DOI: 10.1148/rg.271065073
RadioGraphics 2007;27:33-48
© RSNA, 2007
Lines and Stripes: Where Did They Go? —From Conventional Radiography to CT1
Jerry M. Gibbs, MD,
Chitra A. Chandrasekhar, MBBS,
Emma C. Ferguson, MD and
Sandra A. A. Oldham, MD
1 From the Department of Diagnostic and Interventional Imaging, University of Texas Medical School at Houston, 6431 Fannin St, MSB 2.026, Houston, TX 77030. Presented as an education exhibit at the 2005 RSNA Annual Meeting. Received April 20, 2006; revision requested May 22 and received June 26; accepted June 28. All authors have no financial relationships to disclose.
Address correspondence to J.M.G. (e-mail: jerry.m.gibbs{at}uth.tmc.edu).
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Abstract
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Frontal and lateral radiography has traditionally been used to evaluate the chest, although computed tomography (CT) and high-resolution CT are increasingly being used as an adjunct to conventional radiography for the evaluation of parenchymal and mediastinal disease. Nevertheless, radiography remains a very important modality in this context, and use of chest radiography alone can provide a vast amount of useful information. This information is derived from the configurations and interrelationships of the anatomic structures in the lung, mediastinum, and pleura and forms the basis of the "lines and stripes" concept, which plays a valuable role in establishing a diagnosis before proceeding to CT. The inability to recognize that a chest radiograph is abnormal owing to displacement of one of these lines or stripes may lead to failure to request a potentially valuable CT examination. Radiologists must be familiar with the anatomic basis of these mediastinal lines and stripes and be able to recognize their normal and abnormal appearances. In this way, they can develop an appropriate differential diagnosis prior to obtaining additional information with chest CT.
© RSNA, 2007
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LEARNING OBJECTIVES FOR TEST 2
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After reading this article and taking the test, the reader will be able to:- Discuss the mediastinal "lines and stripes" concept with respect to chest radiography and CT.
- Identify these lines and stripes and the anatomic structures in the chest that create them.
- Describe the abnormal appearances of these lines and stripes and the appropriate differential diagnoses.
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Introduction
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Interpretation of chest radiographs requires radiologists to recognize important mediastinal lines and stripes. 
Lines typically measure less than 1 mm in width and are formed by air, typically within the lung, outlining thin intervening tissue on both sides (1). Lines present on chest radiographs include the anterior and posterior junction lines. Stripes are thicker lines formed by air outlining thicker intervening soft tissue (1). Many stripes are seen on chest radiographs, including the left and right paratracheal stripes and the posterior tracheal stripe. The edge, or interface, represents another component of the "lines and stripes" concept at chest radiography. Interfaces are formed when structures of different densities come in contact with one another. Many interfaces are seen on chest radiographs, including the right and left paraspinal lines and the azygoesophageal recess, which, despite their names, are examples of interfaces that are important in the evaluation of mediastinal disease.
In this article, we discuss and illustrate the normal and abnormal appearances of the important mediastinal lines, stripes, and interfaces seen at chest radiography and correlate these findings with computed tomographic (CT) findings.
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Anterior Junction Line
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The anterior junction line is formed by the apposition of the visceral and parietal pleura of the anteromedial aspects of the lungs with a small amount of intervening mediastinal fat. It appears as an oblique line crossing the superior two-thirds of the sternum from upper right to lower left (Figs 1, 2) (1,2). A small amount of mediastinal fat is normally found within the line; however, increased amounts of intervening mediastinal fat and possibly thymus in younger patients may cause the anterior junction line to appear as a stripe (1,2).
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Figure 1a. Illustration (a) and frontal chest radiograph (b) show a normal anterior junction line (black lines in a, arrows in b) coursing obliquely from the upper right to the lower left over the superior two-thirds of the sternum.
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Figure 1b. Illustration (a) and frontal chest radiograph (b) show a normal anterior junction line (black lines in a, arrows in b) coursing obliquely from the upper right to the lower left over the superior two-thirds of the sternum.
