Anatomy

Authors: Mia Demant, MD, Mia Wagsmo Steffensen, MD

Overview

The borders of the breast include the inframammary fold inferiorly, the clavicula superiorly, the anterior border of the latissimus dorsi muscle laterally, and the sternum medially. 

A cross-section of the breast reveals a superficial fascial system, that divides into a superficial and deep layer that envelopes the breast tissue. Cooper’s ligaments penetrate the deep layer of the superficial fascia, provide suspensory structure to the breast parenchyma, and insert in the superficial layer (1). The glandular part of the breast parenchyma consists of alveoli (the secretory units of the gland), that is clustered together into approximately 20 lobes, which are separated by connective tissue and fat. The alveoli are connected by interlobular ducts that join to form lactiferous ducts. These ducts form lactiferous sinuses just beneath the nipple-areolar complex, which they open into. Generally, a layer of subcutaneous tissue with approximately 1 cm thickness exists between the dermis and the breast tissue (2). This layer is very important to identify and preserve during skin-sparing mastectomies. 

The breast is divided into four quadrants:

• Upper Outer (superolateral)
• Upper Inner (superomedial)
• Lower Outer (inferolateral)
• Lower Inner (inferomedial)

Understanding these quadrants aids in locating masses, determining incision sites, and achieving symmetry in aesthetic and reconstructive procedures.

Blood supply

The internal mammary artery perforators, anterolateral and anteromedial intercostal perforators, lateral thoracic artery, and thoracoacromial artery all supply the breast parenchyma. This rich vascular supply allows for a relatively safe division of breast tissue. 

Sensory innervation

Branches from the cervical plexus provide sensory to the superior medial aspect of the breast, while the anteromedial and anterolateral branches of the thoracic intercostal nerves are responsible for the majority of the breast sensation. The 3rd to 6th anterolateral intercostal nerves pass through the serratus muscles to enter and provide the lateral aspect of the breast, while the 2nd to 6th anteromedial intercostal nerves provide sensory to the medial part of the breast and the nipple-areolar complex.

Lymphatics

The breast has an extensive lymphatic network. Lymph drains to axillary, internal mammary, and supraclavicular nodes. Knowledge of lymphatic pathways is crucial in breast cancer management.

Musculature

The breast is mainly attached to the pectoralis major muscle but has also attachments to the serratus anterior muscle, the superior portion of the rectus abdominis, and the external oblique muscle.

The pectoralis major serves a very important role in reconstructive (and aesthetic) breast surgery by providing muscle coverage for breast implants.