Chapter 16 – Thoracic Vessels




Abstract






  • The upper mediastinum contains the aortic arch with the origins of its major branches. These include the innominate (brachiocephalic) artery, proximal left common carotid artery, and proximal left subclavian artery. The left and right innominate (brachiocephalic) veins join to become the superior vena cava (SVC).
  • The thymic remnant and surrounding mediastinal fat are the first tissues encountered when entering the upper mediastinum. These tissues lie over the left innominate vein and the aortic arch.
  • The left innominate vein is approximately 6–7 cm long and it transverses the upper mediastinum under the manubrium sterni and over the superior border of the aortic arch. It joins the right innominate vein just to the right of the sternum at the level of the first to second intercostal space to form the SVC.
  • The right innominate vein is approximately 3 cm in length and it courses vertically downward and joins the left innominate vein at a 90° angle to form the SVC.
  • The SVC is approximately 6–7 cm in length and is located lateral and parallel to the ascending aorta. A small segment is enclosed within the pericardium.
  • The ascending aorta is contained within the pericardium. The aortic arch begins at the superior attachment of the pericardium. The first branch of the aortic arch is the innominate artery, which then branches into the right subclavian and right common carotid arteries. The next branch of the arch is the left common carotid artery, followed by the left subclavian artery. The innominate artery and the left common carotid artery originate relatively anteriorly, while the left subclavian artery originates more posteriorly. Anatomical variants include a common origin for the left common carotid artery and innominate artery, as well as a common origin for the left subclavian and left common carotid artery.
  • The left vagus nerve travels between the left common carotid and subclavian arteries just anterior to the arch and branches off into the recurrent laryngeal nerve, which loops around and behind the aortic arch, ascending along the tracheoesophageal groove.
  • The right vagus nerve crosses over the right subclavian artery, immediately gives off the recurrent laryngeal nerve, which loops behind the subclavian artery and ascends behind the common carotid artery along the tracheoesophageal groove.
  • The thoracic or descending aorta begins at the fourth thoracic vertebra on the left side of the vertebral column. Below the root of the lung, it courses to a position anterior to the vertebral column as it passes into the abdominal cavity through the aortic hiatus in the diaphragm at the twelfth thoracic vertebra.
  • The esophagus lies on the right side of the aorta proximally. Distally, as it enters the diaphragm, it courses in front of the aorta.
  • The aorta has nine pairs of aortic intercostal arteries that arise from the posterior aspect of the aorta and travel to the associated intercostal spaces. The bronchial and esophageal arteries are additional branches of the aorta as it descends in the thorax.





Chapter 16 Thoracic Vessels


Demetrios Demetriades , Vincent Chong , and Stephen Varga



Surgical Anatomy




  • The upper mediastinum contains the aortic arch with the origins of its major branches. These include the innominate (brachiocephalic) artery, proximal left common carotid artery, and proximal left subclavian artery. The left and right innominate (brachiocephalic) veins join to become the superior vena cava (SVC).





    Figure 16.1 Anatomy of the vessels of the superior mediastinum. Note the left innominate vein traversing over the superior border of the aortic arch and its major branches. RLN, recurrent laryngeal nerve; SVC, superior vena cava.




  • The thymic remnant and surrounding mediastinal fat are the first tissues encountered when entering the upper mediastinum. These tissues lie over the left innominate vein and the aortic arch.



  • The left innominate vein is approximately 6–7 cm long and it transverses the upper mediastinum under the manubrium sterni and over the superior border of the aortic arch. It joins the right innominate vein just to the right of the sternum at the level of the first to second intercostal space to form the SVC.



  • The right innominate vein is approximately 3 cm in length and it courses vertically downward and joins the left innominate vein at a 90° angle to form the SVC.



  • The SVC is approximately 6–7 cm in length and is located lateral and parallel to the ascending aorta. A small segment is enclosed within the pericardium.



  • The ascending aorta is contained within the pericardium. The aortic arch begins at the superior attachment of the pericardium. The first branch of the aortic arch is the innominate artery, which then branches into the right subclavian and right common carotid arteries. The next branch of the arch is the left common carotid artery, followed by the left subclavian artery. The innominate artery and the left common carotid artery originate relatively anteriorly, while the left subclavian artery originates more posteriorly. Anatomical variants include a common origin for the left common carotid artery and innominate artery, as well as a common origin for the left subclavian and left common carotid artery.