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The anterior junction line is the middle component of the anterior junction reflection. The V-shaped superior recess is the more cranial component and is formed by contact between the lungs and the retromanubrial mediastinal fat. The inverted V-shaped inferior recess is formed by separation of the lungs from intervening heart and mediastinal fat (2). The anterior junction line may be seen on 24.5%–57% of frontal chest radiographs (1,3). It may not be seen when the pleural reflections producing the line course obliquely and are no longer tangential to the x-ray beam. The heart, great vessels, sternum, or even the thoracic spine can also obscure the line.
Because of the location of the anterior junction line in the anterior mediastinum, obliteration or abnormal convexity of the line suggests underlying anterior mediastinal disease such as thyroid masses, lymphadenopathy, neoplasms, thymic masses, or lipomatosis (4). Volume loss and hyperinflation of the surrounding lung can also displace the line (Fig 3).
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Figure 3a. Abnormal-appearing anterior junction line in a patient who had undergone a right middle lobectomy. (a) Frontal chest radiograph shows the anterior junction line (arrows) displaced to the right. Note also the volume loss in the right lung as demonstrated by elevation of the right hemidiaphragm. (b) CT scan helps confirm rightward displacement of the anterior junction line (arrow) with volume loss in the right lung.
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Figure 3b. Abnormal-appearing anterior junction line in a patient who had undergone a right middle lobectomy. (a) Frontal chest radiograph shows the anterior junction line (arrows) displaced to the right. Note also the volume loss in the right lung as demonstrated by elevation of the right hemidiaphragm. (b) CT scan helps confirm rightward displacement of the anterior junction line (arrow) with volume loss in the right lung.
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Posterior Junction Line
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The posterior junction line is formed by the apposition of the visceral and parietal pleura of the posteromedial portion of the lungs posterior to the esophagus and anterior to the third through the fifth thoracic vertebrae. It appears as a straight or mildly leftward convex line, typically projecting through the trachea (Figs 4, 5) (1,3,5). The posterior junction line demonstrates more cranial extension than the anterior junction line and, unlike its counterpart, is seen above the clavicles. However, it may also appear as a stripe with varying amounts of intervening posterior mediastinal fat.
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Figure 4a. Illustration (a) and frontal chest radiograph (b) demonstrate a normal posterior junction line (black lines in a, arrows in b) as a straight line projecting through the trachea and extending above the clavicles.
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Figure 4b. Illustration (a) and frontal chest radiograph (b) demonstrate a normal posterior junction line (black lines in a, arrows in b) as a straight line projecting through the trachea and extending above the clavicles.
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Figure 5. CT scan demonstrates a normal posterior junction line (arrow), which lies posterior to the esophagus and is formed by the apposition of the visceral and parietal pleura of the lungs anterior to the thoracic vertebrae.
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The posterior junction line represents the middle component of the posterior junction reflection. The V-shaped superior recess lies above the line and is formed by contact between the posterior apices of the lungs and mediastinum anterior to the first and second thoracic vertebrae. The inverted V-shaped inferior recess lies below the line and is formed by contact between the lungs and the mediastinum surrounding the superior intercostal veins and the posterior azygos and aortic arches (1,5). The posterior junction line has reportedly been seen on 32% of posteroanterior chest radiographs (3).
Abnormal bulging or convexity of the posterior junction line suggests a posterior mediastinal abnormality such as esophageal masses, lymphadenopathy, aortic disease, or neurogenic tumors. As with the anterior junction line, volume loss or hyperinflation of the surrounding lung can also displace the line (1,4,5).
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Right Paratracheal Stripe
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When the visceral and parietal pleura of the right upper lobe come in contact with the right lateral border of the trachea and the intervening mediastinal fat, air within the right lung and trachea outlines these entities to form the right paratracheal stripe (Figs 6, 7) (1,3), which has a maximum normal thickness of 4 mm. It begins superiorly at the level of the clavicles and extends inferiorly to the right tracheobronchial angle at the level of the azygos arch. The right paratracheal stripe is perhaps the most commonly seen mediastinal line or stripe. In their classic series, Woodring and Daniel (3) reported its presence on 97% of posteroanterior chest radiographs.
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Figure 7. CT scan shows that the right paratracheal stripe (arrow) is formed by air within the right upper lobe and trachea outlining the right lateral tracheal wall, right upper lobe pleura, and intervening soft tissues.
