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Breast

General

Anatomy

Author: Belinda Lategan, M.D.

Last author update: 1 December 2014

Last staff update: 14 May 2021

Copyright: 2002-2024, PathologyOutlines.com, Inc.

PubMed Search: Breast [title] anatomy [title]

Table of Contents

Cite this page: Lategan B. Anatomy. PathologyOutlines.com website. https://www.pathologyoutlines.com/topic/breastnormalanatomy.html. Accessed December 26th, 2024.

Definition / general

Specialized modified skin appendage and defining features of class Mammalia (Wikipedia: Mammal)
Demonstrates morphologic alteration throughout the reproductive life cycle (menarche, pregnancy, lactation and menopause, in addition to maternal hormonal effects in utero)
Reference: Mills: Histology for Pathologists, Fourth Edition, 2012

Thelarche

Rapid growth of breasts at onset of puberty, usually age 10 - 11 in females (Wikipedia: Thelarche, Arch Dis Child 1976;51:170)

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)
  - Accessory / supernumerary nipples but also breast parenchyma
  - Both malignant and benign breast disease may arise in these ectopic sites
- 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
- Surrounds large ducts and TDLUs
- Mature adipose tissue (majority of breast volume), fibroconnective tissue (fibroblasts, myofibroblasts), blood vessels and lymphatics, nerves
- Stromal fat varies throughout reproductive life
- Stromal myofibroblasts
  - May express ER and PgR
  - Usually also CD34
- Stromal lesions not specific to breast may arise in interlobular stroma, including angiolipoma, angiosarcoma, desmoid fibromatosis, lipoma, myofibroblastoma
- PASH (pseudoangiomatous stromal hyperplasia) is specific to breast
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