 I'm going to talk about the imaging in the mediastinum. Most of these patients either present to us as asymptomatic lesions that we have detected on our routine chest x-ray or they present to us for some complaints. So what are the aims of imaging when we have a lesion in front of us on the chest radiograph? First we need to decide whether is there a lesion? Is it a mediastinal lesion? In which division or compartment is it formed? What is the content of the lesion? Does it enhance? Are there any associated pulmonary or skeletal abnormalities with it? And based on these division and description, what could it be? Now is there a lesion? Is it a mediastinal lesion? There are a few things we need to note for this. If we have a presence of a soft tissue mass or a mediastinal widening, it is very obvious that there is a lesion out there. But there are few finer things that we must note which will not be very obvious such as displacement of mediastinal lines, widening of stripes and abnormal content of interfaces. Most of these signs on the chest radiograph because that is what the patient presents with and we'll go from the chest radiograph to CT as we go along. So this is a very obvious lesion. We see that there is a soft tissue mass, there is a mediastinal widening and I mean there is no doubt that there is a lesion out here. The corresponding CT shows a large, lobulated heterogeneous lesion which is there and this turned out to be a lymphoma. So these kinds of lesions on the chest radiograph, there is no doubt that there is a lesion. But when there are subtle signs, what we must look at? You must look at the anterior and posterior junction lines, right and left paraspinal lines, right and left paratecule stripe, the AP stripe and window and a few of the interfaces. I'll show you a few of these examples as we go along because it is important to note these. When it is obvious there is no doubt but when there are subtle signs, we must be very careful not to miss this so that we can carry out a CT for further investigations. So what is this anterior junction line? So as you can see, it is formed by the opposition of the viscera and parietal pleura, the anterior-medial aspect of the lung with a small amount of intervening mediastinal flat within. It appears as an oblique line which crosses the superior two-thirds of the sternum from the upper right to the lower left. This is again a normal anterior junction line that we see on a CT scan. It's seen in almost 20 to 50% of frontal chest radiographs and if this gets obliterated, this anterior junction line, it suggests that there is some anterior-mediastinal pathology and we need to investigate further. As you can see, this anterior junction line has got displaced to the right. This is a post-right middle lobectomy patient in which you can see there is some amount of volume loss also in the right lung. Now the posterior junction line, again, this is formed by the opposition of the viscera and parietal pleura of the posterior-medial portion of the lungs and it's posterior to the ucificus and anterior to the third to the fifth thoracic vertebra. What it appears is a straight or slightly leftward conical line projecting through the trachea and extending above the clavicles. This is important to differentiate from an anterior junction line. This projects above the clavicles but as the anterior junction line is below the level of the clavicles. Again, this is a normal posterior junction line seen on almost 30% of radiographs and if there is any abnormal bunging or convexity, it suggests that there is a posterior-mediastinal abnormality on the chest radiograph. The right paraspinal line, it's formed by the right lung and the pleura which come in tangential contact with the posterior-mediastinal soft tissues. It appears straight and typically extends from the eighth through the 12 thoracic vertebral levels. The left paraspinal line is formed by the tangential contact of the left lung and pleura with the posterior-mediastinal fat, the left paraspinal muscles and adjacent soft tissue. This extends vertically from the level of the aortic arch to the diaphragm and typically lies medial to the lateral wall of the descending thoracic vertebra. This is a very important note but sometimes it may lie lateral to the aorta along the inter thoracic course. On the right side, the paraspinal lines are seen about 20% around the left, around 40% of the patients. And again, these can be displaced laterally by osteophyte. It's a prominent mediastinal fat. If there is any abnormal contour or if there is any displacement, again, this suggests that there is some posterior-mediastinal abnormality and this must be investigated further on a CT scan. So as you can see here, this is an abnormal right displaced right paraspinal line. This is a 27-year-old patient who had a traumatic injury and he had a fracture of the transverse processes and this is a paraspinal hematoma that we can see here which is displacing the right paraspinal line. This is a left paraspinal line which is bulging outwards and is displaced out here. This is a cirrhotic patient and he had usavigile varices which were displacing the paraspinal line out here. This is formed when the visceral parietal to the right upper lobe come in contact with the right lateral board of the trachea and the intervening mediastal fat. It begins superiorly at the level of the clavicles and extends inferiorly to the right tracheobronchial angle at the level of the azygillarge. It's the most commonly seen and it's most commonly displaced in right parathecal lesions. So this is an abnormal right parathecal stripe which is seen to be displaced laterally and when we do a CT scan of this, we discover that there is a lesion out here in the right parathecal region. This turned out to be an ectopic parathoride adenoma. The left parathecal strike. This is when there is contact between the left upper lobe and either the mediastal fat adjacent to the left tracheal wall or the left tracheal wall itself. It extends superiorly from the aortic arch to join the reflection from the left subclavian artery. It's visible in about 20 to 30% of frontal radiograph. Again that you can see that there is an abnormal appearing left parathecal stripe in this region which appears thickened. In addition to that, the trachea has seen to be displaced towards the right. This is a case of a metastatic thyroid cancer with a large supraclavicular lymph node which is displacing the trachea to the opposite side. The posterior tracheal stripe. Now this is a vertical stripe which is seen on the lateral chest radiograph that is formed by the contrast between the air within the trachea and the right lung outlining the posterior tracheal wall. It usually measures about 2.5 millimeter in thickness but lower down it can measure up to 5 millimeter in thickness. Now this is an abnormal posterior tracheal stripe. In a patient, you can see it's bulging anteriorly and it's thickened. And this is a patient who had Echinacea cardia with a dilated eustrophicus and that was pushing the tracheal stripe anteriorly. The aotopulmonary stripe. This is a mediastal reflection or interface which is formed by the pleura of the anterior left lung coming in contact with the mediastal fat anterior lateral to the left pulmonary artery and the aotic arch. It's usually straight or mildly convex and crosses laterally over the aotic arch and the main pulmonary artery. So this is how the normal aotopulmonary stripe looks like and it is again displaced or thickened by anterior mediastal disease. Now again, as you can see, there is a displaced abnormal aotopulmonary stripe in a 40-year-old patient. You can see a soft tissue out here which turned out to be conglomerated lymph node mass in a patient with lymphoma. The aotopulmonary window. This is the mediastal space which is posterior to the aotopulmonary stripe. It is bounded superiorly by the inferior wall of the aorta, inferiorly by the superior wall of the left pulmonary artery, anteriorly by the posterior wall of the ascending aorta, posteriorly by the anterior wall of the descending aorta, medially by the trachea anteriorly and the lateral wall of the left main bronchus and the ucevigus posteriorly. So this is a small space which is very important to evaluate. As you can see, there is an abnormal soft tissue which we can be seen in the aotopulmonary window. When we carry out a CT scan, we can see there is a large conglomerated lymph nodal mass which is secondary to a bronchogenic carcinoma. The azygue ucevigal recess. This is the space lying lateral or posterior to the ucevigus and anterior to the spine, extending from the level of the anterior turn of the azygues vein to the level of the aortic heart is inferiorly. Again, this abnormality, either thickening or convexity may be due to either lymphanopathy, hiatal hernias, bronchopulmonary malformations, ucevigal abnormalities. Again, a large hiatal hernia causing an abnormal ucevigal recess which is very well seen on the X-ray out here.