Journal of Medical Imaging and Radiation Oncology 58 (2014) 64–74 bs_bs_banner
RADIOLO GY —P I C T O R I A L E SSAY
‘Felson Signs’ revisited Phiji Philip George,1 Aparna Irodi,1 Shyamkumar Nidugala Keshava1 and Anthony C Lamont2 1 Department of Radiology, CMC Hospital, Vellore, Tamil Nadu, India; and 2Department of Radiology, Townsville Hospital, Townsville, Queensland, Australia
PP George MD, Radiodiagnosis; A Irodi MD, FRCR; S Nidugala Keshava DNB, FRCR, FRANZCR; AC Lamont FRCR, FRANZCR. Correspondence Dr Phiji Philip George, Department of Radiology, CMC Hospital, Vellore, TN 632004, India. Email: [email protected]
Summary In this article we revisit, with the help of images, those classic signs in chest radiography described by Dr Benjamin Felson himself, or other illustrious radiologists of his time, cited and discussed in ‘Chest Roentgenology’. We briefly describe the causes of the signs, their utility and the differential diagnosis to be considered when each sign is seen. Wherever possible, we use CT images to illustrate the basis of some of these classic radiographic signs. Key words: chest; CT; imaging; radiography; sign.
Conflict of interest: None declared. Submitted 29 July 2012; accepted 21 November 2012. doi:10.1111/1754-9485.12031
Introduction Think ‘chest radiography’ and the name that comes to the mind of any radiologist almost instinctively is Dr Benjamin Felson. Among his many notable achievements is the now classic book – ‘Chest Roentgenology’. Exquisitely described in this book are many radiographic signs. Some were described by Felson and some by others (with appropriate acknowledgements of all contributors). Hence, the title of this article: ‘Felson Signs’, and not ‘Felson’s signs’. In an era before that of cross-sectional imaging, these signs evolved from radiologists’ efforts at interpreting chest radiographic appearances to determine the location, extent and sometimes, the pathologic nature of the abnormality. A combination of simple lab experiments, tomography, personal experience and deductive reasoning was used to explain typical radiographic appearances seen in a wide variety of conditions. Cross-sectional imaging modalities now dominate radiology and the emphasis in teaching has shifted towards them. Therefore radiologists – particularly radiology residents – are less likely than before to appreciate many of these classic signs. By revisiting them we intend to review our knowledge and stress the continuing
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importance and relevance of these signs in the interpretation of chest radiographs. This pictorial essay illustrates, with the help of CT sections to further elucidate, these classic signs. We briefly discuss the causes, utility and differential diagnoses to be considered for each.
Illustrative cases Air bronchogram This appearance refers to the visibility of air-filled bronchi against a surrounding background of opacified alveoli, whether by fluid or solid matter (Fig. 1). It is essentially diagnostic of alveolar disease,1 and is to be differentiated from bronchiectasis and chronic bronchitis, where bronchi become visible because of their thickened walls.
Bat’s wing or butterfly shadow These names describe the appearance of bilateral, symmetrical infiltration/consolidation in a predominantly central distribution (Fig. 2), with relative sparing of the peripheral, apical and basal portions of the lungs. It was
© 2013 The Authors Journal of Medical Imaging and Radiation Oncology © 2013 The Royal Australian and New Zealand College of Radiologists
‘Felson Signs’ revisited
Fig. 1. A frontal chest radiograph shows an area of consolidation in the right lower zone. Arrows indicate the air bronchogram. A case of right lower lobe pneumonia.
originally described in, and also considered pathognomonic of, uremic pulmonary edema. However, as Felson himself said, ‘it is not even diagnostic of pulmonary edema, . . . It signifies one thing and one thing only: extensive alveolar disease’.1 As such, this appearance can be seen in cardiogenic and noncardiogenic pulmonary edema, pulmonary haemorrhage, infections including pneumocystis carinii pneumonia, pulmonary alveolar proteinosis and even in neoplastic conditions like lymphoma and bronchoalveolar carcinoma.2,3
Black pleura sign
Fig. 3. (a) A frontal chest radiograph shows the ‘black pleura sign’ on the right side (arrows) in a patient with pulmonary alveolar microlithiasis. (b) CT scan of the same patient as in (a), showing the spared pleura (arrows) appearing ‘black’ relative to adjacent involved lung and the ribs.
