12-09-22 - Thoracic Cavity 2 Flashcards
Learning outcomes
• Describe the relationships of the structures within the mediastina
• Describe the posterior relations of the manubrium
• Describe the clinical anatomy of the thoracic aorta
• Describe the functional anatomy of the trachea
• Describe the clinical anatomy of the oesophagus
• Describe the lymph drainage of the mediastinal nodes
• Describe the clinical anatomy of the thoracic duct
• Discuss the clinical relevance of the structures within the mediastina
• Identify anatomical structures on medical images of the thorax
How are cross-section CT scans orientated?
Label these structures in a cross-section scan of T3 (superior mediastinum).
What is used in scans to make structures more prominent?
What prominent structures of the aortic arch can be seen in this scan of T3?
• The CT scans are taken so that we are looking at the feet upwards (inferiorly to superiorly)
• This means right is left, and left is right
• Contrasting agents (iodine based and barium-sulphate compounds) can be used to make arteries/veins/structures more prominent
• In this cross-sectional scan of T3 (superiormediastinum), we can see the 3 branches of the aortic arch:
1) Brachiocephalic trunk
2) Common carotid artery
3) Left subclavian artery
What 2 important vessels can be seen in a cross-section CT of T4 (superior mediastinum)?
Label these structures on a cross-sectional scab if T4.
• In a cross-section CT of T4, we can see:
1) Cross section of the aortic arch
2) Superior vena cava – right and left brachiocephalic veins have joined to form the superior vena cava
What 2 structures are posterior to the sternoclavicular joint?
What structures are posterior to the first 3 right costal cartilages?
• Posterior to the sternoclavicular joint:
1) Formation of the brachiocephalic veins (BVC) by the internal jugular (IJV) and subclavian (ScV) veins
2) Division of the brachiocephalic trunk to its branches on the right side
• Posterior to 1st right CC – formation of the Superior Vena Cava (SVC) by right and left BCVs
• Posterior to 2nd right CC – Arch of Azygos vein joins the SVC
• Posterior to 3rd right CC – SVC enters the right atrium
What 7 structures are found in the posterior mediastinum?
• Structures found in the posterior mediastinum:
1) Descending aorta
2) Oesophagus (surrounded by vagal trunks)
3) Vertebral bodies
4) Posterior costal segments
5) Proximal segments of posterior intercostal vessels
6) Proximal segments of intercostal nerves
7) Sympathetic chain with ganglia
What is the descending thoracic aorta?
Where does it start and end?
What is its position in reference to thoracic vertebrae?
What do visceral and parietal branches supply?
What are the visceral (5) and parietal branches (2) of the descending thoracic aorta?
• The descending thoracic aorta is the distal continuation of the aortic arch
• The descending thoracic aorta runs between the level of the sternal angle (T4/T5) to the aortic hiatus of the diaphragm (T12) where it will go into the abdominal cavity and become the abdominal aorta
• The descending thoracic aorta lies on the left of the thoracic vertebrae, but moves into the midline in the lower thorax
• Visceral branches of the descending thoracic aorta supply all the organs in the mediastinum, except the heart:
1) Oesophageal arteries
2) Bronchial arteries (usually 2 on left and 1 on right – pulmonary arteries don’t supply lungs)
3) Pericardial branches
4) Mediastinal branches
5) Superior phrenic artery?
• Parietal branches of the thoracic aorta supply the walls of the thoracic cavity:
1) Posterior intercostal arteries (except the first 2)
2) Superior phrenic artery (superior surface of the diaphragm?
What’s the role of the oesophagus?
Where does the oesophagus start?
Where does it enter into the thoracic cavity?
How does its positioning change as it descends?
What structure does it pierce?
• The oesophagus transports food and liquid to the stomach
• The oesophagus starts in the midlines as a continuation of the pharynx at C6 (superior border of the trachea, inferior borer of cricoid cartilage)
• The oesophagus descends in between the trachea and vertebral column into the thoracic cavity
• The arch of the aorta is to its left in the superior mediastinum
• In the lower posterior mediastinum, the oesophagus swings forward and to the left, and pierces the diaphragm at the level of T10.
Why does the oesophagus have constrictions rather than border?
What are the 4 constrictions of the oesophagus?
What are 3 reasons why constrictions are dangerous?
