Mediastinum Flashcards
Learning outcomes
• Describe the location, boundaries and contents of the superior mediastinum and of the discrete divisions of the inferior mediastinum (anterior, middle and posterior divisions)
Divisions of thoracic cavity
2 pulmonary cavities- lungs and pleura
Mediastinum (middle septum/partition)- superior and inferior ( Anterior/middle/posterior- heart and pericardium)
Components of the mediastinum
Middle Mediastinum = pericardium, heart, parts of the great vessels, main bronchi, nerves & lymph nodes
The anterior and posterior mediastina are anterior and posterior to the middle mediastinum respectively.
Sternotomy
The smallest division ( anterior mediastinum) can be accessed through sternotomy
• Median incision between jugular notch & xiphoid
• Osteotomy with saw to cut sternum in midline
• Sternum is retracted, sternopericardial ligaments that attach the pericardium to the internal aspect of the sternum are detached with fingers
Anterior mediastinum
Location:
- Posterior to body of sternum
- Anterior to pericardium
Contains
- Internal thoracic (“mammary”) vessels: from the subclavian vessels, these run inferiorly, just deep to the costal cartilages and give branches to the intercostal spaces.
- Anterior mediastinal lymph nodes
-Sternopericardial ligaments that anchor pericardium to sternum
- Part of the thymus- A bi-lobed, lymphoid organ (T-cells mature in the Thymus)
During development it descends from the neck and after puberty, the thymus starts to atrophy & it is mostly replaced by fatty CT.
Superior mediastinum
Location:
- Inferior to superior thoracic aperture
- Superior to transverse thoracic plane
- Posterior to manubrium
- Anterior to T1-4 vertebrae
- Medial to mediastinal pleurae
Contains:
- Thymus
- Neck muscles
- Great Vessels (Superior vena cava; Inferior vena cava; Pulmonary arteries; Pulmonary veins; Aorta)
- L & R Brachiocephalic veins
- Superior vena cava & Arch of Azygos
- Arch of aorta & branches
- Nerves: Phrenic, Vagus, L Recurrent laryngeal
- Thoracic duct
- Trachea
- Oesophagus
- Thymus
- Lymph nodes
Superior mediastinum- great vessels
Veins
Note-Arteries tend to be posterior & to the left
Veins tend to be anterior & to the right
- L & R Brachiocephalic vv
Formed by union of - Internal jugular vein (drains head and neck)
- Subclavian vein (drains upper limb)
Superior vena cava
-R & L brachiocephalic vv unite to form:
Superior vena cava (drains structures superior to diaphragm)
Arteries -Arch of aorta and branches Bracheocephalic trunk, divides into: -R subclavian a (supplies R upper limb) - R common carotid a (supplies R head and neck)
- L common carotid a (supplies L head and neck)
- L subclavian a (supplies L upper limb)
Superior mediastinum- nerves
Phrenic = “diaphragm”, it supplies diaphragm, pleura & pericardium
Vagus = runs from neck to thorax to abdomen, supplying the muscles of the larynx & parasympathetic
(rest & digest) innervation to the internal organs
Sympathetic chain = contains sympathetic (fight or flight) nerves, gives off splanchnic nerves that innervate the internal organs
Phrenic nerves- formed by C3,4,5 cervical spinal nerves( c345 keep the diaphragm alive)
- run anteriorly to anterior scalene muscle in neck, then pass between the pericardium & pleura to
reach the diaphragm (supplying those structures
with motor and/or sensory innervation)
Pericardiophrenic vessels- Branches from the internal
thoracic vessels that supply the pericardium and run with (“co”) the phrenic nerve
Vagus nerves
Cranial nerve X
- Exits brainstem on both sides, pass through hole in skull (jugular foramen) and runs down neck to thorax with common carotid artery.
Gives branches to innervate the- Pharynx (throat) Larynx (voicebox) via: -Superior laryngeal nerve - Recurrent laryngeal nerve-hooks under aorta (on Left)/subclavian a (on Right) & runs up neck between trachea & oesophagus to larynx (recurrent = running back)
-Vagus nerves then supply parasympathetic innervation to cardiac & pulmonary plexuses (Slows
heartrate/breathing, constricts bronchioles)
-Then pass through diaphragm with oesophagus supplying parasympathetic innervation to most abdominal organs (increases digestive action)
-They also transmit sensory info from the organs to the brain
Positions of the nerves
-L Phrenic n-Descends lateral to L subclavian
a, then superficial to pericardium overlying L atrium & ventricle
-Right phrenic n- Descends lateral to superior vena cava & inferior vena cava, superficial to the pericardium
- L vagus n- Descends between L common carotid a & L subclavian a, runs to L of aortic arch
- R vagus n- Descends lateral to R subclavian a, runs between trachea & R brachiocephalic v
-L Recurrent laryngeal n hooks under aortic arch:
(can be compressed by aneurysm of the aorta or mediastinal tumors which may cause hoarseness of the voice)
-R Recurrent laryngeal n hooks under R subclavian a
How to tell difference between phrenic/vagus nerves? Phrenic nn -anterior to hila/root of lung Vagus nn -posterior to hila/root of lung
Trachea and oesophagus
- Oesophagus = slightly flattened fibromuscular tube extending from pharynx to stomach
- Anterior to bodies of vertebrae & posterior to trachea
- Pierces the diaphragm at T10 level along with the anterior & posterior vagal trunks (continuations of left & right vagus nerves)
Thoracic duct
- Part of lymphatic system
- Largest lymph channel
- Drains lymph from the majority of body to Left Venous Angle
Venous Angle = angle at junction of
subclavian & internal jugular vv
The lymphatic system- functions
- Immune - lymph nodes monitor lymph for pathogens
- Fat absorption – fat is absorbed into lymphatic vessels in intestine (not into blood vessels as fat does not mix well with blood)
- Reabsorbing interstitial fluid = fluid leaks into interstitial space between cells. If not reabsorbed > swelling (oedema)
This Lymph & fat must be returned to the blood circulation
-Most lymph drains to a sac in the abdomen called
the Cisterna chyli which drains to the thoracic duct
The thoracic duct
- Thoracic duct receives lymph from all body parts inferior to diaphragm & left side of upper body.
- Remaining areas drain to the Right lymphatic duct which drains to >R Venous angle
Posterior mediastinum
DATES In Vagus -Descending thoracic aorta • Azygos & hemiazygos venous systems • Thoracic duct • Esophagus • Sympathetic trunks • Intercostal vessels (posterior) • Vagus nerves
