Cardiovascular Anatomy Part 1: Mediastinum Flashcards
- Area between the R & L thoracic pleural sacs; extends vertically from superior thoracic aperture to the diaphragm & laterally from the sternum to the vertebral column (from T1-T9)
- contains all the thoracic viscera except the lungs
- is covered by it’s own pleura
What am I?
Mediastinum
What are the subdivisions of the mediastinum?
- Superior mediastinum - extends from superior thoracic aperature to plane between T4 & T5 spinal discs
- Inferior mediastinum - located between the transverse thoracic plane & the diaphragm between T5 & T9. Can be further divided into the anterior (front), middle (pericardium), and Inferior (back) mediastinum.
The superior vena cava (SVC), brachiocephalic veins, arch of the aorta, thoracic duct, lymphatic trunks, trachea, esophagus, thymus, vagus nerves, left recurrent laryngeal nerve, left common carotid artery, left common subclavian artery & phrenic nerves are all located in which mediastinum subdivision?
The superior mediastinum
I am a mediastinum subdivision that lies posterior to the sternum, anterior to the pericardial sac, continuous with the superior mediastinum at the sternal angle, & limited inferiorly by the diaphragm.
What am I?
Anterior mediastinum
This mediastinum subdivison consists of loose connective tissue (sternopericardial ligaments, fibrous bands that pass from the pericardium to the sternum), fat, lymphatic vessels, a few lymph nodes, and branches of the internal thoracic vessels. In infants and children, it also contains the inferior part of the thymus.
The anterior mediastinum
This mediastinum subdivision contains the pericardium, the heart, ascending aorta, pulmonary trunk, Superior vena cava (SVC), arch of azygos vein, & the main bronchi.
Middle mediastinum
I am located a mediastinum subdivision that is located anterior to vertebrae T5-T12, posterior to the pericardium and diaphragm, and between the parietal pleura of the two lungs.
What am I?
The posterior mediastinum
This mediastinum subdivision the:
• Thoracic aorta
• Thoracic duct
• Posterior lymph nodes (e.g., tracheobronchial nodes)
• Azygos and hemiazygos veins
• Esophagus
• Esophageal plexus
• Thoracic sympathetic trunks
• Thoracic splanchnic nerves
Posterior mediastinum
What does the transverse thoracic plane separate?
The superior mediastinum from the inferior mediastinum. It lies between T4 and T5 vertebrae.
The level of viscera relative to mediastinal division is traditionally described as if a person is in what position?
Supine
What is the order of the major structures in the superior mediastinum from anterior (front) to posterior (back)?
The order of major structures in the superior mediastinum, from anterior to posterior, is: T.S.A.T.E.T/L
- Thymus (most anterior structure; if still present/not involuted)
- SVC & it’s branches (veins)
- Aortic arch & it’s branches (arteries)
- Trachea (airway)
- Esophagus (alimentary tract)
- Thoracic duct (lymphatics; most posterior structure)
A lymphoid organ in the lower part of the neck & anterior part of the superior mediastinum. Lies posterior to the manubrium & extends into the anterior mediastinum. After puberty, this organ undergoes gradual involution and is largely replaced by fat.
The Thymus
Name the 3 great vessels & their origin in the superior mediastinum:
The ARCH OF THE AORTA gives off THREE LARGE BRANCHES while in the sup. mediastinum, also referred to as the great vessels of the superior mediastinum.
- The first branch is the BRACHIOCEPHALIC TRUNK/ARTERY (“right” most great vessel branch from the aortic arch). Further distally, this trunk divides into the R common carotid a. (Medial “right”) and the R subclavian a. (Lateral “right”)
- The second branch of the aortic arch is the L COMMON CAROTID Artery (middle great vessel branch)
- Just beyond that is the third branch, the L SUBCLAVIAN Artery (“left” most great vessel branch)
True or False:
Only about 65% of the branches of the arch of the aorta are “normal”.
