L30-31: Mediastinum I-II

Question 1

Definition of mediastinum. Sub-divisions

Answer 1

• Space between two pleural sacs which contains all structures in thorax except the lung and pleurae
• Superior, inferior (anterior, posterior)

Question 2

Borders of mediastinum

Answer 2

• Superiorly: thoracic inlet
• Inferiorly: thoracic diaphragm
• Anteriorly: sternum and costal cartilages
• Posteriorly: thoracic vertebrae

Question 3

Superior mediastinum. Location and contents

Answer 3

• Superior to sternal angle at T4-5
• Thymus, brachiocelaphic veins, SVC, aortic arch with branches, vagus nerves, left recurrent laryngeal, phrenic nerves, trachea, thoracic duct, esophagus, SCG

Question 4

Inferior mediastinum. Location

Answer 4

• Inferior to sternal angle (T4-5) through T12 vertebra

- Contains anterior, middle and posterior mediastinum

Question 5

Anterior mediastinum. Location, contents

Answer 5

• Sternum/transversus thoracis m and pericardium
• Contains remains of thymus (in infant/child, not adult), fat, loose CT, lymph nodes, vessels?, branches of internal thoracic artery, sternopericardial ligament (xiphoid to pericardium)

Question 6

Middle mediastinum. Location, contents

Answer 6

• Body of sternum, 2nd-6th costal cartilages, 5th-8th thoracic vertebrae
• Contains heart, pericardium, phrenic nerves, primary bronchi, origins of great vessels (SVC, IVC, ascending aorta, pulmonary arteries and veins), nerves?, lymphatics (subepicardial lymph plexus)

Question 7

Posterior mediastinum. Location, contents

Answer 7

• Pericardium, diaphragm and T5-12 vertebrae
• Contains descending aorta with thoracic branches, thoracic ducts, azygos system of veins, esophagus, nerves (esophageal plexus, aortic plexus, thoracic splanchnic nerves with rami communicantes), lymphatics (posterior mediastinal lymph nodes, intercostal lymph nodes, diaphragmatic lymph nodes)

Question 8

In what sub-division of mediastinum is left recurrent laryngeal nerve found?

Answer 8

• Superior mediastinum

Question 9

Divisions of thoracic aorta in posterior mediastinum

Answer 9

• Bronchial – 2 from left, one from right
• Esophageal
• Mediastinal (to lymph nodes)
• Pericardial
• Posterior intercostals (3rd-11th)
• Subcostal (under 12th rib)
• Superior phrenic (last branch – to superior surface of diaphragm)

Question 10

At what level does thoracic duct cross over? What direction? Where does it empty?

Answer 10

• T4-6
• From right to left
• Empties into left internal jugular vein and left subclavian vein

Question 11

Describe azygos system of veins. What is drained?

Answer 11

1. ) Azygos vein
   - Forms from union of right subcostal and right ascending lumbar vein
   - Ascends posterior thoracic wall arches over root of right lung into SVC
   - Drains right side of thoracic and abdominal wall
2. ) Hemiazygos vein
   - Forms from union of left subcostal and left ascending lumbar vein
   - Ascends and crosses over to azygos at vertebral level T9
   - Drains left 9th-11th IC spaces
3. ) Accessory hemiazygos vein
   - Descends left side of thoracic vertebral colum
   - Cross over to azygos at vertebral level T7 or 8
   - Drains left 4th-8th IC spaces
4. ) Right and left superior intercostal vein
   - Right drains 2nd and 3rd IC spaces into azygos
   - Left drains 2nd and 3rd IC spaces into left brachiocephalic vein

Question 12

Describe thoracic splanchnic nerves seen in posterior mediastinum. What fibers are these, where are they going?

Answer 12

• Main source of sympathetics to abdomen, these are pre-ganglionic SNS fibers that are going to pre-aortic ganglion
  1. ) Greater splanchnic nerve (T5-9)
  2. ) Lesser splanchnic nerve (T10-11)
  3. ) Least splanchnic nerve (T12)

Question 13

What sub-division of the mediastinum is the right recurrent laryngeal nerve in?

Answer 13

• Not in the mediastinum, it doesn’t make it into the thorax, only left does

Question 14

AP, PA vs lateral CXR differences

Answer 14

1. ) AP = tube is anterior shooting rays to posterior film
   - Used when pt unable to be transported, heart appears larger and creates shadow, less sharp than PA, rays closer
2. ) PA = tube is posterior shooting rays to anterior film
   - Used when pt able to be transported, images not magnified (no larger appearing heart with shadow), more sharp than AP, most common view in CXR
3. ) Lateral
   - Usually along with PA CXR, left side must be against plate x-rays moving right to left for reduced magnification of heart