Lungs, Removal of Heart, and Posterior Mediastinum

Atlas References

• Netter: 212–217

• McMinn: 182–184, 192–211

• Gray's Atlas: 72–92, 108–119

Opening the Thoracic Cavity

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  With a scalpel, transect the intercostal muscles, serratus anterior muscle, and a portion of the external abdominal oblique muscle ( Figs. 5.1 and 5.2 ).

  
  

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  Make sure that you start your dissection above the emergence of the intercostobrachial nerve (T2) and then descend toward the midaxillary line.

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  With a saw or bone cutter, carefully cut the intercostal musculature from the first intercostal space lateral to the manubrium, then extend these incisions downward, just anterior to the emergence of the anterior cutaneous branches of the intercostal nerves, cutting the ribs and intercostal musculature down to the level of the 10th rib ( Fig. 5.3 ).

  

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  Divide the manubrium transversely above the sternal angle using a bone saw, cutters, or scalpel ( Fig. 5.4 ).

  

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  After making the saw cuts, use a scalpel and bone cutters or mallet and chisel to free the anterior thoracic wall ( Fig. 5.5 ).

  

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  Once bone and connective tissue have been transected, use blunt scissors to lift the anterior thoracic wall. Try to avoid damage to the underlying lungs ( Fig. 5.6 ).

  

Dissection Tip

Often, in the first and second intercostal spaces, you will be able to place your fingertips underneath the internal surface of the anterior thoracic wall and lift it up ( Fig. 5.7 ).

If some parts are still connected to the wall, use a scalpel and bone cutters to free the anterior thoracic wall ( Fig. 5.8 ).

Be careful when you place your fingertips under the exposed ribs; sharp bone spicules are often present and may cause injury. Use a bone cutter or rongeur to remove these.

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  Place your fingertips underneath the openings of the thoracic wall and pull up ( Fig. 5.9 ).

  

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  If the internal thoracic vessels are still intact, cut them and then pull the chest wall inferiorly, exposing the thoracic contents.

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  As you reflect the wall inferiorly, incise the parietal pleura from the internal surface of the anterior thoracic wall with a scalpel, leaving it intact over the lungs ( Fig. 5.10 ).

  

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  Cut the sternopericardial ligaments that connect the pericardial sac to the posterior surface of the sternum.

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  Continue the reflection of the anterior thoracic wall downward until the thoracic viscerae can be clearly seen ( Fig. 5.11 ).

  

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  Keep the wall turned downward as the dissection proceeds ( Fig. 5.12 ).

  

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  Forcing the wall down usually results in sufficient stretching or tearing of tissues so that the anterior wall remains reflected inferiorly. If this is not the case, you can remove the anterior thoracic wall ( Fig. 5.13 ). Using blunt dissection with your hand or blunt-ended scissors from superior to inferior helps guide the anterior connective tissue as desired.

  

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  Observe the internal surface of the anterior thoracic wall, and identify the internal thoracic arteries and veins and their branches ( Fig. 5.14 ).

  

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  Reflect the parietal pleura to expose the intercostal muscles.

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  Reflecting the parietal pleura in the 1st and 2nd intercostal spaces exposes the internal thoracic artery. Identify it.

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  To expose the internal thoracic artery and vein further, reflect the transversus thoracis muscles.

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  Identify the branches of the internal thoracic artery, such as the perforating and anterior intercostal branches ( Fig. 5.15 ).

  

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  Identify the costodiaphragmatic and costomediastinal recesses.

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  After inspecting the subdivisions of the parietal pleura, push the lung away from the heart with your fingertips.

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  Identify the mediastinal pleura separating the lung from the pericardial sac.

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  Insert the scissors and separate the mediastinal pleura from the pericardium ( Figs. 5.16 and 5.17 ).

  
  

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  Identify the phrenic nerve traveling anterior to the hilum of the lung and preserve it ( Fig. 5.18 ).

  

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  Use the separation technique to expose the pulmonary arteries and veins ( Fig. 5.19 ).

  

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  Use the same technique for the contralateral lung ( Figs. 5.20 and 5.21 ).

  
  

Dissection Tip

The costodiaphragmatic recess is usually the location where excess embalming fluids accumulate during dissection. Drain the fluid using a syringe, and place paper towels into the recess ( Figs. 5.22 and 5.23 ). Also, once the lungs are removed, holes can be made in the posterior intercostal spaces so that fluid exits onto the dissection table. This method may necessitate placing a wedge or block under the thorax to lift the body slightly off of the dissecting table.

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  After exposing the pulmonary veins, pulmonary arteries, and primary bronchi at the hila of the left and right lungs, transect them with scissors or a scalpel ( Figs. 5.24, 5.25, 5.26 , and Plate 5.1 ).

  
  
  
  

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  Remove the lungs from the thoracic cavity, and observe the posterior mediastinum covered with parietal pleura ( Figs. 5.27 to 5.30 ).

  
  
  
  

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  Place the lungs onto a tray, and examine the internal surface of each lung separately. For the right lung, identify the oblique and horizontal fissures and their corresponding upper, middle, and lower lobes ( Fig. 5.31 ).

  

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  Inspect the hilum of the lung, and identify the pulmonary arteries, pulmonary veins, and primary bronchi ( Fig. 5.32 ).

  

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  Similar to the right lung, identify the oblique fissure in the left lung and the corresponding upper and lower lobes ( Fig. 5.33 ).

  

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  Inspect the hilum of the lung, and identify the pulmonary arteries, pulmonary veins, and primary bronchi ( Fig. 5.34 ).

  

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  Identify the cardiac notch on the superior lobe of the left lung and lingula.

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  Inferior to the hilum, trace the two layers of visceral pleura fusing together to form the pulmonary ligament ( Fig. 5.35 ).

  

Optional Lung Dissection

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  With your forceps, lift the bronchus, and using blunt dissection, separate it from the lung parenchyma.

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  Remove most of the internal lung parenchyma with your forceps and scissors, leaving its borders and lateral walls intact ( Fig. 5.36 ).

  

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  In the right lung, you will be able to dissect the superior, middle, and inferior lobar bronchi.

Removal of the Heart

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  Before removing the heart from the pericardial cavity, the phrenic nerves must be identified and preserved. Observe the pericardiacophrenic vein at the lateral border of the pericardial sac bilaterally.

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  Dissect the pericardium next to the pericardiacophrenic vein, and identify the phrenic nerve ( Figs. 5.37 and 5.38 ).

  
  

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  Dissect the phrenic nerve along its entire length, from the top of the thoracic cavity to its penetration of the diaphragm ( Figs. 5.39 and 5.40 ).

  
  

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  With toothed forceps, lift the right inferolateral edge of the pericardium near the diaphragm, and make a small incision ( Fig. 5.41 ).

  

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  Note the attachment of the pericardium to the central tendon of the diaphragm.

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  Make a transverse incision in the pericardium parallel to the diaphragmatic surface ( Fig. 5.42 ).

  

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  Make a second, connecting vertical incision through the pericardium along the side of the right atrium ( Fig. 5.43 ) and along the side of the left ventricle ( Fig. 5.44 ).

  
  

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  Note that the parietal pericardium and the visceral pericardium (epicardium) are continuous with the great vessels as they pierce the fibrous pericardium.

External Inspection

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  For orientation of the heart within the pericardial cavity, observe the position of the right atrium, right auricle, right ventricle and its outflow tract, and pulmonary trunk. Note the left atrium, left ventricle and apex of the heart, and anterior and posterior interventricular grooves.