Breast
General
Anatomy


Topic Completed: 1 December 2014

Minor changes: 24 June 2020

Copyright: 2002-2020, PathologyOutlines.com, Inc.

PubMed Search: Breast [title] anatomy [title]

Belinda Lategan, M.D.
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Cite this page: Lategan B. Anatomy. PathologyOutlines.com website. https://www.pathologyoutlines.com/topic/breastnormalanatomy.html. Accessed August 8th, 2020.
Definition / general
Thelarche
  • Signifies entry into Tanner stage II of development
  • Growth is due to fat deposition, periductal connective tissue expansion and the elongation, branching and thickening of ductal system with development of terminal duct lobular units; growth may be sporadic
  • Prior to puberty, breasts of both sexes have ducts with variable branching lined by cuboidal epithelium, no lobules and no necrosis; at puberty in females, lobules develop
  • Influenced by estrogens, growth hormone and prolactin but not progesterone
  • Premature thelarche:
    • Onset prior to age 8 in girls with normal BMI in general population
    • Breast tissue resembles gynecomastia with epithelial hyperplasia in ductal system in a solid or micropapillary configuration (BMC Pediatr 2008;8:27)
    • Excision of initial subareolar disc will lead to amastia after puberty
    • Associated with increased BMI and non-Hispanic black and Mexican American ethnicity (Pediatrics 2009;123:84)
    • May be isolated or part of precocious (central) puberty if other signs of puberty are present
    • No tests currently predict risk of progression to precocious puberty in premature thelarche (J Pediatr 2010;156:466)
    • Earlier onset of thelarche and longer interval between thelarche and menarche may be associated with increased breast cancer risk (Breast Cancer Res 2014;16:R18)

    Tanner staging:

    Stage I: preadolescent

    Stage II: breast budding (thelarche)

    Stage III: enlargement of areolar diameter

    Stage IV: areola / papilla
    form secondary mound
    with separation of contours

    Stage V: mature female breasts

  • 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
        Myoepithelium:
        • 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
    Stroma
    • 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

    Premature thelarche (9 year old girl)

    Proliferation of ducts
    without lobules; intraductal
    epithelial hyperplasia with
    uniform cells and prominent nuclei



    Images hosted on other servers:

    Perforating lymphatic

    Instillation of
    water insoluble and
    differently colored
    dyes in orifices

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