PROCEDURE

Pre-Work Video Guides (pre-work before lab)

Clinical Skills

 Simple Interrupted Suturing (2min)

1. PRE-WORK (before lab) review the organization of the human vertebral column from your atlas or on an articulated skeleton in the lab.
    (Netter193) (Netter197)

a) Thoracic vertebra: Identify the large body and neural arch (pedicles and laminae) which form a 'padlock-like' arrangement. The bodies of the vertebrae 'protrude' several inches anteriorly into the thoracic cavity such that the posterior-most plane of the ribs is approximately level with the plane of the transverse processes of the vertebra.

b) Rib joints: In the thorax, ribs form articulations with the body of each vertebra (costovertebral joint) and with each transverse process (costotransverse joints). These are stabilized by several ligaments spanning the rib to vertebra, but we will not study these specifically.

2. On your donor observe the barrel-shaped arrangement of the ribs and position of the diaphragm.
    (Netter192) (Photo2029)

Ribs are angled from superior on the back at their articulation with the vertebra, to inferior at their costal cartilages anteriorly.

The diaphragm attaches to the sternum and costal margin at a position more superior than the attachment to the posterior wall.

Push your hand deep and posterior along the lateral side of the rib cage and feel the depth of that space. This is the costodiaphragmatic recess.

Move your hand to the most superior point in the pleural cavity on each side and observe how the cavity extends into the neck. The plural cavity (and lungs) extends approximately an inch superior to the thoracic inlet and houses the apex of the lung. Thus, any injury just superior to the clavicle has a risk of lung penetration at the apex.

Radiology - In a CTX, the lucency (less dense apperance) of the lung airspace is readily observed in the root of the neck superior to the clavicles in the anatomic position (Rad2003a). The hemidiaphragms are visible on a coronal film, but the opacity of the liver and intestines obscures a view of the costodiaphragmatic recess. That recess is best observed in a lateral film showing the angled nature of the diaphragm and location of the costodiaphragmatic recess is apparent. (Rad2002a).

3. Examine the heart in situ and use your fingers to trace the anterior aspect and the borders of the heart.
    (Netter216) (Photo2059)

There can be adhesions connecting the visceral and parietal pericardium at the inferior surface of the heart (i.e. the diaphragm side), separate those if present.

The chambers that can be seen from the anterior view are the right atrium, right ventricle, a small part of the left atrium (most of the left atrium is posterior), and left ventricle.

The heart sits rotated in the thoracic cavity such that most of the anterior aspect of the heart is formed by the right ventricle and most of the posterior aspect is formed by the left atrium.

The right border of the in situ heart is formed by the right atrium which receives the superior and inferior vena cava vessels. The left border is formed by the left ventricle and a small part of the left atrium (the left atrial appendage, or left auricle).

Radiology - The left and right borders of the heart are very useful in a chest x-ray as they are readily distinguished beside the lucent appearance of the lung airspaces. Most of the great vessels are obscured by vertebra and midline soft tissues, but the border of the superior vena cava on the right while the aorta (often called the 'aortic knob' due to the distinct bump it makes) and pulmonary trunk visible on the left. (Rad2007)

4. Lift the heart gently and transect the inferior vena cava  just inferior to its entrance into the right atrium.
    (Netter219) (Photo2061)

5. Using your hand place fingers under the inferior side of the heart and push your fingers superiorly along the posterior surface of the heart until your fingers are blocked by the posterior reflections of pericardium around the pulmonary veins.

This 'cul-du-sac' is the oblique pericardial sinus.

Reflection and fusion of the visceral and parietal pericardial layers around the pulmonary veins and inferior vena cava delimit the blind-ended pocket-like space of the oblique pericardial sinus. This has minimal clinical significance.

6. Insert a blunt probe posterior to the pulmonary trunk and ascending aorta, pushing the probe from the left across to the right until it emerges between the superior vena cava and aortic arch.
    (Figure225) (Netter219) (Photo2058)

The probe should pass through approximately 1cm superior to the emergence of these vessels from the heart. This 'pathway' is the transverse pericardial sinus.

The twist of the heart during development brings the output (aorta & pulmonary arteries) and input (vena cava & pulmonary veins) ends of the heart tube together. As they twist together, this leaves a passageway, or sinus, that runs between the great vessels called the transverse pericardial sinus.

