Pancoast Tumor (Pneumonectomy)

This dissection is based on open procedures for right and left pneumonectomies.

Learning Objectives

• Discuss the anatomy that underlies the patient's symptoms.
• Indicate structures close to the hilum that the surgeon needs to avoid and the consequence of injuring them.
• Describe the organization of structures inside the hilum, and the order in which a surgeon would divide them.
• Explain how the organization of the lung into functional units would guide a partial pneumonectomy.

Clinical Case: Lung Cancer

Use the history & physical and laboratory data to answer the following questions:

(Click on the question to show the answer.)

Diagnostic Studies:

Examine this CT of a Pancoast tumor. The red arrow shows the tumor invading a thoracic vertebra. The accompanying VH Dissector image shows a comparable axial slice. T3 is highlighted, but the tumor extends superiorly as high as T1. The spinal nerves, sympathetic chain, scapula, and first rib are included for reference. Rotate the image to demonstrate how the tumor would extend above the rib cage anteriorly.

To learn more about this mass, we order a percutaneous needle biopsy. Pathology Report: lung cancer.

CT showed enlarged mediastinal nodes. To determine whether the nodes were positive for cancer, mediastinal nodes were sampled.

Pathology Report: inflammatory reaction; no evidence of cancer.

Decision: Resectable lung cancer.

Operative Approach

The operative approach for AD would attempt to preserve as much of the lung as possible. Later, we will consider the principles that underlie that attempt. Now, we break from the case and follow the procedures for completely removing the right and left lungs. Nowadays, this would be done thoracoscopically if possible. The following is based on a classical open procedure.

Click this link to set up your session. As you dissect, structures that have already been highlighted will be revealed. For clarity, the right arm and the pectoralis major and minor muscles have been removed. Mouse over the image with the dissection or highlight tool to identify the visible structures.

Right lung

1. The incision is shown in blue for a lateral thoracotomy. The patient's arm is over their head, which rotates the scapula. The incision divides the rhomboid major, latissimus dorsi and serratus anterior.

   

   To emulate this incision, dissect the latissimus dorsi and serratus anterior. (Note: the scapula is not rotated in VH Dissector; the above image was Photoshopped).

   What do the latissimus dorsi, rhomboids, and serratus anterior do?

   Principal functions: latissimus dorsi - adduct and extend the arm; rhomboids - medially rotate and retract the scapula (move it medially); serratus anterior - laterally rotate and protract the scapula (move it laterally).

2. The rib cage and intercostal muscles are exposed. The external and internal intercostal muscle of the fourth intercostal space need to be divided from the ribs.

   Should you make your incision along the superior border of the rib or the inferior border? Why?

   An incision along the superior border avoids the neurovascular bundle traveling just inferior to each rib.

   Dissect the external oblique and then the internal oblique. Zoom in to see the intercostal nerve (yellow), vein (blue), and artery (red) peaking out below each rib.

3. Typically, the surgeon would use retractors to spread open the intercostal space. For a better view remove ribs 3, 4, 5, and 6. This will give you a better view of the neurovascular bundle associated with each rib. Dissect the nerves, arteries and veins. The right lung is seen superiorly and the diaphragm inferiorly. Mouse over the lungs to identify the three lobes and find the borders between them. Use the highlight tool to de-highlight the middle lobe.

   To view the lungs, the surgeon has to divide the costal pleura creating a pnuemothorax. Why? What will happen to the lung?

   The lung will collapse, because 1) air pressure will equalize between the inside and outside of the lung, and 2) elastin fibers in the lung will contract. Think of the pleural membranes as a balloon. Imagine the lung as your fist and punch your fist into the balloon (i.e., inflate the lung) until the membrane covering your fist meets the membrane opposite it. To avoid compressing the air in the "balloon", you would remove air as you expand the lung. Normally, the lumen of the pleural membranes (the balloon) is a vacuum and air in the lungs keeps the visceral pleura of the lung pressed against the parietal pleura that lines the ribs, diaphragm, and mediastinum. When the rib cage expands and the diaphragm moves interiorly, space is created for the lungs to expand, and air is drawn into the lungs. Dividing the pleura allows air to enter and eliminate the vacuum. The lung will collapse to ~ 1/3rd it's normal size. The anesthesiologist can remove more air to make the lung smaller still, affording the surgeon lots of space.

