Pectoral Region And Axilla Notes

Pectoral Region

Breast

Question 1. What is breast? Describe its structure in brief.
Answer.

The breast is a modified sweat gland (apocrine type). It is rudimentary in male and well developed in female at puberty. In adult female, it is seen as a soft hemispherical protruding organ one on either side in the pectoral region.

Structure

The breast is composed of three components: skin, parenchyma and fibrofatty stroma.

Skin:

It presents nipple and areola.

• Nipple: It is a dark conical projection of skin in the centre of breast. It is pierced by 10–15 lactiferous ducts and contains smooth muscle fibres.
• Areola: It is circular blackish discolouration around the nipple. It contains numerous modified sebaceous glands. They secrete oily secretion which lubricates and prevents the nipple from drying and cracking.

Parenchyma:

It consists of glandular part made up of alveoli, lactiferous ducts and lactiferous sinuses.

Fibrofatty stroma:

It consists of fibrofatty tissue.

• Fibrous stroma, consists of fibrous septa (ligaments of Cooper), which extends from skin to the pectoral fascia and divides the gland into 10–15 lobes.
• Fatty stroma, lies between fibrous septa and glandular part.

Question 2. Describe the female breast under the following headings: (a) location and extent, (b) relations, (c) blood supply, (d) lymphatic drainage and (e) applied anatomy.
Answer.

Location

The breast is hemispherical in shape and located one on either side in the superficial fascia of the pectoral region.

Extent

• Vertically: It extends from 2nd to 6th rib in midclavicular line.
• Horizontally: It extends from lateral border of the sternum to the midaxillary line.

Relations

Superficial relations

• Skin
• Superficial fascia

Deep relations

• Pectoral fascia (deep fascia covering the pectoralis major).
• Three muscles: pectoralis major (medially), serratus anterior (laterally) and external oblique (inferomedially).
• Loose areolar tissue of the retromammary space intervenes between the breast and pectoral fascia.

Blood supply

Arterial supply:

The breast is highly vascular organ and is supplied by the following arteries:

• Internal thoracic artery through its 2nd, 3rd and 4th perforating branches.
• Lateral thoracic, superior thoracic and acromiothoracic branches of the axillary artery.
• Lateral branches of the posterior intercostal arteries.

Read And Learn More: Selective Anatomy Notes And Question And Answers

Venous drainage:

The main veins draining area around areola and parenchyma (glandular tissue) are deep veins. They form the circular venous plexus at the base of the gland. From here, they drain into:

• Axillary vein
• Internal mammary vein
• Intercostal veins

Lymphatic drainage

The lymph vessels draining the breast are divided into two sets: (a) A set draining the parenchyma, nipple and areola; (b) A set draining overlying skin, excluding nipple and areola.

• Those draining the parenchyma including areola and nipple form subareolar plexus of Sappey, which drains as follows:
• • Seventy-five per cent (75%) into axillary group of lymph nodes chiefly into anterior (or pectoral) group. Some reach posterior (subscapular) group. Efferents from these pass to central and thence into apical group.
  • Twenty per cent (20%) drain into parasternal (internal mammary) nodes.
  • Five per cent (5%) drain into posterior intercostal nodes.
• Those draining the overlying skin excluding areola and nipple drain into:
  • Axillary nodes – from outer part
  • Supraclavicular nodes – from upper part
  • Parasternal nodes – from inner part
  • Subdiaphragmatic nodes – from inner part

Applied anatomy

Carcinoma of the breast:

The breast is common site of carcinoma. The important points to know about the carcinoma breast are

• The cancer cells may infiltrate the suspensory ligaments (Cooper’s ligaments) and as a result the breast becomes fixed and immobile.
• The contraction of the ligaments causes retraction or puckering of the skin.
• The infiltration of the lactiferous duct and their consequent fibrosis leads to retraction of the nipple.
• Secondary breast cancer are usually lodged in the liver, ovaries or the peritoneum making the prognosis worse.
• The cancer cells may migrate transcelomically to ovary producing a secondary tumour called Krukenberg tumour.
• The cancer cells can also spread to the vertebrae and the brain via venous route, through the communication between the veins draining the breast and the vertebral venous plexus.
• Peau d’orange: In breast cancer, the skin over the breast presents an orange peel appearance. This occurs due to obstruction of cutaneous lymphatics leading to breast oedema and deepening of the mouths of sweat glands and hair follicles.

