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Cardiac silhouette findings and mediastinal lines and stripes: X-ray and computed tomography correlation Poster No.: C-222 Congress: ECR 2009 Type: Educational Exhibit Topic: Chest Authors: R. Marano, G. Savino, C. Liguori, A. Meduri, L. Natale, L. Bonomo; Rome/IT Keywords: Digital Chest Radiography, Chest Computed Tomography, Radiographical Mediastinum Anatomy DOI: 10.1594/ecr2009/C-222 Any information contained in this pdf file is automatically generated from digital material submitted to EPOS by third parties in the form of scientific presentations. References to any names, marks, products, or services of third parties or hypertext links to thirdparty sites or information are provided solely as a convenience to you and do not in any way constitute or imply ECR's endorsement, sponsorship or recommendation of the third party, information, product or service. ECR is not responsible for the content of these pages and does not make any representations regarding the content or accuracy of material in this file. As per copyright regulations, any unauthorised use of the material or parts thereof as well as commercial reproduction or multiple distribution by any traditional or electronically based reproduction/publication method ist strictly prohibited. You agree to defend, indemnify, and hold ECR harmless from and against any and all claims, damages, costs, and expenses, including attorneys' fees, arising from or related to your use of these pages. Please note: Links to movies, ppt slideshows and any other multimedia files are not available in the pdf version of presentations. www.myESR.org Page 1 of 40 Learning objectives Although the increasingly use of the Computed Tomography (CT), the Chest X-Ray (CXR) remains a very important modality for the evaluation of parenchymal and mediastinal disease providing a vast amount of useful informations. These informations are derived from the relationship of the normal anatomic structures of the mediastinum, pleura, and lungs and form the basis of the "cardiac silhouette" and "mediastinal lines and stripes" concepts, which may play an important role in establishing a diagnosis or a spectrum of diagnosis before proceeding to CT. The capability to recognize an abnormal CXR on the base of displacement/distortion or suppression of one of these lines is often mandatory to request a potentially useful CT examination. So, Radiologists and in particular the trainees must be familiar with the anatomic basis of these findings to be able to recognize their normal and abnormal appearance, developing appropriate differential diagnosis prior a subsequent chest CT. Background Mediastinal Lines and Stripes: The Mediastinal Lines correspond to the contours of the upper and middle mediastinum, and represent the edges of a dense, pleural covered structure marginated by the air within the lung. These lines are typically thin, with a thickness of 1 mm. Lines present on CXR: Anterior & Posterior Junction Lines (Figure 1) on page . Page 2 of 40 Fig. The Mediastinal Stripes are thicker lines formed by air outlining thicker intervening soft tissue. Stripes present on CXR: Right & Left Paratracheal Stripes, Aortic-pulmonary Stripe (Figure 2) on page . Page 3 of 40 Fig. The Interfaces are another concept of Mediastinal Lines and Stripes. They are formed by the contiguity of two structures with different density. Interfaces present on CXR: Right & Left Paraspinal Lines, Azygosesophageal Recess, Paraortic line, Paracaval Line, Pararterial line, Aortopulmonary Window, and Cardiac Borders (Figure 3) on page . Page 4 of 40 Fig. The absence of one of the Mediastinal Lines or Stripes is sometimes insignificant, since it may be caused by technical conditions of the CXR or anatomical variations and different is the frequency of their visualization on the CXR (Figure 4) on page . Page 5 of 40 Fig. Anyway, CT shows easier the anatomy and formation's mechanism of the Mediastinal Lines and Stripes explaining the anatomical and pathological reasons for their possible displacement, absence, or suppression. Page 6 of 40 Images linked within the text of this section: Fig. Page 7 of 40 Fig. Page 8 of 40 Fig. Page 9 of 40 Fig. Page 10 of 40 Imaging findings OR Procedure details The Anterior Junction Line It is formed by the apposition of the visceral and parietal pleura of the antero-medial portion of the anterior segments of the upper lobes, with a small amount of intervening anterior mediastinal fat. It normally shows an oblique course from upper right to lower left crossing the superior two-thirds of the sternum (Figure 5) on page . Fig. Normally, it appears as a thin line, but sometimes it may appear as a stripe due to an increased amounts of intervening mediastinal fat (Figure 6) on page or possibly thymus in younger patients. Page 11 of 40 Fig. On the frontal CXR, the line opens superiorly along the innominate veins and it is not typically appreciable above the clavicles, while inferiorly it ends at the level of the pericardium. The anterior junction line may be seen on 24.5%-57% of frontal CXR. The heart, great vessels, sternum, or the thoracic spine can obscure