Seen in pulmonary alveolar microlithiasis, this sign refers to the negative shadow of the pleura between the extensive alveolar calcification and the adjacent rib cage1 (Fig. 3a,b).
Cervicothoracic sign This sign is used to determine whether a superior mediastinal lesion is anterior or posterior. The sign is positive for an anteriorly situated mass, which loses definition above the level of the clavicles as it is silhouetted by the soft tissues of the neck (Fig. 4a,b). ‘The cephalic border of the anterior mediastinum ends at the level of the clavicles, whereas that of the posterior mediastinum extends much higher’.1 The sign is negative for a posteriorly situated mass, which is well defined above the level of the clavicles, as it is sharply outlined by air in the adjacent lung.
Fleischner’s lines
Fig. 2. Chest radiograph, frontal projection, shows bilateral central symmetric perihilar opacities, the outline of which resembles a ‘bat’s wing’. This patient had pneumocystis carinii pneumonia.
These are small and transient, horizontal, band-like opacities commonly seen in the mid and lower zones bilaterally and represent small areas of atelectasis that develop secondary to impaired motion of the diaphragm. Serial chest radiographs show their transient nature and
© 2013 The Authors Journal of Medical Imaging and Radiation Oncology © 2013 The Royal Australian and New Zealand College of Radiologists
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Fig. 4. (a) Chest radiograph, frontal projection, shows a positive cervicothoracic sign, with the lateral border of the mediastinal mass becoming indistinct (arrow) above the level of the clavicle. (b) CT scan image of the same patient as in (a) at the level of the clavicles shows the lateral border of the anterior mediastinal mass merging with the supraclavicular soft tissues – this is the principle of the cervicothoracic sign.
help differentiate them from post-inflammatory scarring (Fig. 5).
Hampton’s hump This sign was described to help differentiate a pulmonary infarct occurring in a favoured site – the costophrenic
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angle – from pleural thickening or fluid. The Hampton’s hump is a pleura-based opacity, with a convex border facing the hilum. Pleural thickening or fluid tends to be concave towards the hilum. Figure 6a,b, of a patient with pulmonary embolism and infarction, explains the basis of this sign, but do not represent a true Hampton’s hump.
© 2013 The Authors Journal of Medical Imaging and Radiation Oncology © 2013 The Royal Australian and New Zealand College of Radiologists
‘Felson Signs’ revisited
Fig. 5. Fleischner’s lines. Two serial chest radiographs (taken 4 days apart) of a post-operative patient illustrate the transience of Fleischner’s lines (arrows). (Insets are magnified views of the atelectatic bands.)
Fig. 6. (a) CT scan images of a patient who presented with acute chest pain and dyspnoea show a pulmonary artery embolus (arrow in image at left), and the resulting infarct (image at right). (b) Chest radiograph of the same patient as in (a). The pulmonary infarct is visible as a pleura-based opacity in the right lower zone, with a convex border facing the hilum. A similar opacity placed in the right costophrenic angle would be a true Hampton’s hump.
© 2013 The Authors Journal of Medical Imaging and Radiation Oncology © 2013 The Royal Australian and New Zealand College of Radiologists
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Fig. 7. (a) Hilum convergence sign. Chest radiograph of a patient, with an abnormal bump in the left hilar region. Inset, depicting magnified view of the left hilum, shows the pulmonary artery branches (arrows) converging on, and ending at, the ‘bump’ (white curve), suggesting an enlarged pulmonary artery. This is a ‘negative’ hilum convergence sign. (b) CT scan images of the same patient as in (a) confirm the enlarged pulmonary artery.
Hilum convergence sign It may be difficult to determine if a hilar/juxtahilar opacity is due to a prominent pulmonary artery or juxtahilar mediastinal mass. If pulmonary artery branches are visible through the opacity and converge towards the
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waist of the heart (hilum convergence sign), then the opacity is due to a juxtahilar mediastinal mass. If, however, the pulmonary artery branches lead towards the abnormal ‘bump’, then the opacity is due to an enlarged pulmonary artery (‘negative’ hilum convergence sign)1,4 (Fig. 7a,b).