Clinically, this is the most useful of the pericardial sinuses as passing a clamp through the transverse pericardial sinus allows all heart output (aorta and pulmonary trunk) to be clamped during some heart surgeries or during heart transplant.

7. Using the probe as a guide, transect the ascending aorta and pulmonary trunk at this level.
    (Photo2060)

8. Position a probe posterior to the superior vena cava, such that the probe lays between the right atrium and the junction of the arch of the azygos.
    (Photo2094)

9. Using the probe as a guide, transect the superior vena cava between the right atrium and the connection of the arch of the azygos vein.
    (Photo2095)

10.  Reflect the heart sufficiently to expose its posterior surface and pull the pulmonary veins through their openings in the pericardial sac.

Since the veins were already transected when removing the lung, they should pull readily out of their pericardial sac openings. However, if they are firmly attached you can transect the pericardial sac attachments.

11. Free any spot adhesions of the visceral and parietal pericardium, or remaining pericardial attachments, and remove the heart.

12. When removed, prepare the heart for the MS2 class who will come in to examine detailed heart features in the Cardiac section in a few days time.

a) Take the white bucket from under your table and half fill the bucket with water.

b) Add a 'slurp' of wetting agent from your wetting agent bottle to the bucket (a slurp is approximately 100ml or equivalent to about 20% of the bottle).

c) Place the heart into the bucket such that it is submerged (if the heart is not submerged add a little more water if needed).

d) Place the bucket on top of the table beside or between the donors legs so that it will be inside the plastic bags when you close up at the end of today.

13. Dissect away the remainder of the pericardium, cutting through its attachments to the great vessels and diaphragm.
    (Figure232) (Netter236) 

Branches of the vagus nerves travel on the surface of the esophagus. Try to minimize damage to these as you remove the posterior pericardium.

Be careful not to cut the phrenic nerve passing to the left and right of the mediastinum.

Observe that immediately posterior to the heart, the esophagus courses just to the right of the midline and the descending thoracic aorta just to the left of the midline.

14. Return to the left vagus nerve as it crosses the arch of the aorta and gave of the left recurrent laryngeal nerve.
    (Netter236) (Netter235) (Photo2021)

Branches of the vagus nerves contribute to the cardiopulmonary plexus

15. Blunt dissect following the left vagus as it courses posterior to the root of the left lung, reaching the esophagus.
    (Netter236) (Photo2024)

At this point branches of the left vagus nerve course onto the anterior side of the esophagus.

The left and right vagus nerves contact the esophagus on the lateral sides. Then, due to a 90 degree rotation of the esophagus during development, the right vagus nerve swings around to become posterior to the esophagus while the left vagus nerve swings around to become anterior to the esophagus.

16. Blunt dissect at the point the left vagus contacts the esophagus and identify branches spreading out from the left vagus over the surface of the esophagus. 
    (Netter243) (Photo2024)

These, together with branches from the right vagus nerve and branches arising the sympathetic chain ganglia, form the esophageal nerve plexus traveling inferiorly along the esophagus.

17. Near the diaphragm, observe that fibers of the esophageal nerve plexus recombine into nerve trunks.
    (Netter243)

The left vagus spreads out into the esophageal plexus primarily on the anterior esophagus. The fibers of this plexus on the anterior side of the esophagus recombine to form the anterior vagal trunk in order to pass through the esophageal hiatus of the diaphragm.

The right vagus nerve spreads out into the esophageal plexus primarily on the posterior side of the esophagus (not visible in our dissection as we have been following only the left vagus). The fibers of the plexus on the posterior side of the esophagus recombine to form the posterior vagal trunk in order to pass through the diaphragm.

There is most typically a single anterior and single posterior trunk. However, the point at which these trunks form can be high or low on the esophagus. In some individuals multiple trunks may be present passing through the diaphragm.

18. Blunt dissect and clean connective tissue attachments from the esophagus mobilizing it free from the posterior wall (vertebral column) working your way inferiorly to the diaphragm. 

Since much of the esophagus is covered by fibers of the esophageal plexus, take care as you clear connective tissue in order to mobilize esophagus that you are not stripping away the major vagus branches of the plexus at the same time.

19. Return to the aorta and follow the arch of the aorta as it courses leftward and posterior into the descending aorta, which continues inferiorly just to the left of the vertebral column.
    (Figure233) (Netter240) 

20. Clear connective tissue away from the anterior and left side of the descending aorta.
    (Figure233) (Netter240) 

As you remove connective tissue, you may observe small branches that arise from the anterior surface of the aorta. These are small and not readily identifiable.

