Mediastinum and Great Vessels

The mediastinum is the thoracic area between the 2 pleural cavities. The mediastinum contains vital structures of the circulatory, respiratory, digestive, and nervous systems including the heart and esophagus Esophagus The esophagus is a muscular tube-shaped organ of around 25 centimeters in length that connects the pharynx to the stomach. The organ extends from approximately the 6th cervical vertebra to the 11th thoracic vertebra and can be divided grossly into 3 parts: the cervical part, the thoracic part, and the abdominal part. Esophagus, and major thoracic vessels including the superior vena cava, inferior vena cava, pulmonary arteries Arteries Arteries are tubular collections of cells that transport oxygenated blood and nutrients from the heart to the tissues of the body. The blood passes through the arteries in order of decreasing luminal diameter, starting in the largest artery (the aorta) and ending in the small arterioles. Arteries are classified into 3 types: large elastic arteries, medium muscular arteries, and small arteries and arterioles. Arteries, pulmonary veins Veins Veins are tubular collections of cells, which transport deoxygenated blood and waste from the capillary beds back to the heart. Veins are classified into 3 types: small veins/venules, medium veins, and large veins. Each type contains 3 primary layers: tunica intima, tunica media, and tunica adventitia. Veins, and aorta. The mediastinum extends from the upper thoracic aperture to the diaphragm Diaphragm The diaphragm is a large, dome-shaped muscle that separates the thoracic cavity from the abdominal cavity. The diaphragm consists of muscle fibers and a large central tendon, which is divided into right and left parts. As the primary muscle of inspiration, the diaphragm contributes 75% of the total inspiratory muscle force. Diaphragm and is bordered by the lungs Lungs Lungs are the main organs of the respiratory system. Lungs are paired viscera located in the thoracic cavity and are composed of spongy tissue. The primary function of the lungs is to oxygenate blood and eliminate CO2. Lungs.

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Editorial responsibility: Stanley Oiseth, Lindsay Jones, Evelin Maza

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Mediastinum

Overview

The mediastinum is the middle of the thoracic cavity, located between the lungs Lungs Lungs are the main organs of the respiratory system. Lungs are paired viscera located in the thoracic cavity and are composed of spongy tissue. The primary function of the lungs is to oxygenate blood and eliminate CO2. Lungs. The mediastinum is subdivided into the superior and inferior compartments, which are further divided into the anterior, middle, and posterior mediastina.

Mediastinal compartments

Mediastinal compartments

Image by Lecturio.

Superior mediastinum

  • Borders:
    • Superior:
      • Jugular notch anteriorly
      • Thoracic (T) 1 vertebra posteriorly
    • Inferior:
      • Sternal angle anteriorly
      • Inferior border of T4 (thoracic plane) posteriorly
  • Contents:
    • Trachea Trachea The trachea is a tubular structure that forms part of the lower respiratory tract. The trachea is continuous superiorly with the larynx and inferiorly becomes the bronchial tree within the lungs. The trachea consists of a support frame of semicircular, or C-shaped, rings made out of hyaline cartilage and reinforced by collagenous connective tissue. Trachea
    • Esophagus
    • Thymus Thymus A single, unpaired primary lymphoid organ situated in the mediastinum, extending superiorly into the neck to the lower edge of the thyroid gland and inferiorly to the fourth costal cartilage. It is necessary for normal development of immunologic function early in life. By puberty, it begins to involute and much of the tissue is replaced by fat. Lymphatic Drainage System (prepubertal)
    • Vessels:
      • Superior vena cava
      • Brachiocephalic veins Veins Veins are tubular collections of cells, which transport deoxygenated blood and waste from the capillary beds back to the heart. Veins are classified into 3 types: small veins/venules, medium veins, and large veins. Each type contains 3 primary layers: tunica intima, tunica media, and tunica adventitia. Veins
      • Aortic arch
      • Innominate artery
      • Thoracic portions of the left common carotid and left subclavian arteries Arteries Arteries are tubular collections of cells that transport oxygenated blood and nutrients from the heart to the tissues of the body. The blood passes through the arteries in order of decreasing luminal diameter, starting in the largest artery (the aorta) and ending in the small arterioles. Arteries are classified into 3 types: large elastic arteries, medium muscular arteries, and small arteries and arterioles. Arteries
    • Thoracic duct
    • Nerves:
      • Phrenic nerve
      • Vagus nerve
      • Left recurrent laryngeal nerve
Cross section of the superior mediastinum trachea

Diagram of a cross-section of the superior mediastinum featuring the spatial relations of the trachea

Image by BioDigital, edited by Lecturio

Inferior mediastinum

The inferior mediastinum is bordered superiorly by the thoracic plane and inferiorly by the diaphragm Diaphragm The diaphragm is a large, dome-shaped muscle that separates the thoracic cavity from the abdominal cavity. The diaphragm consists of muscle fibers and a large central tendon, which is divided into right and left parts. As the primary muscle of inspiration, the diaphragm contributes 75% of the total inspiratory muscle force. Diaphragm, and is further subdivided into the anterior, middle, and posterior mediastina.