Question 3. Describe the development of the breast/mammary gland in brief.
Answer.

• The mammary gland develops in the pectoral region from the milk line.
• The milk line is linear thickening of surface ectoderm that appears in the 4th week of intrauterine life.
• The milk line extends from axilla to the inguinal region on the ventral aspect of the body wall of the embryo.
• The fibrofatty stroma of the breast develops from the underlying mesoderm.

Question 4. Enumerate the congenital anomalies of the breast.
Answer.

• Polymastia: Supernumerary breasts
• Amastia: Absence of breast (rare)
• Athelia: Absence of nipple
• Polythelia: Supernumerary nipples (commonly seen in axilla)

Question 5. Discuss the microscopic/histological structure of the mammary gland.
Answer.

• The mammary gland is a modified sweat gland of apocrine variety. It is also called serous, tubuloalveolar gland according to nature of secretion and secretory units.
• The histological structure of mammary gland differs according to its physiological status, i.e. (a) nonlactating and (b) lactating.

Differences Between Nonlactating and Lactating Breast

Question 6. Enumerate the muscles of pectoral region.
Answer.

• Pectoralis major
• Pectoralis minor
• Subclavius

Question 7. Give the origin, insertion, nerve supply and actions of the pectoralis major muscle.
Answer.

Pectoralis Major Muscle Origin

• Clavicular head: From the anterior surface of the medial 1/2 of clavicle.
• Sternocostal head arises from:
• • Anterior surface of the sternum up to 6th costal cartilage.
  • Medial parts of 2nd to 6th costal cartilages.
  • Aponeurosis of the external oblique muscle.

Insertion

By a bilaminar tendon on to the lateral lip of the bicipital groove in a ‘U-shaped manner’ with two laminae continuous with each other inferiorly.

Nerve supply

Medial and lateral pectoral nerves.

Actions

Adduction and medial rotation of the shoulder.

Question 8. Give the origin, insertion, nerve supply and actions of the pectoralis minor muscle.
Answer.

Origin

Arises from 3rd, 4th and 5th ribs anteriorly near their costal cartilages.

Insertion

Medial border and upper surface of the coracoid process of the scapula.

Nerve supply

Medial and lateral pectoral nerves (C6–C8).

Action

• It draws the scapula forward across the chest wall along with serratus anterior.
• It depresses the shoulder as in bringing the arm down from ‘above head position’.

Question 9. Give the origin, insertion, nerve supply and actions of the serratus anterior muscle.
Answer.

Serratus anterior is a broad flat muscle of trunk in the medial wall of axilla. It lies between the ribs and scapula at the upper lateral part of the chest.

Origin

Arises by eight digitations from outer surfaces and upper borders of upper eight ribs. Each digitation arises from the corresponding rib but the 1st digitation arises from both 1st and 2nd ribs.

Insertion

Into whole length of the medial border of costal surface of the scapula.

The 1st digitation is inserted into a triangular area on the superior angle. The next two or three digitations are inserted in the whole length of the medial border. The lower four or five digitations are inserted into the large triangular area over the inferior angle.

Nerve supply

By the nerve to serratus anterior (also called long thoracic nerve of Bell), which arises from C5, C6 and C7 roots of brachial plexus.

Actions

• Rotation of the scapula which helps in the abduction of shoulder beyond 90°.
• Chief muscle concerned with pushing and punching movements as in boxing. Hence, it is also called ‘boxer’s muscle’.

Question 10. Write a short note on clavipectoral fascia.
Answer.

The clavipectoral fascia is the strong fascial sheet deep to the pectoralis major muscle. It extends from clavicle above to the axillary fascia below.

Attachments

Medial:

Medially, it fuses with anterior intercostal membrane of the upper two intercostal spaces and attaches to the 1st rib.

Lateral:

Laterally, it becomes thick and dense and attaches to the coracoid process.

Above:

It splits to enclose subclavius and attaches to the lips of the subclavian groove of clavicle.

Below:

It splits to enclose pectoralis minor and thereafter it continues downward as suspensory ligament of axilla, which is attached to the convex dome of the axillary fascia.

Modifications

• Costocoracoid ligament: Thickening of clavipectoral fascia between coracoid process and 1st rib.
• Suspensory ligament of axilla (vide supra).

