Breast Anatomy

Breast Anatomy

Breast Structure

Breast tissue extends from below the collarbone to the level of the sixth or seventh rib, and from the breastbone to the underarm (axilla). In the center of the breast is the nipple, or mammilla, and areola (circular area around the nipple). Montgomery's glands, located around the edge of the areola, release a fatty substance that protects the nipples during nursing.

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Each breast contains several milk glands with ducts that carry milk to the nipples. About 15 to 20 ducts come together near the areola to form reservoirs of milk to be drawn from the nipple.

Fibrous connective tissue (fascia) lies between the breast tissue and the skin, and separates breast tissue from the chest muscles. Cooper's ligaments run from the deep fascia throughout the breast tissue and attach to the dermis (second layer of skin).

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Lymphatic System

Most lymphatic vessels in the breast drain into a network of lymph nodes located around the breast's edges, in the underarm, and near the collarbone. These lymph nodes are embedded within fat, which complicates their removal. Axillary (underarm) lymph nodes are often the first site of breast cancer metastasis.

Blood Vessels

The internal mammary, axillary (underarm), and intercostal (between the ribs) arteries supply the breasts with blood; and the internal mammary, axillary, and intercostal veins carry blood away from the breasts. The axillary (underarm) vein has an irregular anatomy, which complicates surgery under the arm.

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The surface veins of the breast encircle the nipple and carry blood to the internal mammary, axillary, and intercostal (between the ribs) veins, and to the lungs. Breast cancer cells can travel to the lungs via surface veins and form metastatic tumors.

The intercostal veins join a complex network of vertebral veins in and around the spine, providing a path for breast cancer cells to spread to bone tissue.

Nerves

The skin of the upper breast is supplied with nerves (innervated) that branch from a network of nerves in the neck. Spinal nerves that pass between the ribs innervate the skin over the lower portion of the breast.

The long thoracic nerve innervates the muscle that helps move the upper arm. Surgeons must be careful not to sever or injure this nerve when operating near underarm lymph nodes that the nerve crosses.

Muscles

Several mastectomy procedures involve removing the fascia (fibrous tissue) overlying the chest muscles or removing the muscles themselves. Chest muscles located under the breasts include the following:

• Major and minor pectorals — attach to the collarbone; breastbone; bone in the upper arm (humerus); shoulder joint; third, fourth, and fifth ribs and the muscles between those ribs (intercostal muscles)
• Serratus magnus — attaches to the first eight or nine ribs and rib muscles, and connects with the shoulder blades in the back
• Rectus abdominus — extends from the pubic bone and attaches to the cartilage of the fifth, sixth, and seventh ribs

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