  • Anterior mediastinum:
    • Extends from the sternum anteriorly to the anterior surface of the pericardium posteriorly
    • Contents:
      • Sternopericardial ligaments
      • Fat
      • Lymph nodes
      • Internal thoracic vessels
      • Remnants of thymus
  • Middle mediastinum:
    • Extends between the anterior and posterior surfaces of the pericardium
    • Contains:
      • Heart and pericardium
      • Ascending aorta
      • Pulmonary trunk
      • Superior vena cava
      • Pericardiophrenic artery
      • Phrenic nerve
  • Posterior mediastinum:
    • Extends between the posterior surface of the pericardium and T4 to T12
    • Contains:
      • Esophagus
      • Thoracic duct
      • Cisterna chyli
      • Thoracic aorta
      • Azygos, hemiazygos, and accessory hemiazygos veins Veins Veins are tubular collections of cells, which transport deoxygenated blood and waste from the capillary beds back to the heart. Veins are classified into 3 types: small veins/venules, medium veins, and large veins. Each type contains 3 primary layers: tunica intima, tunica media, and tunica adventitia. Veins
      • Vagus nerve
      • Esophageal plexus
      • Greater, lesser, and least splanchnic nerves

Great Vessels

The 5 great vessels are located in the mediastinum and consist of the aorta, superior and inferior venae cavae, pulmonary artery, and pulmonary vein.

Aorta

The aorta is the main artery of the body consisting of:

  • Ascending aorta:
    • Originates from the left ventricle
    • Gives rise to the right and left coronary arteries Arteries Arteries are tubular collections of cells that transport oxygenated blood and nutrients from the heart to the tissues of the body. The blood passes through the arteries in order of decreasing luminal diameter, starting in the largest artery (the aorta) and ending in the small arterioles. Arteries are classified into 3 types: large elastic arteries, medium muscular arteries, and small arteries and arterioles. Arteries
    • Located within the pericardium
  • Aortic arch:
    • Connects the ascending aorta and the descending aorta
    • Gives rise to the brachiocephalic trunk, left common carotid artery Common carotid artery The two principal arteries supplying the structures of the head and neck. They ascend in the neck, one on each side, and at the level of the upper border of the thyroid cartilage, each divides into two branches, the external and internal carotid arteries. Carotid Arterial System, and left subclavian artery
    • Located in the middle and posterior mediastinum
    • Runs to the left of the trachea
  • Descending aorta:
    • Starts at the T4 level
    • Passes through the diaphragmatic aortic hiatus at the T12 level
    • Transitions to the abdominal aorta
    • Located in the posterior mediastinum
    • Travels medially and ends anterior to the vertebral column Vertebral column The human spine, or vertebral column, is the most important anatomical and functional axis of the human body. It consists of 7 cervical vertebrae, 12 thoracic vertebrae, and 5 lumbar vertebrae and is limited cranially by the skull and caudally by the sacrum. Vertebral Column
    • Gives rise to the pericardial, bronchial, esophageal, mediastinal, intercostal, subcostal, and phrenic arteries Arteries Arteries are tubular collections of cells that transport oxygenated blood and nutrients from the heart to the tissues of the body. The blood passes through the arteries in order of decreasing luminal diameter, starting in the largest artery (the aorta) and ending in the small arterioles. Arteries are classified into 3 types: large elastic arteries, medium muscular arteries, and small arteries and arterioles. Arteries

Superior vena cava

  • Originates from the confluence of the 2 brachiocephalic veins Veins Veins are tubular collections of cells, which transport deoxygenated blood and waste from the capillary beds back to the heart. Veins are classified into 3 types: small veins/venules, medium veins, and large veins. Each type contains 3 primary layers: tunica intima, tunica media, and tunica adventitia. Veins
  • Drains into the right atrium
  • Carries O2-poor blood from the upper body and head
  • Begins behind the 1st right costal cartilage Cartilage Cartilage is a type of connective tissue derived from embryonic mesenchyme that is responsible for structural support, resilience, and the smoothness of physical actions. Perichondrium (connective tissue membrane surrounding cartilage) compensates for the absence of vasculature in cartilage by providing nutrition and support. Cartilage and descends behind the 2nd and 3rd intercostal spaces
  • Located in the superior and middle mediastina
  • The lower ½ is covered by the pericardium.

