Structure and fascial relations
The mammary gland (glandula mammaria) is a tubuloalveolar structure divided into 15–20 lobes. An excretory duct with a diameter of 2–3 mm extends from each lobe. Approaching the nipple, these ducts dilate to form lactiferous sinuses (ampullae), and then narrow again to open at the apex of the nipple through 8–15 small orifices.
The organ is enclosed in a capsule formed by the splitting of the superficial fascia. Meanwhile, the nipple and areola remain free of fascial covering and adipose tissue. Connective tissue partitions (septa) extend from the capsule deep into the gland, dividing the lobes and serving as pathways for blood vessels and nerves.
Between the fascial capsule of the mammary gland and the deep pectoral fascia (fascia pectoralis) lies the retromammary space. It is filled with loose adipose tissue, which ensures the mobility of the organ relative to the chest wall. Clinically, it is important that the connective tissue septa can limit the spread of purulent processes, leading to the formation of isolated foci of infection.
Blood supply
The vascular network of the mammary gland is formed by branches of several major arteries:
- Internal thoracic artery (a. thoracica interna).
- Lateral thoracic artery (a. thoracica lateralis).
- Intercostal arteries (aa. intercostales).
Venous drainage is carried out by veins that run parallel to the corresponding arteries.
Lymphatic system and drainage pathways
The lymphatic drainage system of the mammary gland is of critical importance due to the pathways of malignant tumor metastasis. Lymphatic vessels are divided into two networks: cutaneous and parenchymal.
Cutaneous lymphatic vessels are located in the premammary adipose tissue and skin, forming a dense network, especially in the outer quadrants. Around the nipple, they form a superficial areolar plexus.
Parenchymal lymphatic vessels originate inside the lobes. From the areola, lymph drains into the deep areolar plexus. It is important to note the presence of multiple anastomoses between the deep and superficial vessels, which explains the "peau d'orange" phenomenon in cancer.
The main drainage pathway (about 80% of the lymph) is directed to the axillary lymph nodes (nodi lymphatici axillares). Efferent vessels run along the outer edge of the fascial sheath of the pectoralis major muscle to the axillary group, which consists of 20–40 nodes. There are 5 groups of axillary nodes: pectoral, subscapular, lateral, central, and apical. Part of the lymph may be filtered in Zorgius nodes (on the 2nd–3rd digitations of the serratus anterior muscle).
Collateral lymphatic circulation
If the main drainage pathway is blocked (e.g., by metastases), lymph is redirected through additional collateral pathways:
- Subclavian pathway — to the nodi lymphatici infraclaviculares.
- Transpectoral pathway — through the thickness of the pectoralis major muscle.
- Interpectoral pathway — bypassing the pectoralis major muscle, into the intermuscular and subclavian nodes.
- Parasternal pathway — along the course of the internal thoracic artery, through the intercostal spaces (most commonly the 2nd and 3rd).
- Subcutaneous anastomoses — connections with the supraclavicular region, preperitoneal tissue, and the contralateral mammary gland.
Briefly: answers to topical questions
Which nerves provide innervation to the mammary gland?
The innervation of the mammary gland is provided by branches of the thoracic and cervical spinal nerves, as well as sympathetic fibers.
- Cutaneous branches of thoracic nerves (rr. cutanei nn. thoracici) — anterior and lateral branches of nerves II–VI provide sensory innervation to the skin and glandular tissue (anterior branches innervate the medial parts, lateral branches innervate the lateral parts).
- Supraclavicular nerves (nn. supraclaviculares) — branches of the cervical plexus that innervate the skin of the upper parts of the gland.
- Sympathetic fibers — run within the cutaneous nerves, innervating vascular smooth muscle, arrector pili muscles, and providing secretory innervation to glandular cells.
The nipple and areola receive a particularly rich innervation.
What are the suspensory ligaments of the mammary gland called and where do they attach (Cooper's ligaments)?
The suspensory ligaments of the mammary gland are called the suspensory ligaments of the breast, or Cooper's ligaments.
- Suspensory ligament of the breast (lig. suspensorium mammae) — thickened bundles of the superficial pectoral fascia.
These ligaments extend from the upper edge of the connective tissue capsule of the gland and attach to the clavicle. They penetrate the glandular tissue, connecting the capsule to the skin, and also connect the two fascial layers to each other. Their main function is to provide structural support and maintain the shape of the organ.
Into which specific veins does venous drainage from the mammary gland occur?
Venous drainage from the mammary gland is carried out by veins that accompany the corresponding arteries and form a dense network with numerous anastomoses.
Drainage occurs into the following deep veins:
- Axillary vein (v. axillaris).
- Subclavian vein (v. subclavia).
- Intercostal veins (vv. intercostales).
- Internal thoracic vein (v. thoracica interna).
When outflow through the inferior vena cava is impaired, blood can be shunted via superficial veins of the chest and abdominal walls. There is also a connection between the veins of the gland and the vertebral venous plexus.
Into which quadrants is the mammary gland topographically divided?
Topographically, the mammary gland is divided into four main quadrants.
The following divisions are distinguished:
- Upper-inner quadrant — medial upper part.
- Lower-inner quadrant — medial lower part.
- Upper-outer quadrant — lateral upper part.
- Lower-outer quadrant — lateral lower part.
In addition to these quadrants, topographic classifications of localizations also distinguish the central part of the mammary gland, the nipple-areola complex, and the posterior axillary tail.
Class and exam questions
Why are purulent abscesses in mammary gland inflammation often isolated (lobular)?
This is due to the presence of dense connective tissue septa that extend from the fascial capsule deep into the gland. They limit the spread of pus within one or more lobes.
Where does the main part of the lymph from the mammary gland drain?
About 4/5 of all lymph (approximately 80%) drains via the axillary pathway into the axillary lymph nodes (nodi lymphatici axillares).
What ensures the mobility of the mammary gland on the chest wall?
The mobility of the organ is ensured by a layer of loose adipose tissue in the retromammary space — between the gland capsule and the deep pectoral fascia.
What else to study on this topic
- Classification of axillary lymph nodes (5 groups)
- Fasciae of the chest wall: superficial and deep layers
- Connections of parasternal lymph nodes with cervical nodes
- Anatomy of the thoracic and subclavian lymphatic trunks
- Cellular spaces beneath the pectoralis major and minor muscles
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