• The oesophagus is made of muscle not cartilage, so it is collapsible, and has constrictions rather than borders
• Constrictions of the oesophagus:
1) The upper oesophageal sphincter
2) Arch of aorta
3) Left main bronchus (arch of aorta and left main bronchus compress the oesophagus)
4) Where the oesophagus passes through the diaphragm (oesophageal hiatus)
• Constrictions are dangerous because they are more likely to:
1) Cause blockage
2) Hinder passage of instruments
3) Slow down the passage of caustic substances (substances that damage tissue), leading to more damage
What 3 venous systems do the upper and middle thirds of the oesophagus drain to?
Where does the lower third drain to?
How do these venous drainage systems connect?
What can be triggered due to cirrhotic liver disease?
• Veins of the upper and middle third of the oesophagus drain to:
1) Azygos
2) Hemiazygos
3) Accessory hemiazygos (systemic)
• Veins of the lower third of the oesophagus drains to the left gastric vein (portal system)
• There are anastomoses between the veins of the middle and lower third known as the portosystemic or portocaval anastomosis, which are between the azygos system and hepatic-portal system
• Cirrhotic liver disease can lead to the liver tissue being inflexible and tough, which compresses the hepatic portal vein, leading to portal hypertension
• Instead of blood from going the hepatic portal vein to the IVC to the heart, it travels to the thoracic cavity and is drained by these veins (e.g azygos)
• These veins can’t handle much blood and will swell, leading to oesophageal varices (expanded blood vessels in the oesophagus)
What is the type of muscle found on each third of the oesophagus?
What type of epithelium lines the oesophagus?
What 3 structures innervate the oesophagus?
What do these structures form?
• Upper 1/3rd of oesophagus – striated muscle (voluntary muscle, as swallowing is voluntary and rapid)
• Middle 1/3rd – mixed striated and smooth muscle
• Lower 1/3rd - smooth muscle
• The oesophagus is lined by stratified squamous epithelium
• The oesophagus is innervated by:
1) Left vagus – forms the anterior vagal trunk
2) Right vagus – forms posterior vagal trunk (the vagus nerve is cranial nerve 10 and descends from the neck into the thorax with the internal jugular and carotid arteries to give off branches)
3) Sympathetic fibres from splanchnic nerves
• All 3 of these structures together form the oesophageal plexus around the oesophagus
Where is the mediastinum rich in?
Where are superior and inferior tracheobronchial nodes found?
What do they receive?
What can this cause to spread?
Where can anterior and posteriormediastinal lymph nodes be found?
• The mediastinum is rich in lymph nodes
• Superior and inferior tracheobronchial nodes are found clustered around the trachea and oesophagus
• They receive lymph from the lung
• This can lead to the spread of lung tumours
• Anterior mediastinal lymph nodes are found round the brachiocephallic veins
• Posterior mediastinal lymphd nodes can be found behind the heart and adjacent to the oesophagus
Describe the route in which lymph is drain to the bronchomediastinal lymph trunks.
What is the venous (pirogoffs) angle?
Where does lymph from the bronchomediastinal trunks drain into on each side?
• Pirogoffs angle also known as the venous angle, is the junction where the internal jugular and subclavian veins merge to form the brachiocephalic vein
• This happens on both sides
Lymph drainage diagram
What is the role of the thoracic duct?
Where does the thoracic duct start?
Where does the thoracic duct enter the thoracic cavity?
What can the thoracic duct be found between in the thoracic cavity?
How does the aorta aid in the function of the thoracic duct?
What does the thoracic duct do at level T4/T5?
Where does it move up to after this?
What does the thoracic duct open into?
What can happen if the thoracic duct is damaged?
• The thoracic duct carries lymph from most of the body, except the thorax, upper limb and head and neck on the right side
• The thoracic duct starts at the cisterna chyli, which is a fusiform sac of lymph that uses the thoracic duct as an output channel
• The thoracic duct enters the thoracic cavity through the diaphragm, where is travels alongside the aorta
• The thoracic duct can be found between the aorta and the azygos vein in the posterior mediastinum
• The pulsation of the aorta promotes lymph flow by compressing the thoracic duct so that lymph can flow superiorly against gravity
• At T4/T5, the thoracic duct crosses behind the oesophagus to ascend on its left side
• The thoracic duct then moves further up and arches over the apex of the left lung and pleura
• The thoracic duct then opens into the left brachiocephalic vein at the junction of the left internal jugular and the left subclavian vein (pirogoffs angle)
• If the thoracic duct is damaged, this can lead to a chylothorax, where lymph can leak into the thoracic cavity.
Thoracic duct on an x-ray
Label these cross-sectional CT scans of the superior mediastinum and at what level they occur at
