## Mediastinal Divisions — Anatomical Landmarks ### Superior vs. Inferior Mediastinum The mediastinum is divided into **superior** and **inferior** compartments by an imaginary transverse plane that passes through: - **Anteriorly:** Sternal angle of Louis (junction of 2nd costal cartilage with sternum) - **Posteriorly:** Lower border of T4 vertebra **Key Point:** The sternal angle of Louis is a palpable bony landmark and serves as the anterior reference for this crucial anatomical division. ### Contents Separated by This Plane | **Superior Mediastinum** | **Inferior Mediastinum** | |---|---| | Great vessels (aorta, SVC, IVC origins) | Heart and pericardium | | Trachea, esophagus, thoracic duct | Esophagus (lower part) | | Thymus gland | Inferior vena cava | | Vagus and phrenic nerves | Thoracic aorta (descending) | **High-Yield:** The sternal angle of Louis (Angle of Louis) is the single most important surface anatomy landmark in thoracic anatomy — it marks the 2nd rib and 2nd costal cartilage, which define the superior-inferior mediastinal boundary. **Mnemonic:** **"LOUIS marks the LEVEL"** — Louis = Level of 2nd rib = Landmark for mediastinal division. **Clinical Pearl:** Clinically, this landmark is used to count ribs during physical examination and to guide needle insertion (e.g., central line placement, thoracentesis). 
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