## Superior Mediastinum Boundaries **Key Point:** The superior mediastinum is separated from the inferior mediastinum by an imaginary transverse plane passing through the **sternal angle of Louis** (also called the angle of Louis or manubrial angle). ### Anatomical Landmarks The sternal angle of Louis is a crucial surface anatomy landmark that corresponds to: - The junction between the manubrium and body of the sternum - The articulation of the 2nd rib with the sternum - The level of the **T4–T5 intervertebral disc** posteriorly ### Clinical Significance **High-Yield:** This plane divides the mediastinum into superior and inferior compartments for clinical and anatomical description purposes. The plane is easily palpable on the anterior chest wall, making it a reliable landmark for counting ribs and identifying thoracic levels. ### Superior Mediastinum Contents Structures above this plane include: - Brachiocephalic veins - Superior vena cava (upper part) - Aortic arch - Trachea (upper part) - Esophagus (upper part) - Thoracic duct - Vagus and phrenic nerves **Mnemonic:** **ABATE** — Aortic arch, Brachiocephalic vessels, Anterior mediastinal structures, Trachea, Esophagus (in superior mediastinum) [cite:Gray's Anatomy 42e Ch Thorax] 
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