© 2013 The Authors Journal of Medical Imaging and Radiation Oncology © 2013 The Royal Australian and New Zealand College of Radiologists
‘Felson Signs’ revisited
Fig. 8. (a) Hilum overlay sign. Frontal chest radiograph of a patient shows an apparently enlarged heart. However, the left pulmonary artery (arrow) is seen more than a centimetre within the lateral edge of the mediastinal border, showing that the abnormality is not cardiac. (b) CT scan images of the same patient as in (a), showing the overlap of the left pulmonary artery (arrow) by a mediastinal teratoma.
Hilum overlay sign Useful in differentiating cardiac enlargement from a mediastinal mass, the hilum overlay sign states that if either the right or left pulmonary artery is visible, more than a centimeter within the lateral edge of the mediastinal silhouette, then the lesion is not
cardiac1,4 (Fig. 8a,b). Dr Felson based this sign on the fact that, in more than 98% of the chest radiographs he reviewed, the visible proximal segment of the pulmonary artery was lateral to or just within the cardiac silhouette. Even when the heart is enlarged or there is pericardial effusion, this relationship remains true.
© 2013 The Authors Journal of Medical Imaging and Radiation Oncology © 2013 The Royal Australian and New Zealand College of Radiologists
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Fig. 10. Chest radiograph, frontal projection, of a patient with a left chest wall mass shown on biopsy to be a Hodgkin’s lymphoma. The profile (arrows) of the extrapleural lesion resembles that of a ‘pregnant woman’.
sign. It referred to the crescent of air – the meniscus – that developed between the hydatid cyst and the host reaction (pericyst) when air dissected between the two. This sign may also be seen with a saprophytic fungus ball (Fig. 9a–c), blood clot in a tuberculous cavity, cavitating carcinoma and invasive aspergillosis.
Pregnant woman sign The profile of an extrapleural lesion, with its sharp convex border, smoothly tapered margins and wide transverse diameter, has been likened to that of a ‘pregnant woman’1 (Fig. 10).
Fig. 9. (a) Meniscus sign. Frontal chest radiograph showing an air crescent (Meniscus sign) in a right upper zone cavity. (b) CT scan image of the same patient as in (a) shows well the solid round lesion lying in the right upper lobe cavity, with a crescent of air surrounding it – the meniscus. (c) CT of the same patient as in (a,b) in the prone position shows mobility of the solid mass within the cavity. This patient had an aspergilloma in an old tuberculous cavity.
Meniscus sign This sign is also known as ‘air cap’, ‘air crescent’ and Monad’s sign.1 It was originally described in the context of a pulmonary hydatid cyst and considered a diagnostic
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Fig. 11. Sail sign. AP chest radiograph of an infant shows the right lobe of a normal thymus resembling a boat’s sail (arrow).
© 2013 The Authors Journal of Medical Imaging and Radiation Oncology © 2013 The Royal Australian and New Zealand College of Radiologists
‘Felson Signs’ revisited
Fig. 12. (a) Silhouette sign. Frontal chest radiograph showing a left upper zone mass causing loss of silhouette of the aortic knuckle, suggesting that the lesion is posteriorly located. The posterior part of the aortic arch actually forms the ‘aortic knuckle’ shadow on the PA chest radiograph as the posterior part is most lateral. (b) CT scan image of the same patient as in (a) shows a mass in the apicoposterior segment of the left upper lobe abutting the aortic knuckle (arrow), replacing what would normally have been air. As air no longer outlines the aortic knuckle, there is a loss of silhouette.
Fig. 13. (a) Negative silhouette sign. A frontal chest radiograph of a patient with an apparent right lung lesion shows that there is no loss of the adjacent mediastinal silhouette. (b) Negative silhouette sign. Ultrasound image of the same patient as in (a), showing an encysted right pleural effusion (located posteriorly) to be the cause of the opacity in the radiograph. A posterior pleural lesion/abnormality will not abut the mediastinum and hence will not cause loss of silhouette.
Sail sign The ‘sail sign’ describes the appearance of the right lobe of the normal thymus in infancy in a frontal chest radiograph and helps to rule out other causes of superior mediastinal widening (Fig. 11).
Silhouette sign When a soft tissue border that is normally outlined by air in the adjacent lung is abutted by soft tissue/fluid, there is a ‘loss of silhouette’ of that particular border.1 This sign is most frequently applied with respect to mediastinal borders and diaphragm, and is helpful in diagnosing collapse of various lung lobes (Fig. 12a,b). The silhouette sign also helps to localise a mediastinal lesion seen on frontal chest radiograph as anterior or posterior mediastinal (Fig. 13a,b).