Functional significance

Acts as a suspensory ligament of axilla to maintain its concavity.

Applied anatomy

The cancer cells from breast may pass across the clavipectoral fascia to invade the Rotter’s lymph nodes lying in front of pectoralis minor muscles. Hence, the knowledge of clavipectoral fascia is of great surgical significance.

Question 11. Enumerate the structures piercing clavipectoral fascia.
Answer.

Clavipectoral fascia is pierced by four structures:

• Lateral pectoral nerve
• Thoracoacromial artery
• Cephalic vein
• Lymphatics from infraclavicular nodes and deep part of breast to apical group of axillary lymph nodes

Axilla

The axilla is a pyramid-shaped space between upper part of the arm and thorax.

Question 1. Describe the axilla under the following headings: (a) boundaries, (b) contents and (c) applied anatomy.
Answer.

Boundaries

Anterior wall:

It is formed by:

• Pectoralis major
• Subclavius muscle
• Clavipectoral fascia
• Pectoralis minor

Posterior wall:

It is formed by:

• Latissimus dorsi
• Teres major
• Subscapularis

Medial wall:

It is formed by serratus anterior muscle, covering the upper part of lateral thoracic wall (upper 4–5 ribs).

Lateral wall:

It is narrow and formed by intertubercular sulcus of the shaft of humerus, which contains coracobrachialis and short head of biceps brachii.

Apex (also called cervicoaxillary canal):

It is triangular and directed upwards and medially towards the root of the neck. It is bounded:

• Anteriorly, by the posterior border of clavicle
• Medially, by the outer border of 1st rib
• Posteriorly, by the upper border of scapula

Base:

It is formed by the axillary fascia extending between anterior and posterior axillaryfolds.

Contents

• Axillary artery and its branches
• Axillary vein and its tributaries
• Cords of brachial plexus
• Axillary lymph nodes
• Fibrofatty tissue
• Long thoracic and intercostobrachial nerves
• Axillary tail of breast (tail of Spence)

Applied anatomy

Axillary abscess:

It occurs due to infection and suppuration of axillary lymph nodes. Axillary abscess is drained by giving an incision midway between the anterior and posterior axillary folds. The direction of edge of knife should face towards the medial wall.

Lymphadenopathy:

Axillary lymph nodes are often infected and enlarged. They should be removed very carefully because of their relationship to major vessels.

Boils:

Due to the presence of abundant hair follicles in axilla, the infection of hair follicles and sebaceous glands is very common and gives rise to multiple boils in the axilla.

Axillary pulse:

Can be felt against the lower part of the lateral wall of axilla.

Question 2. Describe the brachial plexus under the following headings: (a) formation, (b) components, (c) location, (d) branches and (e) applied anatomy.
Answer.

Formation

It is formed by ventral primary rami of C5, C6, C7, C8 and T1.

Components

The brachial plexus consists of four components:

• Roots
• Trunks
• Divisions
• Cords

Location

• Roots and trunks lie in the root of neck.
• Divisions lie behind the clavicle.
• Cords lie in the axilla.

Branches

From roots

• Dorsal scapular nerve (C5) for rhomboids.
• Nerve to serratus anterior (C5, C6 and C7) for serratus anterior as the name implies.

From trunk (only upper trunk gives branches)

• Suprascapular nerve (C5 and C6) for supraspinatus and infraspinatus muscles.
• Nerve to subclavius.

From cords

• Lateral cord
• • Lateral pectoral nerve (C5–C7)
  • Lateral root of median nerve (C5–C7)
  • Musculocutaneous nerve (C5–C7)
    Mnemonic: Laila Loved Majnu.

• Medial cord
• • Medial pectoral nerve for pectoralis major and pectoralis minor
  • Medial cutaneous nerve of arm
  • Medial cutaneous nerve of forearm
  • Medial root of median nerve
  • Ulnar nerve
• Posterior cord
  • Upper subscapular nerve for subscapularis muscle
  • Lower subscapular nerve for subscapularis and teres major muscles
  • Nerve to latissimus dorsi (thoracodorsal nerve)
  • Axillary nerve for deltoid and teres minor muscles
  • Radial nerve
    Mnemonic: ULNAR

Applied anatomy

• Erb paralysis: It occurs due to injury of the upper trunk of brachial plexus at the Erb’s point.
• Klumpke paralysis: It occurs due to injury of the lower trunk of brachial plexus.
• Horner syndrome: It occurs due to involvement of the sympathetic fibres.
• Winging of scapula: It occurs due to injury of the nerve to serratus anterior.

