T1 L4: Superior mediastinum

• Mediastinum?


  central component of the thorax
• Transverse thoracic plane?

  sternal angle to between T4-T5
• Superior mediastinum location?

  above transverse thoracic plane
• Inferior mediastinum location?

  below transverse thoracic plane
• Inferior mediastinum sub-divided into?

  anterior mediastinum: between chest wall and pericardium

  middle mediastinum: heart, beginning of great vessels

  posterior mediastinum: posterior to heart
• Superior thoracic aperture?


  ring of bones formed by manubrium, rib 1, T1 vertebra

  upper boundary of superior mediastinum
• Superior mediastinum organs, arteries, veins, nerves and lymphatics?

  organs: oesophagus, trachea, thymus

  arteries: arch of aorta and branches, pulmonary arteries

  veins: brachiocephalic veins, superior vena cava

  nerves: vagus, phrenic

  lymphatics: vessels feeding into venous angle
• Branches of aorta?

  Ascending aorta:

  left coronary artery LCA

  right coronary artery RCA

  Arch of aorta:

  brachiocephalic trunk

  left common carotid artery

  left subclavian artery

  Descending (thoracic) aorta:

  posterior intercostal artery

  bronchial artery
• Order of veins in superior mediastinum?

  internal jugular vein (4) + subclavian vein (5) → brachiocephalic veins (2 and 3)

  left and right brachiocephalic veins → superior vena cava (1)

  
• In the superior mediastinum, you can find arch of aorta and its 3 branches (in alphabetical order from right to left)?

  1. brachiocephalic trunk
  2. left common carotid artery
  3. left subclavian artery

  
• Superior mediastinum boundaries?

  superior: superior thoracic aperture

  anterior: manubrium

  posterior: T1 - T4/T5 vertebral bodies

  Inferior: transverse thoracic plane

  lateral: mediastinal pleura

  
• Venous angle

  point where jugular vein meets subclavian vein

  left venous angle receives lot more lymph drainage than right

  
• Lymphatic drainage into venous angle?

  Left jugular trunk: lymph from head and neck

  left subclavian trunk: from upper limb

  left bronchomediastinal trunk: from thorax

  thoracic duct: from lower limbs, abdomen, thorax

  
• Phrenic nerve

  Originate from: anterior rami of spinal nerves C3, C4, C5

  Enter superior mediastinum between brachiocephalic veins and subclavian arteries

  Pass anterior to main bronchi

  Motor supply to: diaphragm

  Sensory supply to: diaphragm, pericardium, parietal pleura

  
• Vagus nerves

  Originates from: brainstem (CNX - 'cranial nerve 10')

  Enter superior mediastinum between brachiocephalic veins and subclavian arteries (medial to phrenic nerve)

  Pass posterior to main bronchi

  Recurrent laryngeal branches travel superiorly (loop underneath aorta on left side, underneath right subclavian artery on right side) to provide motor supply to the larynx

  Provides: parasympathetic supply via pulmonary, cardiac and oesophageal plexi

  
• Thymus

  located in: superior mediastinum and anterior mediastinum in children and young adults

  supplied by: branches of internal thoracic artery

  decreases in size after puberty; until becomes fat tissue

  
• Boundaries of the anterior mediastinum

  superior: Level T4 / T5

  posterior: pericardial sac

  anterior: sternum

  inferior: diaphragm

  
• Anterior mediastinum contents

  Thymus (children and young adults)

  Internal thoracic artery and vein

  Parasternal lymph nodes

  
• Development of the heart

  Truncus arteriosus: primitive outflow vessels

  Bulbus cordis: to form the outflow portions of ventricles

  Sinus Venosus: primitive inflow vessels

  
• During the development of the heart in the embryo, the heart tubes fold posteriorly and superiorly.
• Development of inter-atrial septum

  Septum primum: First forming septum

  Ostium primum: first hole in septum primum, gets filled later

  Ostium secundum: remaining hole in septum primum

  Septum secundum: second forming septum

  Foramen ovale: hole in septum secundum

  until birth, blood can flow between atria through foramen ovale and ostium secundum
• Foramen ovale


  Opening between the right and left atria in the foetus that provides a route for (semi) oxygenated blood to by-pass lungs
• Fossa ovalis


  Embryological remnant of the Foramen ovale in the adult inter-atrial septum

  
• Ductus Arteriosus 


  open duct between the pulmonary trunk and aortic arch in the embryo, which fills in after birth

  
• Ligamentum arteriosum 


  embryological remnant of the ductus arteriosus

  good landmark for recurrant laryngeal nerve

  
• 2 distinct features of foetal circulation that allow blood to bypass the lungs

  foramen ovale

  ductus arteriosus