The document provides information on the cross sectional anatomy of the chest, including the boundaries and divisions of the thorax and mediastinum. It describes the contents and boundaries of the superior, anterior, middle, and posterior mediastinum. It also discusses the lungs, bronchopulmonary segments, and six representative chest CT scan levels that are used to interpret mediastinal anatomy. Finally, it presents six clinical cases pertaining to conditions that may appear on chest imaging.

1. CROSS SECTIONALANATOMY OF
CHEST
Dr. Milan Silwal
Resident, 1st year, MD Radiodiagnosis
NAMS

2. BOUNDARIES OF THORAX
• Superior aperture/Thoracic Inlet : Oblique plane covered incompletely
by Suprapleural membrane /Sibson’s fascia.
Ant: upper border of manubrium sterni
Post: Superior surface of body of 1st thoracic vertebra
On each Side: first rib with its cartilage
• Thoracic cage:
 Ant: Sternum
Post:12 Thoracic vertebrae
Sides: 12 ribs +cartilage
• Inferior aperture/ Thoracic outlet: is closed by large
musculocutaneous partition, the diaphragm.

3. MEDIASTINUM
• middle space in thoracic cavity in between the lungs.
• Boundries-
Anteriorly: Sternum
Posteriorly: Vertebral column
Superiorly: Thoracic inlet
Inferiorly: Diaphragm
Laterarly : Mediastinal pleura.
• Divisions:
Superior Mediastinum
Inferior:
 Anterior Mediastinum
 Middle Mediastinum
 Posterior Mediastinum

4. Superior Mediastinum
• is the space between the thoracic inlet and the superior aspect of the
aortic arch
• Boundries:
Anteriorly: Manubrium sterni
Posteriorly: upper four thoracic vertebrae
Superiorly: plane of thoracic inlet
Inferiorly: An imaginary line passing through sternal angle in front and lower
border of body of fourth thoracic vertebrae behind
On each side: Mesdiastinal pleura

5. • Contents:
Trachea and oesophagus
Muscles: origin of sternohyoid, sternothyroid, lower end of longus coli
Arteries: Arch of aorta, Brachiocephalic artery,left common carotid
artery,left subclavian artery
Veins: Right and left brachiocephalic vein, upper half of superior vena cava,
left superior intercostal vein
Nerves: Vagus, Phrenic, cardiac nerve of both side, left recurrrnt laryngeal
nerve
Thymus:
Thoracic duct
Lymph nodes: Paratracheal, brachiocephalic and tracheobronchial

6. Anterior mediastinum:
• is a very narrow space in front of pericardium.
• Boundries:
Anteriorly: Body of sternum
posteriorly : Pericardium
• Contents:
thymus, branches of the internal mammary artery and vein, lymph nodes,
and fat.

7. Middle Mediastinum
• Boundries:
Anteriorly: anterior border of the pericardium and
Posteriorly: an imaginary line drawn 1 cm posterior to the anterior border of
the vertebral bodies on the lateral radiograph
• Contents:
 heart, aorta, superior and inferior vena cavae, brachiocephalic arteries and
veins, pulmonary arteries and veins, thoracic duct, azygos and hemiazygos
veins, phrenic and vagus nerves, mediastinal fat, and lymph nodes

8. Posterior mediastinum
• Boundries:
Anteriorly: line drawn 1 cm posterior to the anterior border of the vertebral
bodies
Posteriorly: the posterior paravertebral gutters.
• Contents:
nerves, fat, vertebral column, and lymph nodes.

10. Mediastinal levels:
• Interpretation of mediastinal anatomy can be assisted by analyzing CT
images at specific levels within the chest that are easily identifiable
because of their characteristic anatomic landmarks and appearance.

11. 1. Thoracic Inlet Level
• At the junction of the neck and the thorax, most of the mediastinal
structures are vascular.
• The two brachiocephalic veins are formed as the internal jugular
veins join the subclavian veins and are located posterior to the
clavicular heads. These veins are the most anterior and lateral of the
six major vessels at this level.
• More medial are the two common carotid arteries, and just posterior
to these are the subclavian arteries.
• The esophagus is posterior or posterolateral to the trachea.

13. 2. Left Brachiocephalic Vein Level
• The left brachiocephalic vein crosses the midline anterior to the
arterial branches of the aorta and joins the more vertically orientated
right brachiocephalic vein to form the superior vena cava .
• The innominate, left common carotid, and left subclavian arteries
are located posterior to the left brachiocephalic vein and anterior to
the trachea. The innominate artery is the more centrally located
artery; the left common carotid artery and the left subclavian artery
are located to the left of the midline in a more lateral and posterior
position.
• The esophagus maintains its position posterior or posterolateral to
the trachea and anterior to the spine.

15. 3. Aortic Arch Level
• The transverse arch crosses the mediastinum anterior to the trachea,
coursing obliquely from right to left and from anterior to posterior.
• The superior vena cava is located adjacent to the anterior aspect of
the transverse aorta to the right of the trachea.
• The fat-filled region posterior to the superior vena cava, anterior to
the trachea, and lateral to the aorta is the pretracheal or anterior
paratracheal space.
• Anterior to the transverse aorta is the fat-filled prevascular space,. If
present, the thymus gland is located in this space. These spaces often
contain a few small lymph nodes.

17. 4. Azygos Arch–Aortopulmonary Window
Level
• The azygos vein, located anterior and slightly to the right of the
spine, arches anteriorly and joins the superior vena cava at this
level.
• The azygos arch may not be seen in its entirety on one slice and may
be confused with lymphadenopathy.
• The aortopulmonary window is a space located between the inferior
aspect of the aortic arch and the superior aspect of the left main
pulmonary artery. The space is fat filled and contains a few small
lymph nodes, the left recurrent laryngeal nerve, and the
ligamentum arteriosum.

