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.
What are the muscular ridges called that are found in the ventricles ?
Trabeculae carnae
What is the fossa ovalis?
Depression in right atrium which is a remnant of the foramen ovale which allowed foetal blood to bypass the lungs. It closes when a newborn baby takes its first breath
Where do the cardiac veins drain into ?
The coronary sinus found in the posterior coronary sulcus which drains into the right atrium
How many pulmonary veins are there?
4- 2 draining each lung, 1 superior and 1 inferior
Where do the right and left coronary arteries arise from?
The two aortic sinuses which are dilations found either side of the aortic valve in the ascending aorta.
What is the ligaments arteriosum?
Remnant of the ductus arteriosus which connected the aortic arch to the pulmonary trunk in foetuses.
In which part of the mediastinum is the heart located?
Middle
List 6 ‘killer conditions’ that should be considered in a primary surgery of a chest trauma patient (ATOM-FC)
Airway obstruction or disruption Tension pneumothorax Open pneumothorax Massive haemothorax Flail chest Cardiac tamponade
What ligament is cut when performing a pulmonary hilar twist?
Inferior pulmonary ligament (wizards sleeve)
Why would a HEMS doctor perform a pulmonary hilar twist?
Last resort damage control procedure that occludes the pulmonary vessels. This reduces pulmonary haemorrhage and likelihood of air embolism
What forms the anterior surface of the heart?
Right ventricle
What forms the posterior surface of the heart
Left atrium
What forms the inferior/diaphragmatic surface of the heart
Right and left ventricle
What forms the left pulmonary surface of the heart
Left ventricle
What forms the right surface of the heart
Right atrium
At what stage in the cardiac cycle do the coronary arteries fill with blood?
Diastole
What are the branches of the left coronary artery?
Left Anterior Descending artery (LAD) otherwise known as the anterior inter ventricular artery
Left marginal artery
Left circumflex artery
What are the branches of the right coronary artery?
Posterior interventricular artery
Right marginal artery
What structures and surface are supplied by the LAD?
Right ventricle, Left ventricle, anterior 2/3rd Interventricular septum
What structures and surfaces are supplied by the right coronary artery?
Right atrium, right ventricle, SA & AVN node, posterior part of the atrioventricular septum
(Portion of left atrium and ventricle)
What structures and surfaces are supplied by the circumflex artery?
Left atrium and left ventricle
What structures and surfaces are supplied by the posterior inter ventricular artery?
Right ventricle, left ventricle, posterior part of the inter ventricular septum
Describe the blood supply to the heart’s conduction system
In the majority of the population... SAN & AVN- RCA Proximal bundle of his- dual blood supply therefore RCA & LCA RBB- LCA LBB- LCA
With reference to the surfaces of the heart, which ECG looks at the: anterior
V2-4
With reference to the surfaces of the heart, which ECG looks at the: lateral
V5&6, aVL, Lead 1
With reference to the surfaces of the heart, which ECG looks at the: inferior
aVF, Lead 2 and Lead 3
With reference to the surfaces of the heart, which ECG looks at the: septal
V1 & V2
What artery would be affected if ST elevation was seen in leads V1-V4
LAD causing an infarction in the anterior lateral wall
What are the typical clinical features and examination features of an abdominal aortic aneurysm?
For AAA normally older male who has collapsed and complains of back/abdominal pain.
Thoracic aortic aneurysm can present with chest pain, tiredness, SOB
On palpation- expansile mass
What imaging techniques could you use to confirm your diagnosis and detect possible leaking?
CT scan with contrast could show calcifications and mediastinal enlargement if thoracic
Which structures are found in a lung hilum?
bronchus, pulmonary artery, two pulmonary veins, bronchial vessels, pulmonary plexus of nerves and lymphatic vessels.
Which lung surface is the lung hilum located on?