Inferior vena cava

  • Largest vein in the body
  • Originates from the right and left common iliac veins Veins Veins are tubular collections of cells, which transport deoxygenated blood and waste from the capillary beds back to the heart. Veins are classified into 3 types: small veins/venules, medium veins, and large veins. Each type contains 3 primary layers: tunica intima, tunica media, and tunica adventitia. Veins
  • Drains into the right atrium
  • Carries O2-poor blood from the lower half of the body
  • Enters the mediastinum through the caval foramen of the diaphragm Diaphragm The diaphragm is a large, dome-shaped muscle that separates the thoracic cavity from the abdominal cavity. The diaphragm consists of muscle fibers and a large central tendon, which is divided into right and left parts. As the primary muscle of inspiration, the diaphragm contributes 75% of the total inspiratory muscle force. Diaphragm at the T8 level
  • Communicates with the superior vena cava through:
    • Azygos vein
    • Vertebral venous plexuses
    • Lumbar veins Veins Veins are tubular collections of cells, which transport deoxygenated blood and waste from the capillary beds back to the heart. Veins are classified into 3 types: small veins/venules, medium veins, and large veins. Each type contains 3 primary layers: tunica intima, tunica media, and tunica adventitia. Veins
  • Located in the middle mediastinum

Pulmonary arteries Arteries Arteries are tubular collections of cells that transport oxygenated blood and nutrients from the heart to the tissues of the body. The blood passes through the arteries in order of decreasing luminal diameter, starting in the largest artery (the aorta) and ending in the small arterioles. Arteries are classified into 3 types: large elastic arteries, medium muscular arteries, and small arteries and arterioles. Arteries

  • The main pulmonary artery originates from the right ventricle.
  • Pulmonary arteries Arteries Arteries are tubular collections of cells that transport oxygenated blood and nutrients from the heart to the tissues of the body. The blood passes through the arteries in order of decreasing luminal diameter, starting in the largest artery (the aorta) and ending in the small arterioles. Arteries are classified into 3 types: large elastic arteries, medium muscular arteries, and small arteries and arterioles. Arteries carry deoxygenated blood to the lungs Lungs Lungs are the main organs of the respiratory system. Lungs are paired viscera located in the thoracic cavity and are composed of spongy tissue. The primary function of the lungs is to oxygenate blood and eliminate CO2. Lungs.
  • Located in the middle mediastinum
  • Divided into the right and left pulmonary arteries Arteries Arteries are tubular collections of cells that transport oxygenated blood and nutrients from the heart to the tissues of the body. The blood passes through the arteries in order of decreasing luminal diameter, starting in the largest artery (the aorta) and ending in the small arterioles. Arteries are classified into 3 types: large elastic arteries, medium muscular arteries, and small arteries and arterioles. Arteries
  • The right pulmonary artery passes under the aortic arch.

Pulmonary veins Veins Veins are tubular collections of cells, which transport deoxygenated blood and waste from the capillary beds back to the heart. Veins are classified into 3 types: small veins/venules, medium veins, and large veins. Each type contains 3 primary layers: tunica intima, tunica media, and tunica adventitia. Veins

  • 4 pulmonary veins Veins Veins are tubular collections of cells, which transport deoxygenated blood and waste from the capillary beds back to the heart. Veins are classified into 3 types: small veins/venules, medium veins, and large veins. Each type contains 3 primary layers: tunica intima, tunica media, and tunica adventitia. Veins: 2 on each side
  • Arise from the pulmonary hilum
  • Drain O2-enriched blood into the left atrium
  • Receive blood from the bronchial veins Veins Veins are tubular collections of cells, which transport deoxygenated blood and waste from the capillary beds back to the heart. Veins are classified into 3 types: small veins/venules, medium veins, and large veins. Each type contains 3 primary layers: tunica intima, tunica media, and tunica adventitia. Veins
  • The superior vena cava and right atrium lie anterior to the right pulmonary veins Veins Veins are tubular collections of cells, which transport deoxygenated blood and waste from the capillary beds back to the heart. Veins are classified into 3 types: small veins/venules, medium veins, and large veins. Each type contains 3 primary layers: tunica intima, tunica media, and tunica adventitia. Veins.
  • The descending thoracic aorta lies posterior to the left pulmonary veins Veins Veins are tubular collections of cells, which transport deoxygenated blood and waste from the capillary beds back to the heart. Veins are classified into 3 types: small veins/venules, medium veins, and large veins. Each type contains 3 primary layers: tunica intima, tunica media, and tunica adventitia. Veins.
Great vessels

