Chest
Special FeaturesCardiac Silhouette Findings and Mediastinal Lines and Stripes: Radiograph and CT Scan Correlation
Section snippets
Cardiac Silhouette
On a normal posterior-anterior (P-A) CXR, the silhouette of the heart borders, the ascending and descending thoracic aorta, the aortic arch, the lateral profile of the superior vena cava (SVC), the azygos vein arch, and the hemidiaphragms should be clear, being outlined by the adjacent air-contained lung. When a consolidating lung (eg, pneumonia, neoplasms, collapse) or soft-tissue mass (eg, mediastinal mass, pleural effusion) contacts one of these structures, its border becomes invisible or
Mediastinal Lines and Stripes
The mediastinal lines and stripes (Fig 6) are both formed by the presence of air in structures that approximate each other, delineating the respectively thinner and thicker intervening tissue on both sides.4 The mediastinal lines correspond to the contours of the middle and superior 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, and include the anterior and posterior
Anterior Junction Line
The anterior junction line 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. On P-A CXR, it normally shows an oblique course from the upper right to the lower left, crossing the superior two-thirds of the sternum (Fig 7A).4, 5 Normally it appears as a thin line (mediastinal line), but sometimes it may become visible as a stripe as the result of an
Posterior Junction Line
The posterior junction line is formed by the apposition of the visceral and parietal pleura of the postero-medial portion of the upper lobes posterior to the esophagus and anterior to the third to the fifth thoracic vertebrae (Figs 8A, 8B). It normally appears as a thin line, typically projecting through the trachea, with a vertical course that superiorly opens along the pleural dome and is, therefore, appreciable above the clavicles, while inferiorly, it ends over the aortic and azygos vein
Right Paratracheal Stripe
The right paratracheal stripe is formed by contact between the right upper lobe (RUL) and the right lateral wall of the trachea in the presence of intervening mediastinal fat (Fig 10). This stripe begins superiorly at the level of the clavicles and extends inferiorly to the right tracheo-bronchial angle at the level of the azygos vein arch. It is the most commonly seen as a mediastinal line or stripe with a visualization frequency on frontal CXR of 83% to 97%.4, 10, 11 An abnormal contour or
Left Paratracheal Stripe
The left paratracheal stripe is formed by contact between the left upper lobe (LUL) and the left lateral wall of the trachea in the presence of intervening mediastinal fat (Fig 12). It extends superiorly from the aortic arch to join with the reflection from the left subclavian artery.13 This stripe is seen less frequently than the right paratracheal stripe, being visible on 21% to 31% of P-A CXRs, and may be obscured by contact between the left lung and either the proximal left common carotid
Aortic-Pulmonary Stripe
The aortic-pulmonary stripe represents the interface formed by the pleura of the anterior segment of the LUL coming in contact with and tangentially reflecting over the mediastinal fat antero-lateral to the main pulmonary trunk/left pulmonary artery and the aortic arch (Fig 13).4, 14 Normally, the stripe is straight or slightly convex. Its normal appearance may be altered by anterior mediastinal disease such as thyroid and thymic masses, and prevascular lymphoadenopathies often cause increased
Aortic-Pulmonary Window
This mediastinal space is limited cranially by the inferior wall of the aortic arch, inferiorly by the superior wall of the left PA, anteriorly by the posterior wall of the ascending aorta, and posteriorly by the anterior wall of the descending aorta. The medial border is formed by the left tracheal wall anteriorly and the anterior wall of the left main bronchus posteriorly. The contact between the left lung and the aortic arch form the lateral border, which extends down to contact the left PA,
Right and Left Paraspinous Lines
The right and left paraspinous lines are formed by tangential contact between the right and left lungs and pleura with the posterior mediastinal soft tissues. Despite their name, they are not true lines, but are interfaces between the lungs and the paraspinous fat and soft tissues (Fig 16).
