Breast

The **breast**is an apocrine gland seen in both males and females. However, in females it has a specific function that is production of milk.

Breast is composed of adipose tissue and glandular tissue. In addition, there are also suspensory Cooper's ligaments and connective tissue such as collagen and elastin. The glandular parenchyma is oestrogen dependent, thus on attaining menopause the glandular parenchyma atrophies.

The adult breast has nearly 14-18 lactiferous lobes which draim into lactiferous ducts which further converge to drain at the nipple-areola complex.

Zone Division:

* Premammary (subcutaneous) zone
	+ Most superficial zone
	+ Anterior margin defined by skin, posterior margin defined by anterior mammary fascia
	+ Contains subcutaneous fat, blood vessels, anterior suspensory (Cooper) ligaments
	+ Cooper ligaments
		- Formed from 2 leaflets of anterior mammary fascia inserting into dermis
		- Provide support for breast
* Mammary zone: posterior to anterior mammary fascia and anterior to posterior mammary fascia.
	+ Contains fibroglandular tissue: Majority of ducts/lobules, stromal fat, and stromal connective tissue
* Retromammary zone: most posterior of 3 zones, behind PMF and anterior to chest wall
	+ Contains fat and posterior suspensory ligaments, which attach fascia to chest wall

Location

The breasts are seen to overlie on the pectoralis major muscles and extend from the level of the second-to-sixth ribs:

* superior: clavicle
* inferior: middle of sternum
* lateral: anterior axillary line
* medial: sternum
* floor: superior 2/3 overlies pectoralis major muscle, lateral portions overlie serratus anterior muscle

There is often an extension of breast tissue into the axilla called axillary tail of Spence.

Arterial supply

* **Medial**
	+ internal thoracic artery perforators (second-to-fifth perforators)
	+ terminal branches of third-to-eighth intercostal perforators
* **Lateral:**
	+ thoracoacromial artery pectoral branch
	+ vessels to serratus anterior
	+ lateral thoracic artery

Venous drainage

* axillary vein
* internal thoracic vein
* posterior intercostal vein

Nerve supply

* thoracic intercostal nerve T3-T5
* supraclavicular nerve from the cervical plexus

Lymphatic drainage: originate from breast lobules and flow into a sub-areolar plexus, called Sappey’s plexus. From this plexus, lymphatic drainage takes place through three main routes:

* **axillary or lateral pathway:**
	+ fed by Sappey’s Plexus, as well as by ducts satellite lymphatics and by most of parenchymal lymphatics.
	+ this pathway runs around the inferior edge of the pectoralis major and reach the pectoral group of axillary nodes.
	+ drains the lateral portion of breast.
* **internal mammary pathway**
	+ originates from both the lateral and medial halves of the breast and passes through the pectoralis major
	+ can lead to directly to the apical nodes of the axilla
	+ medial parts can drain into the parasternal nodes and across the median plane and hence to the contralateral breast
* **retromammary pathway**
	+ comes from the posterior portion of the breast

* Lymphatics toward the lower portion can drain to the sheath of the rectus abdominis and the subperitoneal and subhepatic plexuses.

Usually axillary lymph nodes receive more than 75% of the lymph drained from the breast.

Variant anatomy

* breast hypoplasia
* amastia
* amazia
* polythelia (supranumerary nipple)
* polymastia (accessory breast tissue)