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
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 superior vena cava.
Hemiazygos Vein
– Formed by the union of the left lumbar vein and left subcostal vein. It enters the mediastinum through 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.
Accessory hemiazygos vein
– Formed by the union of the fourth to eighth intercostal veins. It drains into the azygos vein at T7.
What are The sympathetic trunks
The sympathetic trunks are paired bundles of nerves that extend from the base of the skull to the coccyx. In the thoracic region, these nerve bundles are known as the thoracic sympathetic trunks. As they descend through the thorax, they lie within the posterior mediastinum.
What arises from The sympathetic trunks
Arising from these trunks are the lower thoracic splanchnic nerves – they continue inferiorly to supply the viscera of the abdomen.
What is the thoracic duct and where does it join the vascular system?
The thoracic duct is the main lymphatic channel draining lymph from the lower half of the body and the bowel back to the blood stream. The bowel component is important
because fat is absorbed into the lymphatics so this is the only route for fat absorption.
At the confluence of the left subclavian and left internal jugular vein.
What structures are supplied by the three splanchnic nerves and where does a patient appreciate pain felt by these nerves?
Greater splanchnic nerve; fore gut, epigastrium.
Lesser splanchnic nerve: midgut, round the umbilicus. Least splanchnic nerve, hind gut, suprapubic area.
What is supplied by the Greater splanchnic nerve
fore gut, epigastrium.
What is supplied by the Lesser splanchnic nerve:
midgut, round the umbilicus
What is supplied by the Least splanchnic nerve
hind gut, suprapubic area.
What structure lies immediately behind the trachea in the upper thorax and the left atria
in the lower thorax?
The oesophagus
What structures drain blood into the azygous system?
The lateral and posterior chest wall and the lateral and posterior abdominal wall
Why is the left recurrent laryngeal nerve at risk from thoracic disease but not the right?
The left recurrent laryngeal nerve passes into the thorax, round the aortic arch and
back into the neck. The right recurrent laryngeal does not pass through the thorax.
Where do the sympathetic nerves attach to the central nervous system?
The thoracic 1-12 and lumber 1 and 2 spinal segmental nerves.
What happens if the sympathetic nerves to the head and neck are damaged?
There will be no sweating on the face (anhidrosis)
The eye lid will droop (ptosis)
The pupil will be constricted (miosis)
Slightly withdrawn eye ball (enopthalmos)
This is known as Horner’s syndrome; it almost always effects one side only.
anhidrosis
no sweating on the face
ptosis
The eye lid droops
miosis
The pupil is constricted
enopthalmos
Slightly withdrawn eye ball
What is Horner syndrome
Horner syndrome is a combination of signs and symptoms caused by the disruption of a nerve pathway from the brain to the face and eye on one side of the body.
