Posterior Mediastinum Flashcards
The posterior mediastinum is bordered by the following thoracic structures:
Lateral: Mediastinal pleura (part of the parietal pleural membrane).
Anterior: Pericardium.
Posterior: T5-T12 vertebrae.
Roof: Imaginary line extending between the sternal angle (the angle formed by the junction of the sternal body and manubrium) and the T4 vertebrae.
Floor: Diaphragm
Route of aorta in the posterior mediastinum
The thoracic (descending) aorta is a continuation of the arch of the aorta, beginning at the lower edge of the T4 vertebra. It descends through the posterior mediastinum to the left of the vertebrae, becoming more medially located as it moves. At the inferior border of T12, the thoracic aorta becomes the abdominal aorta, and passes through the aortic hiatus of the diaphragm.
A number of branches arise from the thoracic aorta in the posterior mediastinum. These tend to arise in three vascular planes;
unpaired branches to viscera extend anteriorly,
paired branches to viscera extend laterally,
paired segmental parietal branches extend mostly posterolaterally.
Major branches of thoracic aorta
Posterior intercostal arteries
Bronchial arteries
Oesophageal arteries
Superior phrenic arteries
Posterior intercostal arteries
– Paired parietal branches. Nine such pairs branch from the posterior aspect of the aorta, supplying the intercostal spaces (except the first two). Pass posteriorly and laterally, in parallel with the ribs.
Bronchial arteries
– Paired visceral branches, usually one or two. The left bronchial arteries always arise directly from the thoracic aorta, while those on the right usually branch indirectly from a right posterior intercostal artery. They go on to supply the tracheobronchial tree.
Oesophageal arteries
– Unpaired visceral branches, arising from the anterior aspect of the aorta. In most individuals there are two, but there can up to five. As the name suggests, these branches go on to supply the oesophagus.
Superior phrenic arteries
– Arise from the anterior aspect of the thoracic aorta at the aortic hiatus, varying in number. They supply the superior aspect of the diaphragm.
What is The oesophagus
The oesophagus is a muscular tube that connects the pharynx to the stomach; allowing swallowed food to pass into the digestive system.
It passes into the posterior mediastinum from the superior mediastinum, descending posteriorly to the arch of the aorta and the heart.
Whilst initially positioned to the right, the oesophagus deviates to the left as it moves downwards. It leaves the mediastinum via the oesophageal hiatus of the diaphragm.
What is The oesophageal plexus
is a network of nerves surrounding the oesophagus as it descends, comprising of branches from the left and right vagus nerves.
Immediately above the diaphragm, the fibres of the plexus converge to form the anterior vagal trunk and posterior vagal trunk, which travel along the surface of the oesophagus as it exits the thorax.
What is the largest lymphatic vessel in the body
The thoracic duct - allowing return of lymph from most of the body (all but the right superior quadrant) into the venous system.
Where does the thoracic duct originate from
The duct originates from the cisterna chyli in the abdomen, and enters the mediastinum through the aortic hiatus. It ascends to lie directly anterior to the T6-T12 vertebrae, before deviating left as it ascends into the superior mediastinum.
where does the thoracic duct receive lymphatic drainage
While located in the posterior mediastinum, from the intercostal spaces and neighbouring anatomical structures through a number of branches.
Azygos System of Veins purpose
This venous network drains blood from the body walls and mediastinal viscera, and empties into the superior vena cava.
The azygos system of veins consists of three major veins:
Azygos vein
Hemiazygos vein
Accessory hemiazygos vein
