Anatomy of the Breast
The breast is composed of glandular, ductal, connective, and
adipose tissue. Embedded in the fibrous tissue are fat and lobules
which make up the mammary glands, accessories to reproduction in women, but
rudimentary and functionless in men. In men, little fat is present in the
breast, and the glandular system normally does not develop. In women, the
breasts are the most prominent superficial structure on the anterior thoracic
wall, and the amount of fat in the glandular tissue determines the size of the
breasts. A small part of the mammary gland often extends into the axilla,
forming the axillary tail of Spence.
The breasts lie on the deep pectoral fascia (investing the
pectoralis major) and the fascia of the serratus anterior. They are
bounded by the clavicle superiorly, the lateral border of the latissimus muscle
laterally, the sternum medially, and the inframammary fold inferiorly. The breast is
attached to the dermis of the overlying skin by connective tissue structures
known as Cooper's ligaments (aka suspensory ligaments or retinacula cutis),
which suspend the breast on the chest wall. It is these ligaments which
pull on the skin, creating the dimpling (or peau d'orange) associated with
The mammary glands are modified sweat glands and are composed of
15-20 lobules, each drained by a lactiferous duct. Each lactiferous duct
independently drains on the nipple and is preceded by a small dilated portion
known as the lactiferous sinus. It is in the sinus that milk collects
during nursing and is "let down" by the suckling action of the infant.
Blood Supply and Nerves
The blood supply to the breast is derived from 3 sources. The
predominant supply of blood comes from the perforating branches of the
internal mammary arteries, derived from the internal thoracic artery.
The breast is further supplied by the lateral thoracic and
thoracoacromial arteries (branches of the axillary artery) as well as
posterior intercostal arteries (branches of the thoracic aorta).
Venous drainage of the breast is mainly accomplished by the axillary vein.
The subclavian, intercostal, and internal thoracic veins also aid
in returning blood to the heart.
The lymphatic drainage of the breast deserves special attention, due to its
role in the metastasis of cancer cells. The majority of lymph (>75%),
particularly from the lateral quadrants, drains to the axillary lymph nodes.
The remainder of lymph drains to either the parasternal nodes or the
opposite breast (medial quadrants) or the inferior phrenic nodes
(lower quadrants). With the exception of the nipple and areola, lymph from
the skin of the breast drains into the axially, inferior deep cervical,
infraclavicular, and parasternal nodes (depending on the location of the
The innervation of the breast is supplied mainly by branches of the 4th
through 6th intercostal nerves, which convey sensation to the skin of the
breast and sympathetics to the blood vessels and smooth muscle cells in the
overlying skin and nipple. Although not intimately involved with the
innervation of the breast, the long thoracic, thoracodorsal, and
intercostobrachial nerves are important to visualize as they cross through
the anatomic spaces of the breast and axilla, and are thus important to consider
||Internal mammary, lateral thoracic, thoracoacromial, posterior
||Axillary, subclavian, intercostal, internal thoracic
||Axillary, parasternal, inferior phrenic nodes
||4th-6th intercostal nerves
The lateral pectoral nerve passes medially around the medial
pectoralis minor, and the medial pectoral nerve passes laterally around the
pectoralis minor. Injuries to these nerves are rare. The
thoracodorsal nerve is identifiable medial to the thoracodorsal vein, running
along to enter the latissimus dorsi. Injury to this nerve results in
slight weakening of the latissimus muscle. The long thoracic nerve is
located more medially to the axilla. It runs just beneath the investing
fascia or the serratus anterior, medial to the thoracodorsal complex.
Injury to the long thoracic nerve results in winging of the scapula (on
extension). Brachial plexus injuries can be avoided by keeping the
superior extent of the axillary dissection inferior to the lower border of the
axillary vein. The skin of the axilla and upper arm is supplied by the
intercostobrachial nerve. This nerve is often sacrificed during axillary
node dissection, resulting in numbness of these areas.