PECTORAL REGION

 

UPPER LIMB:

          The free upper limb is connected to the thorax by the shoulder girdle – clavicle and scapula.

CHAPTER -1

PECTORAL REGION

Muscles of the pectoral region are

Pectoralis major

Pectoralis minor

Subclavius

Pectoralis major

Origin:         a) from the medial half of the anterior surface of the clavicle

                     b) from the lateral part of anterior surface of sternum

                     c)2^nd to 6^th coastal cartilages

                     d) from the external oblique aponeurosis.

Insertion: Lateral lip of inter tubercular sulcus of humerus

Nerve supply: Medial and lateral pectoral nerves

Actions: Flexion, adduction and medial rotation of shoulder joint

For osteology of clavicle:

https://youtu.be/X4F7KfUeVS4

Pectoralis minor:

Origin:

From the third to fifth ribs and from the intervening fascia covering external intercostals muscle.

Insertion:

Medial border and upper surface of the coracoid process.

Nerve supply: Medial and lateral pectoral nerves

Actions: Protraction of scapula and depression of shoulder joint

FOR MUSCLES OF UPPER LIMB-WATCH THIS VIDEO:

https://youtu.be/dQ5RTbv1Bqg

Subclavius

Origin:

From the first rib and its coastal cartilage

Insertion:

Groove on the undersurface of middle part of clavicle.

Nerve supply: From the nerve to subclavius (C5, C6) a branch from the upper trunk of brachial plexus.

Actions: Steadies the clavicle during movements of shoulder joint

Clavi pectoral fascia:

 It is a strong fascia which stretches from the pectoralis minor to the clavicle.

Attachments:

Above: the fascia splits to enclose the subclavius muscle and is attached to the two lips of the subclavian groove of clavicle.

Below: It splits to enclose the pectoralis minor muscle and reunites as suspensory ligament of axilla which is attached to axillary fascia.

Structures piercing the fascia:

Cephalic vein

Lateral pectoral nerve

Thoraco acromial artery and vein

Lymphatics from the infra clavicular nodes and from the breast to the apical group of axillary lymph nodes.

MAMMARY GLAND:

          The breast or mammary gland is present bilaterally in pectoral region of both sexes. It is rudimentary in males and in females before puberty.

Type of gland:

Modified sweat gland which lies in the superficial fascia of pectoral region.

Axillary tail of Spence:

A tail like projection from the upper and above quadrant of the gland enters the axilla

Extent:

The circular base extends

Vertically: from the second to the sixth ribs in the mid clavicular line.

Horizontally: from the lateral border of sternum to the mid axillary line along the fourth rib.

Mammary bed:

It is formed by

Pectoralis major in the middle 2/3

Serratus anterior in the lateral 1/3

External oblique aponeurosis in the lower medial part.

Retro mammary space is the space between the base of the gland and the deep. fascia overing the structures of the mammary bed. It contains loose connective tissues.

Features of the skin overlying the breast:

Nipple: conical projection below the center of the breast which lies at the level of 4^th intercoastal space in male and nulliparous females. It is pierced by 15 to 20 lactiferous ducts.

Areola: it is a pigmented circular area of skin around the base of nipple. Outer margin of areola contains a number of modified sebaceous glands. They are enlarged during pregnancy and lactation and are known as tubercles of Montgomery.

Structure of the breast:

The mammary gland is made of

Glandular tissue- fibro alveolar type. It consists of 15 to 20 pyramidal lobes each being drained by a separate lactiferous duct. Each duct dilates to form lactiferous sinus beneath the areola. Each lactiferous duct divides into segmental ducts and into terminal ducts. The area of breast parenchyma drained by one terminal duct is known as lobule.

Fibrous tissue- it gives a number of septa which anchor the parenchyma to the overlying skin and the underlying pectoral fascia. These fibrous bands are known as suspensory ligaments of Cooper.

Inter lobar fatty tissue: it gives the round contour of the mammary gland. Fat is absent beneath the areola and the nipple.

MALE BREAST:

Male breast is essentially composed of duct system without the alveoli and is supported by fibro fatty tissue.

Arterial supply of mammary gland:

Lateral thoracic branch

Superior thoracic artery

Perforating branches of internal thoracic artery

Venous drainage:

The venous plexus, circulus venosus is beneath the areola and from the plexus, the veins drain into the axillary, internal thoracic and intercostal veins.

Intercostal veins - azygos veins- internal vertebral venous plexus-intra cranial sagittal and transverse sinuses.

Through this, they establish venous communications with the clavicle, humerus and cervical vertebrae.

Nerve supply: From the anterior and lateral cutaneous branches of 4^th to 6^th intercostals nerves.

Arterial supply:

 

 Lymphatic drainage:

The lymphatics of mammary gland is made of two sets:

Those draining the parenchyma of the breast including nipple and areola.

Those draining the overlying skin excluding areola and nipple.

From the parenchyma:

75% lymphatics from the gland drain into axillary lymph nodes, mainly the anterior group. Few drains into posterior group following the axillary tail

About 20% of the lymphatics drain into para sternal or internal mammary nodes.

About 5% of the lymphatics drain into posterior intercostal nodes.

From the overlying skin:

The lymphatics of the skin excluding areola and nipple drain into:

From the inner part – para sternal lymph nodes

From the outer part – axillary lymph nodes

From the upper part – supra clavicular lymph nodes.

From the lower part – The lymphatics form a sub peritoneal plexus by piercing the upper part of linea alba and these vessels drain into sub diaphragmatic nodes and some through falciparum ligament reach the hepatic nodes.

The cutaneous lymphatics communicate across the middle line with those of the opposite breast.

Schematic – Lymphatics of the skin:

 Applied Anatomy:

Amastia – Agenesis of mammary gland – rare

Poly mastia – Accessory breast may occur along the milk ridge.

Poly thelia – supernumerary nipples over the breast

Benign fibro adenoma of breast – common in young women which may be mobile and soft.

Carcinoma of breast – common in nulliparous females.

Infiltrations of cancer cells occur along the suspensory ligaments of the cooper cause fixation of the humerus to the underlying pectoral fascia.

Infiltration along the lactiferous ducts and fibrosis subsequently lead to the retraction of the nipple.

Obstruction of the cutaneous lymphatics – cause lymphedema around the hair follicles causes peaude’ orange appearance

Krukenberg tumor – secondary deposits on the surface of the ovary caused by the cancer cells from the sub peritoneal plexus.

The diagnosis of breast carcinoma can be confirmed by fine needle aspiration cytology, mammography and ultrasonography.