The more superior of these anterior arteries supply the lung tissue. The more inferior are esophageal arteries (one every few inches along the esophagus). The esophageal arteries are usually transected when mobilizing the esophagus and they will no longer be connected. 

Examine posteriorly, and identify the left posterior intercostal arteries that branch from the descending aorta between each set of ribs. One branch is given off into each intercostal space.

21. On the right side of the vertebral column identify the azygos vein and clean connective tissue away from the vein on its anterior and right sides.
    (Figure234) (Netter241) (Netter240)

As you clean the azygos vein, identify the right posterior intercostal veins that branch between each set of ribs. One branch is given off into each intercostal space. 

The hemiazygos vein (left side, inferior) and accessory hemiazygos vein (left side, superior) are located along the left side of the vertebral bodies. However these are difficult to observe as the descending aorta can obscure view of the veins so we will not dissect them specifically.
(Figure234) (Netter241) (Netter198)

There is considerable variability in the hemiazygos and accessory hemiazygos veins. Connecting vessels bridging between the two are common.

Typically, the accessory hemiazygos vein crosses the body of the eighth vertebra and the hemiazygos crosses the body of the ninth vertebra. However, there is often variability between individuals in where these vessels cross and there can also be multiple crossings.

Posterior intercostal veins drain directly into the azygos from the right.  On the left venous blood from the posterior intercostal veins drain into one of the hemiazygos veins and then cross over to the azygos vein to reach the heart. Venous drainage for virtually all of the posterior body wall (left and right), thus, enters the superior vena cava via the arch of the azygos vein.

22. With the right and left sides of the posterior mediastinum clean of connective tissue, finish mobilizing the esophagus and retract it to the left.

You may need one person to gently hold the esophagus retracted to the left for the next steps.

23. Blunt dissect carefully into the connective tissue to the left of the azygos to find the thoracic duct.
    (Figure234) (Netter242) 

The thoracic duct lies immediately posterior to the esophagus and in-between the azygos and descending aorta.

The thoracic duct looks similar to a small vein, but with no blood, and has small bulges along its length (these are valves inside the duct giving it a beaded appearance from the outside).

The duct is thin walled and easily torn, if you cannot find it against the vertebral bodies, look on the posterior surface of the esophagus as you may have pulled the thoracic duct away with the esophagus.

With care you may find several very small lymphatic ducts draining into the thoracic duct from the intercostal lymphatic vessels (these are very small).

Occasionally, the thoracic duct will exist as a pair of ducts rather than a single duct.

The thoracic duct brings lymph back to the circulation from all of the lower body and from the left upper quarter of the body. The thoracic duct joins to the left venous angle (confluence) of the left internal jugular and left subclavian veins.

The upper right quarter of the body has a separate duct that drains into the right venous angle of the right internal jugular and right subclavian veins.

24. Follow the thoracic duct inferiorly, where it passes through the diaphragm with the descending aorta. 

Do not follow it through the diaphragm at this time.

25. Next follow the thoracic duct some distance superior towards the left venous angle (formed by the confluence of the subclavian vein and internal jugular vein).

Do not try to follow the duct to the termination at the left venous angle at this time as it will damage structures you will dissect later in the course.

26. Identify and dissect at least one intercostal neurovascular bundle (intercostal artery, intercostal vein, and intercostal nerve) from their origination points out laterally.
    (Netter234) (Netter235) (Photo2032) (Photo2093)

Bundles on the right side will be easier to isolate than on the left, as the descending aorta and heart may impede easy access.

You may need to strip posterior parietal pleura from the posterior wall if this had not come away with the lung removal in the previous sessions. Grasp the parietal pleura with forceps and peel back from the rib cage and vertebral column in the area you intend to expose.

In some cases the adhesion between the parietal pleura and the posterior thorax is very tight and you will need to dissect through a little at a time to follow the neurovascular bundle.

In the neurovascular bundle as it courses lateral between the ribs, the vein is the most superior structure, the artery middle, and the nerve inferior (V.A.N. for vein-artery-nerve).

The left intercostal veins branch from the hemiazygos veins and right intercostal veins branch from the azygos vein. 

The intercostal arteries branch as paired vessels from the aorta at each vertebral level.