The 5 great vessels: aorta, pulmonary artery, pulmonary veins Veins Veins are tubular collections of cells, which transport deoxygenated blood and waste from the capillary beds back to the heart. Veins are classified into 3 types: small veins/venules, medium veins, and large veins. Each type contains 3 primary layers: tunica intima, tunica media, and tunica adventitia. Veins, superior vena cava, and inferior vena cava

Image by Lecturio.

Clinical Relevance

Congenital anomalies

  • Coarctation of the aorta Coarctation of the aorta Coarctation of the aorta is a narrowing of the aorta between the aortic arch and the iliac bifurcation commonly around the point of insertion of the ductus arteriosus. Coarctation of the aorta is typically congenital and the clinical presentation depends on the age of the patient. Coarctation of the Aorta: narrowing of the aorta between the aortic arch and the iliac bifurcation. Coarctation of the aorta Coarctation of the aorta Coarctation of the aorta is a narrowing of the aorta between the aortic arch and the iliac bifurcation commonly around the point of insertion of the ductus arteriosus. Coarctation of the aorta is typically congenital and the clinical presentation depends on the age of the patient. Coarctation of the Aorta is most common around the point of insertion of the ductus arteriosus and is congenital in the majority of cases. Neonates present with heart failure upon the closure of the ductus arteriosus, whereas children and adults present with symptoms of hypoperfusion and/or hypertension Hypertension Hypertension, or high blood pressure, is a common disease that manifests as elevated systemic arterial pressures. Hypertension is most often asymptomatic and is found incidentally as part of a routine physical examination or during triage for an unrelated medical encounter. Hypertension. The classic findings on physical exam include a radio- or brachiofemoral delay and lower blood pressure in the lower limbs. Affected individuals should be surgically managed as early as possible to avoid complications of hypertension Hypertension Hypertension, or high blood pressure, is a common disease that manifests as elevated systemic arterial pressures. Hypertension is most often asymptomatic and is found incidentally as part of a routine physical examination or during triage for an unrelated medical encounter. Hypertension. Close follow-up is required as the risk of hypertension Hypertension Hypertension, or high blood pressure, is a common disease that manifests as elevated systemic arterial pressures. Hypertension is most often asymptomatic and is found incidentally as part of a routine physical examination or during triage for an unrelated medical encounter. Hypertension and relapse remains.
  • Transposition of great vessels: a cyanotic congenital heart disease characterized by the “switching” of the great arteries Arteries Arteries are tubular collections of cells that transport oxygenated blood and nutrients from the heart to the tissues of the body. The blood passes through the arteries in order of decreasing luminal diameter, starting in the largest artery (the aorta) and ending in the small arterioles. Arteries are classified into 3 types: large elastic arteries, medium muscular arteries, and small arteries and arterioles. Arteries. Transposition of great vessels accounts for 3% of all cases of congenital heart disease and presents within the neonatal phase of life with cyanosis that is unresponsive to O2 therapy. Diagnosis is confirmed by an echocardiogram and verified by catheterization. A chest X-ray shows the classic “egg on a string” pattern. Treatment is eminently surgical, and the prognosis for surgically corrected cases is good.
  • Truncus arteriosus Truncus arteriosus Truncus arteriosus (TA) is a congenital heart defect characterized by the persistence of a common cardiac arterial trunk tract that fails to divide into the pulmonary artery and aorta during embryonic development. Truncus arteriosus is a rare congenital malformation with a high mortality rate within the 1st 5 weeks of life if not managed promptly. Truncus Arteriosus: a congenital heart defect characterized by the persistence of a common cardiac arterial trunk tract that fails to divide into the pulmonary artery and aorta during embryonic development. Truncus arteriosus Truncus arteriosus Truncus arteriosus (TA) is a congenital heart defect characterized by the persistence of a common cardiac arterial trunk tract that fails to divide into the pulmonary artery and aorta during embryonic development. Truncus arteriosus is a rare congenital malformation with a high mortality rate within the 1st 5 weeks of life if not managed promptly. Truncus Arteriosus is a rare congenital malformation with a high mortality rate within the 1st 5 weeks of life if not managed promptly. Neonates may be asymptomatic at birth but will invariably develop respiratory distress and heart failure. Diagnosis is commonly made prenatally based on screening and ultrasound. Treatment involves medical stabilization immediately after birth and is followed by definitive surgery.