True
Name the great vessels in this image:
What can issue can be caused by a variation in the great arteries where the right subclavian artery arises as a 4th branch of the aortic arch crossing the midline posteriorly to the esophagus to reach the right upper limbs?
This variation results in dysphagia (difficulty swallowing).
The artery crossing posterior to the esophagus may compress the esophagus, causing difficulty swallowing.
What can issue can be caused by a variation in the great arteries where the aorta forms a double arch, forming a vascular ring around the esophagus & trachea?
A double aortic arch variation where the trachea is compressed may result in dysphagia (difficulty swallowing) & may even affect breathing, which may then require surgical intervention
What are the large veins of the superior mediastinum?
Superior vena cava, that branch out into the left & right brachiocephalic veins. Each brachiocephalic vein then further divides into the left & right internal jugular & subclavian veins. The left brachiocephalic vein is long & oblique.
This nerve enters the thorax anterior to (in front of) the right subclavian artery & posterior to the right brachiocephalic vein, where it gives rise to the right laryngeal nerve.
The right vagus nerve (CN X)
This nerve descends in the neck and enters the thorax and mediastinum between the left common carotid & the left subclavian arteries, and posterior to (behind) the left brachiocephalic vein.
The left vagus nerve (CN X)
These nerves supply all the intrinsic muscles of the larynx except one; if injured, the usual sign is dysphonia or aphonia (hoarsenessor temporary loss of voice), or laryngeal spasm.
Recurrent laryngeal nerves
This nerve lies anterior to (in front of) the subclavian artery & the root of the right lung and lies lateral to the vagus nerve.
The right phrenic nerve
This nerve descends between the left subclavian and left common carotid arteries before crossing the left surface of the aortic arch. It lies anterior to(in front of) the left vagus nerve and passes over the left superior intercostal vein before descending further anterior to the root of the left lung.
Left phrenic nerve
This nerve passes posterior to (behind) the right phrenic nerve, the brachiocephalic vein, superior vena cava (SVC), & the root of the right left lung; contributes to the pulmonary esophageal and cardiac plexi; supplies parasympathetic & sensory innervation to the thoracic viscera.
The right vagus nerve
This nerve passes posterior to the left phrenic nerve & anterior to the root of the left lung; contributes to the pulmonary & esophageal plexuses
The left vagus nerve
This structure descends anterior to (in front of) the esophagus, and ends at the level of the sternal angle by dividing into the right & left main bronchi. It’s posterior surface is flat where it’s cartilaginous “rings” are incomplete.
The trachea
This structure is a fibromuscular tube that extends from the pharynx to the stomach. It lies between the trachea & the vertebral column, exiting at T10 ( the __________ hiatus); covered in a ___________ nerve plexus that both the left & right vagus nerves contribute to.
Esophagus; esophageal hiatus; esophageal nerve plexus
This structure, located in the posterior mediasternum, is a continuation of the arch of the aorta, descending on the left sides of the T5-T12 vertebrae, displacing the esophagus to the right.
It lies posterior to the root of the left lung, pericardium & esophagus. The thoracic aortic plexus (autonomic nerve plexus) surrounds it & it leaves the mediasternum through the aortic hiatus @ T12 to enter the abdomen.
The thoracic duct & the azygos vein ascend on its right side and also exit through the aortic hiatus.
The Thoracic Aorta (aka The Descending Aorta/DA)
This structure passes posterior to (behind) the trachea, the left atrium of the heart, the diaphragm, & posterior & to the right of the aortic arch. It then exits the mediastinum, passing through the diaphragm at T10.
The viscera surrounding the esophagus. It exits at T10, the esophageal hiatus.
What are the 3 structures that leave constrictions/compressions in the thoracic part of the esophagus?
- The arch of the aorta (most evident in a posteroanterior (PA) radiograph views)
- The left main bronchus (most evident in lateral PA radiograph views)
- The diaphragm
The first two compressions occur within close proximity to each other on the esophagus.