the line on the frontal CXR. The line can be also absent if its course is not tangential to the X-ray beam. Being located in the anterior mediastinum, its deformation or obliteration can be due to the presence of anterior mediastinal disease (thyroid masses, lymphadenopathy, neoplasms, thymic masses, or lipomatosis). On the other hand, lung volume loss or hyperinflation can also displace the line. The Posterior Junction Line It is formed by the apposition of the visceral and parietal pleura of the postero-medial rd th portion of the upper lobes posterior to the esophagus and anterior to 3 -5 thoracic vertebrae. On the frontal CXR it normally appears as a thin line, typically projecting through the trachea, with a vertical course that superiorly opens along the pleural dome being so appreciable above the clavicles, while inferiorly it ends over the aortic and azygos vein arches (Figure 7) on page . Page 12 of 40 Fig. Sometimes, it may also appear as a stripe with varying amounts of intervening posterior mediastinal fat. The posterior junction line may be seen on 32% of P-A CXR. Deformation of this line may be due to posterior mediastinum disease (esophageal masses,lymphoadenopaties, aortic disease, or neurogenic tumors). Similarly to the anterior junction line, lung volume loss or hyperinflation can also displace the line. The Right Paratracheal Stripe It is formed by contact between the right upper lobe and the right lateral wall of the trachea with the presence of the intervening mediastinal fat. This stripe has generally a normal thickness of 4-mm, and begins superiorly at the level of the clavicles and extends inferiorly to the right tracheo-bronchial angle at the level of the arch of the azygos vein (Figure 8) on page . Page 13 of 40 Fig. It is the most commonly seen mediastinal line or stripe with a visualization frequency on the frontal CXR of 83-97%. Abnormal contour or widening of this stripe could be due to lipoma (Figure 9) on page , lymphoadenopathies (Figure 10) on page , thyroid or parathyroid neoplasms, and tracheal carcinoma or stenosis. Pleural effusion or thickening can also determine widening of the stripe. Page 14 of 40 Fig. Fig. The Left Paratracheal Stripe It is formed by contact between the left upper lobe and the left lateral wall of the trachea with the presence of the intervening mediastinal fat, extending superiorly from the aortic arch to join with the reflection from the left subclavian artery (Figure 11) on page . Page 15 of 40 Fig. This stripe is seen less frequently than the right stripe, being visible on 21%-31% of the frontal CXR, and may be obscured by contact between the left lung and either the proximal left common carotid artery anteriorly or the left subclavian artery posteriorly. Deformation of the stripe can be due to lymphadenopathy, neoplasms, or also mediastinal hematoma Abnormal contour or widening is commonly seen in large left-sided pleural effusion. The Aortic Pulmonary Stripe It represents the interface formed by the pleura of the anterior segment of the left upper lobe coming in contact with and tangentially reflecting over the mediastinal fat anterolateral to the main pulmonary trunk/left pulmonary artery and aortic arch. Normally, the stripe is straight or slightly convex (Figure 12) on page . Page 16 of 40 Fig. Its normal appearance may be altered by anterior mediastinal disease such as thyroid, thymic masses or prevascular lymphadenopathy often causing increased convexity laterally. The Aortopulmonary Window It represents a mediastinal space seen as an interface on frontal CXR, lying posterior to the aortic-pulmonary stripe (Figure 13) on page . Page 17 of 40 Fig. This space is limited cranially by the inferior wall of the aortic arch, inferiorly by the superior wall of the left pulmonary artery, anteriorly by the posterior wall of the ascending thoracic aorta, and posteriorly by the anterior wall of the descending thoracic aorta. The left tracheal wall, anteriorly and the anterior wall of the left main bronchus posteriorly form the medial border. The contact between the left lung and aortic arch form the lateral border, extended inferiorly to contact the left pulmonary artery with a slight concave interface. A straight contour of the AP window may be normal, but is abnormal when previous CXR have shown the normal concave contour. The lost of normal concave aspect with a convexity is considerate abnormal and related to different mediastinal diseases (prominent mediastinal fat, lymphonodes, bronchial artery aneurysms, nerve sheath tumors, or bronchopulmonary-foregut malformations) (Figure 14) on page . Page 18 of 40 Fig. Paralysis of the left vocal cord or diaphragm could suggest a search for disease in the AP window. Disease in structures that form the borders of the AP window (eg, aortic aneurysms) (Figure 15) on page can also determine abnormal appearance of the window. Fig. Page 19 of 40 The Right Paraspinal Line It is formed by the tangential contact between the right lung and pleura with the posterior mediastinal soft tissues (Figure 16) on page . Fig. Despite its name, it is not a true line, but an interface between the lung and the posterior th th