Mediastinum Anatomy Quiz

Cardiac Plexus

• Located in the middle mediastinum
• Formed by the bifurcation of the trachea

Great Vessels in the Middle Mediastinum

• Thoracic aorta
• Thoracic duct
• Posterior mediastinal lymph nodes
• Azygos, hemiazygos, and accessory hemiazygos veins
• Esophagus
• Esophageal plexus
• Thoracic sympathetic trunks
• Thoracic splanchnic nerves

Thoracic Aorta

• Lies posterior to the root of the left lung and pericardium
• Changes its name at the T12 level
• Gives rise to:
  • Left two bronchial arteries
  • Posterior intercostal arteries (3-11)
  • Superior phrenic artery
  • Esophageal artery
  • Mediastinal artery
  • Subcostal artery

Thoracic Duct

• Largest lymphatic channel
• Located in the posterior mediastinum and superior mediastinum
• Receives lymph from the esophagus, pericardium, and diaphragm

Posterior Mediastinal Lymph Nodes

• Located posterior to the pericardium
• Receives lymph from the esophagus, pericardium, and diaphragm

Azygos System of Veins

• Azygos vein: formed by the union of the ascending lumbar vein and subcostal vein
• Right crus of the diaphragm
• Level of T4 venous arch anteriorly
• Receives:
  • Right superior intercostal vein
  • Right posterior intercostal veins
  • Hemiazygos vein
  • Right bronchial vein
• Opens into the superior vena cava

Hemiazygos Vein

• Formed by the union of the left ascending lumbar vein and left subcostal vein
• Left crus of the diaphragm
• Receives:
  • Inferior three posterior intercostal veins (9-11)
  • Inferior esophageal vein
  • Mediastinal veins
• Level of T9
• Opens into the azygos vein

Accessory Hemiazygos Vein

• Receives:
  • Posterior intercostal veins (4-8)
  • Left bronchial vein
• Opens into the azygos vein at the level of T7

Clinical Importance

• If the IVC is blocked, venous blood drains into the SVC through the azygos vein and hemiazygos vein

Sympathetic Trunk

• Extends from the base of the skull to the coccyx
• Has 22-23 ganglia
• Composed of longitudinal and transverse fibers
• Unites with the opposite side at the ganglion impar

Preganglionic Fibers

• First way: terminate at their corresponding ganglia
• Second way: enter the sympathetic trunk without making a synapse at their corresponding ganglia

Mediastinum

Organization of Mediastinum

• Central part of the thoracic cavity
• Covered by mediastinal pleura
• Contains thoracic viscera

Clinical Importance of Sternal Angle

• Bifurcation of the trachea
• Azygos vein → SVC
• Ascending aorta → arch of aorta → descending aorta
• 2nd rib joins with the sternum
• Transverse plane between the superior and inferior mediastinum

Superior Mediastinum

• Posterior to the manubrium and anterior to the first four thoracic vertebrae
• Superior border: superior thoracic aperture
• Inferior border: transverse thoracic plane (sternal angle and IV disc of T4 and T5)
• Laterally: mediastinal pleura

Contents of Superior Mediastinum

• Thymus
• Right and left brachiocephalic veins
• Left superior intercostal vein
• Superior vena cava
• Arch of aorta with its three large branches
• Trachea
• Esophagus
• Phrenic nerves
• Vagus nerves
• Left recurrent laryngeal nerve
• Thoracic duct
• Other small vessels and nerves

Thymus

• Lymphoid organ
• Located in the neck, anterior part of the superior mediastinum, and inferior mediastinum
• Plays an important role in the development of the immune system
• Diminishes at puberty

Right and Left Brachiocephalic Veins

• Formed by the union of internal jugular and subclavian veins posterior to the medial end of the clavicle
• Left vein crosses the midline
• Union of the two veins forms the SVC posterior to the lower border of the right first costal cartilage

Superior Vena Cava

• Terminates at the lower margin of the right third costal cartilage
• Receives:
  • Azygos vein
  • Pericardial and mediastinal veins
• SVC and IVC are oriented along the same vertical axis

Arch of Aorta and its Branches

• Aorta has three parts: arch, ascending, and descending
• Ascending aorta emerges from the heart and forms the arch of aorta
• From right to left:
  • Brachiocephalic trunk
  • Left common carotid
  • Left subclavian

Ligamentum Arteriosum

• In the superior mediastinum
• Fetal circulation: ductus arteriosus
• Connects the pulmonary trunk to the arch of aorta and permits the blood to bypass the lungs during development

Trachea and Esophagus

• Trachea is the midline structure that is palpable in the jugular notch
• Posteriorly: esophagus
• Crossed by the azygos vein on the right side and arch of aorta on the left side
• Bifurcation of trachea, whereas esophagus continues