Mediastinum and Great Vessels Flashcards
What is the mediastinum?
Middle septum” simply an area, it is NOT a
structure. An area that sits in the central core of the thoracic cavity.
What are the subparts of the mediastinum?
The mediastinum is made up of subparts, ‘Superior’ and ‘Inferior’
What are the subparts of the mediastinum separated by?
They are divided by the ‘Plane of Louis’[Trans-thoracic plane] - An imaginary plane, through the thoracic cavity, at the level of the manubrio-sternal joint. (1)
Plane is also at the level of the costal cartilage of Rib 2. (2)
If we look at where Plane of Louis hits, all the way to the back, we can see it would be at the level of the IV disc between T4 and T5. (3)
Bifurcation of the trachea, also occurs at this level. (4)
The inferior mediastinum can be divided into 3 subparts, what are they, and what do they occupy?
‘Anterior’, ‘Middle’ and ‘Posterior’ subparts.
Anterior: Between the heart and the body of the sternum
Middle: contains the heart and the structures immediately surrounding it
Posterior: Between the heart and the vertebrae
When we remove the sternum and clavicle, what is the first structure we see, and what is its function?
Thymus.
It is an immune organ in the development of the immune system, but it becomes redudant at the age of puberty.
In most of the cadavers, you wont see great thymus at all, and that is partly because it is redudant, and shrivelled but also further exaggerated by the embalming process.
If we remove the thymus, what are the structures we see?
1st Layer (superficial layer) - Venous/Veins, you can identify the SVC coming to the right atrium, in the inferior mediastinum, below the plane of louis.
SVC is made up of both brachiocephalic branches.
“brachio” - arm “cephalic” - head, draining from the arm and head.
The left brachiocephalic branch is obviously longer because it needs to cut across to come the right hand side, where the SVC is located.
We will also see:
INTERNAL JUGULAR VEINS (right and left) draining blood from the head, running in the carotid sheath through the neck, unite with the SUBCLAVIAN VEINS (right and left) which each drain blood from the upper limbs (extensions of the axillary veins), which then unite with the internal jugular veins to form the brachiocephalic vein (left and right), each of which drain into the superior vena cava.
What is the intermediate layer in the superior mediastinum?
Immediately deep to the venous layer of great vessels is the arteriolar layer.
- Arch of the aorta occurring from the ascending aorta at the level of the Plane of Louis
=Arches over this plane and the bifurcation of the trachea to main bronchi.
What are the branches of the arch of the aorta?
(1) Brachiocephalic artery (trunk) supplying blood to the arm and head, but only takes it over to the right hand side. Essentially bridging artery from the arch of the aorta heading off to the left and the right common carotid and right subclavian artery- taking blood to the head and upper limb.
(2) Left common carotid artery
(3) Left subclavian artery
What is important to note about the branches of the arch of the aorta interms whether they are the first branches.?
These are not the first branches of the aorta but the first branch of the arch of the aorta. There has been some other branches of the aorta before, the first of which are the coronary arteries.
What artery is between the superior and inferior mediastinum?
Pulmonary artery as branches of the pulmonary trunk
What is the ligament arteriosum?
Remnant of ductus arteriosus which shunted blood from the right side of the heart through pulmonary trunk to the aorta to bypass pulmonary circulation. Thick cord-like structure remains in adulthood and it feels like a ligament therefore it is called a ligament.
What are the 2 main nerves of the mediastinum and where do they run in relation to the root of the lung?
- Phrenic nerve runs anterior to the root of the lung
- Vagus nerve runs posterior to the root of the lung- disappears behind the pulmonary artery and the main bronchi.
What is the name of the branch that the vagus gives off on each side, and how do they travel? What happens if they are injured?
Vagus has one important named branch on each side: recurrent laryngeal nerve. One coming off vagus on the left side, comes off vagus as it runs superficial to the arch of the aorta before disappearing behind the root of the lung. Nerve hooks under tha arch of the aorta before ascending all the way up to the larynx, to provide innervation to some of the intrinsic muscles of the larynx. In surgery, if trying to ligate/ close off patent ductus arteriosus that is still bypassing blood from lungs, have to be cautious of left recurrent laryngeal nerve as it is so close to the ligamentum arteriosum. If this occurs, will result in problems with phonation and speaking.
=Vagus also gives of right recurrent laryngeal nerve which does essentially the same thing but hooks in under the right subclavian artery, before ascending up to the larynx.
What structure do we find deep to the great vessels in the superior mediastinum?
Trachea. Bifurcating at the plane of louis.
What structures do we find directly posterior to the trachea and final layer of the superior mediastinum?
Oesophagus:
- Directly posterior to the trachea
- Relatively central in the superior mediastinum and sits anterior to the upper thoracic vertebral column.
- As it goes to heart, moves off to the left slightly.
Thoracic duct:
- Comes up behind the oesophagus to get access to the left brachiocephalic vein where it drains lymph from everything below the left diaphragm as well as left thorax, left upper limb and left head.
