Breast Anatomy

Breast Anatomy

The breast is a composition of alveoli, lobules and lobes. It receives blood and sensory supply from a diverse number of arteries and nerves.


Overview of Breast Anatomy

5 Key Points


  1. Surface Landmarks
    2nd-6th ribs, sternum to anterior axillary fold.
  2. Functional Units of the Breast
    Alveoli create lobules which create lobes which create breasts
  3. Blood Supply
    Internal mammary perforators, lateral thoracic artery & intercostals.
  4. Sensory Innervation
    Lateral Cutaneous, intercostals, supraclavicular branches
  5. Lymphatic
    The breast primarily drains to the 3 levels of the axilla


Surface Landmarks of the Breast

The anatomy of the breast is often described as "vertical" and "horizontal". Please note some descriptions do vary.

  • Vertical: between ribs 2-6
  • Horizontal: between the lateral sternum and the anterior axillary fold.

Anatomical Landmarks of the Breast

The "ideal" breast has often been described based on 3 measurements

  1. Sternal notch to nipple distance = ~21cm
  2. Nipple to IMF = ~7cm
  3. Areolar Diameter = ~ 3.5cm
  4. From midline: ~10cm

Anatomical Breast Measurements


Anatomy of the Breast Parenchyma

Functional Units

  • A breast has ~15-25 lobes separated by fibrous septa
  • A lobe has a large number of lobules with large ducts
  • A lobule is the functional unit of the breast. It has a large number of alveoli with small interlobular ducts that combine together to form the lobe's large ducts.

Support Structures

The breast is supported by a connection of fascia, septa and the inframammary fold.

Breast Fascia

  • Superficial fascia is near the dermis and can be hard to see
  • A deep layer of the superficial fascia between the superficial and deep layer.
  • A loose areolar plane separates this deep superifical fascia from the deep fascia.  
  • Deep Layer overlying the muscle

Fibrous Septa

  • Adjacent lobes are separated by the suspensory ligaments of Cooper, which penetrates the superficial fascia to the dermis. Laxity of these ligaments results in ptosis.
  • The septum of Würinger is a horizontal septum that arises from the pectoral fascia at the 5th rib to bring the neurovascular supply to the nipple. It contains the thoracoacromial, lateral thoracic, 4-6th intercostal arteries and 4th intercostal nerve to nipple.

 

Inframammary Fold

  • The lower border of the breast
  • Combination of the deep and superficial fascia with the dermis
  • Forms a distinct arrangement of cross-linking fibres that provides support.  


Blood Supply to the Breast


Key Point

The main blood supply to the breast is the internal mammary perforators, lateral thoracic artery, and intercostal perforators. There is also subdermal, pre-glandular and retroglandular plexuses.

The blood supply of the breast has important clinical implications in relation to the reconstruction, reduction and augmentation of the breast.

The anatomy of the breast showing the internal mammary artery, thoracoacromial arteryy and lateral thorax artery being the blood supply to the breast.
Blood supply to the breast

Each anatomical layer of the breast has a specific blood supply.

  • Skin: subdermal plexus (also a pre-glandular & retroglandular plexus)
  • Parenchyma: internal mammary artery, lateral thoracic artery, thoracodorsal artery, intercostal perforators (usually 3rd-5th), thoracoacromial artery
  • NAC: a combination of subdermal and parenchyma supply. It is primarily supplied by the lateral thoracic and internal mammary (Nakajima et al) but this is unpredictable (van Deventer et al).

Specific Vessels

The vascularisation of breasts is characterised by significant individual diversity and collateralisation. The internal mammary artery is the most reliable artery. Here is a more detailed anatomical exploration of the main vessels.

Internal Mammary Artery Perforators:

  • Origin: subclavian artery at anterior scalene
  • Course: deep to phrenic nerve, ~1-2cm from sternum, above parietal pleura.
  • Branches: at each intercostal space
  • Termination: musculophrenic & superior epigastric (usually 6th ICS).