Fig. 14. Snowman heart. Frontal chest radiograph of a patient with total anomalous pulmonary venous drainage. The mediastinal silhouette has the shape of a snowman, shown in the cartoon at right.
© 2013 The Authors Journal of Medical Imaging and Radiation Oncology © 2013 The Royal Australian and New Zealand College of Radiologists
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Fig. 15. S sign of Golden. Frontal chest radiograph of patient with a right hilar mass illustrates the two curves of the ‘S sign of Golden’. The lower curve (thin arrow) is the mass and the upper curve (thick arrow) is the inferior margin of the collapsed right upper lobe. Please note that the two curves together actually form a ‘reverse S‘.
Fig. 16. Third Mogul. Frontal chest radiograph of a patient with mitral stenosis. The third bump on the left cardiac border (arrow) is due to left atrial appendage enlargement. These bumps resemble the bumps – ‘moguls’ – seen on ski slopes (image at right, arrow).
The cervicothoracic sign and thoracoabdominal signs are also based on the principle of the silhouette sign.
Thoraco-abdominal sign
Snowman heart The configuration of the heart shadow in instances of total anomalous pulmonary venous drainage via a left vertical vein flowing into the left innominate vein resembles the profile of a snowman (Fig. 14), hence the name of this sign. The left upper border of the cardiovascular silhouette is the large vertical vein and the right upper border, the enlarged superior vena cava.
A sharply marginated mediastinal mass visible through the diaphragm on either a chest or an abdominal radiograph implies that it is in contact with air, and therefore must lie at least partly within the thorax. To understand this better, it must be recalled that the posterior basal lung extends more caudally than the anterior basal lung. Convergence of the inferolateral border of the mass towards the spine suggests that the mass is probably entirely intrathoracic (Fig. 17a,b), whereas lack of convergence or divergence indicates a segment silhouetted by the soft tissue density of the abdomen – the thoracoabdominal sign.
S sign of Golden This refers to the particular appearance of a combination of right upper lobe collapse and a central mass causing the obstructive lobar collapse1 (Fig. 15).
The third mogul Classically described for left atrial appendage enlargement, this sign refers to the third bump along the ‘ski slope’ of the left cardiac border, the first and second bumps being the aortic knuckle and a prominent pulmonary artery, respectively (Fig. 16). The ‘third mogul’ may also be seen with double left atrial appendage, cardiac aneurysm, cardiac/pericardial tumour or cyst, coronary artery aneurysm/fistula, corrected transposition, or normal thymus.1
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Vanishing tumour A loculated pleural effusion can simulate a mass in the lung (Fig. 18a,b). However, once the pleural effusion has resolved, follow-up chest radiographs will show that the apparent tumour has ‘vanished’, hence the name of this sign.
Conclusion In this pictorial essay, we have revisited classic chest radiographic signs and endeavoured to reiterate their continuing usefulness in present-day radiologic practice. We hope that our readers, especially new radiologists and radiology residents, will benefit from this review.
© 2013 The Authors Journal of Medical Imaging and Radiation Oncology © 2013 The Royal Australian and New Zealand College of Radiologists
‘Felson Signs’ revisited
Fig. 17. (a) Frontal chest radiograph of a patient shows an apparent mediastinal mass with its border visible through the diaphragm. The infero-lateral border of the mass converges towards the spine, suggesting that it is intrathoracic (negative thoraco-abdominal sign). (b) CT scan image of the same patient as in Figure (a) shows the mass lying in the posterior costophrenic recess, almost entirely outlined by air in the right lower lobe. Hence, the chest radiographic appearance.
© 2013 The Authors Journal of Medical Imaging and Radiation Oncology © 2013 The Royal Australian and New Zealand College of Radiologists
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References 1. Felson B. Chest Roentgenology. W.B. Saunders Co., Philadelphia, 1998. 2. Webb WR, Higgins CB. Consolidation and Atelectasis. Thoracic Imaging: Pulmonary and Cardiovascular Radiology. 2, revised. Lippincott Williams & Wilkins, Philadelphia, 2010; 37. 3. Burgener F, Kormano M, Pudas T. Pulmonary Edema and Symmetrical Bilateral Infiltrates. The Chest X-Ray. 2, illustrated, revised. Thieme, Stuttgart, 2006; 143–56. 4. Parker MS, Chasen MH, Paul N. Radiologic signs in thoracic imaging: case-based review and self-assessment module. AJR Am J Roentgenol 2009; 192 (3 Suppl.): S34–48.
