Mediastinum 1 (Jasmine) Flashcards
What is the mediastinum? What is it covered with on each side? What structure does it not contain? What is one example of a structure that passes through more than one mediastinal compartment?
- The mediastinum, occupied by the mass of tissue between the two pulmonary cavities, is the central compartment of the thoracic cavity.
- It is covered on each side by mediastinal pleura
- It contains all the thoracic viscera and structures except the lungs.
- Espophagus
What is the extension of the mediastinum to the diaphragm, sternum and thoracic vertebrae?
The mediastinum extends from the superior thoracic aperture to the diaphragm inferiorly and from the sternum and costal cartilages anteriorly to the bodies of the thoracic vertebrae posteriorly.
The major structures in the mediastinum are surrounded by (5)?
- blood vessels
- lympathic vessels
- lymph nodes
- nerves
- fat
What does the looseness of the connective tissue and the elasticity of the lungs and parietal pleura on each side of the mediastinum enable it to accommodate movement and which two changes in the thoracic cavity? 6 examples of those changes are?
Volume and Pressure
- movements of the diaphragm
- movements of the thoracic wall
- tracheobronchial tree during respiration
- contraction (beating) of the heart
- pulsations of the great arteries
- passage of ingested substances through the esophagus.
The division between the superior and the inferior mediastinum (the transverse thoracic plane) is defined in terms of bony body wall structures and are mostly independent of gravitational effects. The level of the viscera relative to the subdivisions of the mediastinum depends on the position of the person (i.e., gravity).
For example, When lying on one’s side, the mediastinum sags toward the lower side under the pull of gravity.
Is the following statement true or false?
Connective tissue here becomes fibrous and rigid with age; hence the mediastinal structures become less mobile.
True
The mediastinum is divided into what two parts? Explain location of those two parts.
Superior Mediastinum extends inferiorly from the superior thoracic aperture to the horizontal plane that includes the sternal angle anteriorly and passes approximately through the junction (intervertebral disc/IV disc) of the T4 and T5 vertebrae posteriorly, often referred to as the transverse thoracic plane
Inferior Mediastinum between this plane and the diaphragm is further subdivided by the pericardium into anterior, middle, and posterior parts.
What are the three subdivions of the inferior mediastinum? What constitutes the middle mediastinum?
Anterior, Middle, Posterior
- The pericardium and its contents ( the heart and roots of its great vessels) constiute the middle mediastinum
When a person is supine or when a cadaver is being dissected, the viscera are at what position relative to the subdivisions of the mediastinum than when the person is upright?
More Superior
What structures are found in the superior mediastinum?
ThesuperiormediastinumcontainstheSVC,brachiocephalicveins,archoftheaorta,thoracic
duct, trachea, esophagus, thymus, vagus, left recurrent laryngeal, and phrenic nerves.
What structures are found in the anterior mediastinum?
The anterior mediastinum contains the remnants of the thymus gland, lymph nodes, and fat.
What structures are found in the posterior mediastinum?
The posterior mediastinum contains the esophagus, thoracic aorta, azygos and hemiazygos veins, thoracic duct, vagus nerves, sym- pathetic trunks, and splanchnic nerves.
A 32-year-old patient who weighs 275 lb comes to the doctor’s office. On the surface of the chest, the physician is able to locate the apex of the heart:
(A) At the level of the sternal angle
(B) In the left fourth intercostal space
(C) Intheleftfifthintercostalspace
(D) In the right fifth intercostal space
(E) Atthelevelofthexiphoidprocessofthe
sternum
The answer is C. On the surface of the chest, the apex of the heart can be located in the left fifth intercostal space slightly medial to the midclavicular (or nipple) line. The sternal angle is located at the level where the second ribs articulate with the sternum. The xiphoid proc- ess lies at the level of T10 vertebra.
A 45-year-old woman presents with a tumor confined to the posterior mediasti- num. This could result in compression of which of the following structures?
