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Mediastinum• Bulky septum
between the pleural cavities & lungs
Extends-• Root of the
neck to diaphragm
• From the sternum to vertebral column
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Divisions of mediastinum• Divided by an imaginary horizontal plane from
the sternal angle to the intervertebral disc between 4th & 5th vertebra in to
• superior mediastinum• Inferior mediastinum –
Anterior Middle Posterior
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Superior mediastinum• Posterior to the sternum & anterior to the
bodies of first four thoracic vertebra
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Contents of superior mediastinum• Thymus• Rt & Lt brachiocephalic
veins• Left superior intercostal vein• Superior vena cava• Arch of aorta & it’s three
branches• Trachea • Esophagus• Phrenic nerves• Vagus nerves• Lt recurrent laryngeal nerve• Thoracic duct• Other small structures
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Thymus• Asymmetric bilobed gland• Upper extent may reach as high as thyroid gland• Involved in early development of immune system• Large in children • Atrophies after puberty
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Brachiocephalic veins• Located immediatelyposterior to thymus• Formed at the jn. of IJ & subclavian veins.• Begins post to clavicle• Tributaries: vertebral,first post. Intercostal,
int. thoracic, inf. Thyroid, thymic veins
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Left superior intercostal vein
• Drains upper two or three intercostal veins, left bronchial veins & left pericardiophrenic veins
• Drains in to left brachiocephalic veins
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Superior vena cava• Vertically oriented• Begins posterior
to the lower edge of first costal cartilage
• terminates at the lower border of right third costal cartilage
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Arch of aorta & it’s branches• Begins when ascending
aorta emerges from pericardial sac
• Terminates on left side of vertebral level between Th 4th - 5th
Branches-Brachiocephalic trunkLeft CCALeft subclavian Thyroid ima
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Trachea• Midline structure• Present anterior to
esophagus• Swallowing, breathing,
disease & specialized instrumentation causes shift of trachea
• divides just inferior to sternal angle (T3- T4) into Right & Left principal bronchus
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Vagus nerveRight Vagus• lies between right
brachiocephalic vein & trunk
• Descends posteriorly to the root of Right lung to reach esophagus
• Gives branches to esophagus, cardiac plexus & pulmonary plexus
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Left Vagus nerve• Lies between Lt CCA & Lt
subclavian artery• Pass posterior to the root
of lung to reach the esophagus
• Gives branches to esophagus, cardiac & pulmonary plexus
• Also gives Lt recurrent laryngeal nerve- arise at inferior margin of arch of aorta, winds around the aorta & reaches the groove between esophagus & trachea
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Left recurrent laryngeal nerve• arise at inferior margin
of arch of aorta, winds around the aorta & reaches the groove between esophagus & trachea
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Phrenic nerve• Right Phrenic –enters
lateral to Right Vagus & beginning of Right brachiocephalic vein
• continues inferiorly on the Right side of sup vena cava, on entering middle mediastinum descends along the Rt side of pericardial sac anterior to the Rt lung root
• leaves the thorax with inferior vena cava
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Left phrenic nerve• enters similar to
Right Phrenic nerve• Lateral to Vagus & Lt
brachiocephalic vein• Descends on left
lateral surface of arch of aorta
• Passes superficial to Lt vagus & superior intercostal vein
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Left phrenic nerve
• In middle mediastinum lies on the Lt side of pericardial sac anterior to root of Lt lung
• Pierces the diaphragm near the apex of the heart
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Thoracic duct
• Major lymphatic vessel of the body
• Enters sup. mediastinum from below at the level of T4/5
• continues through the superior med. posterior to arch of aorta between the esophagus & Lt pleura
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Esophagus• Starts at the C6th &
terminates at cardiac opening of stomach (T12)
• Descends anterior to vertebral bodies in midline
• Crossed laterally by the azygos vein on the right side & arch of aorta on the left side