Fig. 18. (a) Chest radiograph of a patient shows an apparent right lung mass, or ‘tumour’. (b) CT scan image of the patient in (a) shows a pleural effusion loculated in the right major fissure, and simple left pleural effusion. When the effusion resolves, the apparent ‘tumour’ disappears, hence the ‘vanishing tumour’ sign.
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© 2013 The Authors Journal of Medical Imaging and Radiation Oncology © 2013 The Royal Australian and New Zealand College of Radiologists
RADIOLO GY —P I C T O R I A L E SSAY
‘Felson Signs’ revisited Phiji Philip George,1 Aparna Irodi,1 Shyamkumar Nidugala Keshava1 and Anthony C Lamont2 1 Department of Radiology, CMC Hospital, Vellore, Tamil Nadu, India; and 2Department of Radiology, Townsville Hospital, Townsville, Queensland, Australia
PP George MD, Radiodiagnosis; A Irodi MD, FRCR; S Nidugala Keshava DNB, FRCR, FRANZCR; AC Lamont FRCR, FRANZCR. Correspondence Dr Phiji Philip George, Department of Radiology, CMC Hospital, Vellore, TN 632004, India. Email: [email protected]
Summary In this article we revisit, with the help of images, those classic signs in chest radiography described by Dr Benjamin Felson himself, or other illustrious radiologists of his time, cited and discussed in ‘Chest Roentgenology’. We briefly describe the causes of the signs, their utility and the differential diagnosis to be considered when each sign is seen. Wherever possible, we use CT images to illustrate the basis of some of these classic radiographic signs. Key words: chest; CT; imaging; radiography; sign.
Conflict of interest: None declared. Submitted 29 July 2012; accepted 21 November 2012. doi:10.1111/1754-9485.12031
Introduction Think ‘chest radiography’ and the name that comes to the mind of any radiologist almost instinctively is Dr Benjamin Felson. Among his many notable achievements is the now classic book – ‘Chest Roentgenology’. Exquisitely described in this book are many radiographic signs. Some were described by Felson and some by others (with appropriate acknowledgements of all contributors). Hence, the title of this article: ‘Felson Signs’, and not ‘Felson’s signs’. In an era before that of cross-sectional imaging, these signs evolved from radiologists’ efforts at interpreting chest radiographic appearances to determine the location, extent and sometimes, the pathologic nature of the abnormality. A combination of simple lab experiments, tomography, personal experience and deductive reasoning was used to explain typical radiographic appearances seen in a wide variety of conditions. Cross-sectional imaging modalities now dominate radiology and the emphasis in teaching has shifted towards them. Therefore radiologists – particularly radiology residents – are less likely than before to appreciate many of these classic signs. By revisiting them we intend to review our knowledge and stress the continuing
64
importance and relevance of these signs in the interpretation of chest radiographs. This pictorial essay illustrates, with the help of CT sections to further elucidate, these classic signs. We briefly discuss the causes, utility and differential diagnoses to be considered for each.
Illustrative cases Air bronchogram This appearance refers to the visibility of air-filled bronchi against a surrounding background of opacified alveoli, whether by fluid or solid matter (Fig. 1). It is essentially diagnostic of alveolar disease,1 and is to be differentiated from bronchiectasis and chronic bronchitis, where bronchi become visible because of their thickened walls.
