A patient who has suffered severe chest trauma in an automobile accident is found to have fluid in the right pleural space. A thoracentesis reveals the presence of chylous fluid in the pleural space, suggesting a rupture of the thoracic duct. In which regions of the thorax is the thoracic duct found?

a) Anterior and middle mediastinum

b) Anterior and superior mediastinum

c) Middle and posterior mediastinum

d) Middle and superior mediastinum

e) Posterior and superior mediastinum

CORRECT ANSWER: E

The mediastinum is divided into four regions. The region above the manubriosternal junction (level of fourth thoracic vertebra) is the superior mediastinum. The region below the manubriosternal junction is divided into the anterior mediastinum (anterior to the pericardium), the middle mediastinum (within the pericardium), and the posterior mediastinum (posterior to the pericardium). The thoracic duct enters the thorax through the aortic hiatus of the diaphragm. At this point it lies in the posterior mediastinum, the region posterior to the pericardium. As it ascends through the thorax and passes the level of the fourth thoracic vertebra, it enters the superior mediastinum. The anterior mediastinum (choices A and B) contains the thymus and fatty connective tissue. The middle mediastinum (choices A, C, and D) contains the heart and the roots of the great vessels. In addition to the thoracic duct, the superior mediastinum (choices B, D, and E) contains the ascending aorta, aortic arch, branches of the aortic arch, descending aorta, superior vena cava, brachiocephalic veins, thymus, trachea and esophagus. In addition to the thoracic duct, the posterior mediastinum (choices C and E) contains the descending aorta, azygos vein, hemiazygos vein and the esophagus

A medical student is learning to take an ECG and inadvertently reverses the correct position right arm and left arm electrodes. This is most likely to result in

a) no EKG tracing

b) inversion of lead I

c) inversion of lead III

d) delta waves

e) all leads are inverted

CORRECT ANSWER: B

The most common error in frontal plane recording results from reversal of two of the electrodes. One example is reversal of the right and left arm electrodes In this instance, lead I appears inverted, leads II and III are reversed, leads aVR and aVL are reversed, and lead aVF is correct.