Breast nonmalignant
Normal anatomy of breast

Topic Completed: 1 December 2014

Minor changes: 8 August 2019

Copyright: 2002-2019,, Inc.

PubMed Search: Breast [title] anatomy [title]

Belinda Lategan, M.D.
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Page views in 2020 to date: 924
Cite this page: Lategan B. Normal anatomy of breast. website. Accessed May 26th, 2020.
Definition / general
Gross anatomy
  • Breast Proper:
    • Suspended from anterior chest by ligaments of Cooper (Wikipedia: Cooper's Ligaments) attached to skin and fascia of major and minor pectoral muscles
    • Covered by skin and subcutaneous tissue anteriorly
    • Spans 2nd rib to 6th rib sacroiliac (SI), midaxillary line to medial border at edge of sternum midline, in addition to axillary tail of Spence (Wikipedia: Tail of Spence), which extends into axilla
    • Posterior / deep margin is fascia of pectoralis major muscle
    • Breast tissue may extend beyond these limits into adjacent subcutaneous tissue
      • In some patients, mastectomy removes most but not all breast epithelial elements, raising possibility of breast disease at these sites
    • Accessory breast tissue may be present along the milk line (axilla → anterior chest wall → pubis → upper thighs)
    • Glandular tissue is most abundant in upper outer quadrant of breast; as a result, half of all breast cancers occur here

  • Nipple areolar complex:
    • Located slightly medial and inferior on breast, level of 4th intercostal on nonpendulous breast
    • Cone shaped protuberance, 10 - 12 mm in average height, mean nipple diameter 11 - 13 mm, mean areolar diameter 4 cm
    • Montgomery tubercles - areolar protuberances (10 - 20), more prominent during pregnancy; composed of ducts and sebaceous apparatus

  • Lymphatic drainage:
    • Four major routes => cutaneous, axillary, internal thoracic, posterior intercostal
      • Cutaneous
        • Superficial plexus within dermis
        • Most if not all lymphatics connect to areolar lymphatic plexus (plexus of Sappey)
          • Significant for sentinel lymph node procedure, injection in area of nipple will likely identify sentinel nodes, as would injection in region of tumor
        • Cutaneous lymphatic anastomoses account for rare cases of metastases to contralateral breast in absence of distant metastases
        • Cutaneous lymphatics of inferior breast may drain to epigastric plexus → lymphatic channels of liver and intra-abdominal lymph nodes
      • Axilla
        • Majority (75%) of drainage
        • Initially through 1 - 2 sentinel nodes, first to be involved in 90% of patients with lymph node metastases
        • Three levels
          • Level I - low axilla
          • Level II - mid axilla
            • Includes Rotter nodes (interpectoral)
          • Level III
            • Apical or infraclavicular nodes
            • Metastases here portend a worse prognosis
        • Intramammary nodes
          • May be found anywhere in breast parenchyma
          • Considered as axillary lymph nodes for staging purposes
          • Only very rarely the sentinel node
      • Internal thoracic
        • < 10% of lymphatic flow from breast, may be more prominent if lymphatic drainage is obstructed / disrupted due to disease in axilla or previous treatment
        • Terminates in internal mammary nodes
          • Involvement does not alter treatment in most cases; as a result, rarely sampled when systemic therapy is planned
      • Posterior intercostal
        • Least important route of drainage
      • Supraclavicular nodes
        • Are deemed regional nodes for staging purposes
      • Metastases to all other lymph nodes, including cervical and contralateral axillary nodes, are classified as distant metastases
    • References (lymphatics): Ann Surg Oncol 2008;15:863, Hum Pathol 2001;32:178
Breast proper
  • Epithelial and stromal components; specific lesions arise in each component or may have a dual morphology
  • Epithelium
    • Large ducts
      • Three dimensional arborizing fan shaped system with apex towards the nipple
      • Large ducts → segmental ducts → subsegmental ducts → lobules
      • Lactiferous sinuses are likely artifactual (J Anat 2005;206:525); this study changed commonly held views of anatomy (Wikipedia: Breast)
      • Duct systems are only rarely confined to a single quadrant and may overlap
      • Anastomoses may exist between large duct regions
      • Involvement of multiple duct systems by DCIS (a clonal proliferation) may be explained as follows
        • DICS arising in single large duct system may be present in overlapping quadrants
        • DCIS arising in single large duct system may involve adjacent systems through anastomotic connections
        • Separate foci of DCIS may arise in different duct systems