    Figure 16.2 The roots of the major vessels (aorta, superior vena cava, and pulmonary trunk) are covered by the pericardium.





    Figure 16.3 The major vessels of the aortic arch (innominate artery, left common carotid, left subclavian artery). The left common carotid originates directly from the aorta, while the right common carotid branches from the innominate artery. CCA, common carotid artery; IMA, internal mammary artery; SCA, subclavian artery; TCT, thyrocervical trunk; VA, vertebral artery.





    Figure 16.4 Anatomy of the aortic arch and its major trunks; note the anatomical relationship with the left innominate vein, the left vagus and left phrenic nerves. The vagus nerve is medial and the phrenic nerve lateral to the internal mammary artery. CCA, common carotid artery; IMA, internal mammary artery; RLN, recurrent laryngeal nerve; SCA, subclavian artery; SCV, subclavian vein; VA, vertebral artery.





    Figure 16.5 Anatomical relationship between the vagus nerve and the major vessels. The nerve crosses in front of the proximal subclavian artery. The recurrent laryngeal nerve loops around the subclavian on the right side and around the aortic arch on the left side. CCA, common carotid artery; IMA, internal mammary artery; RLN, recurrent laryngeal nerve; SCA, subclavian artery.




  • The left vagus nerve travels between the left common carotid and subclavian arteries just anterior to the arch and branches off into the recurrent laryngeal nerve, which loops around and behind the aortic arch, ascending along the tracheoesophageal groove.



  • The right vagus nerve crosses over the right subclavian artery, immediately gives off the recurrent laryngeal nerve, which loops behind the subclavian artery and ascends behind the common carotid artery along the tracheoesophageal groove.





    Figure 16.6 The left vagus nerve crosses over the proximal left subclavian artery and the aortic arch. At the inferior border of the arch in gives the left recurrent laryngeal nerve. SCA, subclavian artery.




  • The thoracic or descending aorta begins at the fourth thoracic vertebra on the left side of the vertebral column. Below the root of the lung, it courses to a position anterior to the vertebral column as it passes into the abdominal cavity through the aortic hiatus in the diaphragm at the twelfth thoracic vertebra.



  • The esophagus lies on the right side of the aorta proximally. Distally, as it enters the diaphragm, it courses in front of the aorta.





    Figure 16.7 Anatomical relationship between the esophagus and the thoracic aorta. The esophagus lies on the right side of the aorta. Just above the diaphragm, it courses in front of the aorta.




  • The aorta has nine pairs of aortic intercostal arteries that arise from the posterior aspect of the aorta and travel to the associated intercostal spaces. The bronchial and esophageal arteries are additional branches of the aorta as it descends in the thorax.



General Principles




  • Greater than 90% of thoracic great vessel injuries are due to penetrating trauma. Most patients with penetrating trauma to the major mediastinal vessels die at the scene and never reach hospital care.



  • For those that survive to hospital presentation, most patients arrive with hemodynamic instability and require emergency operation without any diagnostic studies.



  • Patients with no vital signs or imminent cardiac arrest on arrival should be managed with a resuscitative emergency room thoracotomy (See Chapter 4).



  • In hemodynamically stable patients with suspected injuries to the mediastinal vessels, CT arteriography is the most effective screening diagnostic investigation.



  • Thoracic great vessel injuries can present with external or internal hemorrhage, vascular thrombosis from intimal flaps, or pseudoaneurysms. Consequently, the absence of a significant amount of bleeding does not rule out a vascular injury.



Special Surgical Instruments




  • In the operating room, the thoracotomy trauma tray should include vascular instruments, a power sternal saw, Lebsche knife with hammer, and bone cutter. The surgeon should wear a headlamp for optimal lighting in anatomically difficult areas.



Patient Positioning



Positioning for Upper Mediastinal Vascular Injuries




  • The patient is placed in the supine position with both arms abducted at 90° to allow the anesthetist access to the extremities.



  • Skin preparation and draping should include the neck, anterior chest, and hemithoraces. As for all acute trauma operations, the abdomen and groin should be prepared as well in case of an unexpected missile trajectory or the need for saphenous vein conduit.

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Sep 4, 2020 | Posted by in EMERGENCY MEDICINE | Comments Off on Chapter 16 – Thoracic Vessels
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