The right paraspinous line is normally straight, running from the eighth to the 12th thoracic vertebral bodies, and can be appreciated on 23% of frontal CXRs.2, 7 On CT images, this line can be well
Azygos-Esophageal Recess
The azygos-esophagel recess is not a typical mediastinal line or stripe, but is an interface caused by the difference in density between the mediastinum and the postero-medial portion of the right lower lobe (RLL). It is a space within the mediastinum, lying lateral or posterior to the intrathoracic esophagus and anterior to the spine. It extends from the level of the azygos vein arch to the aortic hiatus and the right diaphragm inferiorly, and is bordered anteriorly and medially by esophagus,
Pararterial Line
The paraterial line is visible on P-A CXRs above the aortic arch, with a left-oriented course toward the left lung apex, and is produced by the contact of the lateral margin of the left subclavian artery with the LUL edge (Fig 20). Usually this line shows a left-concave shape.4 Lymphoadenopathies, mediastinal or thoracic inlet masses, lung neoplasms or consolidation, pleural disease, and arterial aneurysm can determine the deformation or suppression of this line.
Paraortic Line
The paraortic line is appreciable on P-A CXRs behind the cardiac shadow, with a straight and vertical course, external to the left paraspinous line (Fig 21). It is composed by the contact of the lateral wall of the descending thoracic aorta with the left lower lobe (LLL). Usually, in its lower third, the line comes nearer to the vertebral bodies at the level of the 11th thoracic vertebra, overlapping the left paraspinous line.4, 10 In the elderly, with the occurrence of atherosclerotic changes
Paracaval Line
In young patients, the paracaval line represents the right superior limit of the cardiac shadow on a P-A CXR (the so-called first right cardiac arch), formed by the contact of the RUL with the lateral margin of the SVC (Fig 1). In elderly patients, it is more frequently composed by the lateral margin of the ascending thoracic aorta because of its enlargement caused by atherosclerosis or hypertension.4 This line is characterized by a straight vertical course, terminating in the right atrium.
Conclusions
Despite the increased dependence on CT imaging in the evaluation of chest disease, traditional chest radiography still remains a valuable tool in the routine setting. Radiologists, trainees, and physicians must be familiar with the anatomic basis of the cardiac silhouette and mediastinal lines-and-stripes concepts seen on CXR to recognize normal and abnormal appearances and to develop a suitable differential diagnosis prior to getting additional information using chest CT imaging.
Acknowledgments
Financial/nonfinancial disclosures: The authors have reported to CHEST that no potential conflicts of interest exist with any companies/organizations whose products or services may be discussed in this article.
References (17)
- et al.
Understanding chest radiographic anatomy with MDCT reformations
Clin Radiol
(2010) - et al.
Diagnostic approach to mediastinal masses
Eur J Radiol
(1998) - et al.
Mediastinal impressions on the dilated esophagus
Radiol Clin North Am
(1984) More chest roentgen signs and how to teach them. Annual oration in memory of L. Henry Garland, M.D., 1903-1966
Radiology
(1968)- et al.
A diagnostic approach to mediastinal abnormalities
Radiographics
(2007) Mediastinal anatomy: emphasis on conventional images with anatomic and computed tomographic correlations
J Thorac Imaging
(1987)- et al.
The anterior junction anatomy
Crit Rev Diagn Imaging
(1983) - et al.
Mediastinal lipomatosis. CT confirmation of a normal variant
Radiology
(1978)
Cited by (12)
Unrecognized Extravascular Misplaced Hemodialysis Catheter Leading to Mediastinal Hematoma
2023, Journal of Emergency NursingCardiac Silhouette
2020, American Journal of the Medical SciencesMultidetector Computed Tomography of Pharyngo-Esophageal Perforations
2016, Seminars in Ultrasound, CT and MRICitation Excerpt :abdominal—from esophageal hiatus and is continuous with the cardia of the stomach at the gastroesophageal junction. It courses inferiorly to the left of the midline in the neck and superior mediastinum, returning to the midline at T5 before coursing to the left again of the midline in the posterior mediastinum, and in its inferior aspect curving anteriorly to pass through the diaphragm into the abdominal cavity, and its relations with other mediastinal structures contribute directly to generate radiological lines and stripes, often fundamental for thoracic pathology recognition.6 There are 3 normal esophageal constrictions that should not be confused for pathologic constrictions and which, because of the narrowed lumen, can be more prone to an injury mechanism:
Paracardiac mass on chest X-ray in a patient with Eisenmenger syndrome
2013, International Journal of Cardiology3D Visual Guide to Lines and Stripes in Chest Radiography
2023, Radiographics
Reproduction of this article is prohibited without written permission from the American College of Chest Physicians (http://www.chestpubs.org/site/misc/reprints.xhtml).