Thoracic Wall

Question 1

What is the thorax?

Answer 1

Region of the body between the neck and abdomen
Enclosed by the bony framework of the thoracic cage

Question 2

Which structures form the thoracic cage?

Answer 2

Anteriorly: Sternum and costal cartilage
Laterally: Ribs and intercostal spaces
Posteriorly: Vertebral column

Question 3

What structures form the superior margin of the thorax?

Answer 3

Anteriorly: Superior border of manubrium sterni
Laterally: Medial border of the 1st ribs and their costal cartilages
Posteriorly: 1st thoracic vertebra

Question 4

What structures occupy the superior margin of the thorax?

Answer 4

Midline structures passing between the neck and thorax (e.g. esophagus and trachea)
Suprapleural membrane on either side of the midline structures

Question 5

What is the suprapleural membrane?

Answer 5

Tent shaped dense fascial sheet that covers the apex of each lung
It is an extension of the endothoracic fascia
Extends approximately an inch superior to the superior thoracic aperture

Question 6

What are the attachment points of the suprapleural membrane?

Answer 6

Laterally to the internal border of the first rib & costal cartilage
At its apex to the transverse process of C7 vertebra
Medially to the fascia covering the structures passing through the superior thoracic aperture

Question 7

What structures form the inferior margin of the thorax?

Answer 7

Anterior: Xiphisternal joint
Lateral: Curving costal margin
Posterior: 12th thoracic vertebra

The opening is closed by the diaphragm

Question 8

What is the purpose of the thoracic cage?

Answer 8

Protects the lungs, heart and large vessels
Provides attachment to the muscles of the thorax, upper limbs, abdomen and back

Question 9

How is the thoracic cage divided?

Answer 9

Mediastinum in the middle
Pleura and lungs laterally

Question 10

What are the thoracic cutaneous nerves?

Answer 10

Anterior wall:
1. Above sternal angle: Supraclavicular nerve
2. Below sternal angle: Segmental innervation by anterior and lateral cutaneous branches of the intercostal nerves

Posterior wall: Segmental innervation by posterior rami of thoracic spinal nerves

Question 11

What does an intercostal space contain?

Answer 11

Intercostal muscles
Intercostal neurovascular bundle
Lymphatics

Question 12

What are the muscles of the intercostal spaces?

Answer 12

Superficial to deep:
1. External Intercostals
2. Internal Intercostals
3. Innermost Intercostals

Question 13

Which nerves supply the intercostal muscles?

Answer 13

Corresponding intercostal nerves

Question 14

What are the actions of the intercostal muscles?

Answer 14

Pull the ribs nearer to each other
Strengthen tissue of the space

Question 15

How can external intercostal muscles be differentiated from other intercostal muscles?

Answer 15

Outermost muscle layer
Fibers directed downward and forward

Question 16

What is the origin and insertion of the external intercostal muscles?

Answer 16

Origin: Lower border of rib above
Insertion: Upper border of rib below

Question 17

What happens to the external intercostal muscles on the anterior surface?

Answer 17

External intercostals are deficient anteriorly and are replaced by the external/anterior intercostal membrane

Question 18

How can internal intercostal muscles be differentiated from other intercostal muscles?

Answer 18

Intermediate muscle layer
Fibers directed downwards and backwards

Question 19

What is the origin and insertion of the internal intercostal muscles?

Answer 19

Origin: from subcostal groove of the rib above
Insertion: upper border of rib below

Question 20

What happens to the internal intercostal muscles on the posterior surface?

Answer 20

Deficient posteriorly & replaced by internal/posterior intercostal membrane

Question 21

How can innermost intercostal muscles be differentiated from other intercostal muscles?

Answer 21

It is the deepest intercostal muscle layer

Question 22

What are the features of the innermost intercostal muscle?

Answer 22

Incomplete layer, divided into three portions
Fibers cross more than one intercostal space
Related externally to intercostal nerve and vessels, and internally to endothoracic fascia

Question 23

What is the endothoracic fascia?

Answer 23

An extrapleural fascia lining the chest wall

Question 24

What is the location of the endothoracic fascia?

