Breast: Anatomy & Physiology

Anatomy

Structure

  • External Features:
    • Nipple – Raised Tissue Through Which Milk is Secreted
    • Areola – Pigmented Region Around the Nipple
      • Montgomery’s Glands – Modified Sweat Glands in the Areola
        • Oily Secretions Protect Nipple During Breastfeeding
  • Internal Features:
    • Cooper’s Ligaments (Suspensory Ligaments of Cooper) – Fibrous Ligaments Radiate from the Superficial Fascia to the Skin to Maintain Structural Integrity
    • Tail of Spence (Axillary Process) – Extension of Breast Tissue into the Axilla
  • Mammary Glands:
    • Lobules – Groups of Alveoli Which Produce Milk
    • Lactiferous (Milk/Galactophorous) Ducts – Drain Milk from the Lobule to the Nipple
      • Each Breast Has 15-20 Ducts
      • Diameter: 2.0-4.5 mm
  • The Upper Outer Quadrant (UOQ) Contains the Majority of the Epithelial Tissue
    • Explains Why the UOQ is the Most Common Site of Both Benign & Malignant Breast Disease – Most are Derived from Epithelial Tissue

Described Quadrants

  • Upper Outer Quadrant (UOQ)
  • Upper Inner Quadrant (UIQ)
  • Lower Outer Quadrant (LOQ)
  • Lower Inner Quadrant (LIQ)

Breast Anatomy 1

Cooper’s Ligaments 2

Breast Cross-Section 3

Density

  • Fibrous & Glandular Tissue Increase Density
  • Fatty Tissue Decreases Density
  • Breasts with Increased Density Increase the Difficulty of Identifying Pathologic Lesions on Mammogram
  • BI-RADS Classification:
    • Class A: Almost Entirely Fatty (10%)
    • Class B: Scattered Fibroglandular Density (40%)
    • Class C: Heterogeneously Dense (40%)
    • Class D: Extremely Dense (10%)
    • *Class C & D are Considered Dense Breasts

Breast Density

Vascular Supply

  • Medial Breast
    • Internal Mammary/Thoracic Artery (IMA) (From Subclavian)
  • Lateral Breast
    • Lateral Thoracic Artery (From Axillary)
    • Thoraco-Acromial Artery (From Axillary)
    • Intercostal Arteries
  • Batson’s Plexus Mn
    • Valveless Veins of Paravertebral Space
    • Connected to Thorax (Breast) and Deep Pelvic Veins (Rectum/Prostate)
    • Reason for Mets to Spine (Often First)

Breast Blood Supply: Internal Mammary Artery (I), Thoracoacromial Artery (T), Lateral Thoracic Artery (L) 4

Nerves

  • Long Thoracic Nerve
    • Location: Medial Border of Axilla Along Chest Wall
    • Innervate: Serratus Anterior
    • Deficit: Winged Scapula
  • Thoracodorsal Nerve
    • Location: Mid-Axilla Just Below Axillary Vein
    • Innervate: Latissimus Dorsi
    • Deficit: Weak Arm Adduction (Pull Ups) & Internal Rotation
  • Medial Pectoral Nerve Mn
    • Innervate: Pectoralis Major & Minor
  • Lateral Pectoral Nerve
    • Innervate: Pectoralis Major
    • Deficit: Muscle Atrophy & Limited Shoulder Motion
  • Intercostobrachial Nerve
    • The Lateral Cutaneous Branch of the Second Intercostal Nerve
    • Innervate: Sensation to Medial Arm/Axilla
    • Deficit: Loss of Sensation to Medial Arm
    • Most Common Injured Nerve in MRM/ALND

Long Thoracic Nerve 5

Winged Scapula 6

Axillary Nerves 7

Intercostal Brachial Nerve 8

Lymphatics

  • Initial Lymph Nodes
    • Pectoral: Lateral
    • Interpectoral Nodes: Superior
    • Parasternal Nodes: Medial/Superior
    • Subphrenic Nodes: Medial/Inferior (Liver/Abd Wall Mets)
    • Anastomoses: Contralateral Breast
  • Sappey Plexus Mn
    • Subareolar Lymphatic Plexus
    • Where All Lymphatics of the Breast Converge
    • Place for Injection During SLNB
  • Drainage
    • Axillary Lymph Nodes (97%)
      • Level I: Lateral to Pectoralis Minor
      • Level II: Deep to Pectoralis Minor
        • Rotter’s Nodes: Between Pectoralis Minor & Major
      • Level III: Medial to Pectoralis Minor
    • Internal Mammary Nodes (2%)
  • Final Drainage
    • Right Lymphatic Duct: Upper Right Side
    • Thoracic Duct: Everything Else
    • Supraclavicular Lymph Nodes
      • Final Nodes at Vascular Emptying
      • Left (Virchow’s Nodes)
        • Sign of Intraabdominal Malignancy

Sappey Plexus 9

Axillary Lymph Nodes Levels 10

Body Lymphatic Drainage 11

Physiology

Hormones

  • Estrogen Mn
    • Duct Development
    • Glandular Growth
    • Breast Swelling
  • Progesterone
    • Lobule Development
    • Glandular Maturation

Mnemonics

Batson vs Sappey Plexus

  • B-B: Batson – Back
  • S-S: Sappey – Subareolar

Pectoral Nerve Innervation

  • M-M: Medial Gets Both M’s (Major & Minor)
  • L-L: Lateral Only Gets Large (Major)

Estrogen vs Progesterone Effects on Breast

  • E-E: Double-E Grows in Size
  • Pro-Pro: Professionals are Mature

References

  1. National Cancer Institute. Wikimedia Commons. (License: Public Domain)
  2. Grant JCB. Wikimedia Commons. (License: Public Domain)
  3. Meyerson A. Wikimedia Commons. (License: CC BY-SA-3.0)
  4. Asamura S, Kurita T, Motoki K, Yasuoka R, Hashimoto T, Isogai N. Efficacy and feasibility of the submuscular implantation technique for an implantable cardiac electrical device. Eplasty. 2014 Oct 30;14:e40. (License: CC BY-2.0)
  5. Martin RM, Fish DE. Scapular winging: anatomical review, diagnosis, and treatments. Curr Rev Musculoskelet Med. 2008 Mar;1(1):1-11. (License: CC BY-NC-2.0)
  6. Wikimedia Commons. (License: CC BY-SA-3.0)
  7. Chandler MH, Dimatteo L, Hasenboehler EA, Temple M. Intraoperative brachial plexus injury during emergence following movement with arms restrained: a preventable complication? Patient Saf Surg. 2007 Dec 19;1:8. (License: CC BY-2.0)
  8. Du J, Liang Q, Qi X, Ming J, Liu J, Zhong L, Fan L, Jiang J. Endoscopic nipple sparing mastectomy with immediate implant-based reconstruction versus breast conserving surgery: a long-term study. Sci Rep. 2017 Mar 31;7:45636. (License: CC BY-4.0)
  9. Suami H, Pan WR, Mann GB, Taylor GI. The lymphatic anatomy of the breast and its implications for sentinel lymph node biopsy: a human cadaver study. Ann Surg Oncol. 2008 Mar;15(3):863-71. (License: CC BY-NC-2.0)
  10. Lu Q, Hua J, Kassir MM, Delproposto Z, Dai Y, Sun J, Haacke M, Hu J. Imaging lymphatic system in breast cancer patients with magnetic resonance lymphangiography. PLoS One. 2013 Jul 5;8(7):e69701. (License: CC Not Specified)
  11. Cancer Research UK. Wikimedia Commons. (License: CC BY-SA-4.0)