Lab Manual - Superior Mediastinum & Lungs

Assignments:

Learning Objectives:

Upon completion of this session, the student will be able to:

  1. Identify the contents of the superior mediastinum.
  2. Identify and trace the tributaries to each of the brachiocephalic veins and the formation of the superior vena cava.
  3. Identify and trace all the branches of the arch of the aorta in the region and the relationship of the vagus and phrenic nerves to them.
  4. Identify the thoracic part of the trachea and describe its blood supply and innervation.
  5. Identify and describe the location of the lungs in the thoracic cavity.
  6. Identify the relations of the pulmonary artery, pulmonary veins, and the bronchi at the hilum of each lung.
  7. Define a bronchopulmonary segment and discuss its general organization.
  8. Name the bronchopulmonary segments and give their approximate location in reference to the lobes of the lungs.
  9. Trace the lymphatic drainage of the lungs and respiratory tract.

Procedure:

1. Define the boundaries of the superior mediastinum and peel away the mediastinal pleura. (Play movie; View images: N 191, 198, 231, TG 4-18, 4-35, 4-35, 4-36, 4-36)

Superior mediastinum. Define its boundaries. Locate the plane of the sternal angle and note what lies cranial and caudal to it. Carefully peel away the mediastinal pleura from the fibrous pericardium (middle mediastinum) and from the structures in the superior mediastinum. Dissect the phrenic nerves from the fibrous pericardium and trace them along their entire course through the thorax to the diaphragm. The nerves are accompanied by pericardiacophrenic arteries and veins. Review the relations of the phrenic nerve to the hilum on each side.

2. Strip the pericardium from the thoracic cavity and identify the parts of the aortic arch, ligamentum arteriosum, pulmonary trunk, trachea, and bronchi. (Play movie; View images: N 199A, 199B, 206, 209, 210, 212, 236, TG 4-19, 4-29, 4-31, 4-34, 4-37, 4-45)

Remove the pericardium to expose the ascending, arch and descending parts of the aorta, the pulmonary veins, pulmonary arteries, the bifurcation of the trachea, and the esophagus. Trace the pulmonary veins to the hila of the lungs, clearing them of all loose connective tissue. Determine which lobes of the lung they enter and their relations to other structures at the hilum. Follow the right and left pulmonary arteries to the hila, noting relations to aorta, the superior vena cava and the bronchi. Find the ligamentum arteriosum. Is there a plexus of nerves on the pulmonary arteries?

CT of a pulmonary tumor
CT of right and left pulmonary arteries

3. Remove the lungs. (Play movie; View images: N 199, 206, 209, 232, TG 4-31, 4-35, 4-36, 4-38)

Locate the tracheal bifurcation and trace the main (primary) bronchi to the hila of the lungs. Note relations to the arch of the aorta and the esophagus, relation of azygos vein (to right bronchus), vagus nerves and pulmonary arteries throughout their length. After the structures and relations of the hilum of each lung have been clearly defined, remove the lungs by cutting the structures of the lung root at the hilum as they enter the lung.

4. Clean and dissect the structures of the superior mediastinum, including the great vessels and remnants of the thymus. (Play movie; View images: N 31, 32, 33, 74, 185, 191, 196, 209, 211, 212, 230, 231, 232, 237, 238, 239, 240, TG 4-04, 4-09, 4-15, 4-18, 4-19, 4-35A, 4-35B, 4-36A, 4-36B, 4-38, 4-39, 4-40, 4-44, 4-45, 7-13, 7-14, 7-15)

The superior mediastinum and root of the neck contain the great vessels that leave or enter the heart. In order to study the great vessels and their structures in the superior mediastinum, it is necessary to elevate the sternocleidomastoid and strap muscles at the root of the neck. Beginning with the junction of the internal jugular and subclavian veins (posterior to sternoclavicular joint) on both sides, trace the right and left brachiocephalic veins. Identify thymic, inferior thyroid, internal thoracic, and left superior intercostal veins. The left superior intercostal vein drains the left second, third and fourth intercostal spaces. Determine the relation of the left superior intercostal vein to the aortic arch and to the phrenic and vagus nerves.