Answer 24

Between the muscles and bones of the thoracic wall and parietal pleura
Extends over the cupola (apex) of the pleura as the suprapleural membrane and forms a thin layer between the diaphragm and the pleura

Question 25

Location of the intercostal neurovascular bundle?

Answer 25

Lies between the innermost and the internal intercostal muscles Runs high in the intercostal space near the subcostal groove of the rib above As the innermost intercostal muscle is not forming a complete layer, the bundle is generally covered on the inside by the endothoracic fascia

Question 26

What is the arrangement of the neurovascular bundle?

Answer 26

Top to bottom (*VAN*): 1. Vein 2. Artery 3. Nerve

Question 27

Number of intercostal nerves?

Answer 27

12 pairs

Question 28

What nerves are the intercostal nerves a branch of?

Answer 28

The anterior primary rami of the thoracic spinal nerves

Question 29

Distribution of intercostal nerves

Answer 29

**1-6**: Distributed in intercostal spaces **7-11**: Supply anterior abdominal wall **Anterior ramus of 12**: Runs forward in abdomen as subcostal nerve

Question 30

What do the intercostal nerves supply?

Answer 30

Skin Muscles of the intercostal space and abdomen Parietal pleura and parietal peritoneum ## Footnote Intercostal nerves are mixed nerves because they are both sensory and motor nerves

Question 31

What are the branches of the intercostal nerves?

Answer 31

**CLAMPPR** Collateral branches Lateral cutaneous Anterior cutaneous Muscular branches Pleural Peritoneal (7th-11th) Rami communicantes

Question 32

What are the atypical intercostal nerves?

Answer 32

First thoracic nerve Second thoracic nerve

Question 33

Why is the first thoracic nerve an atypical nerve?

Answer 33

Has no anterior cutaneous branch Joined to the brachial plexus by a large branch that corresponds to the lateral cutaneous branch

Question 34

Why is the second thoracic nerve an atypical nerve?

Answer 34

Joined to the medial cutaneous nerve of the arm by brachial plexus by a branch called the intercostobrachial nerve that corresponds to the lateral cutaneous branch

Question 35

How many arteries does **each** intercostal space contain?

Answer 35

One posterior and two anterior intercostal arteries ## Footnote Each artery gives off branches to the muscles, skin, parietal pleura and breast tissue

Question 36

What is the origin of the posterior intercostal arteries?

Answer 36

**Upper two**: Superior intercostal artery (branch of costocervical truck of the subclavian artery) **Lower nine**: Branches of thoracic aorta ## Footnote Branching and course of intercostal arteries follows intercostal nerves

Question 37

What is the origin of the anterior intercostal arteries?

Answer 37

**Upper six**: Internal thoracic artery **Lower five**: Musculophrenic artery ## Footnote Anterior and posterior intercostal arteries form anastomosis

Question 38

What are the characteristics of intercostal veins?

Answer 38

Accompany intercostal arteries and nerves Each space has posterior & anterior intercostal veins Eleven posterior intercostal and one subcostal vein Lie deepest in the costal grooves Contain valves which direct the blood posteriorly

Question 39

Where do the posterior intercostal veins on the right side drain?

Answer 39

**First space**: Right brachiocephalic vein **All other intercostal spaces**: Azygous vein

Question 40

Where do the posterior intercostal veins on the left side drain?

Answer 40

**Upper three intercostal spaces**: Left brachiocephalic vein **Rest of intercostal spaces**: Hemiazygos and accessory hemiazygos veins, which drain into the azygos vein

Question 41

Where do the anterior intercostal veins drain?

Answer 41

**Lower five spaces**: Musculophrenic vein (tributary of internal thoracic vein) **Upper six spaces**: Internal thoracic vein (which drains into subclavian vein)

Question 42

Where do lymph vessels drain?

Answer 42

Anteriorly drain into anterior intercostal nodes that lie along the internal thoracic artery Posteriorly drain into posterior intercostal nodes that lie in the posterior mediastinum ## Footnote Deep lymphatics generally follow arteries