W2: Mediastinum Flashcards
What does the mediastinum contain?
All the thoracic viscera and structures, except for the lungs
Lungs are in their own plural cavity
What are the inferior and superior borders of the mediastinum?
Inferior = diaphragm Superior = superior thoracic aperture
What is the sternum divided into?
Manubrium, body and xiphoid process
What can the inferior mediastinum be divided into?
Anterior, middle and posterior
What is in the superior mediastinum?
- Aortic arch and great vessels
- 3 major branches of aortic arch (brachiocephalic, left common carotid, left subclavian)
- Superior vena cava (brachioceophalic veins, left superior intercostal vein, supreme intercostal vein, azygos vein which gets blood from right posterior intercostal veins. The left intercostal veins drain into hemiazygos and accessory hemiazygos veines before joining azyos vein at T7-T9)
- Thymus - extends into anterior mediastanum
- Trachea - bifurcates to primary bronchi at sternal angle
- Oesophagus
- Phrenic nerve
- Cardiac nerves and plexuses
- Sympathetic trunk
- Vagus nerve
- Split into right and left vagus nerves
- The left recurrent laryngeal nerve comes from left vagus as it passes aortic arch
Easy way to remember contents of superior mediastinum
LET VPL
Longus colli muscles
Esophagus
Trachea
Vagus nerve
Phrenic nerve
Left recurrent laryngeal nerve
Then we have superior vena cava and arch of aorta
Then thymus
What is in the anterior mediastinum?
No major structrues
Thymus gland → mainly in children - mainly replaced by adipose in adult
Ectopic parathyroid → where parathyoid do not allow appropriate path in development, often found in anterior mediastinum
Thyroid tissue - uncommon though, most likely ectopic
What is in the middle mediastinum?
- Heart in pericardial sac
- Tracheal bifurcation
- Ascending aorta
- Pulomary trunk - gives rise to left and right pulmonary arteries
- Superior vena cava
- Cardiac plexus - network of nerves at base of heart - both sympathetic and parasympathetic
- Phrenic nerves - major innervation of the diaphragm
- Tracheobronchial lymph nodes - enlarged in certain lung pathologies
What is in the posterior mediastinum?
- Descending aorta and its branches
- Oesophagus (from superior), descends posteriorly to aortic arch
- Thoracic duct - largest lymphatic vessel
- Thoracic sympathetic trunk
- Thoracic splanchnic nerves - supply this viscera
Easy trick for contents of the inferior mediastinum
Posterior
TED SAHAV
Thoracic duct
Esophagus
Descending aorta
Spanchnic nerves
Azygous nerve
Hemiazygous vein
Accessory hemiazygous vein
Vagus nerve
Middle
- Heart, bifurcating trachea, phrenic nerve, cardiac plexus
Anterior
- Inferior part of thymus
What is thoracic inlet syndrome?
The upper extremity is bounded by the inlet to the thorax which is a narrow space through which the trachea, oesophagus, major vessels and nerves pass between the neck and thorax. Any structure which increases in size here (for example a low thyroid gland, lymph nodes with the secondary tumour) can compress the trachea and other structures, creating a ‘thoracic inlet syndrome’.
Symptoms - difficultly breathing, distension of veins and swelling of neck, face and upper limbs (from compression of subclavian and jugular veins
What is thoracic inlet syndrome?
The upper extremity is bounded by the inlet to the thorax which is a narrow space through which the trachea, oesophagus, major vessels and nerves pass between the neck and thorax. Any structure which increases in size here (for example a low thyroid gland, lymph nodes with the secondary tumour) can compress the trachea and other structures, creating a ‘thoracic inlet syndrome’.
Symptoms - difficultly breathing, distension of veins and swelling of neck, face and upper limbs (from compression of subclavian and jugular veins
Useful mnemonic for thoracic plane structs
RATPLANT
Rib 2
Aortic arch
Tracheal bifurcation
Pulmonary trunk
Ligamentum arteriosum
Azygos vein
Nerves (loop of recurrent laryngeal)
Thoracic duct
Draw superior mediastinum contents
Where is the thoracic inlet?
From superior manubrium to T1
Describe vagus nerve
- Preganglionic parasympathetic innervation to respiratory tract, heart and all derivatives of foregut and midgut after passing through the diaphragm into the abdomen
- Enter the superior mediastinum through posterior part of carotid sheath (travels with the jugular vein and the common carotid artery)
- At the base of the neck, left and right vagus nerves have different pathways
- For example, right recurrent laryngeal = under right subclavian and ascends towards larynx, left = loops under aortic arch
- The right vagus nerve, as it crosses the subclavian artery, produces the right recurrent laryngeal nerve, which loops beneath the right subclavian artery and runs superiorly to the larynx
- The left vagus nerve, as it crosses the aorta, produces the left recurrent laryngeal nerve, which loops beneath the ligamentum artierosum and then ascends to supply the larynx
Discuss phrenic nerves
The left and right phrenic nerves supply diaphragm (motor) and pleura, pericardium and peritoneum
Phrenic nerves formed from C3-C5
Descend along anterior scalene muscle
‘C3, 4, 5 keeps the diaphragm alive’
Costodiaphragmatic recesses - discuss
Angles between thoracic wall and diaphragmatic pleurae
May contain fluid in diseases such as heart failure, lung cancer and pneumonia
Causes blunting of usual sharp endges
Damage to the phrenic nerves
One = paralysis of half of diaphragm - can be identified on radiogrpahs on breathing in
Usually the diaphragm should descend. The paralysed ascends due to push of abdominal viscera below
It descends in expiration due to positive pressure from the lungs
Damage to vagus nerves
Distention of aortic arch (aneurysm and dissection) → compression of left recurrent laryngeal nerve
Results in paralysis of laryngeal muscles on left side - hoarse voice
Distally, damage to the vagus nevre will reduce parasympathetic innervation to the foregut and midgut structures, resulting in gastroparesis - stomach does not empty in normal way - motility affected
