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.
Note: This article will consider the structure of the breasts in the female.
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:
- Circular body – largest and most prominent part of the breast.
- Axillary tail – smaller part, runs along the inferior lateral edge of the pectoralis major towards the axillary fossa.
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.
Connective Tissue Stroma
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:
- Attach and secure the breast to the dermis and underlying pectoral fascia.
- Separate the secretory lobules of the breast.
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:
- Lateral thoracic and thoracoacromial branches – originate from the axillary artery.
- Lateral mammary branches – originate from the posterior intercostal arteries (derived from the aorta). They supply the lateral aspect of the breast in the 2nd 3rd and 4th intercostal spaces.
- Mammary branch – originates from the anterior intercostal artery.
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.
- Nipple and areola – drains to the subareolar lymphatic plexus.
The breast is innervated by the anterior and lateral cutaneous branches of the 4th to 6th intercostal nerves. These nerves contain both sensory and autonomic nerve fibres (the autonomic fibres regulate smooth muscle and blood vessel tone).
It should be noted that these nerves do not control the production and secretion of milk. This is regulated by the hormones prolactin and oxytocin, which are secreted from the pituitary gland.
Clinical Relevance: Breast Cancer
Breast cancer is the most common type of cancer to be diagnosed within the UK. After lung cancer it has the second highest death rate due to cancer. It is more common in women than men.
Common presentations associated with breast cancer are due to blockages of the lymphatic drainage. Excess lymph builds up in the subcutaneous tissue, resulting in clinical features such as nipple deviation and retraction, and prominent skin between small dimpled pores (peau d’orange). Larger dimples are generally caused by cancerous invasions and fibrosis. This causes traction of the suspensory ligaments, causing them to shorten.
Metastasis commonly occurs through the lymph nodes. It is most likely to be the axillary lymph nodes that are involved. They become stony hard and fixed. Following this, the cancer can spread to distant places such as the liver, lungs, bones and ovary.
To assess a suspected breast cancer a triple assessment is carried out. This involves clinical examination, imaging using a mammogram and ultrasound scan and finally 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. The operation is local and aims to remove only the affected tissue area. Failing this it is considered that a mastectomy is the best option. Adjuvant chemotherapy is also known to improve survival rates.