Anatomy of the thorax Flashcards
What are the divisions of the mediastinum?
Superior
Anterior, Middle, Posterior
What is the mediastinum?
Central compartment of the thoracic cavity located between the two pleural sacs. It contains most of the thoracic organs
What imaginary line divides the mediastinum into two - a superior and inferior mediastinum
A line travelling from the sternal angle posteriorly towards T4 vertebra.
What are the borders of the superior mediastinum
Superior- thoracic outlet (hole at top of ribs)
Inferior- continuous with inferior mediastinum at level of sternal angle
Anterior- manubrium of sternum
Posterior- T1-T4 vertebrae
Lateral- pleura of the lungs
What neural, vascular and respiratory structures are found in the superior mediastinum
Vascular- aortic arch, right and left brachiocephalic vein, SVC.
Nerves- Right and left vagus nerve. Phrenic nerve. Cardiac nerves originating from the superficial (aortic arch) and deep plexus (trachea). Sympathetic trunk (vertebral bodies)
Respiratory
Trachea (carina at T4/sternal angle)
Thoracic duct
Describe the path of the right and left vagus nerve in the superior mediastinum
Right- Runs parallel to trachea and passes posterior to SVC and right bronchus
Left- In between left common carotid and left subclavian. Follows arch of the aorta, to the left of ligamentum arteriosum to form the left recurrent laryngeal nerve where it continues its journey in the tracheo-oesophageal groove and supplies the larynx
What muscle does the phrenic nerve runs along in the superior mediastinum?
Anterior scalene
Does the phrenic nerve run anterior or posterior to the lung hilum?
Anterior
Where does the phrenic nerve travel in the neck? Is it medial or lateral to the carotid sheath?
Lateral
What is the most anterior structure in the superior mediastinum?
Thymus
What is the surface anatomy of the position of the venous angle (junction between internal jugular vein and subclavian vein)
Between manubrium and 1st rib
Where are central lines placed? Why?
In a hospital environment, would preferably be placed in the IJV. In PHM can be placed in SC vein. Femoral vein can also be used. Both are favoured because they are proximal to the central circulation
Where does the phrenic nerve travel in the neck in relation to the carotid sheath?
Lateral to carotid sheath
Approximately what vertebral level do the pulmonary arteries bifurcate?
T4/T5
Why do you think the aortic arch is prone to disruption during deceleration accidents?
The isthmus of the aorta is a transition zone between the ascending aorta and the relatively fixed descending thoracic aorta. It is therefore fundamentally weaker and vulnerable to stretching during deceleration
What are the attachments of the fibrous pericardium
Diaphragm, great vessels , sternum
What are the borders of the middle mediastinum?
Anterior- anterior margin of the pericardium.
Inferior- superior surface of the diaphragm
Superior- imaginary line running from sternal angle-T4
Posterior- posterior border of pericardium
Lateral- mediastinal pleura of lungs
Which compartment of the mediastinum is the heart in?
Middle
Which compartment of the mediastinum are the origins of the great vessels found?
Middle
Which nerves are associated with the middle mediastinum?
phrenic nerves runs down middle mediastinum to superior surface of diaphragm
Which lymphatics are found in the middle mediastinum?
Tracheobronchial lymph nodes
What does the anterior mediastinum contain?
Thymus (mostly fat cells in adults), loose connective tissue which helps attach the pericardium to the sternum, lymphatic vessels, lymph nodes and branches of the internal thoracic vessels (not that important)
What are the borders of the posterior mediastinum
Roof- imaginary SA->T4 line
Anterior- Pericardium
Posterior- T5-T12 vertebra
Floor- diaphragm
What major blood vessel passes through the posterior mediastinum?
Thoracic aorta
What level does the thoracic aorta become the abdominal aorta by passing through the diaphragm?
Passes through the diaphragm via the aortic hiatus at T12
State the main arteries that come off the thoracic aorta. State whether these arteries come off the aorta laterally or anteriorly
Paired posterior intercostal arteries- lateral
Paired bronchials- lateral
Oesophageal- anterior
Superior phrenic- anterior (diaphragm)
Name the contents of the posterior mediastinum
Thoracic aorta + branches, oesophagus, Thoracic duct, azygos system of veins, sympathetic trunks
What are the attachments of the fibrous pericardium?
Tunica adventitia of great vessels
Diaphragm
Sternum
Why does a cardiac tamponade lead to a reduced cardiac output?
Accumulation of fluid in pericardial space puts pressure on the heart and prevents it from expanding completely and therefore filling completely with blood. Less blood is able to leave the heart resulting in a reduced cardiac output. There is also a reduced systemic BP and narrowing of pulse pressure
What happens to the pulse pressure in a cardiac tamponade?
Narrows
Where do cardiac tamponades occur?
Between the serous layers (parietal and fibrous) of the pericardium
What prevents the heart from stretching to accommodate a cardiac tamponade?
Fibrous pericardium- very rigid
What nerve innervates the pericardium?
Phrenic nerve. Pericarditis pain can be referred to the shoulder
Describe the layers of the pericardium
Fibrous pericardium , parietal (serous) pericardium, visceral (serous) pericardium which form the outer layer of the heart ‘epicardium’
Explain the mechanism behind the venous distension seen in Kussmaul’s sign
Rise in venous pressure and venous distension seen with inspiration (JVP should fall with inspiration) caused by restricted right ventricular filling
How is tamponade diagnosed?
FAST scan
How is traumatic tamponade relieved? What structures do they cut though?
Treat definitely with surgical pericardotomy. As an interim, a subxiphoid pericardiocentesis can be done. If patient rapidly deteriorates, may indicate need to do an open thoracotomy.
What is the function of the papillary muscles and chordae tendinae ?
During ventricular systole, the papillary muscles contract and pull the thread like chordae tendinae which are attached to the three tricuspid/two mitral cusps. This stops the valves from prolapsing during systole.