Year 2 – Unit II – Problem 7 Anatomy: Posterior Mediastinum

1. Kingdom of Bahrain Arabian Gulf University College of Medicine and Medical Sciences Year 2 – Unit II – Problem 7Anatomy: Posterior Mediastinum Ali JassimAlhashli www.alhashli.com

2. Introduction • Mediastinum: it is the central compartment of thoracic cavity located between the two pleural sacs. • It is posterior to the pericardial sacand diaphragm and anterior to the bodies of the mid and lower thoracic vertebrae. • Major structure in posterior mediastinum are: • Esophagus. • Thoracic aorta. • Azygos venous system. • Thoracic duct. • Sympathetic trunks. • Thoracic splanchnic nerves.

3. Introduction

4. Esophagus • It is a muscular tube passing between the pharynx in the neck and the stomach in the abdomen (from C6 – T11). • Descends on the anterior aspect of the bodies of the vertebrae, generally in the midline position as it moves through the thorax. • As it approaches the diaphragm, it moves anteriorly and to the left, crossing from the right side of the thoracic aorta to eventually assume a position anterior to it. • Then it passes through the esophagial hiatus, an opening in the muscular part oh the diaphragm (at the level of T10).

5. Esophagus • The esophagus is a flexible, muscular tube that can be compressed or narrowed by surrounding structures at four locations (demonstrated on the figure)

6. Esophagus • Arterial supply: • Esophagial arteries (from the thoracic aorta). • Branches of the left gastric artery. • Bronchial arteries. • Venous drainage: • Azygos vein. • Hemiazygos vein • Branches to the left gastric vein.

7. Esophagus • Visceral afferents from the vagus nerves: • Information about physiological process and reflexes. • Not pain! • Visceral afferents passing through sympathetic trunks: • Pain. • Esophageal plexus: after passing posteriorly to the root of the lungs, the right and left vagus nerves approach the esophagus. As they reach the esophagus, each nerve divides into several branches that spread over this structure, forming the esophageal plexus.

8. Thoracic Aorta • It is a continuation of arch of aorta extending from (T4 – T12). • At the level of T12 it passes through the aortic hiatus in the diaphragm. • Situated to the left of the vertebral column superiorly, it approaches the midline inferiorly. • Throughout is course, it gives off a number of branches: • Pericardial branch. • Bronchial branches. • Esophageal branch. • Mediastinal branch. • Posterior intercostal arteries. • Superior phrenic arteries. • Subcostal arteries.

9. Azygos System of Veins • Azygos vein:arising at level L1 or L2 at the junction between the right ascending lumbar vein and the right subcostal vein. • Hemiazygos vein: arising at the junction between the left ascending lumbar vein and the left subcostal vein. Joins azygos vein at level T9. • Accessory hemoazygos vein: joins azygos vein at level T8.

10. Thoracic Duct • Principle channel through which lymph from most of the body is returned to the venous system. • From L2 (cisternachyli) to the root of the neck (junction between internal jugular vein and subclavian vein) • At level T5, the thoracic duct moves to the left of midline.

11. Thoracic Duct

12. Sympathetic Trunks • Consisting of two parallel cords punctuated by 11 or 12 ganglia. • Superior portion: anterior to the neck of the ribs. • Inferior portion: lie on the lateral aspect of the vertebral bodies. • Branches: • Cardiac and pulmonary plexi (T1-T4). • Greater splanchnic nerve (T5 – T9). • Lesser splanchnic nerve (T10 – T11). • Least splanchnic nerve (T12).