ANATOMY OF BREAST
The breasts are the most prominent superficial structures in the anterior
thoracic wall, especially well developed in women
The mammary glands are in the subcutaneous tissue overlying the pectoralis
major and minor muscles
At the greatest prominence of the breast is the nipple, surrounded by a circular
pigmented area of skin, the areola
The mammary glands within the breasts are accessory to reproduction in
women. They are rudimentary and functionless in men, consisting of only a few
small ducts or epithelial cords
FEMALE BREASTS
The amount of fat surrounding the glandular tissue determines the size of non-
lactating breasts
The roughly circular body of the female breast rests on a bed that extends
transversely from the lateral border of the sternum to the midaxillary line and
vertically from the 2nd through 6th ribs
Two thirds of the bed of the breast are formed by the pectoral fascia overlying
the pectoralis major; the other third, by the fascia covering the serratus
anterior
Between the breast and the pectoral fascia is a loose connective tissue plane or
potential space—the retromammary space (bursa), containing a small amount
of fat, allows the breast some degree of movement on the pectoral fascia
A small part of the mammary gland may extend along the inferolateral edge of
the pectoralis major toward the axillary fossa (armpit), forming an axillary
process or tail (of Spence). Some women discover this (especially when it may
enlarge during a menstrual cycle)
The breast is firmly attached to the overlying skin by condensation of
connective tissue called the suspensory ligaments (of Cooper), which help to
support the lobules of the breast
For descriptive purposes, the breast is divided into four quadrants: upper and
lower lateral, and upper and lower medial
The most prominent feature of the breast is the nipple
The nipple is surrounded by the areola, a circular
pigmented area of skin
The areola contains sebaceous glands, following a
pregnancy these secrete an oily substance to protect the
mother's nipple from irritation during nursing.
The breast is composed of 15 to 20 lobules of glandular
tissue, formed by the septa of the suspensory ligaments
The mammary glands are modified sweat glands that are
formed from the development of milk-secreting alveoli,
arranged in clusters
Each lobule is drained by a lactiferous duct
Each lactiferous duct opens on the nipple
VASCULATURE OF BREAST
The arterial supply of the breast derives from the:
Medial mammary branches of perforating
branches and anterior intercostal branches of the
internal thoracic artery, originating from the
subclavian artery
Lateral thoracic and thoracoacromial arteries,
branches of the axillary artery
Posterior intercostal arteries, branches of the
thoracic aorta in the 2nd, 3rd, and 4th intercostal
spaces
The venous drainage of the breast is mainly to the axillary vein, but there is some drainage to the internal thoracic vein
The lymphatic drainage of the breast is important
because of its role in the metastasis of cancer cells.
From this plexus:
o Most lymph (>75%), especially from the
lateral breast quadrants, drains to the
axillary lymph nodes, initially to the anterior
or pectoral nodes for the most part.
However, some lymph may drain directly to
other axillary nodes or even to interpectoral,
deltopectoral, supraclavicular, or inferior
deep cervical nodes
o Most of the remaining lymph, particularly
from the medial breast quadrants, drains to
the parasternal lymph nodes or to the
opposite breast, whereas lymph from the
inferior quadrants may pass deeply to
abdominal lymph nodes (subdiaphragmatic
inferior phrenic lymph nodes). It is important
to note that lymph from the medial
quadrants can cross to the opposite breast.
Thus secondary metastases of breast
carcinoma can spread to the opposite breast
in this way
Lymph from the skin of the breast, except the nipple
and areola, drains into the ipsilateral axillary, inferior
deep cervical, and infraclavicular lymph nodes and into
the parasternal lymph nodes of both sides
Lymph from the axillary nodes drains into clavicular
(infraclavicular and supraclavicular) lymph nodes and
from them into the subclavian lymphatic trunk, which
also drains lymph from the upper limb
Lymph from the parasternal nodes enters the
bronchomediastinal lymphatic trunks, which also drain
lymph from the thoracic viscera
The termination of these lymphatic trunks varies;
traditionally, these trunks are described as merging with each other and with the jugular lymphatic trunk, draining the head and neck to
form a short right lymphatic duct on the right side or entering the termination at the thoracic duct on the left side
However, in many (perhaps most) cases, the trunks open independently into the junction of the internal jugular and subclavian veins,
the right or left venous angles, that form the right and left brachiocephalic veins. In some cases, they open into both of these veins.
