Prelab Images - Posterior Mediastinum

Prelab should consist of reading the lab manual and dissector answers and viewing the dissection video. To begin your study, you may find it useful to look over the Netter's or LWW Atlas images listed below.

Step 1. Identify the vagus nerves as they pass posterior to the roots of the lungs; examine the esophagus throughout its length. (Play movie)

Plates N209 or TG4-38 and N240 or TG4-45 show the course of the left and right vagus nerves and how they form the esophageal plexus. These plates also show branches to the cardiac and pulmonary plexuses. Plates N209 or TG4-36 and N240 or TG4-46 show branches from the sympathetic chain going to the cardiac and pulmonary plexuses. Plates N240 or TG4-45, N74, and N75 or TG7-92 show the course of the recurrent laryngeal nerve as it branches off the vagus nerve and moves superiorly to innervate many of the muscles of the larynx. Plates N206 or TG4-29 and N212 or TG4-36 show the recurrent laryngeal nerve wrapping around the aortic arch behind the ligamentum arteriosum.

Plate N232 or TG4-38 shows the esophagus. Plates N194 and N195 or TG5-33 show the esophageal hiatus of the diaphragm. Plates N63 or TG7-10, N234, and N235 show the esophagus beginning deep to the larynx and inferior to the laryngopharynx. Plate N236 or TG4-37 shows the esophagus ending at the stomach and plate N236 is a close-up of this. Plates N234 and N235 show that the esophagus has an inner (circular) muscle layer and an outer (longitudinal) muscle layer. The innervation of the esophagus is shown in plates N209 or TG4-38 and N240 or TG4-45. The blood supply and venous drainage of the esophagus is shown in plates N237 or TG4-38 and N238 or TG4-40.

Step 2. Identify the branches of the descending thoracic aorta. (Play movie)

Remove any remaining mediastinal pleura. Plates N212 or TG4-37, N232 or TG4-38, and N237 or TG4-39 show the course of the desecending aorta and its relations to the pulmonary trunk, tracheal bifurcation, left pulmonary artery, esophagus, and vertebral bodies. Plates N194 and N195 or TG5-33 show the aorta passing through the diaphragm. Plates N207 or TG4-38 and N237 or TG4-39 show the aorta giving off bronchial and esophageal arteries. Plates N169 or TG1-21, N192 or TG4-38, and N237 or TG4-39 show the aorta giving off posterior intercostal arteries. Plate N260 or TG4-39 shows the subcostal artery, which will not be seen in this dissection (this is a segmental artery, like a posterior intercostal artery, that runs underneath the 12th rib). Plate N192 or TG4-09 and TG4-10 reviews the blood supply of an intercostal space. Plates N171 and N172 or TG1-21 show the posterior branch of the posterior intercostal artery going to help supply the spinal cord. Plates N191 or TG4-09 show the relation of the vein, artery, and nerve to each other within the intercostal space (VAN). Plates N191 or TG4-09 and N192 or TG4-10 show the intercostal artery running deep to the internal intercostal muscles, but superficial to the innermost intercostal layer. Plate N258 or TG4-10 identifies the subcostal muscles.

Step 3. Identify the azygos system of veins. (Play movie)

Plate N238 or TG4-10 shows the posterior intercostal veins forming the azygos vein and the right superior intercostal vein on the right side of the body and the hemiazygos vein, accessory hemiazygos vein, and left superior intercostal vein on the left side of the body. If you look closely at plate N238 or TG4-40 you will see that the hemiazygos and accessory hemiazygos veins run underneath the esophagus to communicate with the azygos vein. The first posterior intercostal vein drains directly into the brachiocephalic vein on each side. You will also find bronchial and esophageal branches draining into the azygos system (esophageal drainage is shown in plate N238). It is important to notice in plate N238 or TG5-28 the esophageal branches of the left gastric vein. This forms a portal-caval anastomoses (the portal vein can be traced to the vena cava by going through the left gastric vein and its esophageal branches to the esophageal plexus to the azygos vein to the superior vena cava).

Step 4. Identify the thoracic duct. (Play movie)

Plate N266 or TG5-37 shows the thoracic duct being formed at the cisterna chyli (this will be seen later) and running into the thorax with the aorta. It then runs underneath the esophagus from the right side to the left before emptying into the left subclavian vein (see plates N238 and N266 or TG4-44). Plate N239 or TG4-44 shows the posterior mediastinal lymph nodes. Plate N208 or TG4-42 shows the bronchomedistinal lymph trunks, which are covered in detail with the lungs.

Step 5. Clean and identify the sympathetic trunks and their branches. (Play movie)

Plate N166 or TG8-01 shows a schematic of the sympathetic nervous system. Plates N130 or TG7-15 show the cervical sympathetic trunk (with superior, middle, and cervicothoracic/stellate ganglia). The cervical trunk is continuous with the thoracic sympathetic trunk. Plate N209 or TG4-46 shows the cervicothoracic (stellate ganglion) and gray and white rami communicantes. Plate N254 shows the gray and white rami communicantes from a different angle. Plates N209 or TG4-45 and N240 or TG4-46 show thoracic sympathetic nerves to the cardiac and pulmonary plexuses. Plate N209 or TG4-46 shows the greater thoracic splanchnic nerve (T5-T9). The lesser (T10 and T11) and least (T12) thoracic splanchnic nerves are also seen in plate N209 or TG4-45, but will not be seen in this dissection.