(A) Trachea
(B) Descending aorta
(C) Archoftheaorta
(D) Arch of the azygos vein
(E) Phrenicnerve
The answer is B. The descending aorta is found in the posterior mediastinum. The superior mediastinum contains the trachea and arch of the aorta, and the middle mediastinum contains the ascending aorta, arch of the azygos vein, and main bronchi. The phrenic nerve runs in the middle mediastinum.
A 17-year-old boy was involved in a gang fight, and a stab wound severed the white rami communicantes at the level of his sixth thoracic vertebra. This injury would result in degeneration of nerve cell bodies in which of the following structures?
(A) Dorsal root ganglion and anterior horn of the spinal cord
(B) Sympathetic chain ganglion and dorsal root ganglion
(C) Sympathetic chain ganglion and posterior horn of the spinal cord
(D) Dorsal root ganglion and lateral horn of the spinal cord
(E) Anterior and lateral horns of the spinalcord
The answer is D.
The white rami communicantes contain preganglionic sympathetic GVE fibers and GVA fibers whose cell bodies are located in the lateral horn of the spinal cord and the dorsal root ganglia. The sympathetic chain ganglion contains cell bodies of the postgan- glionic sympathetic nerve fibers. The anterior horn of the spinal cord contains cell bodies of the GSE fibers. The dorsal root ganglion contains cell bodies of GSA and GVA fibers.
A 75-year-old patient has been suffering from lung cancer located near the cardiac notch, a deep indentation on the lung. Which of the following lobes is most likely to be excised?
(A) Superior lobe of the right lung
(B) Middlelobeoftherightlung
(C) Inferiorlobeoftherightlung
(D) Superior lobe of the left lung
(E) Inferior lobe of the left lung
The answer is D.
The cardiac notch is a deep indentation of the anterior border of the superior lobe of the left lung. Therefore, the right lung is not involved.
A thoracentesis is performed to aspirate an abnormal accumulation of fluid in a 37-year-old patient with pleural effusion. A needle should be inserted at the midaxillary line between which of the following two ribs so as to avoid puncturing the lung?
(A) Ribs 1 and 3
(B) Ribs 3 and 5
(C) Ribs 5 and 7
(D) Ribs 7 and 9
(E) Ribs 9 and 11
The answer is D.
A thoracentesis is performed for aspiration of fluid in the pleural cavity at or posterior to the midaxillary line one or two intercostal spaces below the fluid level but not below the ninth intercostal space and, therefore, between ribs 7 and 9. Other intercos- tals spaces are not preferred.
When the individual is standing or sitting erect the levels of the viscera are at the lower position. Why is this?
This occurs because the soft structures in the mediastinum (especially the pericardium and its contents), the heart and great vessels, and the abdominal viscera supporting them sag inferiorly under the influence of gravity.
In the supine position:
- The arch of the aorta lies in what position to the transverse thoracic plane?
- What is transected by the tranverse thoracic plane?
- Central tendon of the diaphragm (or the diaphragmatic surface or inferior extent of the heart) lies at what junction/vertebra?
- Superior
- Bifurcation of the trachea
- Xiphisternal junction and the vertebra T9
* The base of the pericardium lies at the xiphisternal junction and vertebra of T9
When standing or sitting upright, the:
- What structure is transected by the transverse thoracic plane?
- Tracheal bifurcation occurs at what position to the transverse thoracic plane?
- Central tendon of the diaphragm may fall to the level of what structure and vertebra?
- Arch of the aorta
- Inferior
- Middle of the xiphoid process and the T9/T10 intervertebral disc
What are the two methods to study the mediastinum?
- Mediastinoscopy
- They insert the endoscope through a small incision at the root of the neck, just superior to the jugular notch of the manubrium, into the potential space anterior to the trachea.
- Anterior Thoracotomy
What are some common examples for widening of the mediastinum?
- Enlargement (hypertrophy) of the heart (occurring with congestive heart failure) is a common cause of widening of the inferior mediastinum.
- Malignant lymphoma (cancer of lymphatic tissue) produces massive enlargement of mediastinal lymph nodes and widening of the mediastinum.
- After trauma resulting from a head-on collision, for example, which produces hemorrhage into the mediastinum from lacerated great vessels such as the aorta or superior vena cava (SVC).
