cycle and responds to fluctuating hormone levels every month. Early in the proliferative phase of the menstrual cycle, changes in the epithelium occur. Later in the secretory phase, the ducts and veins increase in size, the stroma becomes edematous, and the epithelium produces secretions. These changes may account for premenstrual breast discomfort. At the onset of menses, the breast tissues decrease in size.

Pregnancy During pregnancy, there is considerable change in the breast tissue. The TDLUs increase in size as the epithelium begins to swell. The acinar cells enlarge in response to a variety of hormones including estrogen and progesterone, and lactogen, prolactin, and chorionic gonadrotrophin from the placenta. Late in the pregnancy, the lactiferous ducts increase in size.

Lactation Shortly after birth, the estrogen and progesterone levels diminish rapidly and Prolactin dominates. This hormone causes the acinar cells to secrete milk. After the termination of breast-feeding, the ducts and lobules return to their normal size in approximately 3 months.

Menopause In the prei-menopausal female, the lobules of the breast involute (roll inward, invert). Also, the connective and stromal tissues are largely replaced by fat. Involuation is thought to begin long before menopause as a gradual decrease in glandular tissue with fatty replacement. There are only a few situations, however, when breast parenchyma or glandular tissue increase with age. The most common causes of increased glandular tissue development are: pregnancy/lactation Hormone replacement therapy (HRT) Significant weight loss The ratio of glandular to fatty tissue in the breasts is determined by Total body fat : Total body weight

End modules one, two, three Next week Test on modules one, two, and three.