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A wide variety of disease entities can cause widening or abnormal contour of the right paratracheal stripe, such as paratracheal lymphadenopathy, thyroid or parathyroid neoplasms (Fig 8), and tracheal carcinoma or stenosis. Pleural disease such as effusion or thickening is among the most common causes for widening of the right paratracheal stripe (1,3,4).
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Figure 8a. Abnormal right paratracheal stripe caused by a large ectopic parathyroid adenoma in a 52-year-old man. (a) Frontal chest radiograph demonstrates widening of the right paratracheal stripe (arrow). (b) CT scan helps confirm a large right paratracheal mass (arrow) with diffuse osteopenia from primary hyperparathyroidism.
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Figure 8b. Abnormal right paratracheal stripe caused by a large ectopic parathyroid adenoma in a 52-year-old man. (a) Frontal chest radiograph demonstrates widening of the right paratracheal stripe (arrow). (b) CT scan helps confirm a large right paratracheal mass (arrow) with diffuse osteopenia from primary hyperparathyroidism.
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Left Paratracheal Stripe
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The left paratracheal stripe is formed by contact between the left upper lobe and either the mediastinal fat adjacent to the left tracheal wall or the left tracheal wall itself. Air within the trachea outlines the intervening soft tissues, thereby forming the left paratracheal stripe. The stripe extends superiorly from the aortic arch to join with the reflection from the left subclavian artery and thus may be referred to as the left paratracheal reflection (Fig 9) (6).
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Figure 9a. Illustration (a) and frontal chest radiograph (b) demonstrate a normal left paratracheal stripe (black line in a, arrows in b) extending from the aortic arch to join with the reflection from the left subclavian artery superiorly.
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Figure 9b. Illustration (a) and frontal chest radiograph (b) demonstrate a normal left paratracheal stripe (black line in a, arrows in b) extending from the aortic arch to join with the reflection from the left subclavian artery superiorly.
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Visible on 21%–31% of posteroanterior chest radiographs, the left paratracheal stripe is seen less frequently than the right paratracheal stripe, since it may be obscured by contact between the left lung and either the proximal left common carotid artery anteriorly or the left subclavian artery posteriorly (3,6). As with the right paratracheal stripe, abnormal contour or widening is commonly seen in large left-sided pleural effusions. Left paratracheal lymphadenopathy, neoplasm (Fig 10), or mediastinal hematoma may also alter the normal appearance of the left paratracheal stripe (3).
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Figure 10a. Abnormal-appearing left paratracheal stripe in a 47-year-old patient with metastatic thyroid carcinoma. (a) Frontal chest radiograph demonstrates widening of the left paratracheal stripe (arrows) with mass effect on the trachea. (b) CT scan reveals a large thyroid mass (arrow) and associated supraclavicular lymphadenopathy.
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Figure 10b. Abnormal-appearing left paratracheal stripe in a 47-year-old patient with metastatic thyroid carcinoma. (a) Frontal chest radiograph demonstrates widening of the left paratracheal stripe (arrows) with mass effect on the trachea. (b) CT scan reveals a large thyroid mass (arrow) and associated supraclavicular lymphadenopathy.
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Aortic-Pulmonary Stripe
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First described by Keats (7), the aortic-pulmonary stripe actually represents a mediastinal reflection or interface formed by the pleura of the anterior left lung coming in contact with and tangentially reflecting over the mediastinal fat anterolateral to the left pulmonary artery and aortic arch. The stripe is straight or mildly convex, crossing laterally over the aortic arch and the main pulmonary artery (Figs 11, 12) (1,7,8).
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Figure 11a. Illustration (a) and frontal chest radiograph (b) demonstrate a normal aortic-pulmonary stripe (black line in a, arrows in b) as a straight interface crossing the aortic arch and the main pulmonary artery.
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Figure 11b. Illustration (a) and frontal chest radiograph (b) demonstrate a normal aortic-pulmonary stripe (black line in a, arrows in b) as a straight interface crossing the aortic arch and the main pulmonary artery.
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Figure 12. CT scan shows a normal aortic-pulmonary stripe (arrows) formed by the anterior left lung contacting and tangentially reflecting over the mediastinal fat antero-lateral to the left pulmonary artery and aortic arch.
