Mediastinum Flashcards
What is the mediastinum?
The thoracic compartment between the two pleural sacs
Contains the major organs of the thoracic cavity
- except the lungs
- highly mobile
What is the plane of Ludwig (trans thoracic plane)?
An imaginary horizontal plane across the thorax
What are the anterior and posterior boundaries of the plane of ludwig?
Anterior boundary:
-manubriosternal joint
AKA, angle of Louis
-2nd costal cartilage
Posterior boundary
-T4/5 intervertebral disc
What are the structures of the plane of Ludwig?
- Superior vena cava enters the pericardium
- Arch of the aorta
- Trachea bifurcation
- pulmonary trunk bifurcation
Define the superior, inferior, posterior and anterior borders of the superior mediastinum
Superior: 1st rib, T1, jugular notch
Inferior: transthoracic plane
Posterior: T1-T4 vertebrae
Anterior: manubrium
What are the contents of the superior mediastinum?
Contents:
- esophagus
- thoracic duct
- thymus
- trachea
- aortic arch and major vessels
- left and right brachiocephalic veins
- superior vena cava
- pulmonary arteries
- nerves
- phrenic
- recurrent laryngeal
- phrenic
Where is the thymus located?
Located in the anterior part of superior mediastinum, posterior to the manubrium
What occurs to the thymus in puberty?
Involuted after puberty (replaced by fat)
What is the arterial blood supply of the thymus?
Internal thoracic and anterior intercostal
What is the veinous drainage of the thymus?
Into brachiocephalic, internal thoracic, and inferior thyroid veins
What 8s the lymphatic drainage of the thymus?
Into parasternal, brachiocephalic and tracheobronchialnlymph nodes
What is the trachea?
- Continuation from the larynx at C6
- Lies anterior to the esophagus
- terminates at transthoracic plane
- bifurcates into right and left main bronchi
-Is crossed over by the arches of the aorta and the azygos vein
What is the trachea?
- Continuation from the larynx at C6
- Lies anterior to the esophagus
- terminates at transthoracic plane
- bifurcates into right and left main bronchi
-Is crossed over by the arches of the aorta and the azygos vein
What are the 3 branches of the aortic arch?
Brachiocephalic trunk
- right Subclavian
- right common carotid
Left common carotid
Left Subclavian
What are brachiocephalic veins?
Formed by the union of the Subclavian and internal jugular veins
Located posterior to the sternoclavicular joints
What is the Subclavian artery divided by?
Divided into 3 parts by the anterior scalene muscle
What is the first part of the Subclavian artery?
Vertebral artery
Internal thoracic artery
Thyrocervical trunk
What is the second part of the Subclavian artery?
Costocervical trunk
What is the third part of the Subclavian artery?
Dorsal scapular (May arise from 1st or 2nd part of Subclavian artery
When does the Subclavian artery become the axilla artery?
Becomes the axillary artery at the lateral border of rib 1
What is the impact of the vagus nerve in the mediastinum?
- Travels along the common carotid artery
- Divides inti several branches as it reaches the esophagus, forming the esophageal plexus
- Continues down in abdomen
- Anterior vagal trunk mainly from the left vagus nerve.
- Posterior vagal trunk mainly from the right vagus nerve
Parasympathetic and visceral afferent to the thoracic vertebra
What is the impact of the recurrent laryngeal nerve in the mediastinum ?
- Arise from vagus nerves on either side
- Left associated with arch of the aorta
- Right associated with Right Subclavian artery
What is the impact of the phrenic nerves in the mediastinum?
- enters superior mediastinum between the Subclavian artery and the root of the brachiocephalic vein
- Courses along the pericardium, pierces through the diaphragm
- sensory and motor innervation to the diaphragm
What can thoracic outlet syndrome be caused by?
- extra rib attaching to the 7th cervical vertebra and rib 1
- muscular abnormalities
- trauma, tumor
What does the thoracic outlet syndrome cause?
Leads to compression of axillary inlet components:
-Subclavian artery/vein: thrombosis/ embolization
-Nerves (C8-T1): sensory deficit, muscle wasting
What are the symptoms of thoracic outlet syndrome?
May be present with intermittent or consistent symptoms
- neurological: pain, parasthesia, paresis/paralysis
- Vascularm pallor, pulselessness, poikilothermia (cold), edema (venous compression)
What are the superior, inferior, anterior and posterior borders of the inferior mediastinum ?
Superior: transthoracic plane
Inferior: diaphragm
Anterior: body of the sternum
Posterior: T5-T12
What are the divisions of the inferior mediastinum ?
- Anterior
- Middle
- Posterior
What are the anterior and posterior borders of the anterior mediastinum?
Anterior: sternum
Posterior: pericardium
What are the contents of the anterior mediastinum?
- thymus(or what remains)
- lymph nodes
- connective tissue
What is the middle mediastinum bounded by?
Bounded by the fibrous layer and parietal layer of serous pericardium on all sides.
-pericardium is tightly adhered to the diaphragm inferiorly
What are the contents of the middle mediastinum?