    • Terminal duct lobular units (TDLU)
      • "Functional unit" of breast (lacation)
      • Postulated as origin of most epithelial neoplasms (breast or myoepithelial)

    • Two types of epithelia: luminal cells and myoeptihelium
      Luminal cells ("epithelial cells"):
      • Innermost layer of bilayered ductolobular system
      • Usually express luminal keratins LMWCK, CK7, CK8, CK18, CK19
      • May express "basal keratins" HMWCK, CK5 / 6, CK14, CK17 (J Histochem Cytochem 1986;34:869)
      • Most express ER-α and or PgR in a heterogeneous pattern at any given time
      • Also expresses E-cadherin, mammaglobin and GCDFP-15
      • Outer layer resting on basement membrane
      • Contractile meshwork partially covering basement membrane, i.e. incomplete on cross section
      • Usually expresses "basal" keratins HMWCK, CK5 / 6, CK14, CK17
      • Also smooth muscle actin, calponin, smooth muscle myosin heavy chain, in addition to p63, S100, CD10, P-cadherin and mapsin
      • Does NOT express ER or PgR
      • Loss of myoepithelium usually considered hallmark of invasive process, with the exception of microglandular adenosis, encapsulated papillary carcinoma and solid papillary carcinoma
  • Interlobular
  • Intralobular
    • Surrounds acini in TDLUs
    • Compared to interlobular stroma, looser in appearance or even myxoid
    • Often small numbers of inflammatory cells
    • Lesions arising here are biphasic involving epithelial and stromal components, including fibroadenoma, phyllodes tumor
Nipple areolar complex
  • Ramifying duct system terminating in 15 - 20 major ducts, which open onto areola
  • Covered in pigmented skin
  • Toker cells
    • Cytologically benign cells with clear / pale cytoplasm
    • Immunoprofile similar to luminal epithelial cells
    • Are most abundant adjacent to duct orifices
    • Must distinguish from mammary Paget disease (DCIS involving nipple)
  • Keratin producing squamous cells extend into proximal 1 - 2 mm of large ducts
    • Squamous metaplasia of lactiferous ducts (SMOLD) is extension of squamous epithelium beyond proximal 1 - 2 mm; associated with smoking
    • Keratin entrapment may cause epidermal inclusions and abscess formation with marked inflammatory response
  • Basement membrane of ducts and duct lobular system is contiguous with that of skin
    • Tumor cells may extend onto skin from DCIS without crossing basement membrane (Paget disease)
  • External shape / size of the breast is not predictive of internal anatomy or its lactation potential
  • References (nipple): Breast Cancer Res Treat 2007;106:171, Eur Surg Res 2006;38:545, Cancer 2004;101:1947, Aesthetic Plast Surg 2009;33:295, Am J Surg 2007;194:433, Arch Pathol Lab Med 1982;106:60
Diagrams / tables

Images hosted on other servers:

Milk lines

Breast anatomy

Netter drawings (vasculature and lymphatics)

Regional lymph nodes - schematic

Radical mastectomy

Supraclavicular fossa

Radiograph of lymphatics

Tracing of lymphatics

Gross images

Images hosted on other servers:

Nipple orifices, some cannulated with guide wires

Microscopic (histologic) images

Images hosted on other servers:

Perforating lymphatic

Instillation of
water insoluble and
differently colored
dyes in orifices

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