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Keats’ original study described elevation of the aortic-pulmonary stripe in two patients with pneumomediastinum (7). Anterior mediastinal disease such as thyroid or thymic masses or pre-vascular lymphadenopathy (Fig 13) may alter the normal appearance of the stripe, causing increased convexity laterally (8).
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Figure 13a. Abnormal-appearing aortic-pulmonary stripe in a 42-year-old patient with lymphoma. (a) Frontal chest radiograph demonstrates abnormal contour of the aortic-pulmonary stripe (arrows). (b) CT scan shows anterior mediastinal lymphadenopathy (arrows) within the prevascular space.
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Figure 13b. Abnormal-appearing aortic-pulmonary stripe in a 42-year-old patient with lymphoma. (a) Frontal chest radiograph demonstrates abnormal contour of the aortic-pulmonary stripe (arrows). (b) CT scan shows anterior mediastinal lymphadenopathy (arrows) within the prevascular space.
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Aortopulmonary Window
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The aortopulmonary (AP) window represents a mediastinal space that is seen as an interface on frontal chest radiographs. Because of their similar names, the AP window is often confused with the previously discussed aortic-pulmonary stripe. The AP window actually lies posterior to the aortic-pulmonary stripe. It is bounded superiorly by the inferior wall of the aortic arch and inferiorly by the superior wall of the left pulmonary artery. The posterior wall of the ascending aorta forms the anterior boundary of the AP window, whereas the anterior wall of the descending aorta forms the posterior boundary. The medial border is formed by the trachea anteriorly, the lateral wall of the left main bronchus, and the esophagus posteriorly (1,8).
The lateral border forms the interface representing the AP window on frontal chest radiographs. It is formed by the left lung and pleura coming in contact with the aortic arch and extending inferiorly to contact the left pulmonary artery. The left lung extends into the space connecting the aortic arch and the left pulmonary artery, thereby forming the normal concave reflection (reflection B) along the mediastinal side (Figs 14, 15) (1,8). A convex contour of the AP window is considered abnormal. A straight contour of the AP window may be normal but is considered abnormal when previous chest radiographs showed the contour to be concave (1,8).
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Figure 14. Frontal chest radiograph demonstrates a normal AP window as a shallow concave interface (*) between the aorta and the pulmonary artery. Note the normal aortic-pulmonary stripe (arrows) and its relation to the AP window.
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Figure 15. CT scan shows the normal AP window (*). The concave interface seen in Figure 14 actually represents the lateral border (arrow) of the AP window formed by the left lung and pleura contacting the aortic arch and extending to the pulmonary artery.
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An abnormal appearance of the AP window may be related to disease of its underlying contents, which include the left recurrent laryngeal nerve, left vagus nerve, ligamentum arteriosum, mediastinal fat, lymph nodes, and left bronchial arteries. Abnormal convexity of the AP window may be due to prominent mediastinal fat, lymph-adenopathy (Fig 16), bronchial artery aneurysms, or nerve sheath tumors (1). Paralysis of the left vocal cord or diaphragm should also prompt a search for disease in the AP window (1,3,8). Disease in structures that form the borders of the AP window (eg, aortic aneurysms) can also cause the window to have an abnormal appearance.
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Figure 16a. Abnormal-appearing AP window in a 64-year-old patient with bronchogenic carcinoma. (a) Frontal chest radiograph demonstrates an abnormal bulge in the AP window (arrow). Thickening of the right paratracheal stripe (*) is also noted, along with left lower lobe consolidation and left pleural effusion. (b) CT scan shows a significant soft-tissue mass within the AP window and subcarinal space, a finding that is compatible with metastatic lymphadenopathy. Lymphadenopathy in the paratracheal region was also noted, accounting for the thickened right paratracheal stripe.
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Figure 16b. Abnormal-appearing AP window in a 64-year-old patient with bronchogenic carcinoma. (a) Frontal chest radiograph demonstrates an abnormal bulge in the AP window (arrow). Thickening of the right paratracheal stripe (*) is also noted, along with left lower lobe consolidation and left pleural effusion. (b) CT scan shows a significant soft-tissue mass within the AP window and subcarinal space, a finding that is compatible with metastatic lymphadenopathy. Lymphadenopathy in the paratracheal region was also noted, accounting for the thickened right paratracheal stripe.
