After reading this post you will know:
- Cutaneous nerves supplying pectoral region.
- Origin, insertion, nerve supply and action of muscles of pectoral region.
- Clavipectoral fascia- its extent, muscles enclosed by it and structures piercing it.
- Location, extent, deep relations, structure of mammary gland.
- Blood supply, nerve supply of mammary gland.
- Lymphatic drainage of mammary gland and its clinical significance.
Cutaneous Innervation of Pectoral Region
Q. Draw labelled diagram to show cutaneous innervation of pectoral region.
Muscles of Pectoral Region
Q. Enumerate the muscles of pectoral region and write their nerve supply.
A. Muscle Nerve Supply
a. Pectoralis major Medial ( C8,T1) & lateral pectoral (C5-C7) nerves
b. Pectoralis minor Medial ( C8,T1) & lateral pectoral (C5-C7) nerves
c. Subclavius Nerve to subclavius (C5,6)
d. Serratus anterior Long thoracic nerve ( C5,6,7)
Q. Write origin, insertion, action and nerve supply of:
a. Pectoralis major
b. Serratus anterior
A. a. Pectoralis major
i. Anterior surface of medial ½ of the clavicle
ii. Anterior surface of sternum up to the 6th costal cartilage.
iii. 2nd to 6th costal cartilages.
iv. Aponeurosis of external oblique muscle.
Insertion: Lateral lip of bicipital groove of humerus.
i. When both Clavicular & Sternocostal parts act – adduction and medial rotation of arm.
ii. Action of only Clavicular part – Flexion of the arm
iii. Action of only sternocostal part – Extension of the flexed arm.
iv. When the arm is fixed – Climbing (raising the trunk)
Nerve supply: Medial & lateral pectoral nerves
b. Serratus anterior
Origin: Outer surface of upper eight ribs & fascia covering the intervening intercostal muscles.
Insertion: Costal surface of the medial border of scapula.
i. Protraction of upper limb i.e. pulling the scapula forwards around the chest wall during pushing & punching actions.
ii. Rotate the scapula laterally and upward (along with trapezius) so that glenoid cavity faces upwards and thereby help in overhead abduction.
Nerve Supply: Long thoracic nerve (C 5,6,7).
Q. What is the anatomical basis of ‘Winging of scapula’?
Á. Paralysis of serratus anterior muscle due to injury to long thoracic nerve produces ‘Winging of scapula’.The medial border and inferior angle of scapula become unduly prominent specially when the patient tries to do pushing and punching actions.
Q. Describe Clavipectoral fascia under the following heading:
b. Muscles enclosed
c. Structures piercing
A. Clavipectoral fascia is a fibrous sheet present deep to the clavicular part of the pectoralis major muscle.
a. Extent: From clavicle above to the axillary fascia below.
b. Muscles enclosed: Subclavius and pectoralis minor.
c. Structures piercing:
i. Lateral pectoral nerve
ii. Cephalic vein
iii. Thoraco-acromial vessels
iv. Lymphatics from mammary gland to the apical group of axillary lymph nodes.
Q. Describe mammary gland under the following headings:
b. Deep relations
d. Arterial supply
e. Lymphatic drainage
f. Applied anatomy
A. Mammary gland
– is a modified sweat gland situated in the superficial fascia of pectoral region.
– a small extension called axillary tail of Spence pierces deep fascia and lies in the axilla.
a. Extent: Vertically from 2nd to 6th rib and horizontally from lateral border of the sternum to the mid-axillary line.
b. Deep relations: From superficial to deep are:
• Loose areolar tissue (retromammary space)
• Deep fascia (pectoral fascia)
• Three muscles – pectoralis major, serratus anterior and external oblique
c. Structure: Is made up of the following two components:
• Parenchyma (glandular tissue)
- Is made up of glandular tissue comprising 15 to 20 radially arranged in pyramidal lobes.
- Each lobe has a cluster of alveoli which is drained by a lactiferous duct.
- Lactiferous ducts open on the nipple and just before its termination each duct is dilated to form lactiferous sinus.
• Stroma (fibrofatty tissue)
- Fatty tissue forms the main bulk of the gland but is absent beneath the areola and nipple.
- The fibrous septa (suspensory or Cooper’s ligament) anchor skin overlying the gland and the gland to the pectoral fascia.
d. Arterial supply: Following arteries supply the gland:
i. Perforating branches of internal thoracic artery
ii. Branches of axillary artery (superior thoracic, thoracoacromial and lateral thoracic)
iii. Lateral branches of 2nd, 3rd and 4th posterior intercostals arteries.
e. Lymphatic drainage:
- Lymphatic drainage of mammary gland is of great clinical significance because carcinoma of breast spreads mainly along the lymphatics.
- Lymphatic vessels of the breast are arranged into two groups:
- Superficial lymphatic vessels drain the lymph from the overlying skin except nipple and areola.
- Deep lymphatic vessels drain the parenchyma along with nipple and areola.
Lymph from the mammary gland is drained into the following groups of lymph nodes:
i. 75% of the lymph drains into axillary lymph nodes.
ii. 20% of the lymph drains into internal mammary (parasternal) lymph nodes.
iii. 5% of the lymph drains into posterior intercostal lymph nodes.
iv. Lymph from superior quadrants drains into supraclavicular lymph nodes.
v. Lymph vessels from infero-medial quadrant communicate with the subperitoneal lymph plexus.
f. Applied anatomy:
i. Obstruction of superficial lymph vessels leads to stagnation of lymph resulting in odema of skin (peau d’orange appearance – like the skin of orange)
ii. Cancer cells may infiltrate the suspensory ligaments resulting in fixation of breast to pectoral fascia and retraction or puckering of skin.
iii. Infiltration of lactiferous ducts by cancer cells leads to fibrosis of lactiferous ducts which causes retraction of nipple.
iv. As lactiferous ducts run radially, incisions into the breast are usually made radially to prevent damage to the lactiferous ducts.
v. Cancer may spread from one breast to the other because of the communication between the superficial lymphatics across the midline.
vi. Lymph vessels from inferomedial quadrant communicate with with subperitoneal lymph plexus.Cancer cells therefore may spread to the liver may drop into the pelvis and produce secondary tumour in the ovary ( Krukenberg’s tumour).
vii. Besides lymphatics cancer may spread via the veins. Intercostal veins draining mammary gland communicate with the internal vertebral venous plexus. Cancer from breast therefore, may spread via this communication to the vertebrae and to the brain