MEDIASTINUM Subdivisions and contents v Mediastinum is a

MEDIASTINUM Subdivisions and contents

v Mediastinum is a central partition between the 2 pleural sacs limited on either sides by the mediastinal pleura v Extent In front – Sternum Behind – Bodies of 12 thoracic vertebrae Above – Thoracic inlet Below – The diaphragm On each side – Mediastinal pleura

v Subdivisions An imaginary horizontal plane extending from the sternal angle to the lower border of T 4 into superior and inferior Mediastinum Superior Inferior

v Inferior mediastinum is further divided by the pericardial sac into anterior, middle and posterior Inferior Anterior Middle Posterior

v Superior mediastinum • Boundaries In front – Manubrium sterni Behind – Bodies of upper 4 thoracic vertebrae, intervertebral discs and anterior longitudinal ligament Above – Thoracic inlet Below – The diaphragm On each side – Mediastinal pleura

v Anterior mediastinum • Boundaries In front – Body of the sternum Behind – Pericardium Above – Imaginary horizontal plane extending from sternal angle to the lower border of T 4 Below – The diaphragm On each side – Mediastinal pleura

v Contents • Superior and inferior sternopericardial ligaments • Loose areolar tissue • Retrosternal lymph nodes • Mediastinal branches of internal thoracic artery

v Middle mediastinum • Widest subdivision • Occupied mainly by the heart and pericardium • Limited on each side by mediastinal pleura

v Contents • Heart enclosed in the pericardium • Arteries – Ascending aorta and pulmonary trunk dividing into right and left pulmonary arteries • Veins – Lower part of superior venacava, arch of azygos vein and 4 pulmonary veins • Nerves – phrenic, deep cardiac plexus • Lymph nodes – inferior tracheobronchial nodes • Tubes – bifurcation of trachea, right and left bronchi

Contents of middle mediastinum Ascending aorta Phrenic nerve Deep cardiac plexus Left pulmonary artery Left bronchus Pulmonary veins Heart within pericardium

v Posterior mediastinum • Boundaries In front (from above downwards) – Bifurcation of trachea, pulmonary vessels, fibrous pericardium, posterior sloping surface of the diaphragm Behind – Bodies of lower 8 thoracic vertebrae, intervertebral discs and anterior longitudinal ligament Above – Imaginary horizontal plane Below – The diaphragm On each side – Mediastinal pleura

• Contents Thoracic duct Left recurrent laryngeal nerve Aorta and its branches Left vagus Azygos vein oesophagus

Oesophagus Arteries – Descending thoracic aorta and its branches Veins – Azygos, Hemiazygos, Accessory hemiazygos Nerves – Vagus, splanchnic nerves Lymph nodes – posterior mediastinal nodes Thoracic duct

v Surgical importance / Applied anatomy • Mediastinitis – Structures of mediastinum are embedded in loose connective tissue. The posterior mediastinum is continuous with the neck through the superior mediastinum. Therefore infection from these regions may spread to superior and posterior mediastina • Deflection of mediastinum – In pneumothorax, the lung on that side immediately collapses and mediastinum is deflected to opposite side the patient suffers from breathlessness & upon examination trachea and heart displaced to opp side

• All large veins of sup medaistinum are located on the right side. Therefore during increased venous return, the veins expand whereas the arteries do not expand at all. Thus there is much dead space on the right, and hence tumours or fluids tend to project on this side. • Mediastinal tumours • Mediastinal syndrome – compression of mediastinal structures by any growth or tumour

• Mediastinoscopy – surgical procedure to look at the organs, tissues and lymph nodes between the lungs for abnormal areas. An incision is made at the top of the breastbone and endoscope is inserted into the chest. Tissue and lymph nodes may be taken by biopsy.