and Edgar D. Guzman-Arrieta3
(1)
Department of Surgery Advocate Illinois Masonic Medical Center, University of Illinois Metropolitan Group Hospitals Residency in General Surgery, Chicago, IL, USA
(2)
University of Illinois at Chicago, Chicago, IL, USA
(3)
Vascular Specialists – Hattiesburg Clinic, Hattiesburg, MS, USA
Keywords
MediastinumHeartPericardiumAortaApproaches to the heart and great vessels1.
Mark the false statement:
(a)
The superior mediastinum contains from anterior to posterior the internal mammary vessels, thymus, great vessels, trachea, esophagus, and sympathetic trunks.
(b)
The trachea occupies the anterior mediastinum.
(c)
The middle mediastinum contains the pericardium, phrenic nerves, heart, and roots of the great vessels.
(d)
The posterior mediastinum contains the descending aorta, esophagus, thoracic duct, sympathetic chains, azygos system, and vagus nerves.
(e)
The posterior mediastinum is continuous with the retropharyngeal space.
Comments
The mediastinum is a space with the following boundaries:
Anterior – Sternum
Posterior – Thoracic vertebrae and ribs
Lateral – Mediastinal pleura
Superior – Thoracic outlet
Inferior – Diaphragm
An imaginary plane drawn from the angle of Louis to the T4–T5 junction divides the mediastinum into superior and inferior. In turn, the inferior mediastinum is divided by the pericardial sac into anterior, middle, and posterior. The anterior mediastinum contains the caudal aspects of the thymus, lymph nodes, and connective tissue. The trachea is located in the posterior aspect of the superior mediastinum. It divides at the angle of Louis and hence does not reach into the inferior mediastinum (Fig. 5.1).
Fig. 5.1
As the name states, the mediastinum is a partition which “stands in the middle” of the two hemithoraces. In the embryo, major cardiac, vascular, lymphatic, and solid organ transitions occur at the level of T4. A line drawn between the lower end of the manubrium and T4/T5 divides the mediastinum into a superior and inferior compartment. The pericardial sac divides the inferior mediastinum into anterior, middle, and posterior divisions, each with characteristic pathology
Answer
b
2.
Mark the incorrect statement.
(a)
The posterior intercostal arteries are longer on the right than the left side.
(b)
The posterior intercostal arteries are posterior to the azygos, hemiazygos, and the sympathetic trunks.
(c)
The thoracic duct starts crossing from right to left at the level of T6 as it courses cephalad.
(d)
The thoracic duct collects the lymph from the upper right hemithorax and right arm.
(e)
The cisterna chyli collects all the lymph from the abdomen and lower extremities.
Comments
The position of the descending aorta, to the left of the vertebral column, determines that the posterior intercostal arteries arising from it are longer on the left than on the right. The relationship of the sympathetic trunks with the vasculature becomes relevant during thoracoscopic or open sympathectomies.
The thoracic duct is often exposed to injuries during thoracic and mediastinal procedures. It arises from the cisterna chyli and carries the lymph from the abdomen and the lower extremities. As it courses towards the left subclavian vein, it receives lymph from the left hemithorax, left upper extremity, and left jugular territory. The upper right hemithorax, upper extremity, and head drain into the right thoracic duct, which starts in the thorax and empties into the right subclavian vein [1]. This distribution of lymphatic drainage often determines the route of cancer spread (Figs. 5.2 and 5.3).
Fig. 5.2
Cognitive pearls in lymphatic drainage. The thoracic duct begins to the right of the vertebral column, just below the diaphragm and starts its turning and twisting course up the thorax into the left side of the neck. The thoracic duct is the major lymphatic channel draining lymph and chyle from most of the body into the systemic circulation at the junction of the left subclavian and the internal jugular veins.Virhcow’s lymph node is the last lymph node station in this course. An abnormal and or enlarged Virchow’s node may represent an advanced abdominal/pelvic malignancy. The right lymphatic duct collects the lymph from the ipsilateral head, neck, thorax, lung, and upper extremity. It also collects lymph from the right side of the heart and the bare area of the liver. The bare area of the liver is at its dome where all the ligaments reflect away from the liver leaving an area without a covering of Glisson’s capsule
Fig. 5.3
Lymphatics generally follow the veins but as opposed to veins have the physiologic ability to drain large protein molecules. The thoracic duct additionally drains fatty acid-rich chyle from the intestinal trunk to the cisterna chyli. The lymph from the right and the left side of the head, neck, and upper extremities drains through the jugular and subclavian trunks into the right lymphatic duct and the thoracic duct, respectively. Lumbar trunks drain the lower extremities into the cisterna chyli. Tumors that spread through the lymphatics will therefore metastasize to similar locations if they drain through the same channels
Answer
d
3.
Mark the false statement.
(a)
The anterior scalene node (Virchow’s node) may harbor metastasis from the mediastinum, thorax, breasts, and abdominal organs.
(b)
Mediastinal masses are most often symptomatic.
(c)
Indirect signs of mediastinal masses are displacement of the apical heartbeat and tracheal deviation.
(d)
The most common tumors of the superior mediastinum are thymomas, lymphomas, thyroid tumors, and parathyroid adenomas.
(e)
The most common tumors of the posterior mediastinum are neurogenic tumors and enteric cysts.
Comments
Rudolf Virchow (1821–1902), considered the father of pathology, described that enlarged left-sided supraclavicular nodes were harbingers of intra-abdominal malignancy. This node, later named after Virchow, is the highest in the bronchomediastinal chain. It is located at the confluence of the thoracic duct and the left subclavian vein. When enlarged, it can be palpated in the left supraclavicular fossa, just above the middle third of the clavicle [2, 3].
