A pediatric hea surgeon has just divided the sternum in a child to repair a cardiac malformation. A lobulated gland-like structure is seen immediately obscuring the hea. This is most likely which of the following
Correct Answer: Thymus
Description: The anterior mediastinum lies immediately posterior to the sternum and contains the thymus in children. The mediastinum is the central poion of the thoracic cavity, and it lies between the two pulmonary cavities. It is bounded laterally by the mediastinal pleura. It contains all the thoracic viscera except the two lungs. Superior and inferior divisions are described, with the latter fuher divided into anterior, middle, and posterior divisions. The superior mediastinum extends from the superior thoracic apeure bounded by the superior border of the manubrium, first rib, and T1 veebral body. The inferior boundary is a horizontal line from the sternal angle posterior to the interveebral disc between T4 and T5. The superior mediastinum contains the following structures, from anterior to posterior: adipose tissue with remnants of the thymus gland, right and left brachiocephalic vein, SVC, aoa with its brachiocephalic trunk, left common carotid and left subclan aerial branches,trachea,esophagus,and thoracic duct. Related to these structures are the phrenic, vagus, left recurrent laryngeal and cardiac nerves, and anterior mediastinal lymph node group. The inferior mediastinum is bounded anteriorly by the sternum,posteriorly by veebral bodies T5 through T12, and the diaphragm inferiorly. The anterior mediastinum poion lies between the sternum and the pericardial sac and contains small branches of the internal thoracic aery and a few nodes of the parasternal lymph node group. The thymus gland is present during childhood. The middle mediastinum contains the pericardial sac with the hea, terminations of the SVC, inferior vena cava (IVC), and pulmonary veins, the ascending aoa, the pulmonary trunk and its bifurcations into the right and left pulmonary aeries, lung roots, phrenic nerve, and bronchial lymph nodes. The posterior mediastinum lies between the pericardial sac and veebral bodies T5 through T12. It contains the esophagus, descending thoracic aoa and right intercostals and esophageal aeries, azygous venous system, thoracic duct, vagus and splanchnic nerves, and posterior mediastinal lymph nodes. The body's main lymphatic vessel, the thoracic duct, originates in the abdomen at the level of L1 as a highly variable dilation called the cisterna chili. It enters the posterior mediastinum through the aoic hiatus and lies on the right anterior surface of the thoracic veebral bodies, posterior to the esophagus between the azygous venous system and the thoracic aoa. By the level of the sternal angle, the duct completes a shift to the left side, traverses the superior mediastinum, and terminates by emptying into the venous system near the junction of the left internal jugular and subclan veins. The thoracic duct receives lymph drainage from the lower limbs, abdomen and left hemithorax, upper limb, and head and neck. A small right lymphatic duct receives lymph drainage from the right hemithorax, upper limb, and head and neck. The thoracic and right lymphatic ducts are described as receiving lymph from jugular, subclan, and broncho mediastinal trunks, although these trunks may variably unite or empty into veins independently. Ref:- BD Chaurasia
Category:
Anatomy
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