A: Mediastinum notes Flashcards
Subdivisions of mediastinum
Contents of superior mediastinum
Spread of cancer from mediastinal lymph nodes can include:
- Nerves: R/L vagus, L recurrent laryngeal branch of L vagus, R/L phrenic nerves
- Arteries: aortic arch + branches (brachiocephalic, L subclavian, L common carotid)
- Veins: R/L brachiocephalic, SVC, arch of azygos vein
- Thymus gland
- Trachea, oesophagus (viscera)
- Thoracic duct
(NAV TTT)
Contents of posterior mediastinum
Spread of cancer from mediastinal lymph nodes can include:
- Descending aorta, thoracic aorta + branches
- Azygos and hemiazygos veins
- Thoracic duct and associated lymph nodes
- oEsophagus
- Sympathetic trunks + associated nerves
- vagus nerves
Contents of anterior mediastinum
- Thymus gland
- Fat
- Lymph nodes
- Sternopericardial ligaments (sternum to pericardium)
- Connective tissue
(T/F, L S C)
Which vein is more prone to injury in children and why?
Left brachiocephalic vein because it rises above the upper border of manubrium in childdren
Where do the brachiocephalic veins form?
Behind medial ends of clavicles at junction of internal jugular vein + subclavian vein
Where do the brachiocephalic veins join?
Behind lower edge of first right costal cartilage to form the SVC
Which vein does the SVC receive immediately before it enters the pericardial sac?
Azygos vein
Explain the course of azygos vein
- Arises at L1 or L2 by junction of veins (communicate with IVC)
- Passes through adductor hiatus –> enters posterior mediastinum
- Continues upwards on the right side of the thoracic vertebrae bodies
- Receives posterior intercostal veins
- Forms an arch over the root of right lung –> enters posterior SVC immediately before it enters the pericardial sac
- Drains mediastinum and the posterior thoracic + abdominal walls on the right
Explain the course of hemiazygos vein
- Arises at abdomen by junction of veins (communicate with IVC)
- Passes through adductor hiatus –> enters posterior mediastinum
- Continues upwards on the left side of the thoracic vertebrae bodies
- Receives posterior intercostal veins
- Crosses to the right side (posterior to thoracic aorta) to enter azygos vein
- Drains mediastinum and the lower posterior thoracic + abdominal walls on the left
What does the accessory hemiazygos vein drain?
Mediastinum and upper posterior thoracic wall on left
What does the azygos system anastomose?
IVC and SVC if IVC is blocked
Where does the aorta arise?
Left ventricle, posterior to origin of pulmonary artery
Where is the ascending aorta and what are its branches?
Behind the sternum
Branches = right and left coronary arteries
Explain the course of aortic arch and its branches
Course:
- Begins at level of sternal angle, arches posteriorly and to the left.
- Initially anterior to trachea, but later lies lateral to trachea and oesophagus
- Continues as descending aorta at T4/T5 junction
Branches:
- Brachiocephalic trunk (divides into right subclavian and common carotid arteries behind right sternoclavicular joint)
- Left common carotid artery
- Left subclavian artery (passes between anterior and middle scalene to enter axilla)
Explain the course of the descending aorta and its branches?
Course:
- Begins at T4/T5 junction
- Descends through posterior mediastinum (left of upper thoracic vertebrae and anterior to lower thoracic vertebrae)
- Passes through adductor hiatus of the diaphragm at T12 to enter the abdomen
Branches:
- Posterior intercostal arteries supply intercostal spaces and thoracic wall: 9 pairs (first 2 spaces supplied by subclavian artery)
- Right and left bronchial arteries to bronchi and lung tissue
- Oesophageal branches to oesophagus
Patent ductus arteriosus
Congenital heart defect where ductus arteriosus fails to close at birth. Oxygenated + deoxygenated blood mix.
What type of innervation do the vagus nerves provide?
- Parasympathetic innervation to the thoracic viscera
- They carry sensory fibers from thoracic viscera about normal physiology processes and reflex processes
- Do NOT carry pain sensation
Explain the course of right vagus nerve
Descends to the right of trachea –> posterior to root of the lung –> oesophagus
Explain the course of left vagus nerve
Descends between left common carotid and left subclavian arteries –> crosses left side of aortic arch –> posterior to root of the lung –> oesophagus
How do the vagus nerves enter the abdomen?
Through oesophageal opening in the diaphragm
Where do the vagus nerves pass to enter the superior mediastinum?
Posterior to brachiocephalic veins
Explain course of left recurrent laryngeal nerve
Arises from the left vagus nerve close to the aortic arch and loops under it
Explain course of right recurrent laryngeal nerve
Loos around the right subclavian artery in the root of the neck
Where do the recurrent laryngeal nerves ascend?
In the groove between trachea and oesophagus to reach the larynx
What disease is more likely to involve the left recurrent laryngeal nerve rather than the right and what are the consequences?
Diseases of the thorax (such as enlarged lymph nodes associated with lung cancer) –> paralysis of left vocal cord only –> hoarseness of the voice
What disease is more likely to involve the right recurrent laryngeal nerve rather than the left and what are the consequences?
Cancer of the apex of the right lung –> paralysis of right vocal cord only –> hoarseness of the voice
Explain course of phrenic nerves
- Arise from cervical plexus (C3-5)
- Enter superior mediastinum
- Right phrenic nerve descends on the right of SVC
- Left phrenic nerve descends on the left of aortic arch
- Entering middle pericardium, each phrenic nerve descends within the pericardial sac (anterior to the root of the lung) –> diaphragm
- Trick: PHrenic nerve in Front of root of lung
Explain innervation of phrenic nerves
- Motor innervation to diaphragm
- Sensory innervation to central aspects of: diaphragm, fibrous pericardium and parietal layer of serous pericardium
What system are the sympathetic trunks a part of?
Autonomic nervous system (ANS)
What connects the trunks to the thoracic spinal nerves?
White and gray rami communicans
What is sympathectomy?
Division of sympathetic trunks to reduce blood pressure in severe cases of hypertension by preventing vasoconstriction and reducing peripheral resistance
Branches of sympathetic trunks and what type of fibres/nerves they carry
Greater, lesser and least splanchnic nerves
They carry:
- Preganglionic sympathetic fibres from the thoracic ganglia to prevertebral ganglia of abdomen
- Visceral afferent nerves from the abdomen
Explain course of thoracic duct
- Lymphatic duct that begins as cysterna chyli in the abdomen
- Passes through aortic opening in diaphragm to enter posterior mediastinum
- Ascends on vertebral bodies, posterior to oesophagus, right of midline
- moves to left of midline, ascends through superior mediastinum and enters neck
- Drains into venous system at junction of left internal jugular and left subclavian veins
What are the openings in the diaphragm?
T8 = Inferior vena cava in the central tendon (I8)
T10 = oesophageal hiatus for oEsophagus + vagus nerves (10 Eggs)
T12 = aortic hiatus for Aorta + Thoracic duct (At 12)
Mnemonic: I8 (I ate) 10 Eggs AT 12
I8 = Inferior vena cava
10 Eggs = (o)Esophagus (+ vagus nerves) (T10)
AT 12 = Aorta + Thoracic duct (T12)
Trick for neurovascular bundle: VAN (posterior inercostal Vein, Artery and Nerve from top to bottom)
