The breast develops initially as a ventral ectodermal thickening along the so-called ‘milk line’ in mammals (Figure 1.1). Through a process of regression and maturation, discrete collections of nascent breast progenitor cells collect at specific sites along this milk line. This line extends from the axilla all the way down to the groin. Occasionally full regression fails to occur and ectopic breast formation outside of the usual location at the fourth intercostal space can develop anywhere along this line. Most commonly this is represented as an accessory nipple located at the left inframammary fold (Figure 1.2 A,B). Occasionally, a surprisingly well-formed rudimentary areola can form in association with the ectopic nipple (Figure 1.2 C). Also, it is not unusual for some women to undergo actual accessory breast parenchymal development. This usually occurs in the axilla, either unilaterally or bilaterally, and may or may not be associated with an overlying nipple or areola rudiment. This tissue can actually enlarge during pregnancy to the point where surgical excision is desired once the post-gestational period is reached (Figure 1.3 A–D). Typically, however, the breast bud located at the fourth intercostal space eventually develops on each side into the mature breast. Development starts with the onset of puberty, usually around the age of 11 or 12, and variably continues through the teenage years. Generally speaking, initial primary breast growth is completed by the age of 18 to 20. Subsequent secondary changes in the size and shape of the breast then continue under the influence of a wide variety of causes including pregnancy, weight gain or loss, hormonal changes, aging and breast-feeding. The net result is that the breast undergoes an evolution of change in appearance over the life of a woman. It is important for the aesthetic surgeon to understand this evolution when surgical alterations in breast size or shape are considered. Certainly, how the breast looks today may not necessarily be how the breast looks in ten years. Understanding and, when possible, predicting these changes can greatly improve the results of aesthetic breast surgery.

Figure 1.1 The ‘milk line’ extends from the axilla to the groin. At puberty, aberrant breast and/or vestigial nipple and areola development can occur anywhere along this line.

Figure 1.2 (A,B) An accessory nipple located just below left inframammary fold. (C) A rudimentary nipple and areola located on the breast just above the right inframammary fold along the embryonic ‘milk line’.

Figure 1.3 (A,B) Preoperative appearance of a woman with persistent unilateral aberrant axillary breast development after pregnancy. (C) The involved skin and underlying gland is marked for excision. (D) Final appearance after local excision of the involved tissue.

Understanding of the arterial anatomy of the breast is enhanced when it is realized that this anatomy is in place and fixed before the breast even begins to develop. Essentially, it is the vascular anatomy of the chest wall. Then, as the breast begins to enlarge, the available arterial and venous supply simply grows with the breast. As a result, the blood supply of the breast is diffuse and comes from a variety of potential sources including the internal thoracic artery via large anteriorly located intercostal perforators, the lateral thoracic artery, branches from the thoracoacromial axis through perforators running through the pectoralis major muscle, and anterior and posterior branches from the intercostal arteries, particularly branches from the 5th and 6th intercostal spaces (Figure 1.4). As a result, the breast can be accessed through many different incisions using a host of variably oriented pedicles and still have blood supply to the NAC preserved. Despite this diffuse blood supply, it is helpful to note that the dominant blood supply to the breast comes from the internal mammary system. These perforators off the internal mammary have an impressive pressure head due to their proximity to the heart, as anyone who has done a free flap anastomosis to the internal mammary can attest. Also, the internal mammary perforators interconnect with all other vascular sources to the breast. For this reason, throughout this book, many of the described procedures will preserve the internal mammary perforators whenever possible. The versatility these vessels provide allows division of all other vascular sources without risk of tissue necrosis.

Figure 1.4 The arterial supply of the breast.

The patterns of venous drainage mirror the arterial inflow. However, the superficial venous system is well developed and, in some patients, can often be prominently visualized through the skin. During surgical procedures, preservation of this superficial venous network is performed whenever possible as this may prevent venous congestion postoperatively. It is important to note that patients who have a prominent superficial venous arcade preoperatively may experience a distressing increase in the prominence of these vessels after a procedure such as a breast augmentation. Discussing these types of issues preoperatively may head off disappointment after the procedure if patients are adequately informed ahead of time.

The lymphatic drainage of the breast is also diffuse and variable. Traditionally recognized lymphatic basins include the axillary nodes as well as the nodes along the internal mammary vessels. Typically, while aesthetic breast procedures may interrupt some lymphatic channels in the breast, the drainage pattern is diffuse enough that there are essentially no untoward sequelae to lymph drainage of the breast after cosmetic breast surgery. Certainly, as opposed to reconstructive breast surgery, because the lymph nodes are left largely undisturbed by nearly any type of aesthetic breast procedure, lymph flow proceeds unimpeded and does not become an issue postoperatively.

In keeping with the tone set by the vascular supply to the breast, the innervation of the breast is also diffuse and variable. Multiple nerve branches from the lateral and anterior cutaneous branches of the 2nd through 6th intercostal nerves as well as the supra­clavicular nerves enter and ramify within the breast (Figure 1.5