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Right Paraspinal Line
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The right paraspinal line is formed by the right lung and pleura coming in tangential contact with the posterior mediastinal soft tissues. Despite its name, the right paraspinal line is not a true mediastinal line. Rather, it represents an interface between the right lung and the posterior mediastinal fat and soft tissues. A thin white line enhancing the edge of the right paraspinal line does not truly exist but is perceived visually and represents a positive Mach band phenomenon. It is caused by lateral inhibition of the retina from differences in contour and optical density of structures at a well-defined interface (9).
The right paraspinal line appears straight and typically extends from the 8th through the 12th thoracic vertebral levels (Figs 17, 18) (1,3). Wood-ring and Daniel (3) reported its presence on 23% of posteroanterior radiographs. The right paraspinal line may be displaced laterally by osteophytes or prominent mediastinal fat. However, abnormal contour or displacement may also suggest a posterior mediastinal abnormality such as a mediastinal hematoma (Fig 19), a mass, or extramedullary hematopoiesis (1,3,4).
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Figure 17a. Illustration (a) and frontal chest radiograph (b) demonstrate a normal right paraspinal line (black line in a, arrows in b) as a thin straight line extending lateral to the thoracic spine.
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Figure 17b. Illustration (a) and frontal chest radiograph (b) demonstrate a normal right paraspinal line (black line in a, arrows in b) as a thin straight line extending lateral to the thoracic spine.
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Figure 19a. Abnormal-appearing right paraspinal line in a 27-year-old patient who had sustained traumatic injury. (a) Frontal chest radiograph demonstrates an abnormal bulge in the right paraspinal line inferiorly (arrows). (b) CT scan reveals a large mediastinal hematoma (arrow) from multiple right-sided transverse process fractures of the thoracic spine and an associated right hemothorax.
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Figure 19b. Abnormal-appearing right paraspinal line in a 27-year-old patient who had sustained traumatic injury. (a) Frontal chest radiograph demonstrates an abnormal bulge in the right paraspinal line inferiorly (arrows). (b) CT scan reveals a large mediastinal hematoma (arrow) from multiple right-sided transverse process fractures of the thoracic spine and an associated right hemothorax.
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Left Paraspinal Line
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The left paraspinal line is formed by tangential contact of the left lung and pleura with the posterior mediastinal fat, left paraspinal muscles, and adjacent soft tissues. The left paraspinal line extends vertically from the aortic arch to the diaphragm and typically lies medial to the lateral wall of the descending thoracic aorta (Figs 18, 20) (1). In some instances, however, it may lie lateral to the aorta along the lower intrathoracic course of the aorta. Like the right paraspinal line, the left paraspinal line actually represents a lung-mediastinum interface and is associated with a positive Mach band phenomenon, having the appearance of a line etched in white (9). Reported on 41% of posteroanterior radiographs, the left paraspinal line is seen more frequently than the right paraspinal line due to the presence of the descending thoracic aorta on the left, which promotes the tangential contact of the left lung necessary to produce the lung-mediastinum interface (1,3).
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Figure 20a. Illustration (a) and frontal chest radiograph (b) demonstrate a normal left paraspinal line (black line in a, arrows in b) as a thin straight line extending from the aortic arch to the diaphragm. The normal left paraspinal line typically lies medial to the lateral wall of the descending thoracic aorta.
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Figure 20b. Illustration (a) and frontal chest radiograph (b) demonstrate a normal left paraspinal line (black line in a, arrows in b) as a thin straight line extending from the aortic arch to the diaphragm. The normal left paraspinal line typically lies medial to the lateral wall of the descending thoracic aorta.
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As with the right paraspinal line, osteophytes or prominent mediastinal fat can cause an abnormal contour of the left paraspinal line; however, tortuosity of the descending thoracic aorta may also displace it. Abnormal contour or displacement may also suggest additional posterior mediastinal abnormalities such as a mediastinal hematoma, a mass, extramedullary hematopoiesis, or esophageal varices (Fig 21) (1,4,5).
