Introduction

The breast consists mainly of fat and glandular tissue, the latter varying throughout life, in response to female hormones. It approximately overlies the second to sixth ribs and is entirely enveloped in chest wall fascia, which forms septae called Coopers suspensory ligaments. These support the breast, running from the fascia of the pectoralis muscles posteriorly to the skin anteriorly (Fig. 8.1). The internal mammary (thoracic) and lateral thoracic arteries are the main blood supply, supplemented by anterior intercostal and thoracoacromial branches. Venous drainage essentially corresponds to the arteries, with some passage via the azygous system. Lymphatic drainage is of special significance, as spread of primary breast cancer is most commonly disseminated via this route. The majority of lymph passes towards the axilla, where surgically three levels of axillary nodes are denoted in relation to the pectoralis minor muscle (Fig. 8.2). Level 1 nodes are inferolateral, level 2 are posterior and level 3 are superomedial. Part of the medial breast also drains to the internal mammary nodes.

Embryology/mimics

The breasts develop from an ectodermal milk line running from the axilla to the groin on each side. This thickens and gives rise to 15 to 20 outbuddings which in turn form ducts and then lobes. Several lobules compose each lobe, subdivided by fibrotic and fatty stroma. Each lobule is composed of several acini, the blind saccules that secrete the milk of lactation, as well as their draining ducts. The smallest anatomical unit within the breast is termed the terminal duct lobular unit (TDLU), where the majority of malignant pathologies arise (Fig. 8.3).