The superior mediastinum can be found in what position to the transverse thoracic plane? What anatomical landmark does it pass through? What is the vertebral location of the superior mediastinum?
The superior mediastinum is superior to the transverse thoracic plane, passing through the sternal angle and the junction (IV disc) of vertebrae T4 and T5.
What are the contents of the superior mediastinum from anterior to posterior?
*********thymus, veins, arteries, airway, alimentary tract, and lymphatic trunks.
- Thymus
- Great vessels, with the veins (brachiocephalic veins and SVC) anterior to the arteries (arch of the aorta and the roots of its major branches — the brachiocephalic trunk, left common carotid artery, and left subclavian artery) and related nerves (vagus and phrenic nerves and the cardiac plexus of nerves).
- Inferior continuation of the cervical viscera- (trachea anteriorly and esophagus posteriorly) and related nerves (left recurrent laryngeal nerve).
- Thoracic duct and lymphatic trunks
Mediastinum
What is the thymus? What is the function? Where is the thymus located?
- The thymus, a primary lymphoid organ, is located in the inferior part of the neck and the anterior part of the superior mediastinum.
- It lies posterior to the manubrium and extends into the anterior mediastinum, anterior to the fibrous pericardium.
- The thymus plays an important role in the development and maintenance of the immune system (production of T-lymphocytes).
- After puberty, the thymus undergoes gradual involution and is largely replaced by fat. For some infants the thymus can compress the trachea.
What are the great vessels? Where are they located? What structrure is formed as a result of the brachiocephalic veins?
- The brachiocephalic veins are formed posterior to the sternoclavicular (SC) joints by the union of the internal jugular and subclavian veins.
- At the level of the inferior border of the 1st right costal cartilage, the brachiocephalic veins unite to form the superior vena cava (SVC).
Which brachiocephalic vein is longer? Why is it longer? What is the function?
- The left brachiocephalic vein is more than twice as long as the right vein because it passes from the left to the right side, passing over the anterior aspects of the roots of the three major branches of the arch of the aorta.
- It shunts blood from the head, neck, and left upper limb to the right atrium.
Where is the superior vena cava (SVC) located? What is the function of the SVC? Which nerve lies between the SVC and the mediastinal pleura?
- The superior vena cava (SVC) returns blood from all structures superior to the diaphragm, except the lungs and heart.
- It passes inferiorly and ends at the level of the 3rd costal cartilage, where it enters the right atrium of the heart.
- The SVC lies in the right side of the superior mediastinum, anterolateral to the trachea and posterolateral to the ascending aorta.
- The right phrenic nerve lies between the SVC and the mediastinal pleura.
Where can the terminal half of the SVC be found? What does it form the posterior boundary of?
The terminal half of the SVC is in the middle mediastinum, where it lies beside the ascending aorta and forms the posterior boundary of the transverse pericardial sinus.
Where does the ascending aorta begin? What mediastinum is it considered a part of? Why?
- The ascending aorta, approximately 2.5 cm in diameter, begins at the aortic orifice.
- Its only branches are the coronary arteries, arising from the aortic sinuses.
- The ascending aorta is intrapericardial; for this reason and because it lies inferior to the transverse thoracic plane, it is considered a content of the middle mediastinum (part of the inferior mediastinum).
The arch of the aorta is considered a continuation of what structure? What is the vertebral location of the arch of the aorta?
- The arch of the aorta (aortic arch), the curved continuation of the ascending aorta, begins posterior to the 2nd right sternocostal joint at the level of the sternal angle and arches superiorly, posteriorly and to the left, and then inferiorly.
- T4/T5
What is the location of the arch of the aorta? Where does the arch of aorta end? The arch descends posterior to the root of the lung on the left side of the body of the T4 vertebra.
- The arch descends posterior to the root of the lung on the left side of the body of the T4 vertebra.
- The arch of the aorta ends by becoming the thoracic aorta posterior to the 2nd left sternocostal joint
- The arch of the azygos vein occupies a corresponding position on the right side of the trachea over the root of the right lung, although its contents are flowing in the opposite direction.