mediastinal fat and soft tissues. It is normally straight, along the 8 -12 thoracic vertebral body and appreciated on 23% of frontal CXR. A lateral displaced of the line can be due to osteophytes or prominent mediastinal fat, but it can suggest a posterior mediastinal abnormality (mediastinal hematoma, mass, or extramedullary hematopoiesis). The Left Paraspinal Line It is formed by tangential contact of the left lung and pleura with the posterior mediastinal fat and adjacent soft tissues, extending vertically from the aortic arch to the diaphragm medially to the lateral wall of the descending thoracic aorta (paraortic line) (Figure 17) on page . Page 20 of 40 Fig. Sometimes, it may lie lateral to the paraortic line along the lower descending thoracic aorta. It occurs on 41% of frontal CXR, more frequently than the right paraspinal line due to the presence of the descending thoracic aorta on the left, which endorse the tangential contact of lung-mediastinum interface. Similarly to the right, the abnormal contour of the line can be due to osteophytes or prominent mediastinal fat while a displacement may suggest posterior mediastinal abnormalities (mediastinal hematoma, mass, extramedullary hematopoiesis, or esophageal varices). The Azygoesophageal Recess It is not a typical mediastinal line or stripe, being an interface caused by differences in density between the mediastinum and the postero-medial portion of the right lower lobe. It is a space within the mediastinum lying lateral or posterior to the intra-thoracic esophagus and anterior to the spine, extending from the level of the arch of the azygos vein to the aortic hiatus and right diaphragm inferiorly (Figure 18) on page , Page 21 of 40 Fig. being bordered anteriorly and medially by esophagus, the azygos vein, and left atrium. In its upper third the recess is continuous with the subcarinal space and may either be straight or concave relative to the right lung; a right superior convexity may be seen in children and younger adults but is abnormal in the elderly. In its middle third, the recess is usually straight, but may be slightly convex relative to the right lung near the right pulmonary veins or shows mild leftward convexity, while the lower third is usually straight. Abnormal contour/convexity may be due to different conditions affecting the middle/posterior mediastinal compartments: lymphonodes, bronchopulmonary-foregut malformations, esophageal neoplasms, pleural abnormalities, left atrial enlargement, hiatal hernias (Figure 19) on page or gastroesophageal varices (Figure 20). on page Page 22 of 40 Fig. Page 23 of 40 Fig. The Cardiac Silhouette Sign When examining the lung fields of a normal frontal CXR, the silhouettes of the heart borders, the ascending and descending thoracic aorta, the aortic knob and the hemidiaphragms should be clear. Borders, outlines and edges seen on plain CXR depend on the presence of two adjacent areas of different density (soft tissue and air). More or less, only 4 natural different densities are detectable on plain films: air, fat, soft tissue and calcium. If two soft tissue densities lie adjacent, they will not be visible separately. If, however, they are separated by air, the borders of both will be seen. Obliteration of any of these silhouettes can be caused by different condition (pneumonia, pleural effusion, neoplasms, collapse, etc.) and is known as the 'silhouette sign'. All of these structures are in contact with a specific portion of the lung, therefore by determining exactly which structure is obliterated, it is possible to determine the side of the pathology (Figure 21) on page . Page 24 of 40 Fig. This is a useful sign for detecting/localizing abnormalities in the P-A CXR without a lateral view: if an opacity were present in the left hemitorax overlapping the left ventricle with the LV edge still present, the lesion lies posterior (absence of the silhouette sign)(Figure 22) on page . Page 25 of 40 Fig. Otherwise, if the right heart border were lost due to the presence of an opacity in the right cardio-frenic angle, this finding lies anterior (presence of the silhouette sign) (Figure 23) on page . Page 26 of 40 Fig. Anyway, if the right heart border were still present the opacity in the right cardio-frenic could have a lower density (Figure 24) on page . Fig. Page 27 of 40 Images linked within the text of this section: Fig. Fig. Page 28 of 40 Fig. Fig. Page 29 of 40 Fig. Fig. Page 30 of 40 Fig. Fig. Page 31 of 40 Fig. Fig. Page 32 of 40 Fig. Fig. Page 33 of 40 Fig. Fig. Page 34 of 40 Fig. Page 35 of 40 Fig. Fig. Page 36 of 40 Fig. Fig. Page 37 of 40 Fig. Page 38 of 40 Conclusion Despite the increased dependence on CT in the evaluation of chest disease, traditional chest radiography remains a precious tool in the routinely setting. Radiologists and in particular the trainees must be familiar with the anatomic basis of the mediastinal lines, mediastinal stripes, and cardiac silhouette seen on CXR and able to recognize their normal and abnormal appearances to develop an suitable differential diagnosis prior to get additional information with chest CT. Personal Information Fig. References Page 39 of 40 Fig. Page 40 of 40