The breasts are paired structures located on the anterior thoracic wall, in the pectoral region. They are present in both males and females, yet are more prominent in females following puberty. In females, the breasts contain the mammary glands - an accessory gland of the female reproductive system. The mammary glands are the key structures involved in lactation. In this article, we shall look at the anatomy of the breasts - their structure, innervation, vascular supply and any clinical relevance.
The breast is located on the anterior thoracic wall. It extends horizontally from the lateral border of the sternum to the mid-axillary line. Vertically, it spans between the 2nd and 6th costal cartilages. It lies superficially to the pectoralis major and serratus anterior muscles.
The breast can be considered to be composed of two regions:
At the centre of the breast is the nipple, composed mostly of smooth muscle fibres. Surrounding the nipple is a pigmented area of skin termed the areolae. There are numerous sebaceous glands within the areolae – these enlarge during pregnancy, secreting an oily substance that acts as a protective lubricant for the nipple.
The breast is composed of mammary glands surrounded by a connective tissue stroma.
The mammary glands are modified sweat glands. They consist of a series of ducts and secretory lobules (15-20). Each lobule consists of many alveoli drained by a single lactiferous duct. These ducts converge at the nipple like spokes of a wheel.
The connective tissue stroma is a supporting structure which surrounds the mammary glands. It has a fibrous and a fatty component. The fibrous stroma condenses to form suspensory ligaments (of Cooper). These ligaments have two main functions:
The base of the breast lies on the pectoral fascia – a flat sheet of connective tissue associated with the pectoralis major muscle. It acts as an attachment point for the suspensory ligaments. There is a layer of loose connective tissue between the breast and pectoral fascia – known as the retromammary space. This is a potential space, often used in reconstructive plastic surgery.
Arterial supply to the medial aspect of the breast is via the internal thoracic artery (also known as internal mammary artery) – a branch of the subclavian artery. The lateral part of the breast receives blood from four vessels:
The veins of the breast correspond with the arteries, draining into the axillary and internal thoracic veins.
The lymphatic drainage of the breast is of great clinical importance due to its role in the metastasis of breast cancer cells. There are three groups of lymph nodes that receive lymph from breast tissue – the axillary nodes (75%), parasternal nodes (20%) and posterior intercostal nodes (5%). The skin of the breast also receives lymphatic drainage - skin – drains to the axillary, inferior deep cervical and infraclavicular nodes.
In conclusion, the anatomy of the breast includes mammary glands, connective tissue stroma, pectoral fascia, vessels and lymphatics. These are all important parts of the breasts, which help to maintain their structure, function and normal physiology.
The breast is a complex and multifaceted organ composed of two distinct regions – a circular body that is the largest and most prominent part of the breast, which is surrounded by the axillary tail, a much smaller region that runs along the inferior lateral edge of the pectoralis major towards the axillary fossa. At the centre of the breast is the nipple, a structure composed mostly of smooth muscle fibres surrounded by the areolae, a pigmented area of skin containing numerous sebaceous glands. During pregnancy, these glands enlarge and secrete an oily substance that acts as a protective lubricant for the nipple.
The breast is composed of mammary glands surrounded by a connective tissue stroma and is supported by suspensory ligaments known as Cooper’s ligaments. The mammary glands are modified sweat glands, consisting of a series of ducts and secretory lobules (15-20). Each lobule is comprised of many alveoli drained by a single lactiferous duct. These ducts radiate outward from the nipple like spokes on wheel. The connective tissue stroma has two components – fibrous and fatty tissue, which is supplied by both the internal thoracic (internal mammary) artery as well as the second to sixth intercostal arteries.