Observe the formation of the superior vena cava (confluence of both brachiocephalic veins), and relate its position to the manubrium and other great vessels. Note the azygos vein, which enters its dorsal side after arching over the root of the right lung. The azygos vein ultimately drains most of the intercostal spaces, as we will see later.

Cut through the mid-point of the left brachiocephalic vein and reflect to the right and left. Trace the vagus nerve on each side until it disappears behind the root of the lung. Are there cardiac nerves arising from the left vagus? Identify and trace all branches of the arch of the aorta: brachiocephalic, left common carotid, and left subclavian arteries. Do you find a vertebral artery from the arch of the aorta? Now define the arch of the aorta, its course and relations. In cleaning the great vessels you may find some lymph nodes of the anterior mediastinal group. Read about these nodes and the areas drained by them.

5. Explore the tracheal bifurcation and the main (primary) bronchi. (Play movie; View images: N 33, 74, 199, 202, 206, 207, 209, 230, 231, 232, 240, TG 4-29, 4-31, 4-33, 4-34, 4-35, 4-36, 4-37, 4-38, 4-39, 4-45, 7-13, 7-14)

Pull the aortic arch toward the left and observe the thoracic portion of the trachea. What innervates it and how? Blood supply? What structure does it lie upon? Locate the right and left bronchial arteries; what is their source, how do the two sides differ in number? Cut open the tracheal bifurcation and identify the carina.

Explore the tracheal bifurcation and trace the main (primary) bronchi to the hila of the lungs. Note the level of bifurcation, its relation to the arch of the aorta and the esophagus, the angle of bifurcation, differences in length and caliber of bronchi, relation of azygos vein (to right bronchus), vagus nerves and pulmonary arteries throughout their length. What is the difference between the root of the lung and its hilum? Locate the cardiac plexus lying inferior to the aortic arch and anterior to the tracheal bifurcation. The nerves found along the lung roots are the pulmonary plexuses. The cardiac and pulmonary plexuses are anatomically continuous. How do they differ? Where do they distribute?

3D image of the tracheal bifurcation
3D image of the tracheal bifurcation
CT of tracheal bifurcation
Tracheal cancer

6. Examine the surfaces and hilum of the lung. Identify the lymph nodes involved in lymphatic drainage of the lungs. (Play movie; View images: N 196, 197, 198, 199, TG 4-13A, 4-13B, 4-15, 4-16, 4-17, 4-31)

For each lung define apex, base, surfaces, borders, lobes and fissures (oblique and horizontal (right)). Where and what is the cardiac notch? What is the average projection of each lung and its fissures to the rib cage? Look at the mediastinal surface of each lung and compare impressions with structures of the mediastinum. Examine the hilar reflection of the pleura and the pulmonary ligament. Dissect the structures at the hilum and note the different arrangement on right and left lungs (bronchi, pulmonary artery, pulmonary vein, and bronchial arteries).

Series of lung CT images

7. Dissect the bronchi, defining the lobar branches. (Play movie; View images: N 195, 199, 201, 202, 203, 204, 205, 208, TG 4-30, 4-31, 4-32AB and 4-32CD, 4-33, 4-34A, 4-34B, 4-42, 4-44)

Dissect the bronchi into the lung, defining lobar (secondary) bronchi (superior, middle and inferior lobar in right lung, and superior and inferior lobar in left lung). Note relation to pulmonary artery throughout. In the right lung, identify bronchus intermedius. What is the lingular bronchus? Learn about the segmental (tertiary) bronchi and the bronchopulmonary segments of both lungs:

RIGHT lung:
LEFT lung:
Superior lobe:
apical
anterior
posterior
apicoposterior
anterior
superior lingular
inferior lingular
Middle lobe:
medial
lateral
N/A
N/A
Inferior lobe:
superior
medial basal
lateral basal
anterior basal
posterior basal
superior
medial basal
lateral basal
anterior basal
posterior basal

Although you should know the names and general location of all the above bronchopulmonary segments, you are asked to dissect only one: the superior segmental of the right inferior lobar bronchus. What is its significance? Note the relationship of the pulmonary arteries and bronchi to segments, and the pulmonary veins to the intersegmental plane.

Define pulmonary, bronchopulmonary, tracheobronchial (superior and inferior), and tracheal (paratracheal), node groups. Consider the lymphatic drainage of the lungs.

Views of the lungs

Lung cancer