Thorax : thoracic wall BMDC curriculum 2021 dissection

 

Important vertebral level of thorax

STRUCTURE	VERTEBRAL LEVEL
Jugular notch	Lower border of T2
Sternal angle	Lower border of T4
Xiphisternal joint	Lower border of T8
Tip of ninth costal cartilage	L1
Lowest extent of costal margin	L3

 

Thoracic inlet: boundary

§  Posteriorly: first thoracic vertebra

§  Laterally: first pair ribs and their costal cartilage .

§  Anteriorly: superior border of manubrium sterni. 

 Structures that pass through the superior thoracic aperture include:

1.      Trachea

2.     Oesophagus

3.     Thoracic duct

§  Nerves : Vagus, Phrenic,Left recurrent laryngeal,Sympathetic trunks

§  Arteries: Left and right common carotid arteries, Left and right subclavian arteries

§  Veins: Internal jugular veins, Brachiocephalic veins, Subclavian veins

§  Lymph nodes and  lymphatic vessels

Contents of a typical intercostal space are:

1.      Intercostal muscles ( external, internal and innermost intercostal)

2.     Intercostal nerve and its branches

3.     Anterior and posterior intercostal arteries and vein  

 Intrinsic muscles of thoracic wall are:

1.      External intercostals (outer layer)

2.     Internal intercostals ((intermediate layer)

3.     Innermost intercostals

4.     Sternocostalis

5.     Subcostalis

 Branches of a typical intercostal nerve (3^rd – 6^th intercostal nerves ) are:

1.      Muscular branches: Number of muscular branches that suppy intercostal muscles, subcostalis and sternocostalis.

2.     Two communicating branches (white and gray ramus) which connect it to the corresponding sympathetic ganglion.

3.     Cutaneous branches:

§  Lateral cutaneous branch (reaches skin by piecing muscles at midaxillary line and divides into anterior and posterior branches)

§  Anterior cutaneous branch(reaches skin by piecing muscles about 1cm. lateral to the sternum and divides into medial and lateral branches).

4.    Collateral branch that supplies parietal pleura and periosteum of rib besides supplying intercostal muscles.

  Arteries supply:

1.      Superior intercostal artery ( a branch of costocervical trunk from the second part of subclavian trunk) gives posterior intercostals arteries first two intercostal spaces.

2.     Two anterior intercostal arteries for each intercostal space (in upper six intercostal spaces they are direct branches of internal thoracic artery (ITA) and in 7^th , 8^th & 9^th  they aris from musculphrenic artery ,a branch of ITA, 10^th and 11^th intercostals spaces don’t have anterior intercostal arteries ).

3.     Posterior intercostal arteries: for 3^rd to 11^th intercostal space they arise from descending thoracic aorta.

Importance of Sternal angle

1.      Ascending aorta ends

2.     Arch of aorta begins and ends

3.     Descending aorta begins

4.     Trachea bifurcates into right and left principal bronchii.

5.     Pulmonary trunk divides into right and left pulmonary arteries.

6.     Azygous veins drains into superior vena cava

7.     Upper border of heart lies at this level

* Sternal angle (angle of Louis) which can be easily palpated is used for counting ribs. The second costal cartilage articulates with sternum at this level.