Mediastinal surface
How does the size and shape of the lungs differ from the pleural cavity? Anterior and posterior
The visceral Pleura
Mid clavicular section of lung ends Rib 6
Mid auxiliary section of lung ends rib 8
Posterior- paravertebral line T10
Parental pleura
Mid clavicular- rib 8
Mid axillary- rib 10
Posterior paravertebral line T12
How many bronchopulmonary segments are there?
10 in the right lung and 8 in the left lung
What is the management for a haemothorax?
Decompress using a chest drain and if there’s a high volume and bleeding continues a thoracotomy may be indicated.
What nerve supplies the parietal pleura on the thoracic wall?
Intercostal nerves
What nerve supplies the parietal pleura on the diaphragmatic pleura ?
Phrenic nerve
What nerve supplies the parietal pleura on the mediastinal pleura?
Phrenic nerve
In the intercostal space, where does the neuromuscular bundle lie in relation to
a) the rib
b) the intercostal muscle
c) why is this important with regards to chest drain placement?
NVB sits inferior to the rib
NVB sits in between the internal and innermost intercostal muscles
Chest drains therefore should be inserted in the 4/5th IC space, anterior to the mid-axillary line SUPERIOR to the rib.
What layers are penetrated when a chest drain is inserted?
Skin, Superficial fascia, external intercostal, internal intercostal, innermost intercostal, endothoracic fascia, parietal pleura
When would it hurt a patient the most when a chest drain is being inserted?
Parietal pleura (hardest for lidocaine to access as deepest layer)
What is a flail segment?
2 or more adjacent ribs that have fractured in 2 or more places.
The fractured segment moves paradoxically: inward on inspiration and outwards on expiration
What are the two main problems that result in impairment of gas exchange in the context of a flail segment?
Incredibly painful therefore reduces patients ability to take deep breaths
Pulmonary contusions which can cause localised oedema and inflammation increasing the distance gas exchange has to occur
How does intubation and positive pressure ventilation help to restore normal gas exchange?
Keep alveoli patent and stops them from collapsing
What is the difference between pneumothorax and tension pneumothorax?
Pneumothorax- air in pleural space in the thoracic cavity
Tension pneumothorax- one way valve, mediastinal shift
What happens to the position of the mediastinum and the trachea with tension pneumothorax?
Mediastinal shift resulting in the trachea deviating away from the pneumonthoraxed lung.
Why is a tension pneumothorax a medical emergency?
Patient eventually becomes shocked because of impeded venous return (due to pulmonary veins being compressed) and cardiac output will reduce.
How is a tension pneumothorax treated?
Needle decompression “thoracocentesis”
What is an open pneumothorax ?
An open pneumothorax occurs when there is a pneumothorax associated with a chest wall defect, such that the pneumothorax communicates with the exterior. Air travels the path of least resistance and will enter through the wound when it’s size is roughly 50% greater than the trachea diameter. Gas exchange doesn’t occur and a tension pneumothorax may develop if a skin flap is created (allowing air in but not out).
What is a tension pneumothorax?
Penetrating or blunt trauma causes air to be sucked into the pleural space either through a whole in the chest wall or through perforation of viscera. Should a flap be formed, from pleura or other soft tissue, a one-way valve can be greater which stops air from escaping during expiration.
What is the initial management for an open pneumothorax?
Create flap valve that blocks the defect on inspiration but opens on expiration (if it doesn’t open on inspiration then suspect a tension). Definitive management is to insert a chest tube
What is the immediate management for a tension pneumothorax?
2nd ICS MCL
Wide bore needle decompression
Name two things that could worsen a tension pneumothorax
Coughing and positive pressure ventilation
What signs would you expect in a patient with a tension pneumothorax?
Rapid respiratory rate, decreased air entry, hyper-resonant hemithorax, rapid but weak pulse, unequal chest expansion, decreased GCS, deviated trachea, raised JVP (if not also hypovolaemic), cyanosis
What is becks triad
Muffled heart sounds
Distended neck veins
Low blood pressure
What artery would be affected if there was ST elevation in leads avF, lead 2 and lead 3
RCA
What artery would be affected if there was ST elevation in leads V5, V6, aVL, lead 1
LCX