No constrictions/impressions will be visible in an empty esophagus; barium is swallowed as the radiographs are taken, & as the esophagus expands during filling/swallowing, these structures will then compress it’s walls, constricting the esophagus in these areas.
This structure is the largest lymphatic channel in the body; usually thin wall, dull white incolor, & often having a beaded appearance due to it’s numerous valves.
It ascends from it’s starting point, the cisterna chyli (part of lymphatics that originate in the intestines) esophagus with the descending/thoracic aorta on the left, the azygos vein on it’s right, the esophagus anterior to (in front of) it, and the spine posterior to (behind) it.
As it ascends into the superior mediastinum, it crosses to the left of the aortic arch between T4-T6, still posterior to the esophagus.
Fragile, easy to break;
The Thoracic Duct
What is Chylothorax? What is it caused by? How can it be removed?
The accumulation of lymph or chyle in the pleural space.
Can be caused by laceration of the thoracic duct, or lymph of chyle from the lacteals of the intestines entering the pleural cavity & producing chylothorax.
This fluid can be removed by performing a needle tap, thoracentesis or ligation of the thoracic duct.
What are the 3 main/chief veins found in the posterior mediastinum?
- Azygos vein (right side)
- Hemiazygos vein (left side)
- Acessory hemiazygos vein (left side)
The left side hemiazygos veins cross over the midline to join the azygos vein on the right.
These veins provide venous drainage of the thoracic wall that eventually empties into the superior vena cava.
Which nerves, found in the posterior mediastinum, supply the viscera inferior to the diaphragm?
The greater, lesser, and least splanchnic nerves, which are apart of the abdominopelvic splanchnic nerves.
Which splanchnic nerves are POSTsynaptic sympathetic fibers and at which spinal levels do these fibers exit from?
Cardiopulmonary splanchnic nerves.
They innervate the heart, lungs, bronchi, larynx, & trachea.
The exit the spine between Cervical (C3-C8) & Thoracic (T1 -T5) sympathetic trunk regions (where their synapses are located)
Which splanchnic nerves are PREsynaptic sympathetic fibers and at which spinal levels do these fibers exit from?
Abdominopelvic splanchnic nerves.
Also referred to as the greater, lesser, & least splanchnic nerves.
The abdominopelvic splanchnic nerves innervate abdominal/ thoracic trunk viscera regions below the diaphragm (but not actually as far down as the pelvis, like the name suggests).
They exit the spine prior to synapse (thus why they are PREsynaptic), between T5-T12 thoracic sympathetic trunk and then synapse at the target organs.
True or False:
The cardiac, pulmonary, and esophageal mixed plexuses only contain sympathetic innervation from splanchnic nerves.
False.
The cardiac, pulmonary, and esophageal MIXED plexuses are formed by the joining of BOTH the parasympathetic innervation from the vagus nerves (CN X), AND the sympathetic innervation from the splanchnic nerves.
List the 8 major nerves of the thorax, their origins, and their distribution/innervation. (V.Ph.Ic.Sc.Rl.Cpl.Ppl.Epl) OR (VPISRCPE)
Vagus, Phrenic, Inter & Sub-costals, Recurrent laryngeal (branch of vagus), & the plexuses (Cardiac, Pulmonary, & Esophageal)
Correctly identify the 8 major thoracic nerves on each side (if applicable) in the diagram below:
Vagus, Phrenic, Recurrent laryngeal, Intercostal, Subcostal, Cardiac plexus, pulmonary plexus, & esophageal plexus.
Correctly identify the numbered structures, vessels & thoracic nerves in the diagram below:
Correctly identify the structures, nerves, and vessels in the diagram below:
(1, 2 & 3 exist in the “arch of the aorta”/aortic arch)
1. BA = Brachiocephalic artery
2. LCC = Left common carotid artery
3. LSC = Left subclavian artery
- SVC = superior vena cava
- Right phrenic nerve
- Right vagus nerve
- Trachea
- Azygous vein
- E = esophagus
- TD = thoracic duct
- Left recurring laryngeal nerve
- Left vagus nerve
