Download Lab 6 Thoracic Aneur..

Thoracic Aortic Aneurysm
This laboratory exercise is in two parts. First, you will follow a surgical procedure to
repair an aneurysm of the descending thoracic aorta. Second, you complement the
procedure with an anatomical dissection of the posterior and superior mediastinum.
CC: End-stage ischemic cardiomyopathy
Essential Question:
How does embryonic folding affect the structure of the posterior and superior
mediastinum?
Guiding Questions:
 What are the contents of the posterior mediastinum? Superior mediastinum?
 Why does the recurrent laryngeal nerve recur about different structures on the
right and left sides?
 Which vessels in the superior mediastinum are derived from embryonic arches
four and six?
 Describe the arterial anastamoses within the chest wall.
 How is blood supplied to the vertebral column?
 Describe the course of parasympathetic nerves in the mediastinum.
 What is the major lymphatic vessel of the posterior mediastinum?
Use the history and physical and laboratory data to answer the following questions:
What evidence is there of cardiovascular disease?
Flash movie hp_1
Where is the aneurysm located?
Flash movie hp_2
Why is high blood pressure a problem for a patient with an aneurysm?
Flash movie hp_3
Diagnostic Studies:
Andy: do we have any plain films or CT’s of this patient’s aneurysm? I believe
Ann shows an aneurysm of the arch in her workshop
It is essential to preserve the blood supply to the spinal cord (arteries of Adamkiewicz).
To do this, intercostal arteries were injected with contrast dye. The arteries of
Adamkiewicz generally originate from intercostal arteries 9 or 10.
Operative approach:
In an actual case, you would use a left lateral thoracotomy in the fifth intercostal space
and direct the anesthesiologist to collapse the left lung, but you have already removed the
chest plate and lungs to provide you ample access to the aorta. A bypass machine would
be installed in the femoral artery and vein. The blood would be cooled to 18oC and the
head packed in ice. This would stop the heart and enable the brain and spinal cord to
tolerate the absence of blood-flow for 45 minutes. You can take more time to do today’s
procedure.
1. In preparation for suturing in a graft, detach the descending aorta from the
esophagus and thoracic spine. Which veins will be placed at risk and what
territories to they drain?
Flash movie oa_1a
Which arteries are placed at risk and what territories to they supply?
Flash movie oa_1b
Which lymphatic vessels are placed at risk and what territories to they drain?
Flash movie oa_1c
What nerves are placed at risk and what would be the consequence of injuring
them?
Flash movie oa_1d
2. Make an incision along the length of the descending aorta. In an actual case
the length of the incision would correspond to the length of the aneurysm, but
you should make your incision about 7-8 cm. What nerve is potentially placed
at risk at the superior end of the incision? Locate on your donor an important
branch of this nerve where it wraps around the aorta. What landmark will
help you identify this branch?
Flash movie oa_2
3. Make transverse incisions about half the diameter of the aorta at each end of
your longitudinal incision. Open the aorta, remove any clotted blood and
examine the paired branches of intercostal arteries. Generally, these are not
connected to the graft, but are ligated shut. How will the intercostal spaces be
perfused?
Flash movie oa_3a
What circumstance, discussed earlier, would lead the surgeon to connect a pair of
intercostal arteries to the graft?
Flash movie oa_3b
Normally, the graft is laid into the open bed of the aorta, sutured to the healthy aorta at
each end and the diseased wall of the aorta folded over the graft and sutured back
together. However, we will continue with an anatomic exploration of the superior and
posterior mediastinum. This will demonstrate the challenges for aneurysm repairs in
other parts of the thoracic aorta and other surgical procedures in the region.
1. Posterior to the manubrium, you may recognize a fatty/fibrous mass that is the
remnant of the thymus. What was the function of the thymus? When does it begin
to atrophy?
Flash movie eh_1
2. Find the two brachiocephalic veins and their junction to form the superior vena
cava. Which brachiocephalic vein crosses the midline deep to the manubrium?
How would this vessel appear of on a sagittal view of an MRI?
Flash movie eh_2
3. Divide the left brachiocephalic vein along the midline and reflect the vein
laterally to view branches of the arch of the aorta. How does the branching
pattern of your donor compare to common variations? Identify these vessels on a
arteriogram and trace them through the axial slices of a CT.
4. Find the ligamentum arteriosum and the recurrent laryngeal branch of the left
vagus. Note that the region is rich in lymph nodes. Why? If a neoplasia or
enlarged lymph node compressed the recurrent laryngeal nerve, with what
symptom(s) would the patient present?
Flash movie eh_4
5. Where does the right recurrent laryngeal branch from the vagus? Why is this
different from the left recurrent laryngeal nerve?
Flash movie eh_5
6. Trace the vagus nerves towards the esophagus and observe how they ramify to
form a nerve plexus about the esophagus. Which vagus nerve do you observe
ramifying on the anterior surface of the esophagus? The posterior surface? Why
do the right and left vagus nerves travel on the anterior and posterior surfaces of
the esophagus rather than on the right and left sides?
Flash movie eh_6
7. Look for the thoracic duct. Inject it with paint and massage the paint superiorly.
How far can you trace the paint? Where should it go? What does this vessel do?
What would happen if it were severed during surgery?
Flash movie eh_7