Heart
- ascending aorta
- intrapericardial superior vena cava
- pulmonary trunk
Main bronchi
What are the anterior and posterior boundaries of the posterior mediastinum?
Anterior: pericardium
Posterior: vertebrae T5-T12
What are the contents of the posterior mediastinum ?
Sympathetic chain
Esophagus
Esophageal plexus
Azygos venous system
Descending thoracic aorta
Thoracic duct
Where are sympathetic chains located?
Sympathetic chains are located laterally to the vertebral column
-contain interconnected sympathetic ganglia
Forms 3 distinct splachnic nerves
-greater, lesser and least
What are the distinct splachnic nerves?
Greater
- T5-9 with some variation
- Joins the celiac ganglion
Lesser
- T10-11
- Joins aortico-renal ganglion
Least
- T12 but not always present
- Joins the renal plexus
Describe the course of the esophagus
The continuation of the pharynx from C6 vertebral level
- Enters the thorax through the superior thoracic aperture
- Changes position as it travels downward
- Passes through the diaphragm at T10 level
- Ends where it enters the stomach at the cardiac sphincter
What are the constrictions of the esophagus ?
- Junction with the pharynx. (C6)
- Where crossed by arch of aorta
- Where crossed by left main bronchus (T4/5)
- Passage through the diaphragm at the esophageal hiatus (T10)
What is the arterial blood supply of the thoracic portion of the esophagus?
Thoracic aorta & bronchial arteries
What is the innervation of the thoracic portion of the esophagus ?
Esophageal plexus, sympathetic trunks
What is the arterial supply of the abdominal portion of the esophagus?
Left gastric artery, left inferior phrenic
What is the innervation of the abdominal portion of the esophagus ?
Vagal trunks, greater splachnic nerves
What is the veinous drainage of the thoracic portion of the esophagus?
Azygos, hemiazygos veins
What is the lymphatic drainage of the thoracic portion of the esophagus ?
Thoracic duct, posterior mediastinal nodes
What is the veinous drainage of the abdominal portion of the esophagus?
Left gastric vein
What is the lymphatic drainage of the abdominal portion of the esophagus?
Left gastric nodes
What is the azygos system?
- Form a collateral drainage pathway between the IVC and SVC
- Drain the back, thoracoabdominal wall, and mediastinal viscera
What does the azygos system of veins consist of?
- The azygos and hemiazygos are formed from roots of the IVC and/or renal veins merging with ascending lumbar and subcostal veins
- Hemiazygos from the inferior left half of the body and accessory hemiazygos from upper left side (T5-T8) cross over to drain into azygos
- Azygos runs along the right side of the body in the posterior mediastinum, ascends along the inferior 8 thoracic vertebrae, arches over the root of right lung at T4, to drain into to the SVC
What are the branches of the descending aorta?
- posterior intercostal arteries
- 1 or 2 bronchial arteries
- Pericardial and mediastinal branches
- Esophageal branches
- Superior phrenic artery
- Subcostal artery
What is the trajectory of the descending thoracic aorta?
- Continuation from aortic arch (T4/5)
- Travels along the left side of the esophagus in its entire length down the thorax
- Pierces aortic hiatus at T12 level to becomes the abdominal aorta
What is the diaphragm?
Separation between thorax and abdomen
What are the 3 openings of the diaphragm?
T8= inferior vena cava (right)
T10= esophagus (left)
T12= aorta (midline)
The what is the largest and most prominent lymphatic vessel in the body?
Thoracic duct
Where does the thoracic duct start and end?
Starts in the abdomen as confluence (cisterna chyli)
- Travels on the right for the most part
- Passes through the diaphragms aortic hiatus
- Travels between the azygos vein on the right and aorta on the left; esophagus anterior and vertebral bodies and posteriorly
- Crosses midline at T5 to the left side of the thorax
- Enters the root of the neck to drain into the junction of left Subclavian and left internal jugular veins
What is the function of the thoracic duct?
Carries lymph from the entire body except: the right head and neck, right upper limb and right thorax (drain to right lymphatic duct)
Where does the thoracic duct receive lymph from?
Receive lymph from:
-Confluence from lymph trunks from abdomen, pelvis, perineum, and lower limbs
- Lymphatic ducts from posterior diaphragmatic and posterior mediastinal nodes
- Descending trunks draining lower 6-7 intercostal spaces on both sides
- Lymphatic trunks from upper left 5-6 intercostal spaces
- Also often drains the left jugular trunk- drains left side of head & neck, left Subclavian trunk (drains left upper limb)
What are the causes of an injury to the thoracic duct?
- pathology affecting, lungs, great vessels, esophagus, spine, lymph nodes
- penetrating trauma
- Susceptible to inadvertent injury during medical interventions because the thoracic duct is thin walled and dull white
- Catheterizations (e.g. internal jugular vein)
- Surgeries (e.g. esophagostomy)
What does injury to thoracic duct present with?
Presence of chyle (fluid mixture of lipids, proteins, lymphocytes) in
- Chylothorax
- Chylomediastinum
- Chylopericardium