Mediastinal tumors are most often asymptomatic and discovered incidentally. When they cause symptoms these tend to be due to compression of adjacent structures. Mediastinal tumors are derived from the structures normally found in its compartments or from their embryologic forebears. For example, the preponderance of neurogenic and enteric cysts in the posterior mediastinum reflects the posterior location of the neural crest and foregut, respectively. The middle mediastinum gives rise to mesenchymal tumors (pericardial cysts, lipomas, liposarcomas, fibromas, and fibrosarcomas). The superior mediastinum may present any of the tumors found in the compartments of the inferior mediastinum, as well as tumors extending from the neck (e.g., retrosternal goiter) [4–7] (Fig. 5.4).
Fig. 5.4
Tumors in the mediastinum are formed of the embyological tissue that developed in the corresponding compartment. The most common tumors of the superior mediastinum are retrosternal goiters. These are often accessed through the neck. The posterior mediastinum harbors tumors from neural crest cells and foregut-derived cysts. Lymph node-derived neoplasms, primary and metastatic, dominate the middle mediastinum. The trachea is located in the superior mediastinum and bifurcates below the T4 vertebra into the posterior mediastinum. This area is surrounded by hilar lymph nodes draining the lungs as well as other mediastinal structures. The anterior mediastinum is the most common site for extragonadal germ cell tumors. 50–70 % of these tumors are found in this location
Answer
b
4.
The following statements regarding the thymus are correct except:
(a)
The thymus shares a common origin with the superior parathyroids.
(b)
Hassall’s corpuscles are the histological hallmark of the thymus.
(c)
The main blood supply to the thymus comes from the inferior thyroid arteries and the internal mammary arteries.
(d)
The thymic veins drain to the SVC on the right and the brachiocephalic vein on the left.
(e)
The thymus lacks efferent lymphatics.
Comments
The thymus shares a common origin with the inferior parathyroids. Both are derived from the third branchial pouch. When inferior parathyroids cannot be found, the thymus is often searched for and removed. Hassall’s corpuscles represent concentric layers of medullary epithelial cells surrounding an eosinophilic, partially keratinized core. Their function is thought to be related to the selection and maturation of thymocytes. Their numbers have been found to increase with age. Unlike what occurs in lymph nodes, lymphocytes exit the thymus through veins [8].
Answer
a
5.
Mark the false statement regarding heart development
(a)
A common mesodermal atrium and ventricle undergo septation.
(b)
The aorta and pulmonary artery are derived from two independent arterial trunks.
(c)
Neural crest-derived cells contribute to the formation of the cardiac conduction system.
(d)
Pericardial defects may lead to congenital cardiac herniation.
(e)
Pericardial cysts represent remnants of the pleuropericardial canal.
Comments
During the first 3 weeks of gestation, the human embryo obtains its nutrients by diffusion. At this time, paired mesoderm-derived endocardial tubes fuse to form the primitive heart. This single chamber structure already has contractile properties. The primitive heart then folds upon itself. In this process the atria, which were originally caudal, take a posterocephalic location, whereas the ventricles become anterior and caudal.
As the folding of the primitive heart occurs, septations form within it, under the influence of neural crest-derived cells [9]. Failure in this septation process results in abnormal communication between chambers, the most common of which are atrial septal defect and ventricular septal defect. The common ventricular outflow tract also undergoes division to form the aorta and pulmonary artery. Defects in this process lead to the transposition of great vessel and persistence of the truncus arteriosus [10, 11].
Defects in the formation of the pericardium may form orifices through which the heart (most commonly the left atria) can herniate. While largely asymptomatic, these defects may cause paroxysmal chest pain. The herniated heart may become incarcerated and compromise of coronary circulation may occur. Treatment of this pathology is surgical and involves attempts to close the defect or enlarge it to a size in which strangulation no longer occurs [12, 13].
Pericardial cysts, along with bronchial and enteric cysts, are embryologic remnants found in the mediastinum.
Answer
b
6.
Mark the incorrect statement in relation to congenital heart malformations.
(a)
Cyanotic cardiac malformations involve right to left shunting.
(b)
Eisenmenger’s syndrome consists of secondary left to right shunting due to increases in pulmonary vascular resistance.
(c)
Left to right shunting allows survival in the presence of transposition of the great vessels.
(d)
When present, a left persistent superior vena cava drains into the left atrium.
(e)
Ventricular septal defects are the most common congenital cardiac anomaly.
Comments
Congenital cardiac malformations may be classified into cyanotic and noncyanotic, with the former being more severe. Cyanotic cardiac malformations cause blood to shunt from the right heart to the left heart, bypassing the lungs and creating desaturation that does not respond to oxygen therapy. Some examples are the tetralogy of Fallot, truncus arteriosus, and transposition of the great vessels. In noncyanotic cardiac malformations oxygenated blood is shunted from the left heart to the right, causing an increased load for the latter. This shunting occurs across atrial and ventricular defects as well as a patent ductus arteriosus. Over time, the right heart hypertrophies to compensate for the increased workload and comes to generate pressures greater than those found in the left heart. At this point, a reversal in flow occurs, and right to left shunting takes place. This is known as Eisenmenger’s syndrome [14, 15].
Transposition of the great vessels generates two independent parallel circulatory circuits. In this scenario, venous blood returning from the systemic circulation is sent back to the systemic arteries without passing through the lungs. A patent ductus arteriosus allows oxygenated blood to cross into the arterial circulation sustaining life.
Answer
b
7.
Get Clinical Tree app for offline access
Mark the incorrect statement about pericardial anatomy.
(a)
A rim of air seen around the pericardium, continuing along the diaphragmatic surface, is radiologically indicative of esophageal perforation.
(b)
Pericardiotomy should be performed in transverse fashion.
Stay updated, free articles. Join our Telegram channel
Full access? Get Clinical Tree