Bat’s wing or butterfly shadow These names describe the appearance of bilateral, symmetrical infiltration/consolidation in a predominantly central distribution (Fig. 2), with relative sparing of the peripheral, apical and basal portions of the lungs. It was
© 2013 The Authors Journal of Medical Imaging and Radiation Oncology © 2013 The Royal Australian and New Zealand College of Radiologists
‘Felson Signs’ revisited
Fig. 1. A frontal chest radiograph shows an area of consolidation in the right lower zone. Arrows indicate the air bronchogram. A case of right lower lobe pneumonia.
originally described in, and also considered pathognomonic of, uremic pulmonary edema. However, as Felson himself said, ‘it is not even diagnostic of pulmonary edema, . . . It signifies one thing and one thing only: extensive alveolar disease’.1 As such, this appearance can be seen in cardiogenic and noncardiogenic pulmonary edema, pulmonary haemorrhage, infections including pneumocystis carinii pneumonia, pulmonary alveolar proteinosis and even in neoplastic conditions like lymphoma and bronchoalveolar carcinoma.2,3
Black pleura sign
Fig. 3. (a) A frontal chest radiograph shows the ‘black pleura sign’ on the right side (arrows) in a patient with pulmonary alveolar microlithiasis. (b) CT scan of the same patient as in (a), showing the spared pleura (arrows) appearing ‘black’ relative to adjacent involved lung and the ribs.
Seen in pulmonary alveolar microlithiasis, this sign refers to the negative shadow of the pleura between the extensive alveolar calcification and the adjacent rib cage1 (Fig. 3a,b).
Cervicothoracic sign This sign is used to determine whether a superior mediastinal lesion is anterior or posterior. The sign is positive for an anteriorly situated mass, which loses definition above the level of the clavicles as it is silhouetted by the soft tissues of the neck (Fig. 4a,b). ‘The cephalic border of the anterior mediastinum ends at the level of the clavicles, whereas that of the posterior mediastinum extends much higher’.1 The sign is negative for a posteriorly situated mass, which is well defined above the level of the clavicles, as it is sharply outlined by air in the adjacent lung.
Fleischner’s lines
Fig. 2. Chest radiograph, frontal projection, shows bilateral central symmetric perihilar opacities, the outline of which resembles a ‘bat’s wing’. This patient had pneumocystis carinii pneumonia.
These are small and transient, horizontal, band-like opacities commonly seen in the mid and lower zones bilaterally and represent small areas of atelectasis that develop secondary to impaired motion of the diaphragm. Serial chest radiographs show their transient nature and
© 2013 The Authors Journal of Medical Imaging and Radiation Oncology © 2013 The Royal Australian and New Zealand College of Radiologists
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PP George et al.
Fig. 4. (a) Chest radiograph, frontal projection, shows a positive cervicothoracic sign, with the lateral border of the mediastinal mass becoming indistinct (arrow) above the level of the clavicle. (b) CT scan image of the same patient as in (a) at the level of the clavicles shows the lateral border of the anterior mediastinal mass merging with the supraclavicular soft tissues – this is the principle of the cervicothoracic sign.
help differentiate them from post-inflammatory scarring (Fig. 5).
Hampton’s hump This sign was described to help differentiate a pulmonary infarct occurring in a favoured site – the costophrenic
66
angle – from pleural thickening or fluid. The Hampton’s hump is a pleura-based opacity, with a convex border facing the hilum. Pleural thickening or fluid tends to be concave towards the hilum. Figure 6a,b, of a patient with pulmonary embolism and infarction, explains the basis of this sign, but do not represent a true Hampton’s hump.
© 2013 The Authors Journal of Medical Imaging and Radiation Oncology © 2013 The Royal Australian and New Zealand College of Radiologists
‘Felson Signs’ revisited
Fig. 5. Fleischner’s lines. Two serial chest radiographs (taken 4 days apart) of a post-operative patient illustrate the transience of Fleischner’s lines (arrows). (Insets are magnified views of the atelectatic bands.)
Fig. 6. (a) CT scan images of a patient who presented with acute chest pain and dyspnoea show a pulmonary artery embolus (arrow in image at left), and the resulting infarct (image at right). (b) Chest radiograph of the same patient as in (a). The pulmonary infarct is visible as a pleura-based opacity in the right lower zone, with a convex border facing the hilum. A similar opacity placed in the right costophrenic angle would be a true Hampton’s hump.
© 2013 The Authors Journal of Medical Imaging and Radiation Oncology © 2013 The Royal Australian and New Zealand College of Radiologists
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Fig. 7. (a) Hilum convergence sign. Chest radiograph of a patient, with an abnormal bump in the left hilar region. Inset, depicting magnified view of the left hilum, shows the pulmonary artery branches (arrows) converging on, and ending at, the ‘bump’ (white curve), suggesting an enlarged pulmonary artery. This is a ‘negative’ hilum convergence sign. (b) CT scan images of the same patient as in (a) confirm the enlarged pulmonary artery.
