TBL13 - Posterior Mediastinum

Question 1

Where is the posterior mediastinum located between? Where does the esophagus travel?

Answer 1

1) The posterior mediastinum is between the middle mediastinum and the bodies of vertebrae T5 to T12
2) The esophagus courses adjacent to the vertebral column through the superior mediastinum and into the inferior mediastinum

Question 2

What mainly makes up the posterior aspect of the heart? Where does it lie?

Answer 2

The posterior aspect of the heart is formed mainly by the left atrium, which lies immediately anterior to the esophagus

Question 3

What is the esophagus slightly compressed by proximally? distally?

Answer 3

1) The esophagus is slightly compressed proximally by the arch of the aorta and left main bronchus
2) At vertebra T10, the esophageal hiatus of the diaphragm compresses the esophagus distally

Question 4

Why can dysphagia and pulmonary hypertension result from mitral valve stenosis?

Answer 4

Mitral valve stenosis results in an increase in blood pressure in the left atrium, causing pulmonary hypertension and dysphagia by pressing on the esophagus

Question 5

How are the esophageal compressions typically observed?

Answer 5

1) The esophagus may have three impressions, or “constrictions,” in its thoracic part
2) These may be observed as narrowings of the lumen in oblique chest radiographs that are taken as barium is swallowed
3) The esophagus is compressed by three structures: (1) the arch of the aorta, (2) the left main bronchus, and (3) the diaphragm

Question 6

Where does the aortic hiatus reside? Cite the two structures that accompany the descending aorta through the hiatus.

Answer 6

1) The aortic hiatus resides at vertebra T12

2) The thoracic duct and azygos vein ascend on its right side and accompany the descending aorta through this hiatus

Question 7

Where is the thoracic duct located? What is its function?

Answer 7

1) The thoracic duct is immediately to the right of the descending aorta
2) The duct returns lymph from the lower limbs, pelvis, abdomen, left side of the thorax, left upper limb, and left side of the head and neck to the left venous angle

Question 8

Where does the left venous angle reside?

Answer 8

The left venous angle resides at the junction formed by the left internal jugular vein and left subclavian vein i.e., the origin of the left brachiocephalic vein

Question 9

Where does the smaller right lymphatic duct return lymph from and to?

Answer 9

The smaller right lymphatic duct returns lymph from the right upper limb and the right side of the thorax, head, and neck to the right venous angle

Question 10

Where is the azygos vein located? Where does it originate from?

Answer 10

1) The azygos vein is immediately to the right of the thoracic duct
2) The azygos vein is formed by the union of the ascending lumbar veins and right subcostal veins at the level of T12

Question 11

Where does the azygos vein empty into? What is another function of the azygos vein?

Answer 11

1) The azygos vein drains blood from the walls of the thorax and abdomen and empties into the SVC
2) The azygos vein also provides a collateral pathway between the IVC and SVC

Question 12

How do alternate venous pathways to the right atrium differ after obstruction of the SVC superior to the entrance of the azygos vein and after obstruction of the IVC?

Answer 12

1) The azygos, hemi-azygos, and accessory hemi-azygos veins offer alternate means of venous drainage from the thoracic, abdominal, and back regions when obstruction of the IVC occurs
2) In some people, an accessory azygos vein parallels the azygos vein on the right side. Other people have no hemi-azygos system of veins
3) A clinically important variation, although uncommon, is when the azygos system receives all the blood from the IVC except that from the liver. In these people, the azygos system drains nearly all the blood inferior to the diaphragm, except from the digestive tract
4) If obstruction of the SVC occurs superior to the entrance of the azygos vein, blood can drain inferiorly into the veins of the abdominal wall and return to the right atrium through the azygos venous system and the IVC

Question 13

At vertebra T8, what is formed? What does this allow?

Answer 13

At vertebra T8, a hiatus in the central tendon of the diaphragm forms the caval opening, which enables the IVC to ascend from the abdomen into the thorax

Question 14

What is the central tendon of the diaphragm derived from? What facilitates the formation of the caval opening and when does this occur?

Answer 14

1) The central tendon of the diaphragm is derived from the septum transversum
2) During fusion of the horseshoe-shaped endocardial tube to form the single heart tube, the sinus venosus remains embedded in the septum transversum thereby facilitating the formation of the caval opening

Question 15

Where are the bilateral sympathetic trunks and greater splanchnic nerves located?

Answer 15

The bilateral sympathetic trunks and greater splanchnic nerves are located on the posterior thoracic wall

Question 16

What types of fibers are the greater splanchnic nerves? Where do they originate? What do they join?

Answer 16

1) The greater splanchnic nerves are presynaptic sympathetic fibers that originate in spinal cord segments T5 to T9 and join the anterior rami of spinal nerves T5-T9
2) The presynaptic fibers subsequently join the white communicating rami to enter the segmental paravertebral ganglia

Question 17

Where do the presynaptic greater splanchnic nerves travel to? Where do they synapse?

Answer 17

1) Rather than synapsing, the presynaptic greater splanchnic nerves traverse the segmental sympathetic ganglia to directly enter the thoracic cavity
2) The greater splanchnic nerves exit the thoracic cavity via tiny apertures in the diaphragm and synapse in sympathetic ganglia of the abdomen