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Figure 21a. Abnormal-appearing left paraspinal line in a 52-year-old patient with liver cirrhosis and esophageal varices. (a) Frontal chest radiograph reveals a focal lateral bulge in the left paraspinal line (arrow). (b) CT scan shows extensive esophageal varices (arrow), which are responsible for the abnormal contour of the left paraspinal line.
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Figure 21b. Abnormal-appearing left paraspinal line in a 52-year-old patient with liver cirrhosis and esophageal varices. (a) Frontal chest radiograph reveals a focal lateral bulge in the left paraspinal line (arrow). (b) CT scan shows extensive esophageal varices (arrow), which are responsible for the abnormal contour of the left paraspinal line.
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Posterior Tracheal Stripe (Tracheoesophageal Stripe)
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The posterior tracheal stripe is a vertical stripe seen on lateral chest radiographs that is formed by air within the trachea and right lung outlining the posterior tracheal wall and intervening soft tissues (Figs 22, 23) (10,11). It typically measures up to 2.5 mm in thickness. When the posterior trachea comes in contact with the anterior wall of the esophagus, however, the esophageal wall, the posterior tracheal wall, and intervening soft tissues combine to form a thicker tracheoesophageal stripe, which may measure up to 5.5 mm (10–12).
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Figure 23. CT scan reveals that the posterior tracheal stripe (arrow) is formed by air within the trachea and right lung outlining the posterior tracheal wall and intervening soft tissues.
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The posterior tracheal stripe forms the anterior border of the retrotracheal space (Raider or retro-tracheal triangle), with the remaining borders being the spine posteriorly, the aortic arch inferiorly, and the thoracic inlet superiorly. Franquet et al (10) observed that the most common abnormalities within the retrotracheal space are congenital developmental anomalies of the aortic arch. Acquired vascular lesions, esophageal lesions, lymphatic malformations, mediastinitis, and post-traumatic hematomas may also cause abnormal thickening of the posterior tracheal stripe (Fig 24).
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Figure 24a. Abnormal posterior tracheal stripe in a 49-year-old patient with achalasia. (a) Lateral chest radiograph shows widening of the posterior tracheal stripe (arrows). (b) CT scan demonstrates a dilated esophagus (arrow) filled with food and contrast material.
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Figure 24b. Abnormal posterior tracheal stripe in a 49-year-old patient with achalasia. (a) Lateral chest radiograph shows widening of the posterior tracheal stripe (arrows). (b) CT scan demonstrates a dilated esophagus (arrow) filled with food and contrast material.
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Azygoesophageal Recess
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Although not considered a mediastinal line or stripe, the azygoesophageal recess remains an important mediastinal interface caused by differences in density between the mediastinum and the posteromedial portion of the right lower lobe. The azygoesophageal recess represents a space lying lateral or posterior to the esophagus and anterior to the spine, extending from the level of the anterior turn of the azygos vein to the level of the aortic hiatus inferiorly (1). The right infraazygos pleuroesophageal stripe may also outline the recess and is formed when an air-filled esophagus and intervening pleura come in contact with the right lower lobe (12).
Superiorly, the recess is continuous with the subcarinal space and may demonstrate mild leftward convexity in that location (1,13). The middle third of the recess may be the most variable in appearance but typically is straight edged or shows mild leftward convexity. The lower third typically appears as a straight edge (Figs 25, 26). Right superior convexity may be seen in children and younger adults but is abnormal in the elderly. Abnormal contour and convexity may be due to lymphadenopathy, hiatal hernias (Fig 27), bronchopulmonary-foregut malformations, esophageal neoplasms, pleural abnormalities, and cardiomegaly with left atrial enlargement (1,13).
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Figure 25a. Illustration (a) and frontal chest radiograph (b) demonstrate a normal azygoesophageal recess (black line in a, arrows in b) with mild leftward convexity superiorly and a straight edge inferiorly.
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Figure 25b. Illustration (a) and frontal chest radiograph (b) demonstrate a normal azygoesophageal recess (black line in a, arrows in b) with mild leftward convexity superiorly and a straight | |
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Abstract
LEARNING OBJECTIVES FOR TEST...