4. Dissect the middle lobe. Identify the bronchi and arteries of the middle lobe. Notice how arteries and bronchi identified by VHD branch together. If all the bronchi could be colored, each artery would have an accompanying bronchus. Be careful to preserve the lobar artery and bronchus, as you dissect all the branches labeled "segmental".

   What is the functional significance of bronchi branching together with arteries?

   As the airway and artery branch in parallel, they get narrower and narrower. When the airway is at its thinnest, so is the artery (now a capillary), and gases exchange between the two. The lung is divided into lobes and bronchopulmonary segments. The first branch of the trachea defines left vs. right lung. The second branch defines a lobe. The third branch defines a bronchopulmonary segment.

5. Dissect the superior lobe. Now you see veins in addition to the arteries. Veins do not branch in parallel with bronchi. Instead, they travel between bronchopulmonary segments. Avoiding tbe veins, preserve branches labeled "lobar" as you dissect arterial and bronchial branches labeled "segmental".

6. Dissect the lower lobe. Rotate the image to appreciate the distribution of airways, arteries, and veins. Leave the veins and dissect anything labeled "segmental".

7. Observe the bronchopulmonary lymph nodes, colored green. Note that they are wrapped around the main and lobar bronchi. This region is the hialus of the lung (the region where vessels and airways enter/leave the lung). Dissect the lymph nodes.

8. Trace the veins to where they enter the left atrium of the heart. The muscle of the left atrium (myocardium) is colored pink and the lumen of the atrium is brown. Dissect each vein. Rotate the image to find two rings of atrial myocardium. This where the veins entered the left atrium. Use the index to look up the right pulmonary veins. Toggle them on and off to confirm they enter the heart at this location. It will help to rotate the image as you do this.

9. By now, your dissection should look something like this. For clarity, we highlighed the superior vena cava and de-highlighted the superior lobar artery. This view looks head-on at the hilum of the right lung. The hilum is bounded by the superior vena cava, arch of the azygos vein and azygos vein. Mouse around to identify the: pulmonary artery; superior, middle, and inferior lobar arteries; trachea; main (primary) bronchus; superior, middle, and inferior lobar (secondary) bronchi . Determine which primary branch is most anterior. The pulmonary veins have been removed from this view of the hilum. To confirm they lie inferior to the airway and artery, infer their position by re-identifing the left atrium, as viewed through anular rings of myocardium.

   Which regions are drained by the arch of the azygos vein?

   The posterior walls of the chest and abdomen.

   Bonus question: In what order do you imagine a surgeon would divide the structures within the hilum?

   Historically, the surgeon divided the artery first, because it is anterior most and exposes the main bronchus. After dividing the bronchus, the pulmonary veins are divided. The logic was that if you divide the veins first, the arterial pressure would increase too much. Although true for removing other organs, pulmonary arterial pressure is low to begin with. Consequently, the increased blood pressure is not a big factor. Current data indicates that cancer is more likely to spread if you divide the artery first. Consequently, surgeons now start with the pulmonary veins and work their way superiorly.

10. Recall that for artery and bronchi there is one primary branch for each lung and one secondary branch for each lobe of the lung. The next, tertiary branches, define functional subunits of each lobe, known as bronchopulmonary segments.

    How would you use this information to perform a partial pneumonectomy?

    Instead of dividing the main bronchus and pulmonary artery, you would divide the lobar branches for a lobectomy, or the first segmental (tertiary) branche(s) to remove one (or more) bronchopulmonary segments. By re-inflating a tertiary bronchus, that bronchopulmonary segment is clearly distinguished from the rest of the lobe. This enables removal of the lung without compromising neighboring bronchopulmonary segments

11. Identify two additional structures near the hilum that might be injured during a surgical procedure to divide the right hilum and its contents: the vagus nerve and the phrenic nerve (the accompanying phrenic artery and vein were not identified by VHD).

    What is the consequence of injuring the right vagus nerve?

    Parasympathetic innervation would be compromised for the embryonic, right side of the esophagus and abdominal 2/3 of the GI tract.

    What is the consequence of injuring the right phrenic nerve?

    Paralysis of the right hemi-diaphragm would impair breathing.

12. Rotate the image to appreciate the three-dimensional relationships. End up with this view to examine the hilum along its edge.

Left lung

The left lateral approach to lung is similar to right lateral approach. The beginning of this dissection corresponds to step (4), above.