Erb paralysis

• Site of injury: Erb’s point (the region of upper trunk where six nerves meet, i.e. ventral rami of C5 and C6, anterior and posterior divisions of the upper trunk, and suprascapular nerve and nerve to subclavius).
• Cause: Undue (i.e. too much) separation of head from shoulder, e.g. (a) pulling of fetal head by forceps during delivery (birth injury) and (b) fall on shoulder.
• Clinical features:
• • Arm hangs by the side. It is adducted and medially rotated, i.e. person is unable to abduct and laterally rotate the arm.
  • Forearm is extended and pronated, i.e. person is unable to flex and supinate the forearm.
  • Loss of sensations over a small area on the lower part of the deltoid.

Klumpke paralysis

• Site of injury: Lower trunk of brachial plexus involving C8 and T1, mainly T1.
• Causes: Undue abduction of arm from body, e.g. (a) birth injury (pulling of upper limb during delivery) (b) reflex catching of something with hand while falling from a height, i.e. branch of a tree while falling from a tree.
• Clinical features:
• • Claw hand, due to paralysis of intrinsic muscles of the hand
  • Sensory loss along the medial border of forearm and hand
  • Horner syndrome due to involvement of sympathetic nerve to head and neck

Question 3. Describe the axillary artery in brief.
Answer.

Source and extent

• It is a continuation of subclavian artery into axilla.
• It extends from the outer border of 1st rib to the inferior border of teres major.

Parts

It is divided into three parts by pectoralis minor:

• First part: Proximal to the muscle
• Second part: Deep/behind to the muscle
• Third part: Distal to the muscle

Branches

They are six in number:

• First part gives one branch: Superior thoracic artery.
• Second part gives two branches: (i) thoracoacromial artery and (ii) lateral thoracic artery.
• Third part gives three branches: (i) subscapular artery, (ii) anterior circumflex humeral artery, and (iii) posterior circumflex humeral artery.

Applied anatomy

The axillary artery can be effectively compressed against the upper part of shaft of humerus (lower part of the lateral wall of axilla).

Question 4. Describe the axillary vein in brief.
Answer.

Source and extent

• It begins at the lower border of teres major by the union of basilic vein and venae comitantes of brachial artery.
• It runs upwards and medially to continue as subclavian vein at the outer border of 1st rib.

Tributaries

• Veins corresponding to the branches of axillary artery, i.e. lateral thoracic, subscapular, etc.
• Cephalic vein.

Applied anatomy

Spontaneous thrombosis of axillary vein may occasionally occur following unaccustomed movements of the arm at shoulder joint.

Question 5. Describe the arterial anastomosis around scapula.
Answer.

The arterial anastomosis around scapula is formed between the branches of the first part of subclavian artery and the branches of third part of the axillary artery.

The following branches from first part of the subclavian artery and third part of the axillary artery take part in this anastomosis:

Clinical importance

This anastomosis around scapula provides collateral channels to ensure adequate circulation to the upper limb in case the subclavian artery or axillary artery is blocked anywhere between the first part of subclavian artery and third part of axillary artery.

Question 6. Describe the axillary lymph nodes in brief and discuss their applied importance.
Answer.

Location

In fibrofatty tissue of axilla.

Groups

Axillary lymph nodes are 15–20 in number which are divided into five groups

Anterior group

• Lies along the inferior border of pectoralis minor/lateral thoracic vein.
• It drains most of the lymph from the breast.

Posterior (subscapular) group

• It lies along the subscapular vein and drains lymph from axillary tail of the breast.

Lateral group

• It lies posteromedial to axillary vein along the upper part of humerus.
• It drains lymph from entire upper limb.

Central group

• It lies in the upper part of axilla.
• It receives lymph from other groups (vide supra).

Apical group

• It lies at the apex of axilla along the medial side of axillary vein. It receives lymph from central group, breast and thumb.

Applied anatomy

• Axillary lymph nodes are involved and enlarged in breast cancer.
• Axillary lymph nodes are also enlarged if infection occurs anywhere in areas of their drainage. They are routinely palpated by the clinicians while examining a patient.