Mediastinum

Mediastinum Overview - Central Chest Zone

• Central zone of the thoracic cavity, located between the two pleural sacs.
• Boundaries:
  • Superior: Thoracic inlet (superior thoracic aperture).
  • Inferior: Diaphragm.
  • Anterior: Sternum and costal cartilages.
  • Posterior: Bodies of thoracic vertebrae (T1-T12).
  • Lateral: Mediastinal pleura of lungs.
• Major Divisions:
  • Superior Mediastinum.
  • Inferior Mediastinum (below transverse thoracic plane):
    • Anterior: Pre-pericardial; between sternum and pericardium.
    • Middle: Contains pericardium & heart.
    • Posterior: Retro-pericardial; between pericardium and vertebrae.

⭐ The transverse thoracic plane, extending from the sternal angle (of Louis) anteriorly to the T4-T5 intervertebral disc posteriorly, divides the superior from the inferior mediastinum. This plane is a key anatomical landmark for locating mediastinal structures.

Superior Mediastinum - Neck's Downstairs Neighbor

• Boundaries: Sup: Thoracic inlet; Inf: Transverse thoracic plane (Sternal angle/T4-T5 IVD); Ant: Manubrium; Post: T1-T4 vertebrae; Lat: Mediastinal pleura.
• Contents: 📌 Mnemonic: BATS & TENT
  • Brachiocephalic veins, Aortic arch (& its 3 branches: Brachiocephalic trunk, L. Common Carotid a., L. Subclavian a.), Thymus, SVC.
  • Trachea, Esophagus, Nerves (Phrenic nn., Vagus nn., L. Recurrent Laryngeal n.), Thoracic duct.

⭐ Key relation: The left recurrent laryngeal nerve hooks inferiorly around the aortic arch (specifically, posterior to the ligamentum arteriosum) before ascending towards the larynx. This makes it vulnerable during procedures involving the arch or ductus arteriosus remnants.

Inferior Mediastinum: Anterior & Middle - Heart's Cozy Condo

• Anterior Mediastinum
  • Location: Posterior to sternum, anterior to pericardium.
  • Contents:
    • Remnants of thymus gland (especially in children).
    • Lymph nodes.
    • Loose connective tissue.
    • Sternopericardial ligaments.
• Middle Mediastinum
  • Most important & largest part of inferior mediastinum.
  • Contents:
    • Pericardium & Heart.
    • Ascending Aorta.
    • Pulmonary trunk & arteries.
    • Superior & Inferior Vena Cava (lower parts).
    • Phrenic nerves (C3, C4, C5).
    • Main bronchi.
    • Tracheobronchial lymph nodes.

⭐ Phrenic nerves (C3,4,5) pass through the middle mediastinum, anterior to lung roots, between fibrous pericardium and mediastinal pleura. 📌 "C3, 4, 5 keeps the diaphragm alive!"

Posterior Mediastinum - Spine's Front Porch

• Location: Anterior to T5-T12 vertebrae, posterior to pericardium & diaphragm. Extends from transverse thoracic plane to diaphragm.
• Contents (📌 DATES):
  • Descending (Thoracic) Aorta
  • Azygos & Hemiazygos venous system
  • Thoracic Duct
  • Esophagus & esophageal plexus
  • Sympathetic trunks & Splanchnic nerves
  • Posterior mediastinal lymph nodes

⭐ The thoracic duct commences at L1 (cisterna chyli), enters the thorax via the aortic hiatus (T12), and drains into the left venous angle (junction of left internal jugular and left subclavian veins).

Mediastinal Clinical Correlates - When Space Gets Squeezed

• SVC Syndrome: Superior Vena Cava obstruction (e.g., lung cancer, lymphoma). Causes facial/arm edema, dyspnea, venous distension.
• Mediastinitis: Inflammation (e.g., esophageal perforation, post-surgery). Presents with chest pain, fever, dysphagia. Hamman's sign (mediastinal crunch).
• Mediastinal Masses by Location:
  • Anterior: Thymoma, Teratoma, (Terrible) Lymphoma, Thyroid. (📌 4 T's)
  • Middle: Lymphadenopathy (lymphoma, sarcoidosis), Bronchogenic/Pericardial cysts.
  • Posterior: Neurogenic tumors (e.g., schwannoma), Esophageal tumors.

⭐ Most common tumors: Anterior - Thymoma; Middle - Lymphoma (also anterior); Posterior - Neurogenic tumors (e.g., schwannoma).

High‑Yield Points - ⚡ Biggest Takeaways

• Superior mediastinum: great vessels, trachea, esophagus, thymus, phrenic & vagus nerves.
• Anterior mediastinum: thymus remnants, lymph nodes; site for thymoma, lymphoma.
• Middle mediastinum: heart, pericardium, phrenic nerves, roots of great vessels.
• Posterior mediastinum: esophagus, thoracic aorta, azygos system, thoracic duct, vagus nerves.
• Most common posterior mediastinal tumor in adults: neurogenic tumor.
• Transverse thoracic plane (Angle of Louis, T4/T5) divides superior & inferior mediastinum.