1. Click this link to set up your session. Note that we also removed ribs 7 and 8 for clarity.

2. Use your mouse to identify the upper and lower lobes of the left lung. De-highlight the lower lobe to appreciate the boundary between the two. Rotate the image to find the superior-most pole of the lower lobe. Dissect the scapula and the superior serratus posterior. This will allow you to identify vertebrae.

   Which vertebra corresponds to the superior-most pole of the lower lobe?

   T4. This is also true on the right side. To auscultate the superior lobe from the back, your stethoscope needs to be placed above T4. Otherwise you are listening to the lower lobe.

   Dissect the lower lobe.

3. Identify (but do not memorize!) all the segmental arteries and trace them proximally to the left pulmonary artery (dark brown because it is not highlighted). Note that there is no lobar artery. Dissect the segmental arteries. Preserving the left superior lobar bronchus, repeat this procedure for the segmental bronchi. Rotate the image until you see the inferior pulmonary vein enter the left atrium of the heart.

4. Rotate the image to an anterior view. Notice how the inferior aspect of the heart is not covered by the left lung. This is the cardiac notch and is where a needle can be used to enter the pericardial sac without puncturing the lung. Dissect the left lung to view more of the heart. Use control-(or command-)z to replace the lung. Toggle the lung on and off to appreciate the thin portion of lung that covers the anterior surface of the heart. With the lung dissected, rotate the image to a lateral view to appreciate the thin space between the heart and the anterior chest wall. The portion of the lung that occupies this space is the lingula (tongue-shaped). The lingula corresponds to the middle lobe of the right lung. It is smaller than the right middle lobe, because the heart occupies the space where the middle lobe would be.

5. Identify and dissect the superior and inferior lingual arteries, and then the lingual artery. Trace all the segmental arteries back to the pulmonary trunk and dissect them. Preserving the left inferior and superior lobar bronchi, repeat this procedure for the segmental and lingual bronchi. Rotate the image until you can see both lobar bronchi branching from the left main bronchus. Dissect the lobar bronchi.

6. Rotate back to a lateral view. Trace the pulmonary veins to where they enter the left atrium. Dissect the pulmonary veins and highlight the left pulmonary artery. By now, your dissection should look something like this. Instead of the arch of the azygos vein, the left hilum of the lung is related to the arch of the aorta. As with the right lung, a careless surgeon might injure the left phrenic or left vagus nerve. Note the branch of the vagus nerve, the left laryngeal nerve. Not seen are cardiophrenic nerves that branch from the left vagus nerve at this point.

7. Rotate the image to appreciate the three-dimensional relationships. End up with this view to examine the hilum along its edge.

8. Compare this axial section through the left and right hila to this analogous slice of a CT.

   

   The slices are not exactly the same. Use the arrow keys to move the VHD image superiorly and inferiorly. Be sure you mouse is hovered over the Axial window. Scan the VHP image to find the branch point (Carina) of the trachea and the inferior pulmonary artery entering the left atrium.

Take Home Lessons

When performing this procedure a surgeon should be aware of the following important anatomical concepts:

• Lymphatics in the lungs drains to hilar lymph nodes and then to mediastinal nodes. Even though the tumor in our case invaded the posterior wall of the upper thorax, you would evaluate the spread of cancer by sampling mediastinal and hilar nodes.

  The donor used for VH Dissector did not have cancer. Why did he have so many enlarged hilar and mediastinal nodes?

  Dirt in the air. The lungs are part of the first line of defense that protects from pollutants, bacteria and viruses found in the air. A lifetime of breathing leads to enlarged nodes.

• The Pancoast tumor is distinguished from other lung tumors only by its location in the apex of the lung. Here it can invade the sympatheic chain to disrupt autonomic functions and invade the C8 and T1 spinal nerves that supply specific regions of the upper limb. Knowledge of the brachial plexus allows clinicians to use the upper limb as a reporter to locate pathologies that lie near the spinal column.
• The hilum of the lung lies near the azygos vein on the right side. Both left and right hilums relate to the phrenic neurovascular bundle anteriorly and the vagus nerve posteriorly.
• The pulmonary arteries lie anterior to the main stem (primary) bronchi. The pulmonary veins are inferior.
• Bronchopulmonary segments are functional subunits of the lung that are defined by the tertiary branches of the airway and pulmonary artery.