Mediastinum Anatomy Quiz

Mediastinum

• The mediastinum is a compartment in the thoracic cavity, between the two pleural sacs and containing the heart, esophagus, trachea, major nerves, and blood vessels.

Plane of Ludwig

• Located at the level of T4/T5 posteriorly and the second rib anteriorly.
• Divides the mediastinum into superior and inferior divisions.
• Structures at the plane of Ludwig include the superior vena cava entering the pericardium, the beginning and end of the aortic arch, the trachea bifurcation, and the pulmonary trunk bifurcation.

Superior Mediastinum

• Contains the aortic arch and its branches, brachiocephalic veins, superior vena cava, phrenic nerves, vagus nerves, left recurrent laryngeal nerve, thoracic duct, thymus, trachea, esophagus, and other small nerves, blood vessels, and lymphatics.

Anterior Mediastinum

• Contains the thymus, fat, connective tissue, lymph nodes, mediastinal branches of the internal thoracic vessels, and sternopericardial ligaments.

Middle Mediastinum

• Contains the pericardium, heart, origins of the great vessels, and main bronchi.

Posterior Mediastinum

• Contains the thoracic aorta and its branches, azygos system of veins, esophagus and its nerve plexus, sympathetic trunks, thoracic splanchnic nerves, thoracic duct, and lymph nodes.

Superior Thoracic Aperture

• Superior boundary of the superior mediastinum, formed by the first rib, T1, and jugular notch.

Thymus

• Located in the anterior part of the superior mediastinum, posterior to the manubrium.
• Extends into the neck superiorly and the anterior mediastinum inferiorly.
• Arterial supply: internal thoracic and anterior intercostal arteries.
• Venous drainage: brachiocephalic, internal thoracic, and inferior thyroid veins.
• Lymphatic drainage: parasternal, brachiocephalic, and tracheobronchial lymph nodes.

Trachea

• Continuation of the larynx at C6.
• Lies anterior to the esophagus.
• Terminates at the Plane of Ludwig.
• Bifurcates into right and left main bronchi.
• Crossed by the aortic arch and the azygos vein.

Aortic Arch Branches

• Brachiocephalic trunk: branches into right subclavian artery and right common carotid artery.
• Left common carotid artery.
• Left subclavian artery.
• All three branches are crossed anteriorly by the left brachiocephalic vein.

Brachiocephalic Veins

• Formed by the union of the subclavian and internal jugular veins.
• Located posterior to the sternoclavicular joints and the thymus.
• Clinically important because the left brachiocephalic vein crosses the midline, and must be considered during tracheotomy.

Vagus Nerves

• Contribute to the cardio-pulmonary plexuses.
• Divide into several branches that spread over the esophagus to form the esophageal plexus.
• Just above the diaphragm, these fibers converge into two trunks:
• Anterior Vagal Trunk: mainly from the left vagus nerve.
• Posterior Vagal Trunk: mainly from the right vagus nerve.

Recurrent Laryngeal Nerves

• Arise from vagus nerves on either side.
• Function to innervate some intrinsic muscles of the larynx.
• Damage to the recurrent laryngeal nerves can lead to hoarseness or loss of voice.
• Left recurrent laryngeal nerve hooks around the ligamentum arteriosum and passes up on the right side of the aortic arch.
• Right recurrent laryngeal nerve hooks around the right subclavian artery.

Phrenic Nerves

• Sensory innervation to the mediastinal pleura, fibrous pericardium, and parietal layer of serous pericardium.
• Sensory and motor innervation to the diaphragm and associated membranes.

Cervical Rib

• Articulates posteriorly with vertebrae CVII and anteriorly with the superior border of the anterior aspect of rib I.
• Structures that normally pass over rib I are elevated and pass over the cervical rib and band.
• Can cause thoracic outlet syndrome.

Thoracic Outlet Syndrome

• Caused by arterial compression or embolization, tension on the T1 nerve, or compression of the subclavian vein.
• Can also be caused by muscular abnormalities, trauma, or tumors in the region.
• Symptoms include:
  • Arterial compression and embolization: atheroma and distal embolization.
  • Tension on the T1 nerve: sensory disturbance.
  • Compression of the subclavian vein: axillary vein thrombosis.

Esophagus

• Continuation of the pharynx from C6 vertebral level.
• Enters the thorax through the superior thoracic aperture.
• Passes through the diaphragm at T10 level.
• Ends where it enters the stomach at the cardiac sphincter.
• Four Normal Constrictions:
  • Junction with the pharynx (C6) - cricopharyngeal constriction
  • Aortic arch constriction (T4)
  • Bronchial constriction (T5)
  • Diaphragmatic constriction (T10)

Arterial Supply of Esophagus

• Thoracic Portion:
  • Inferior thyroid artery
  • Descending thoracic aorta
  • Bronchial arteries
  • Posterior intercostal arteries
• Abdominal Portion:
  • Left gastric artery
  • Short gastric arteries
  • Left inferior phrenic arteries

Venous Drainage of Esophagus

• Thoracic Portion:
  • Inferior thyroid veins
  • Azygos and hemiazygos veins
  • Esophageal veins
• Abdominal Portion:
  • Left gastric veins
  • Short gastric veins
  • Left inferior phrenic veins

Lymphatic Drainage of Esophagus

• Thoracic Portion:
  • Posterior mediastinal lymph nodes
  • Tracheobronchial lymph nodes
• Abdominal Portion:
  • Left gastric lymph nodes
  • Celiac lymph nodes

Innervation of Esophagus

• Supplied by the esophageal plexus, which is formed by the vagus nerves and sympathetic nerves.
• Sympathetic fibers constrict the esophagus and inhibit peristalsis.
• Parasympathetic fibers relax the esophagus and promote peristalsis.

Azygos Venous System

• Drains blood directly into the superior vena cava.
• Formed by the union of the right ascending lumbar vein and the right subcostal vein.
• Drains blood from the posterior wall of the thorax, abdomen, and pelvis.

Greater Splanchnic Nerves

• Originate from T5-9 (with some variation).
• Join the celiac ganglion.

Lesser Splanchnic Nerves

• Originate from T10-11.
• Join the aortico-renal ganglion.

Least Splanchnic Nerves

• Originate from T12 (but not always present).
• Join the renal plexus.

Diaphragm Openings

• T8: Inferior vena cava (right)
• T10: Esophagus (left)
• T12: Aorta (midline)

Thoracic Duct

• The largest lymphatic vessel in the body, and the primary lymphatic pathway for drainage of the lower limbs, abdomen, and left thorax.
• Susceptible to medical interventions due to its location and course.
• Lacerations can lead to leakage of chyle into the thorax, mediastinum, or pericardium, known as chylothorax, chylomediastinum, and chylopericardium, respectively.

Test your knowledge on the structures and divisions of the mediastinum. This quiz covers key anatomical features, including the plane of Ludwig and the contents of the superior and anterior mediastinum. Perfect for students studying anatomy or healthcare professionals looking to refresh their knowledge.