Regarding the contents of the posterior mediastinum, all of the following are TRUE EXCEPT:

## Posterior Mediastinum — Anatomical Boundaries and Contents ### Definition and Boundaries The posterior mediastinum lies **posterior to the pericardium and esophagus**, extending from the sternal angle 2 (T4/T5) to the diaphragm (T12). ### Authentic Posterior Mediastinal Contents **Key Point:** The posterior mediastinum contains: - **Esophagus** (vertical course, anterior to vertebral column) - **Thoracic (descending) aorta** (posterior and to the left; passes behind the esophagus at the diaphragm) - **Azygos venous system** (azygos, hemiazygos, accessory hemiazygos veins) - **Thoracic duct** (lymphatic vessel) - **Sympathetic trunks and splanchnic nerves** - **Vagus nerves** (descending) - **Posterior mediastinal lymph nodes** ### Location of the Phrenic Nerve — The Trap **High-Yield:** The **phrenic nerve and pericardiacophrenic vessels lie in the ANTERIOR mediastinum**, NOT the posterior mediastinum. Specifically: - They run **lateral to the pericardium** (between pericardium and mediastinal pleura) - They descend on the **lateral surface of the pericardium** - They are **anterior to the root of the lung** - They are supplied by the internal thoracic artery (a branch of the subclavian artery) **Clinical Pearl:** The phrenic nerve's anterior mediastinal course makes it vulnerable to injury during cardiac surgery, pericardiocentesis, or mediastinal masses — but it is NOT a posterior mediastinal structure. ### Comparative Table: Anterior vs. Posterior Mediastinal Nerves | Nerve | Location | Course | |-------|----------|--------| | **Phrenic nerve** | **Anterior mediastinum** | Lateral to pericardium, descends to diaphragm | | **Vagus nerve** | Posterior mediastinum (lower portion) | Descends with esophagus, forms esophageal plexus | | **Sympathetic trunks** | Posterior mediastinum | Bilateral, posterior to pleura | | **Splanchnic nerves** | Posterior mediastinum | Arise from sympathetic trunks, pierce diaphragm | **Mnemonic: EATS (Esophagus And Thoracic Structures in Posterior Mediastinum):** - **E**sophagus - **A**orta (thoracic/descending) - **T**horacic duct - **S**ympathetic trunks & splanchnic nerves (Phrenic nerve is **NOT** part of this — it's anterior.) ### Diaphragmatic Relationships ```mermaid flowchart TD A[Posterior Mediastinum at Diaphragm] --> B[Esophagus] A --> C[Thoracic Aorta] A --> D[Azygos Vein] A --> E[Thoracic Duct] B --> F[Passes through esophageal hiatus at T10]:::outcome C --> G[Passes through aortic hiatus at T12]:::outcome D --> H[Passes through caval opening at T8]:::outcome E --> I[Passes through aortic hiatus at T12]:::outcome J[Phrenic Nerve] --> K[Anterior mediastinum]:::action K --> L[Passes through separate opening in diaphragm]:::outcome ```