1

THE THORACIC REGION

DESCRIPTION: This is the part of the trunk, which is located between the root of the neck and the

superior border of the abdominal region.

SHAPE : T

It has the shape of a truncated cone (T) with the apex located rostrally and

the base caudally.

APERTURES (Fig 1a & b): Normal cone Truncated cone

a. Superior aperture (Inlet): This is made up of the upper border of the manubrium, inner (medial)

margin of the first ribs and their costal cartilages and the upper border of the first thoracic vertebra

b. Inferior aperture (Outlet): This is composed of the xiphisternal joint, costal margins (Left &

Right), lower borders of the twelfth ribs and the twelfth thoracic vertebra. The musculo-aponeurotic

thoracoabdominal diaphragm is attached to the margins of this aperture.

Figure. 1a

2

Figure. 1b: Horizontal section of the thoracic cavity

BOUNDARIES OF THE THORAX (WALLS) (Fig. 1):

a. Anterior: The sternum, anterior parts of the ribs and their costal cartilages.

b. Lateral: Twelve pairs of ribs. The ribs and their cartilages are separated by 11 intercostal spaces,

which are occupied by the intercostal muscles and membranes

c. Posterior: The bodies of the twelve thoracic vertebrae and the intervertebral discs between

them.

3

IMPORTANT LANDMARKS ON THE THORACIC WALL (Fig. 2)

Understanding the applied anatomy of the thoracic wall is dependent on our knowledge of important

landmarks on this anatomical region of the body. This understanding is also vital to the correlation of

internal structures to the chestwall. The following are the anatomical landmarks of the chestwall

ANTERIOR THORACIC WALL

1. Jugular notch (Suprasternal notch). This is the upper border of the manubrium: T2/T3

2. Manubrosternal (Sternomanubrial) junction. The manubrium articulates with the body of sternum at

this point: T4/T5

Other events occurring at the level of T4/T5 include:

a. Location and articulations of second costal cartilages with the sternum. ***

b. End of the ascending aorta.

c. Commencement of the arch of the aorta.

d. End of the arch of the aorta.

e. Commencement of the descending thoracic aorta.

f. Bifurcation of the pulmonary trunk.

g. Location of the ligamentum arteriosum.

h. Point of drainage of the Azygos vein into the superior vena cava.

i. Upper border of the fibrous pericardium.

NB. b. to i. are all vascular events.

j. Point at which the Left recurrent laryngeal nerve (a branch of the vagus nerve) hooks around the

arch of the aorta.

k. Inferior border of the superior mediastinum.

l. Superior border of the inferior mediastinum.

m. Bifurcation of the trachea.

n. Location of the root of the lungs.

o. Location of the superior tracheobronchial lymph nodes.

p. Location of the cardiac nerve plexuses.

Other Landmarks include: 3. Xiphisternal (Xiphosternal) joint T9.

4. Subcostal plane (Tip of 10th

costal cartilage) L3.

POSTERIOR THORACIC WALL

Superior angle of the scapular T2.

Spine of the scapular T3.

Inferior angle of the scapular T8.***

4

Figure 2.

THE THORACIC CAVITY (Figure 3):

SUBDIVISIONS:

a. Two pleural (Lateral thoracic) cavities, which contain the lungs and the pleural membranes.

b. The mediastinum: This is the bulky, mobile, midline septum sandwiched between the two pleural

cavities. It extends anteroposteriorly (Front to back) from the sternum and the costal cartilages to

the vertebral bodies of T1 to T12 and rostrocaudally (From above downwards) from the thoracic

inlet to the diaphragm, which seals the thoracic outlet.

5

Figure 3.

COMPARTMENTS OF THE MEDIASTINUM:

The compartments of the mediastinum consist of:

a. Superior mediastinum and

b. Inferior mediastinum. The inferior mediastinum is further subdivided by the pericardial sac into:

Anterior mediastinum.

Middle mediastinum and

Posterior mediastinum.

ANATOMICAL LANDMARKS FOR SUB-DIVIDING THE MEDIASTINUM:

a. Manubriosternal junction (Sternal angle of Louis), which corresponds to the level of the

intervertebral disc between T4 and T5. This landmark subdivides the entire mediastinum into a

superior and an inferior mediastinum.

b. The pericardial sac: This landmark subdivides the inferior mediastinum into anterior, middle and

posterior compartments. Note that the pericardial sac encloses most of the contents of the middle

mediastinum.

CONTENTS OF THE MEDIASTINAL COMPARTMENTS:

6

THE SUPERIOR MEDIASTINUM

The contents of the superior mediastinum include the following:

1. Thymus gland or its degenerative remains in the adult

2. The great vessels, which include:

a. Right and Left Brachiocephalic veins.

b. The Superior Vena cava.

c. The arch of the aorta and its’ branches which include:

i. The Brachiocephalic trunk (Innominate artery).

ii. The left common carotid artery.

iii. The left subclavian artery.

3. The Trachea

4. The Oesophagus

5. The Phrenic nerve

6. The Vagus nerve

7. The Left Recurrent Laryngeal nerve

8. The Cardiac nerve plexuses

9. The thoracic duct

10. The left superior intercostal vein

11. The prevertebral fascia

12. The longus colli muscles

13. The terminal part of the sternothyroid muscle.

14. The terminal part of the sternohyoid muscle.

7

Figure 4. (Contents of the superior mediastinum)

THE ANTERIOR MEDIASTINUM

The Thymus gland or its degenerative remains

Lymph nodes and lymph vessels.

Fat and loose connective tissues.

Branches of the Internal thoracic (Internal mammary) artery.

The sternopericardial ligaments

8

THE MIDDLE MEDIASTINUM

Boundaries of the middle mediastinum:

Anterior Anterior mediastinum

Posterior Posterior mediastinum (From T5 to T8).

Inferior Thoracoabdominal diaphragm.

Superior Superior mediastinum.

Lateral Mediastinal surfaces of the Lungs, which are covered by the pleura

CONTENTS OF THE MIDDLE MEDIASTINUM:

1. The fibrous pericardial sac, which contains:

The heart.

The parietal and visceral serous pericardium.

The transverse and oblique pericardial sinuses.

The lower half of the superior Vena Cava.

Terminal part of the inferior vena cava

The ascending aorta.

The pulmonary trunk.

Serous fluid.

2. The pericardiacophrenic artery.

3. The phrenic nerve.

4. The tracheal bifurcation and the principal bronchi

5. The pulmonary vessels

6. The tracheobronchial lymph nodes

7. The cardiac plexuses

8. Termination of the azygos vein.

THE POSTERIOR MEDIASTINUM

Boundaries of the posterior mediastinum:

Anterior: The bifurcation of the trachea, pulmonary vessels, the pericardium and the

diaphragm.

Posterior: The bodies of the lower 8 thoracic vertebrae and intervening discs.

Lateral: Mediastinal surfaces of the Lungs covered by pleural membrane

CONTENTS OF THE POSTERIOR MEDIASTINUM:

1. The descending thoracic aorta.

2. The oesophagus

3. The oesophageal nerve plexus (Which is derived from the vagus nerve).

4. The thoracic duct.

5. The azygos vein.

9

6. The hemiazygos. vein

7. The accessory hemiazygos veins.

8. Proximal parts of the posterior intercostal vessels

9. The splanchnic nerves

10. The posterior mediastinal lymph nodes and vessels

11. The prevertebral fascia and the longus colli muscles.