The left posterior intercostal arteries run posterior to the hemiazygos vein. The right posterior intercostal arteries pass over the anterior and lateral region of the vertebrae and run posterior to the azygos vein to enter the neurovascular plane on the right. 

Remember this neurovascular bundle courses between the innermost and internal intercostal muscles. In the posterior thoracic wall the internal intercostal is mostly membranous in structure and the innermost muscles indistinct.

27. On both lateral sides of the vertebral column tightly adherent to the vertebral bodies, find and expose a portion of the sympathetic trunk (also called the sympathetic chain).
    (Netter243) (Netter234) (Netter235) (Photo2093)

It may be necessary to gently remove connective tissue covering over the sympathetic chain to visualize the ganglia and connecting nerves.

Each vertebral level has a pair of sympathetic ganglia that are joined by nerve fibers to sympathetic ganglia lying superior and inferior.

Gray and white rami communicantes connect the ganglia of the trunk posteriorly to the spinal nerves.

It is impossible in donors to identify gray and white rami communicantes based on color, however the one arising most laterally from the spinal nerve/ventral primary ramus of the two should be the white rami communicantes.

28. Observe nerves emerging anteriorly from the sympathetic trunk ganglia, these are contributions from each vertebral level to the splanchnic nerves.
    (Netter234) (Netter235) (Photo2093)

Use a probe to identify the greater splanchnic nerve, which receives contribution branches from the fifth through ninth thoracic sympathetic ganglia.

These branches pass diagonally inferiorly across the lateral body of thoracic vertebrae. The contribution branches from the individual vertebral levels come together at lower thoracic levels to form into the single greater splanchnic nerve.

The splanchnic nerves pass through the diaphragm associated with the aorta and end in ganglia in the abdominal cavity, which we will examine later in the course.

The lesser splanchnic nerve arises from the tenth and eleventh thoracic sympathetic ganglia, and the least splanchnic nerve from the twelfth sympathetic ganglia. Due to the curvature of the diaphragm, the lesser and least splanchnic nerves cannot yet be seen clearly at this time.

There can be variation in where the splanchnic contributions arise, with contributions able to come from one thoracic vertebra sympathetic ganglion level higher or lower.

You may also have observed nerve branches descending against the vertebrae from higher thoracic (and cervical) origins. These are the cardiac splanchnic nerves which terminate in the cardiopulmonary nerve plexus.

29. Using your fingers, explore the superior surface of the diaphragm and note the major openings allowing passage of thoracic structures into the abdominal cavity.
    (Netter200)

Caval opening (also termed caval foramen or caval hiatus) - this opening allows passage of the inferior vena cava through the diaphragm.

Esophageal hiatus - the opening through which the esophagus and anterior/posterior vagal trunks pass through the diaphragm.

Aortic hiatus - the opening for the aorta, azygos vein, hemiazygos vein, and thoracic duct. This is the most posterior opening, and due to curvature of the diaphragm it is also quite inferior.

CLINICAL EXERCISE - Simple interrupted suturing

30. Any surgical intervention involves an opening through the integument and deeper structures that must be closed to repair the structure or prevent infection. The most traditional and common method of closing an opening is by suture (additional methods utilizing staples and surgical adhesives depending on the procedure).

In this clinical exercise, you have the chance to suture muscle/subcutaneous tissues in your donor as a mock surgical intervention (note, the sutures we use will not penetrate skin itself).

A video of simple interrupted suturing is available in the introduction section of the Dissector and can be brought up with this link ------ video ------>

For the steps to perform:
                               ------ click here ------

Post-Lab Daily Clinical Review Cases

Each lab has several multiple choice practice cases to reinforce understanding of the material within the lab and associated lectures. These are optional to review at home for consolidating and testing understanding.

Case 01

Case 02

CHECKLIST

Soft Structures

Esophagus

Descending aorta

Costodiaphragmatic recess

Transverse sinus

Vagus
    Vagus nerve
    Esophageal nerve plexus
    Vagal trunk

Azygos vein

Sympathetic trunk (chain)
    Sympathetic ganglia
    Rami communicantes
    Greater splanchnic nerve

Thoracic duct

Intercostal neurovascular bundle
    Posterior intercostal vein
    Posterior intercostal artery
    Intercostal nerve

Diaphragm
    Caval foramen
    Esophageal hiatus
    Aortic hiatus