20. 5. Left Pulmonary Artery Level
• The main pulmonary artery is anterior and to the left of the ascending aorta.
• The left pulmonary artery curves posteriorly from its origin from the main
pulmonary artery and is located anterolateral to the left main bronchus at the
level of the carina.
• The left superior pulmonary veins are located lateral to the posterior portion of
the left pulmonary artery.
• On the right, at the level of the carina, is the origin of the right upper lobe
bronchus. Anterior to the right upper lobe bronchus lies the right upper lobe
pulmonary artery, the truncus anterior. The right superior pulmonary veins are
located anterior and lateral to the truncus anterior. The azygos vein is located
posterior and to the right of the esophagus, while the hemiazygos vein parallels
the course of the azygos but is to the left of the spine.

21. • The superior pericardial recess, a crescent-shaped extension of the pericardial
space, is contiguous to the posterior aspect of the ascending aorta.
• The space often contains a small amount of fluid and may occasionally be
confused with a lymph node. However, its characteristic location, shape, and low
attenuation allow confident identification.
• Occasionally, the superior pericardial recess extends more cephalad, to the level
of the brachiocephalic vessels, and may be mistaken for a mass or mediastinal
cyst. The use of thin sections can be helpful to distinguish this so-called high-
riding pericardial recess from pathologic conditions by showing that the “mass” is
of water attenuation and by demonstrating continuity with the superior
pericardial recess at the level of the ascending aorta.
• The concave extension of the right lung into the mediastinum anterior to the
spine is the azygoesophageal recess, which extends inferiorly from the subcarinal
region to the level of the diaphragm.

24. 6. Right Pulmonary Artery Level
• The main pulmonary artery is anterior and to the left of the ascending
aorta.
• The right pulmonary artery extends posteriorly and to the right from
the main pulmonary artery, passing anterior to the bronchus
intermedius and posterior to the superior vena cava.
• The right superior pulmonary vein is to the right of and lateral to the
intrapulmonary portion of the right pulmonary artery. Anterior to the
left main and upper lobe bronchi is the left superior pulmonary vein,
and posterior to the left upper lobe bronchus is the left lower lobe
pulmonary artery.

27. 7. Left Atrial Level
• Anterior to the superior vena cava is the right atrial appendage,
curving around the ascending aorta.
• The aorta is located centrally within the mediastinum, and anterior
and to the left of the aorta is the pulmonary outflow tract.
• Posterolateral and to the left of the pulmonary outflow tract is the
left atrial appendage. Within the fat between the left atrial
appendage and the aortic root is the left main coronary artery.
• The left superior pulmonary vein enters the left atrium immediately
posterior to the left atrial appendage. The right superior pulmonary
veins enter the left atrium just posterior to the superior vena cava.

30. 8. Four-Chamber Level
• The posteriorly located left atrium is the most cranial of all the chambers.
The right and left inferior pulmonary veins enter the posterolateral aspect
of the left atrium.
• Anterior and to the right is right atrium.
• To the left and anterior to the right atrium is the right ventricle, located
behind the sternum. The left ventricle is to the left and posterior to the
right ventricle.
• The coronary arteries can be detected if they are calcified or if there is fat
surrounding the heart. The right coronary artery lies in the right
atrioventricular groove. The circumflex coronary artery lies in the left
atrioventricular groove, and the left anterior descending coronary artery
lies in the interventricular groove between the left and right ventricles.

33. 9. Three-Chamber Level
• The ventricles and right atrium are identified at this level; the left
atrium, because of its more cranial position, is not visible.
• The right atrium is located to the right. To the left and anteriorly, the
thin-walled right ventricle is located just beneath the sternum.
• The thick-walled left ventricle makes up the posterolateral left portion
of the mediastinum.
• Between the left ventricle and the inferior vena cava's opening into
the right atrium is the coronary sinus.

35. LUNGS

36. Lungs
• Lungs are a pair of respiratory organs situated in a thoracic
cavity. Right and left lung are separated by the mediastinum.
Right lung: 2 fissures: oblique and horizontal;
3 lobes: superior, middle & inferior
Left lung: 1 fissure: Oblique
2 lobes: Superior & Inferior

37. Bronchopulmonary segments
• Bronchopulmonary segments of lungs are well defined sectors of
lung,each of which is aerated by a tertiary or segmental
bronchus.Each segment is pyramidal in shape with its apex directed
towards the root of the lung.
• No. of bronchopulmonary segments:
Right lung: 10
Left lung: 8

39. • Intersegmental planes
• Each segment is surrounded by connective tissue which is continuous on the
surface with visceral pleura.Thus the brochopulmonary segments are
independent respiratory units.

40. • Relation to pulmonary artery
• Branches of pulmonary artery accompany the bronchi. The artery lies
dorsolateral to bronchus. Thus each segment has its own separate artery.
• Relation to pulmonary vein
• Pulmonary vein do not accompany bronchi or pulmonary artery. They run in
intersegmental planes. Thus each segment has more than one veins &each
vein drains more than one segment.

41. 1. Section till trachea is visible

42. • Till trachea is visible

43. 2. At level of tracheal bifurcation

44. 3. Cardiac ventricular level

47. Case 1. 56 yr male with chronic SOB, cough and cachexia

48. Case 2. 5 day history of fever and cough

49. Case 3. 45 male with chronic cough and hemoptysis

50. Case 4. Case of pulmonary embolism

51. Case 5. Case of bronchiectasis and cavitatory lesion

52. Case 6. Known case of follicular Ca of thyroid

53. References:
• CT and MRI of the whole body by John R. Haaga et al, Sixth edition
• BD Chaurasia’s Human Anatomy, volume 1, Sixth edition

54. Thank You !