2.4: The Breast

 

Breast (167-9)

Base: from ribs 2-6; from sternal edge to near midaxillary lines;

Overlies: pec major, serratus anterior, small part of rectus and external oblique.

A modified sweat gland, breast is confined between superficial and deep layers of superficial fascia.

Axillary tail extends to axilla, lying in subcutaneous fat

-           rarely may penetrate deep fascia of axillary floor to lie adjacent to axillary lymph nodes

The retromammary bursa = space between post. aspect of breast, between deep layer of superficial fascia and pectoralis fascia; contains lymphatic channels.

Suspensory ligs of Cooper - fibrous septae from superficial to deep layer of superficial fascia; cause the protuberance of the young breast (atrophy with age), contraction in carcinoma & peau d’orange.

Male breast has no lobules or alveoli, small nipple over 4th ICS.

Blood

Mainly lateral thoracic – branches curl round or perforate pec major.

-           also Branches of internal thoracic (largest via 2nd & 3rd spaces)

-           small perforators penetrate from posterior intercostals.

-           and also pectoral branches of the thoracoacromial branch of axillary artery ® upper part.

Veins: intercostal veins 2-6 (& on to vertebral veins ® metastatic spread), deep veins parallel with lat thoracic & thoracoacromial arteries; internal thoracic vein.

Lymphatics

Anastomoses exist with abdominal wall (and hence ® posterior mediastinal nodes through diaphragm)

75% drains to axilla (mainly anterior axillary nodes, but some directly ® central or apical). 

-           few channels pass deep with intercostal perforators ® intercostal nodes.

-           some drainage to supraclavicular nodes possible

-           medial part can ® parasternal nodes.

Alternative pathways usually only occur when normal breast ducts blocked.

Nerves

Cutaneous via T4-T6; sympathetics to vessels & glands with these.  Lactation is hormonal.

Structure

~20 lactiferous ducts each drain a lobe, converge on the nipple surrounded by areola

-           each lactiferous duct has a dilated sinus at its terminus; smooth muscle cells in nipple ® erect

-           each duct connected at other end to tree of ducts and lobules, formed into lobes by c.t.

Sebaceous / areolar glands form small elevations (tubercles of Montgomery) ® enlarge in pregnancy.

The resting breast is mostly fibro/fatty tissue/  Size variations are due to fat content.

-           during pregnancy alveoli bud off and organ hypertrophies

 

Development

Modified sweat gland, begins as early as 4th week:

-           mammary ridge develops (ectoderm) from axilla to inguinal region.

-           ® supernumerary nipples or even glands proper.

Lobules form after puberty in the female.


Surgical Anatomy Notes on Breast

1. Retromammary space
Contains lymph and small vessels.
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2. Axilla

Begins at the edge of pec minor
- contains an average of 50 nodes in a radical mastectomy
- less are retrieved with current less-radical approaches.
- apex is Halstead's ligament (costoclavicular ligament)
--> here the axillary vein passes to thorax --> subclavian vein.

3. Axillary Nodal Levels
I : lat to pec minor
- external mammary, scapular, axillary vein, central axillary groups.
II : beneath pec minor
III : medial to pec minor
- include subclavicular nodes
Rotter's nodes : (intra-pectoral group)
- b/n the pecs, not removed in typical surgical procedures.
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4. Flow of Lymph
Skin --> subareolar plexus --> intralobular lymphatics of breast parenchyma.
75% --> axilla
25% --> pectoral nodes / internal mammary nodes.
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5. Nerves
Long thoracic: Runs down on medial axillary wall, close to chest wall --> serratus anterior.
Thoracodorsal: from posterior cord --> lat dorsi.
Pectoral nerve bundle: around lat border pec minor.
Intercostobrachials: sensate to arm.
- denervation leads to chronic / uncomfortable pain in a minority.
- leave the superior-most if possible; sensation to posterior upper arm.

6. Microscopic Anatomy
Typically it is said that mammorgraphy in women <30 is not useful due to dense glandular tissue
- this is not always true.
- fat provides the definition in older women.
Lobules drain into ductules; surrounded by myoepothelial cells.
The basement membrane defines DCIS vs invasive breast cancer.
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