Thoracoacromial Artery (Pectoral Branches):

  • Origin: middle section axillary artery
  • Branches: connections with internal mammary artery, lateral thoracic artery and intercostal arteries.

Lateral thoracic artery:

  • Origin: middle section of the axillary artery.
  • Used in a lateral pedicle breast reduction.

💡
Clinical Significance in Breast Reductions: Design is based on perforators from different intercostal spaces: superior pedicle uses perforators from 1st and 2nd intercostal space, medial pedicle from 2-3rd intercostal space, inferior pedicle from 4th intercostal space, 


Nerve Supply to the Breast


Key Point

Skin, the parenchyma and the nipple all have a nerve supply. Their innervation comes primarily from 3 nerves: intercostal nerves (2nd-6th), supraclavicular nerves, and lateral cutaneous nerves.

Skin, the parenchyma and the nipple all have a nerve supply. Their innervation comes primarily from 3 nerves:

  • Intercostal nerves 2nd-6th (mainly 3rd and 4th)
  • Lateral cutaneous nerves 3rd-6th (4th supplies the nipple)
  • Supraclavicular branches of cervical plexus

😎
Fun Fact: The anterior cutaneous branches from intercostal nerves travel superficially towards the medial border of the areola. The lateral innervation travels deep within the pectoral fascia (Shlenz et al)

The breast anatomy recieves sensory nerve innervation from the intercostal nerves, lateral cutaenous nerves and the supraclavicular branches of the cervical plexus.
Nerve Supply Breast Anatomy

Other branches of the brachial plexus provide motor innervation to nearby muscles. For example, medial and lateral thoracic nerves to the pectoral muscles; long thoracic nerve to serratus anterior, and thoracodorsal nerve to latissimus dorsi.

Nipple-Areolar Complex Innervation

The nipple-areolar complex can have variations in its sensory innervation. It is primarily innervated by the 4th lateral cutaneous nerve and 2nd-6th intercostal nerves.  

The nipple receives sensory innervation to from the 4th lateral cutaneous nerve and the intercostal nerves.
Nipple Sensation Anatomy

4th lateral cutaneous nerve

  • Main sensory supply to the nipple.
  • Travels medially in the deep fascia to the mid-clavicular line and then directs itself towards the deep surface of the nipple.

Intercostal nerves from 2nd to 6th

  • Anteromedial branches of intercostal nerves 2nd–6th
  • Providing innervation to the mammary gland and overlying skin
  • Travel with the ligaments of Cooper and form an extensive network of connections innervating the areola skin.


Lymphatic Drainage of the Breast


Key Point

There is a superficial and deep lymphatic system in the breast. The majority of the breast drains into the 3 levels of axillary nodes

Superficial System

  • Starts at the periareolar lymphatic plexus
  • Follows the veins!

Deep System

  • Individual lymphatic channels draining each duct
  • Travels through the pectoralis fascia and muscle to the central axillary nodes, then apical axillary nodes, then supraclavicular nodes.

3 Levels of Axillary Nodes

  1. Lateral to the border of pectoralis minor
  2. Posterior to pectoralis minor, inferior to the axillary vein
  3. Medial to the medial border of pectoralis minor


Embryology of Breast Anatomy


Key Point

At the 4th week of gestation, the breast arises from the ectoderm. Over several months, mammary ridges, buds and areolae form.

The breast is derived from the ectoderm at the 4th week of gestation. After this, a series of steps follow this approximate timeline.

  • Week 6: mammary ridge forms
  • Week 8: breast grows into a primary bud which forms a secondary bud
  • Week 20: areolae forms

Congenital anomalies can occur anywhere along the milk ridge. It most commonly occurs on the left chest wall below the inframammary fold. For example:

  • Polymastia: supernumerary breasts
  • Polythelia: supernumerary nipples.


Flashcards

Evidence-based flashcards are designed for active recall & spaced repetition using the Feynman Technique.

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