Anatomy of the mediastinum Flashcards
What is dysphagia?
- difficulty swallowing
Where is the mediastinum situated?
- the mediastinum is the area that lies in between the lungs
The mediastinum is split into what 2 parts?
- superior
- inferior
Where does the superior mediastinum begin?
- at the THORACIC INLET level of the 1st rib/ T1 vertebra/ jugular notch
What is thoracic outlet syndrome?
- when the vessels/nerves are compressed around the thoracic inlet
- causes pain in the arm
Where is the inferior mediastinum?
- situated below the transverse thoracic plane
- at the level between the sternal angle and T4/T5 interspace
How many sections is the inferior mediastinum split into?
- 3
- anterior/ middle/ posterior
Name a structure in the anterior mediastinum (that is usually only present during childhood)
- thymus
What does the thymus gland do?
- secretes hormones (e.g. thymosin)
- produces T lymphocytes
What does the thymus convert to after puberty?
- adipose tissue
Name 3 different types of tumour that can affect the thymus
- thymoma (benign)
- thymic carcinoma (malignant)
- lymphoma (blood tumour)
Name the structures found in the middle mediastinum
- pericardium
- heart
- inferior part of SVC
- superior part of IVC
- pulmonary trunk
- proximal part of pulmonary arteries
- distal part of pulmonary veins
- ascending aorta
Name the structures found in the posterior mediastinum
- vagus nerves/ vagal trunk
- azygous veins
- sympathetic chains
- thoracic aorta
- thoracic duct
- superior part of IVC
- oesophagus
Where does the vagal trunk pass through?
- through the diaphragm with the oesophagus (oesophageal hiatus) into the abdomen
Blood from where drains into the azygous vein?
- blood from intercostal veins drains inferiorly to azygous vein
Where is the azygous vein located?
- right side of posterior mediastinum
- arches anterior + superior to lung hilum
- sits anteriorly + medially to oesophagus
Where does blood from the intercostal veins drain to anteriorly?
- the internal thoracic (internal mammary) veins
How many (bilateral) posterior intercostal arteries are there?
- 11 (one per intercostal space)
What arteries branch from the thoracic aorta’s anterior surface?
- bronchial
- oesophageal
- mediastinal
- pericardial
- phrenic
BOMPP!
What do the bronchial arteries do?
- supply arterial blood for the lung tissue
What do the phrenic arteries do?
- supply blood to diaphragm (visceral afferent nerve innervation from phrenic nerve!)
What branches off from the arch of the aorta?
- brachiocephalic trunk (containing right common carotid + subclavian arteries)
- left subclavian artery
- left common carotid
What is located at the ascending aorta (at the position of the aortic sinuses on the semilunar valve)?
- coronary arteries
Where does the thoracic duct drain to?
- venous angle (situated at site of sternoclavicular joint)
What lymphatic vessels drain to the thoracic duct?
- all deep + superficial lymphatic vessels of the body (minus a few on the right hand side)
Where does the thoracic duct lie in relation to the a) oesophagus b) azygous vein
a) posteriorly
b) left
Where does the thoracic duct begin + what is the mass of lymph nodes found there called?
- superior retroperitoneum
- cisterna chyli
What hiatus in the diaphragm does the thoracic duct pass through?
- aortic hiatus
Name 2 types of lymph nodes found in the lungs (that drain into the thoracic duct)
- hilar (bronchopulmonary)
- tracheobronchial
What happens to the thoracic duct at the sternal angle?
- shifts to left hand side of body
What other major lymphatic vessel in the body (which drains structures on the right hand side) drains to the venous angle?
- right lymphatic duct
Describe the vagus nerve
- longest cranial nerve
- contains motor/sensory fibres
- passes through neck/thorax/abdomen
- widest nerve distribution in body
- somatic/visceral afferent + efferent fibres
Describe the course + position of the vagus nerve within the body
- descends vertically within the carotid sheath
- posterolateral to the internal/common carotids
- medial to the internal jugular vein
Describe the course of the right vagus nerve (in detail)
- crosses in front of the 1st part of the subclavian artery
- reaches the thorax on the right side of the trachea (this separates it from the right pleura)
- inclines BEHIND the hilum of the right lung
- courses medially towards the oesophagus to form the oesophageal plexus with the left vagus nerve
Describe the course of the left vagus nerve (in detail)
- crosses intron of the left subclavian artery
- enter thorax between left common carotid + subclavian arteries
- descends on the left side of the aortic arch (this separates it from the pleura)
- inclines BEHIND the root of the left lung
- deviates medially to reach the oesophageal plexus with the right vagus nerve
In the superior mediastinum, name the structures from anterior to posterior
- branchiocephalic veins
- SVC
- arch of the aorta
- trachea
- oesphagus
- thoracic duct
In the superior mediastinum name the structures from lateral to medial
- phrenic nerve
- vagus nerve
- recurrent laryngeal nerve
Describe the course of the right recurrent laryngeal (inferior) nerve
- branches from the vagus nerve at the root of the neck (around the right subclavian artery)
- courses superiorly in the tracheoesophageal groove
- enters the larynx between the cricopharynxgeus and oesophagus
- HOOKS UNDER RIGHT SUBCLAVIAN ARTERY (doesn’t enter the chest!)