What is considered the remnant of the fetal ductus arteriosus? Where is it located?
- Ligamentun arteriosum
- Passes from the root of the left pulmonary artery to the inferior surface of the arch of the aorta
What is the brachiocephalic trunk? Where is it located?
- The brachiocephalic trunk, the first and largest branch of the arch of the aorta,
- arises posterior to the manubrium
- where it is anterior to the trachea and posterior to the left brachiocephalic vein.
- It ascends superolaterally to reach the right side of the trachea and the right sternoclavicular joint
- where it divides into the right common carotid and right subclavian arteries.
What is the left common carotid artery? Where is it found? What joint does it past posterior to when entering the neck?
- The left common carotid artery, the second branch of the arch of the aorta, arises posterior to the manubrium, slightly posterior and to the left of the brachiocephalic trunk.
- It ascends anterior to the left subclavian artery and is at first anterior to the trachea and then to its left.
- It enters the neck by passing posterior to the left sternoclavicular joint.
What is the left subclavian artery? Where is it located? What is the joint that it passes posterior to when it leaves the thorax and enters the roof of the mouth?
- The left subclavian artery, the third branch of the arch, arises from the posterior part of the arch of the aorta, just posterior to the left common carotid artery.
- It ascends lateral to the trachea and left common carotid artery through the superior mediastinum; it has no branches in the mediastinum.
- As it leaves the thorax and enters the root of the neck, it passes posterior to the left sternoclavicular joint.
What is an aneurysm? How can an aneurysm develop in the ascending aorta?
- The distal part of the ascending aorta receives a strong thrust of blood when the left ventricle contracts.
- Because its wall is not reinforced by fibrous pericardium (the fibrous pericardium blends with the aortic adventitia at the beginning of the arch; an aneurysm (localized dilation) may develop.
Patients with an aneurysm usually complain about pain that radiates into what part of the body?
The aneurysm will be evident on a chest film (radiograph of the thorax) as an enlarged ascending aorta outline.
Back
Variations in the great arteries occurs in what percentage of people?
65%
In 27% of people, the left common carotid originates from what structure?
If this structure fails to form, then the ; in these cases each of the four arteries (right and left common carotid and subclavian arteries) originate independently from the arch of the aorta.
What is the structure?
Brachiocephalic Trunk
What accessory artery to the thyroid gland may arise from the arch of the aorta or the brachiocephalic artery?
the thyroid ima artery (arteria thyroidea ima),
What is the retroesophageal right subcalvaian artery? Where is it located?
A retroesophageal right subclavian artery sometimes arises as the last (most-left-sided) branch of the arch of the aorta.
The artery crosses posterior to the esophagus to reach the right upper limb and may compress the esophagus, causing difficulty in swallowing (dysphagia).
Sometimes the arch of the aorta curves over the root of the right lung and passes inferiorly on the right side, forming a right arch of the aorta.
In some cases, the abnormal arch, after passing over the root of the right lung, passes posterior to the esophagus to reach its usual position on the left side.
What structures does the abnormality of a double arch surround? What are symptoms of an aneurysm of the arch of the aorta? Why is it good if you have a double arch of the aorta?
- A double arch of the aorta forms a vascular right around the esophagus and trachea
- A trachea that is compressed enough to affect breathing may require surgical divison of the vascular ring
- An aneurysm of the arch of the aorta may also exert pressure on the trachea and esophagus, causing difficulty in breathing and swallowing.
- You have two arches so you can sacrifice the posterior one.
What is coarctation of the aorta? What is the most common site for coarctation of the aorta?
- In coarctation of the aorta, the arch of the aorta or descending aorta has an abnormal narrowing (stenosis) that diminishes the caliber of the aortic lumen, producing an obstruction to blood flow to the inferior part of the body.
- The most common site for a coarctation is near the site of the ductus or ligamentum arteriosum.
The collateral vessels may become so large that they cause notable pulsation in the intercostal spaces and erode the adjacent surfaces of the ribs, which is visible in radiographs of the thorax.