The blood supply to the breast is also derived from the axillary artery. This artery gives rise to the anterior intercostal arteries which supply the pectoral fascia and the deeper parts of the breast. The anterior intercostal arteries also travel in the intercostal spaces, supplying the superficial skin overlying the breasts. The breast’s lymphatic drainage is to the axillary nodes, with the superficial lymphatics of the nipple draining to the subareolar lymphatic plexus. The axilla may contain up to five groups of lymph nodes – the lateral, anterior, medial, apical and posterior axillary lymph nodes, with the apical nodes draining the majority of the breast tissue and the parasternal nodes receiving lymphatics from the areas in between the sternum and the nipple.
The pectoral fascia, which is a flat sheet of connective tissue associated with the pectoralis major muscle, serves as the base of the breast and provides an attachment point for the suspensory ligaments. The suspensory ligaments have two primary functions – to attach and secure the breast to the dermis and underlying pectoral fascia, and to separate the secretory lobules of the breast. Between the breast and pectoral fascia lies a layer of loose connective tissue, known as the retromammary space, which is often used in reconstructive plastic surgery.
The arterial supply to the medial aspect of the breast is via the internal thoracic artery, while the lateral part of the breast receives its blood from four vessels – the lateral thoracic and thoracoacromial branches (which originate from the axillary artery), the lateral mammary branches (which originate from the posterior intercostal arteries), and the mammary branch (which originates from the anterior intercostal artery). The veins of the breast correspond to the arteries, draining into the axillary and internal thoracic veins.
Of great clinical importance is the lymphatic drainage of the breast, which plays a role in the metastasis of breast cancer cells. There are three groups of lymph nodes that receive lymph from breast tissue – the axillary nodes (75%), parasternal nodes (20%) and posterior intercostal nodes (5%). The skin of the breast also receives lymphatic drainage – the skin drains to the axillary, inferior deep cervical and infraclavicular nodes, while the nipple and areola drain to the subareolar lymphatic plexus.
The breast is innervated by the anterior and lateral cutaneous branches of the fourth to sixth intercostal nerves. These nerves contain both sensory and autonomic nerve fibres, with the autonomic fibres regulating smooth muscle and blood vessel tone.
The breasts, or mammary glands, are modified sweat glands situated on the anterior thoracic wall of the chest. They are surrounded by connective tissue stroma containing a highly vascularised pectoral fascia, and the medial attachment of the breasts is the sternum. Within the stroma lies the internal thoracic artery, axillary artery, and anterior intercostal artery, and lymphatic drainage from the breasts passes mainly to the axillary nodes, parasternal nodes, posterior intercostal nodes, and then to the parasternal and internal mammary nodes. The nipple, the most superior portion of the breast, is surrounded by the circular areola containing a few sebaceous glands, and is innervated by autonomic nerve fibers, causing it to be raised in response to cold or touching.
Though the nerves within the breast tissue do not regulate the production or secretion of milk, this fundamental process is instead regulated by the hormones prolactin and oxytocin, which are secreted by the pituitary gland.
Breast cancer is the most common type of cancer diagnosed within the UK. After lung cancer, it has the second highest death rate due to cancer, and is more common in women than men. Common presentations associated with breast cancer are due to blockages of the lymphatic drainage, with excess lymph building up in the subcutaneous tissue and resulting in nipple deviation/retraction, and prominent, dimpled skin between small pores (peau d’orange). Larger dimples, meanwhile, are generally caused by cancerous invasions and fibrosis, which pull the suspensory ligaments, causing them to shorten.
Metastasis commonly occurs through the lymph nodes, and it is most likely the axillary lymph nodes that are affected. They become stony hard and fixed, and from there, the cancer can spread to distant places such as the liver, lungs, bones, and ovary. The triple assessment is used to assess a suspected case of breast cancer, which includes a clinical examination, imaging with a mammogram and ultrasound scan, and a biopsy. The staging of breast cancer uses the I-IV system or the Tumour Node Metastasis (TNM) system.
Surgical treatment with adjuvant radiotherapy is the recommended treatment option, with the goal being to just remove the affected tissue area. In the event of this not being possible, mastectomy is considered the best option. Adjuvant chemotherapy is also present to improve survival rates.
