All of the following structures are located in the anterior mediastinum EXCEPT:

Explanation

## Mediastinal Divisions and Contents ### Anterior Mediastinum The anterior mediastinum lies anterior to the pericardium and great vessels. Its key contents are: **Key Point:** The anterior mediastinum contains structures that are primarily **anterior to the pericardial sac** and **anterior to the roots of the great vessels**. ### Contents of Anterior Mediastinum - **Thymus gland** — large in children, involutes with age; located anterior to pericardium - **Anterior cardiac plexus** — autonomic nerve plexus on the anterior surface of the pericardium - **Lymph nodes** — anterior mediastinal nodes draining the thoracic viscera - **Connective tissue and fat** - **Sternal branches of internal thoracic vessels** ### Why Main Bronchi Are NOT in Anterior Mediastinum **High-Yield:** The **main bronchi** are located in the **middle mediastinum** (central mediastinum), as they form at the bifurcation of the trachea at the level of T4–T5 vertebra. They lie within the **hilum of the lungs** and are surrounded by the **pericardium** and **mediastinal pleura**. ### Mediastinal Divisions Summary | Division | Boundaries | Key Contents | |----------|-----------|---------------| | **Superior** | T1–T4, above sternal angle | Aortic arch, SVC, azygos vein, trachea, esophagus, thoracic duct | | **Anterior** | Anterior to pericardium | Thymus, anterior cardiac plexus, lymph nodes | | **Middle** | Pericardium and contents | Heart, main bronchi, pulmonary vessels, phrenic nerve | | **Posterior** | Posterior to pericardium | Esophagus, thoracic aorta, azygos system, sympathetic chain | **Clinical Pearl:** When evaluating anterior mediastinal masses ("4 Ts": Thymus, Teratoma, Terrible lymphoma, Thyroid), remember that the **main bronchi are NOT anterior mediastinal structures** — they belong to the middle mediastinum. **Mnemonic:** **SALT** for anterior mediastinum contents — **S**ternal branches, **A**nterior cardiac plexus, **L**ymph nodes, **T**hymus. ### Clinical Significance Anteromediastinal masses (thymic tumors, lymphomas, germ cell tumors) present with chest pain, cough, or superior vena cava syndrome. Main bronchi involvement would indicate middle mediastinal pathology (e.g., bronchogenic carcinoma, bronchial stenosis).