Describe the course of the left recurrent (inferior) laryngeal nerve
- branches from vagus nerve at root of neck
- loops around aortic arch distal to the ligamentum arteriosum
- HOOKS UNDER ARCH OF AORTA (does enter chest!)
What is the ligamentum arteriosum?
Remnant of the ductus arterioles (primitive aorta/pulmonary trunk) from embryo
The main trunk of the recurrent laryngeal nerve lies in a triangle. Name what is is bound by a) laterally b) medially
a) common carotid artery; IJV; vagus nerve
b) trachea; oesophagus
Name the nerves of the superior mediastinum (from lateral to medial)
- phrenic nerve
- vagus nerve
- recurrent laryngeal nerve
What is the phrenic nerve formed by?
-anterior rami of spinal nerves C3/4/5
Were does the phrenic nerve course?
- through the neck on the anterior surface of the scalenus anterior
- course through the chest between the mediastinal parietal pleura + the fibrous pericardium
- enters the diaphragm
What is the function of the phrenic nerve?
SOMATIC SENSORY INNERVATION: mediastinal parietal pleura; diaphragmatic parietal pleura; fibrous pericardium; muscle + central tendon of the diaphragm; diaphragmatic parietal peritoneum
SOMATIC MOTOR INNERVATION: skeletal muscle of diaphragm
VISCERAL AFFERENT INNERVATION: all the arterioles of the above structures
What is the vagus nerve?
- cranial nerve X
What is the function of the vagus nerve?
SOMATIC SENSORY: laryngopharynx + larynx
SOMATIC MOTOR: pharynx + larynx
AUTONOMIC PARASYMPATHETIC: thoracic + abdominal organs
What is the recurrent laryngeal nerve?
- branch of vagus nerve
What is the function of the recurrent laryngeal nerve?
- supplies pharynx + larynx
Once the vagus nerve has given off its recurrent laryngeal branches what does it contain?
-only parasympathetic nerves (innervation of thorax + abdomen)
Why does inflammation of the gallbladder cause pain in the shoulder?
- referred pain
- the diaphragmatic parietal peritoneum is irritated
- diaphragm is innervated by the phrenic nerve
- phrenic nerve = C3/4/5
- the SUPRACLAVICULAR NERVE also arises fromC3/4
- supraclavicular nerve supplies the dermatomes over the tip of the shoulder
- therefore the brain refers the pain to a more superficial structure: shoulder (via supraclaviuclar nerves) and not the gallbladder (via phrenic nerves)
If a patient’s tracheobronchial lymph nodes are infiltrated by cancer - why can this cause hoarseness and dysphagia?
- tracheobronchial lymph nodes compress various nervous structures in the mediastinum (e.g. the vagus/recurrent laryngeal nerve etc)
- these nerves innervate the pharynx + larynx (motor + sensory)
- therefore compression of these nerves can prevent the patient from swallowing/sensing - causing dysphagia and hoarseness
Where can we feel the peripheral pulses?
- bifurcation of the common carotid artery
- upper limb = brachial + radial
- lower limb = femoral; popliteal; posterior tibial; dorsalis pedis
Where is bifurcation of the common carotid artery situated?
- anterior to the sternocleidomastoid at the level of the upper border of thyroid cartilage
Why do we specifically auscultate the common carotid?
- carotid bruits
Where are the following situated? a) brachial artery b) radial artery
a) medial to the biceps tendon in the popliteal fossa
b) lateral to the tendon of the FLEXOR CARPI RADIALIS
Where are the following situated?
a) femoral artery
b) popliteal artery
c) posterior tibial artery
d) dorsalis pedis artery
a) inferior to the midpoint of the inguinal ligament (halfway between ASIS + pubic tubercle)
b) in popliteal fossa (immediately posterior to knee joint)
c) between posterior border of the medial malleolus + achilles tendon
d) medial to tendon of EXTENSOR HALLUCES LONGUS (distal to ankle joint)
Name 3 points of arterial access to left side of heart + the purposes of each
1) subclavian: insertion of cardiac pacing wire (under US guidance)
2) radial: cannulation for arterial BP/ ABG sampling
3) femoral: intravascular interventions
Name 2 points of venous access to the right side of the heart + the purposes of each
1) IJV: insertion of a central line (under US guidance)
2) femoral: insertion of central line + intravascular interventions
Why are venous access points situated very close to the heart?
- to allow the conditions to be as close as possible to that of the right atrium
Name the 2 major lymphatic vessels
- thoracic duct
- right lymphatic duct