Inflammatory disorders

Mediastinitis Mediastinitis Mediastinitis refers to an infection or inflammation involving the mediastinum (a region in the thoracic cavity containing the heart, thymus gland, portions of the esophagus, and trachea). Acute mediastinitis can be caused by bacterial infection due to direct contamination, hematogenous or lymphatic spread, or extension of infection from nearby structures. Mediastinitis: an infection or inflammation Inflammation Inflammation is a complex set of responses to infection and injury involving leukocytes as the principal cellular mediators in the body's defense against pathogenic organisms. Inflammation is also seen as a response to tissue injury in the process of wound healing. The 5 cardinal signs of inflammation are pain, heat, redness, swelling, and loss of function. Inflammation involving the mediastinum. Acute mediastinitis can be caused by bacterial infection either due to direct contamination, hematogenous or lymphatic spread, or extension of infection from nearby structures. Chronic mediastinitis, also known as fibrosing mediastinitis, is commonly related to chronic inflammatory conditions that cause connective tissue Connective tissue Connective tissues originate from embryonic mesenchyme and are present throughout the body except inside the brain and spinal cord. The main function of connective tissues is to provide structural support to organs. Connective tissues consist of cells and an extracellular matrix. Connective Tissue proliferation. Mediastinitis Mediastinitis Mediastinitis refers to an infection or inflammation involving the mediastinum (a region in the thoracic cavity containing the heart, thymus gland, portions of the esophagus, and trachea). Acute mediastinitis can be caused by bacterial infection due to direct contamination, hematogenous or lymphatic spread, or extension of infection from nearby structures. Mediastinitis is treatable with supportive care, broad-spectrum antibiotics, or surgery in severe cases. Mortality from this condition is high.

Degenerative disorders

Thoracic aortic aneurysm Aneurysm An aneurysm is a bulging, weakened area of a blood vessel that causes an abnormal widening of its diameter > 1.5 times the size of the native vessel. Aneurysms occur more often in arteries than in veins and are at risk of dissection and rupture, which can be life-threatening. Extremity and Visceral Aneurysms ( TAA TAA Thoracic aortic aneurysm (TAA) is the abnormal dilation of a segment of the thoracic aorta, usually the ascending aorta. Most TAAs are due to degenerative aortic disorders, commonly in patients > 65 years of age. Most TAAs are asymptomatic (incidentally found in imaging) but could present with symptoms from its effects on surrounding structures. Thoracic Aortic Aneurysms): dilatation of the arterial wall by > 50% of its diameter. The ascending aorta is most commonly involved. Most TAAs are due to degenerative aortic disorders, commonly occurring in individuals > 65 years of age. Genetic TAAs account for 20% of cases and are frequently found in younger individuals. Thoracic aortic aneurysm Aneurysm An aneurysm is a bulging, weakened area of a blood vessel that causes an abnormal widening of its diameter > 1.5 times the size of the native vessel. Aneurysms occur more often in arteries than in veins and are at risk of dissection and rupture, which can be life-threatening. Extremity and Visceral Aneurysms may be associated with Marfan syndrome Marfan syndrome Marfan syndrome is a genetic condition with autosomal dominant inheritance. Marfan syndrome affects the elasticity of connective tissues throughout the body, most notably in the cardiovascular, ocular, and musculoskeletal systems. Marfan Syndrome. Among diagnostic imaging studies, CT angiography is the most widely used. Close monitoring is indicated for asymptomatic cases. Operative repair is recommended for symptomatic TAAs or in the case of increasing aortic diameter (criteria vary with location and the underlying condition).

References

  1. Bamalan, O.A., Soos, M.P. (2021). Anatomy, Thorax, Heart Great Vessels. StatPearls. Treasure Island (FL): StatPearls Publishing. https://www.ncbi.nlm.nih.gov/books/NBK547680/ 
  2. Rizvi, S., Wehrle, C.J., Law, M.A. (2021). Anatomy, Thorax, Mediastinum Superior and Great Vessels. StatPearls. Treasure Island (FL): StatPearls Publishing. https://www.ncbi.nlm.nih.gov/books/NBK519576/ 
  3. Gulwani, H. (2020). Mediastinum, general anatomy. Pathology outlines. Retrieved August 25, 2021, from https://www.pathologyoutlines.com/topic/mediastinumgeneral.html

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