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Anatomy: Breast & Axilla



  • The Breast Parenchyma: The breast is the specialized human tissue located on the chest between the pectoralis muscle, i.e. the superficial fascia and the subcutaneous tissue, i.e. right beneath the skin.
  • The Retromammary Space: The breast rests on a rich vascular and lymphatic network within the pectoralis fascia. This represents the retromammary space which is positioned between the deep pectoralis fascia and the superficial pectoralis fascia.
  • The Nipple-Areolar Complex: The Nipple-Areolar complex is the center of the breast. It is the end portion of the largest lactiferous duct.

The Microscopic Anatomy:

The microscopic anatomy is best visualized by analyzing the lactiferous complex. The breast is a milk producing organ and its microscopic anatomy is based on this function.

  • The Lobules: The lobules, also called the lobular units, are responsible for the production of milk.
  • The Ductal System: The milk is collected by distal lactiferous ducts or acini which merge into minor and then major lactiferous ducts. In most instances, these empty into the major duct or sinus which ends in the nipple. The ductal system has a ductal epithelium surrounded by a myo-epithelium. This ductal epithelium is responsible for the propulsion of milk through the ductal system as it has contractile capabilities. This ductal system is sealed and surrounded by an uninterrupted basement membrane.
  • The Stroma: This interlobular tissue, also referred to as connective tissue, contains capillaries and other specialized cells.
  • Cooper's Ligaments: These are dense strands of fascia found throughout the entire breast which end on the skin itself.
  • The Basement Membrane of the Ductal System: It is essential to visualize the basement membrane in the microscopic analysis of a malignant breast tumor. This will assist in the assessment as to whether a tumor is "in situ" (has not grown through the basement membrane) or "invasive" (has grown through the basement membrane).

The microscopic anatomy of the breast demonstrates why most breast cancers are ductal or lobular in origin.

Age Dependant Anatomical Changes of the Breast:

With age, the breast tissue will change. In a young woman, the breast tissue is dense and parenchyma rich. As the woman ages, the fat content of the breast tissue will increase. This explains the overall aspect of the breast, as it will begin to droop. The increased fat content of the breast in older patients accounts for the higher quality of their mammograms (increased fat content equals increased image quality).

Pathology Dependant Anatomical Changes:

  • Peau d'Orange: From the French term, orange skin, this identifies a malignant obstruction of the superficial lymphatic channels.
  • Skin Retraction: Skin or Cooper's ligament pulled in by a malignant lesion.
  • Nipple Inversion: Inward retraction of the nipple by a malignant ductal lesion.
  • Breast Abscess: Fluctuant, purulent collection within the breast parenchyma
  • Mondor's Disease: Thrombophlebitis of a superficial vein, usually by a nonmalignant lesion
  • Inflammatory Breast Carcinoma: Malignant invasion of the superficial skin lymphatic channels seen in advanced breast cancer.
  • Gynecomastia: This is an activation and hypertrophy of the breast tissue in men. It can occur frequently in young men (pubertal hypertrophy) and in older men. It can also be caused by numerous medications and hormones.

Changes Secondary to Breast Augmentation Surgery

All surgeons should be familiar with the pathology generated by the placement of breast implants during augmentation mammoplasty. Earlier augmentation mammoplasty techniques placed the implants behind the skin or breast parenchyma. Newer techniques are placing it behind the pectoralis major muscle.


The anatomy of the axilla or the axillary basin is important to all oncologic surgeons as it represents the principal lymphatic drainage region of the breast. Lymphatic metastasis from a malignant breast lesion will most often occur in this region. For inner quadrant lesions, it can occur in the internal mammary chain. Lymphatic metastasis can also be present in the supraclavicular nodes.

The surgeon should have an extensive knowledge of the anatomy of the axilla and its contents in order to perform a safe, precise and appropriate axillary dissection.

The lymph node bearing area has been divided into three axillary regions:

  • Level I: Lymph nodes lateral and inferior to the pectoralis minor muscle
  • Level II: Lymph nodes under the pectoralis minor muscle
  • Level III: Lymph nodes under and deep to the pectoralis minor muscle

Most axillary dissections include lymph nodes from Level I and II. In order to remove these lymph nodes with minimal morbidity, several structures will have to be identified unequivocally. They are as follow:

  1. The lateral border of the Pectoralis Minor and Major muscle
  2. The Latissimus Dorsi Muscle
  3. The Axillary Vein
  4. The Long Thoracic Nerve which innervates the Serratus Anterior Muscle
  5. The Thoraco-Dorsal Nerve which innervates the Latissimus Dorsi Muscle
  6. The Intercostal Brachial Nerve which is a sensory nerve for the inferior aspect of the arm and the posterior aspect of the axilla
  7. The Lateral Pectoral Nerve which innervates portions of the pectoralis muscle






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