Areas - Posterior Mediastinum

Question 1

Borders?

Answer 1

Lateral - mediastinal pleura (part of the parietal pleura 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)a nd teh T4 vertebrae.

Floor - diaphragm.

Question 2

Contents - thoracic aorta?

Answer 2

This is a continuation of the arch of the aorta, beginning at the lower edge of the T4 vertebra. It descends down the posterior mediastinum to the left of the vertebra, 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.

Branches

These tend to arise in three vascular planes; unpaired branches to viscera extend anteriorly, paired branches to viscera extend laterally, and paired segmental parietal branches extend mostly posterolaterally.

1) Posterior intercostal arteries - paired parietal branches - nine pairs branches from the posterior aspect of the aorta, supplying the intercostal spaces (except the first two). Pass posteriorly and laterally, in parallel with the ribs.
2) Bronchial arteries - paired visceral branches, usually one or two. The left bronchial arteries always arise directly from the thoracic aortal, while those on the right usually branch indirectly from a right posterior intercostal artery. They go on to supply the tracheobronchial arteries.
3) Oesophageal arteries - unpaired visceral branches, arising from the anterior aspect of the aorta. In most individuals there are two, but there can be up to five. As the name suggests, these branches go onto supply the oesophagus.
4) 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.

Question 3

Contents - Oesophagus?

Answer 3

The oesophagus is a muscular tube the 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.

The oesophageal plexus is a network of nerves surroudning 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.

Question 4

Contents - thoracic duct?

Answer 4

This is the largest lymphatic vessel of the body, allowing return of lymph from most of the body (all but the right superior quadrant into the venous system).

The duct originates from the cisterna chyli in the abdomen and enters the mediastinum via the aortic hiatus. It ascends to lie directly anterior to the T6-T12 vertebrae, before deviating left as it ascends into the superior mediastinum. While located in the posterior mediastinum, the thoracic duct receives lymphatic drainage from the intercostal spaces and neighbouring anatomical structures through a number of branches.

Question 5

Contents - azygos system of veins?

Answer 5

The venous network drains blood from the body walls and mediastinal viscera and empites into the SVC. It consists of three major veins:

1) Azygos vein - formed by the union of the right lumbar vein and the right subcostal vein. It enters the mediastinum via the aortic hiatus and drains into the SVC.
2) Hemiazygos vein - formed by the union of the left lumbar vein and the left subcostal vein. It enters the mediastinum thorugh the left crus of the diaphragm, ascending on the left side. At the level of T8, it turns to the right and combines with the azygos vein.
3) Accessory hemiazygos vein - formed by the union of the 4th to 8th intercostal veins. It drains into the azygos vein at T7.

Question 6

Contents - sympathetic trunks?

Answer 6

The thoracic sympathetic trunks lie within the posterior mediastinum.

Arising from these trunks are the lower thoracic splanchnic nerves - they continue inferiorly to supply the viscera of the abdomen.