NERVES OF BREAST
The nerves of the breast derive from anterior and lateral cutaneous branches of the 4th-6th intercostal nerves
The branches of the intercostal nerves pass through the pectoral fascia covering the pectoralis major to reach overlying subcutaneous
tissue and skin of the breast
The branches of the intercostal nerves convey sensory fibers from the skin of the breast and sympathetic fibers to the blood vessels in the
breasts and smooth muscle in the overlying skin and nipple
Sources: Moore anatomy, Netter
Histology of Breast
Each mammary gland consists of 15–25 lobes of the compound tubuloalveolar type whose function is to secrete milk
Each lobe, separated from the others by dense connective tissue and much adipose tissue, is really a gland in itself with its own excretory
lactiferous ducts, 2–4.5 cm long, emerge independently in the nipple, which has 15–25 openings, each about 0.5 mm in diameter
Immediately before opening onto the surface, the duct forms a dilatation called the lactiferous sinus
The lactiferous sinuses are lined with stratified squamous epithelium at their external openings. This epithelium very quickly changes to
stratified columnar or cuboidal epithelium
The lining of the lactiferous ducts and terminal ducts is formed of simple cuboidal epithelium covered by closely packed myoepithelial
cells
The nipple contains bands of smooth muscle orientated in parallel to the lactiferous
ducts and circularly near the base; contraction of this muscle causes erection of the
nipple
Within each lobe of the breast, the main duct branches repeatedly to form a number
of terminal ducts, each of which leads to a lobule consisting of multiple acini
Each terminal duct and its associated lobule is called a terminal duct-lobular unit
The lobules are separated by moderately dense collagenous interlobular tissue,
whereas the intralobular supporting tissue surrounding the ducts within each lobule is
less collagenous and more vascular
The skin surrounding the nipple, the areola, is pigmented and contains sebaceous
glands that are not associated with hair follicles
The inactive mammary gland an abundance of conn. tissue and a scarcity of glandular elements. A glandular lobule (1) consists of small tubules
or intralobular ducts (4,7) that are lined with a cuboidal or low columnar epithelium. At the base of epithelium are the contractile myoepithelial
cells (6). The larger interlobular ducts (5) surround the lobules and the intralobular ducts. Intralobular ducts (4,7) are surrounded by loose
intralobular conn.tissue (3,8) that contains fibroblast, lymphocytes, plasma cells, and eosinophils. Surrounding the lobules (1) is a dense
interlobular conn,tissue (2,10) that contain blood vessels, such as venules and arterioles (9)
Mammary gland during proliferation and early pregnancy During the first half of pregnancy, the intralobular ducts undergo rapid
proloferation and form terminal buds that differentiate into alveoli (2,7). At this stage, most alveoli are empty, and it is difficult to distinguish
them from small intralobular excretory ducts (10) which however, appear more regular, with a more distinct epithelial lining. The intralobular
excretory ducts (10) and alveoli (2,7) are lined by two layers of cells, the luminal epithelium and a basal layer of flattened myoepithelial cells (8). A
loose intralobular connective tissue (1,9) surrounds the alveoli (2,7) and the intralobular excretory ducts (10). A denser conn.tissue with adipose
cells (6) surrounds the individual lobules and forms interlobular conn.tissue septa (3)
Mammary gland during late pregnancy during pregnancy, the glandular epithelim is prepared for lactation. The alveolar cells become secretory,
and the alveoli (2,8) and the ducts (1,7,13) enlarge. Some of the alveoli contain a secretory product (2). Secretion of milk by the mammary gland
however, does not begin until after parturition. Because the intralobbular excretory ducts (1) of the mammary glands also contain secretory
material, distinguishing between alveoli and ducts is difficult. As the pregnancy progresses, the amount of interlobular conn.tissue (4,11) decreases,
whereas interlobular conn.tissue increases due to enlargement of the glandular tissue. Surrounding the alveoli are the flattened myoepithelial celss
(10,12).
Mammary gland during lactation the lactating mammary gland contains a large number of distended alveoli filled with secretions and vacuoles
(2,9). The alveoli show irregular branching patterns (3). Because of the increased size of the glandular epithelium (alveoli), the interlobular
conn.tissue (4) is reduced. During lactation, the histology of individual alveoli varies. Not all alveoli exhibit secretory activity. The active alveoli (2,9)
are lined with low epithelium and filled with milk that appears as eosinophilic (pink) material with large vacuoles of dissolved fat droplets. Some
alveoli accumulate secretory product in their cytoplasm (8), and their apices appear vacuolated because of the removal of fat during tissue
preparation. Other alveoli appear inactive (6,11) with empty lumina that are lined by a taller epithelium.
Sources: junquiera, whether, d’fiore
