Cross-sectional Anatomy: Thorax

Mediastinal Divisions - Chest's Central Maze

• Central thoracic zone between pleural cavities; divided by transverse thoracic plane (sternal angle to T4-T5 IVD) into Superior and Inferior. Inferior part is subdivided by pericardium.
• Superior Mediastinum:
  • Contents: Thymus, brachiocephalic veins/artery, aortic arch, trachea, esophagus, thoracic duct, phrenic/vagus nerves.
• Inferior Mediastinum:
  • Anterior: Sternum to pericardium.
    • Contents: Thymus (children), lymph nodes, fat. Retrosternal clear space.
  • Middle: Contains pericardium.
    • Contents: Heart, ascending aorta, pulmonary trunk, SVC, IVC, phrenic nerves.
  • Posterior: Pericardium to vertebrae.
    • Contents: Esophagus, descending aorta, azygos/hemiazygos veins, thoracic duct, vagus nerves.
• Key Lines: Aortopulmonary window, azygoesophageal recess, paratracheal stripes.

⭐ Thymoma is a common anterior mediastinal mass, often associated with Myasthenia Gravis.

Lungs & Airways - Breath-Taking Views

• Lungs & Lobes: Identify on CT.
  • Right Lung: Superior, Middle, Inferior lobes.
  • Left Lung: Superior, Inferior lobes; Lingula (part of LUL).
• Fissures: Boundaries between lobes.
  • Major (Oblique) Fissure: Bilateral, separates lower lobes from upper/middle lobes.
  • Minor (Horizontal) Fissure: Right side only, separates RUL from RML.
• Airways:
  • Trachea bifurcates at Carina (level of T4-T5) into:
  • Main Bronchi: Right (wider, shorter, more vertical); Left.
• Hila (Lung Roots): Medial aspect of each lung.
  • Contents: Pulmonary arteries, pulmonary veins, main bronchi, lymphatics.
  • 📌 RALS: Right Pulmonary Artery is Anterior to bronchus; Left Pulmonary Artery is Superior to bronchus.
• Pleura: Serous membranes.
  • Visceral Pleura: Adherent to lung surface.
  • Parietal Pleura: Lines thoracic cavity.
  • Pleural Space: Potential space; common site for fluid (effusion) or air (pneumothorax).

⭐ The lingula of the left upper lobe is the developmental equivalent of the right middle lobe.

Cardiac Anatomy - Pumping Power Plan

• Cardiac Chambers & Septa:
  • Right Atrium (RA): Receives SVC, IVC, coronary sinus; forms right heart border.
  • Right Ventricle (RV): Most anterior; coarse trabeculations, moderator band (key identifier).

    ⭐ The moderator band, containing the right bundle branch, is a key radiological identifier for the morphological right ventricle.

  • Left Atrium (LA): Most posterior; receives 4 pulmonary veins; forms base.
  • Left Ventricle (LV): Forms apex & left heart border; thickest myocardium.
  • Septa: Interatrial Septum (IAS), Interventricular Septum (IVS) - thicker muscular part.
• Pericardium: Fibroserous sac; normal thickness <2mm on CT/MRI.
• Great Vessels (GV):
  • Aorta:
    • Ascending: Arises from LV.
    • Arch: 📌 "ABC'S" - Brachiocephalic trunk, Left Common Carotid (LCC), Left Subclavian (LSA).
    • Descending: Thoracic & abdominal portions.
  • Pulmonary Trunk (PT): Arises from RV; bifurcates into Right (RPA) & Left Pulmonary Arteries (LPA).
  • Vena Cavae: Superior (SVC) & Inferior (IVC) drain into RA.

Chest Wall & Vasculature - Ribs, Roof & Routes

• Bony Thorax:
  • Ribs (12 pairs): True (1-7), False (8-10), Floating (11-12).
  • Sternum: Manubrium, body, xiphoid. Sternal angle (Louis) at T4-T5.
  • Thoracic Vertebrae (T1-T12): Costal facets.
• Diaphragm:
  • Separates thorax/abdomen; R hemidiaphragm typically ↑.
  • Crura: To lumbar vertebrae.
  • Hiatuses: Caval (T8), Esophageal (T10), Aortic (T12). 📌 "I Ate Ten Eggs At Twelve" (IVC T8, Esophagus T10, Aorta T12).
• Vasculature:
  • Azygos System: Drains posterior thorax/abdomen to SVC.
    • Azygos (R), Hemiazygos & Accessory Hemiazygos (L).

    ⭐ The azygos vein arches over the right main bronchus to drain into the SVC; its enlargement can indicate SVC obstruction or IVC interruption with azygos continuation.

  • Internal Thoracic Artery/Vein: Para-sternal.
• Thoracic Duct: Cisterna chyli (L1-L2) → aortic hiatus → crosses at T5 → L venous angle.

High‑Yield Points - ⚡ Biggest Takeaways

• Aortic knob: Formed by distal aortic arch; key structure on imaging.
• Carina: Tracheal bifurcation at T4-T5; crucial for ET tube placement.
• Right Ventricle (RV): Most anterior cardiac chamber, behind sternum.
• Left Atrium (LA): Most posterior cardiac chamber, anterior to esophagus.
• Aortopulmonary (AP) window: Between aortic arch & pulmonary artery; site for nodes.
• Hilum: Bronchus posterior, pulmonary artery superior, pulmonary veins anteroinferior.
• Descending aorta: In posterior mediastinum, left of vertebral column.