Hilum convergence sign It may be difficult to determine if a hilar/juxtahilar opacity is due to a prominent pulmonary artery or juxtahilar mediastinal mass. If pulmonary artery branches are visible through the opacity and converge towards the
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waist of the heart (hilum convergence sign), then the opacity is due to a juxtahilar mediastinal mass. If, however, the pulmonary artery branches lead towards the abnormal ‘bump’, then the opacity is due to an enlarged pulmonary artery (‘negative’ hilum convergence sign)1,4 (Fig. 7a,b).
© 2013 The Authors Journal of Medical Imaging and Radiation Oncology © 2013 The Royal Australian and New Zealand College of Radiologists
‘Felson Signs’ revisited
Fig. 8. (a) Hilum overlay sign. Frontal chest radiograph of a patient shows an apparently enlarged heart. However, the left pulmonary artery (arrow) is seen more than a centimetre within the lateral edge of the mediastinal border, showing that the abnormality is not cardiac. (b) CT scan images of the same patient as in (a), showing the overlap of the left pulmonary artery (arrow) by a mediastinal teratoma.
Hilum overlay sign Useful in differentiating cardiac enlargement from a mediastinal mass, the hilum overlay sign states that if either the right or left pulmonary artery is visible, more than a centimeter within the lateral edge of the mediastinal silhouette, then the lesion is not
cardiac1,4 (Fig. 8a,b). Dr Felson based this sign on the fact that, in more than 98% of the chest radiographs he reviewed, the visible proximal segment of the pulmonary artery was lateral to or just within the cardiac silhouette. Even when the heart is enlarged or there is pericardial effusion, this relationship remains true.
© 2013 The Authors Journal of Medical Imaging and Radiation Oncology © 2013 The Royal Australian and New Zealand College of Radiologists
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Fig. 10. Chest radiograph, frontal projection, of a patient with a left chest wall mass shown on biopsy to be a Hodgkin’s lymphoma. The profile (arrows) of the extrapleural lesion resembles that of a ‘pregnant woman’.
sign. It referred to the crescent of air – the meniscus – that developed between the hydatid cyst and the host reaction (pericyst) when air dissected between the two. This sign may also be seen with a saprophytic fungus ball (Fig. 9a–c), blood clot in a tuberculous cavity, cavitating carcinoma and invasive aspergillosis.
Pregnant woman sign The profile of an extrapleural lesion, with its sharp convex border, smoothly tapered margins and wide transverse diameter, has been likened to that of a ‘pregnant woman’1 (Fig. 10).
Fig. 9. (a) Meniscus sign. Frontal chest radiograph showing an air crescent (Meniscus sign) in a right upper zone cavity. (b) CT scan image of the same patient as in (a) shows well the solid round lesion lying in the right upper lobe cavity, with a crescent of air surrounding it – the meniscus. (c) CT of the same patient as in (a,b) in the prone position shows mobility of the solid mass within the cavity. This patient had an aspergilloma in an old tuberculous cavity.
Meniscus sign This sign is also known as ‘air cap’, ‘air crescent’ and Monad’s sign.1 It was originally described in the context of a pulmonary hydatid cyst and considered a diagnostic
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Fig. 11. Sail sign. AP chest radiograph of an infant shows the right lobe of a normal thymus resembling a boat’s sail (arrow).
© 2013 The Authors Journal of Medical Imaging and Radiation Oncology © 2013 The Royal Australian and New Zealand College of Radiologists
‘Felson Signs’ revisited
Fig. 12. (a) Silhouette sign. Frontal chest radiograph showing a left upper zone mass causing loss of silhouette of the aortic knuckle, suggesting that the lesion is posteriorly located. The posterior part of the aortic arch actually forms the ‘aortic knuckle’ shadow on the PA chest radiograph as the posterior part is most lateral. (b) CT scan image of the same patient as in (a) shows a mass in the apicoposterior segment of the left upper lobe abutting the aortic knuckle (arrow), replacing what would normally have been air. As air no longer outlines the aortic knuckle, there is a loss of silhouette.
Fig. 13. (a) Negative silhouette sign. A frontal chest radiograph of a patient with an apparent right lung lesion shows that there is no loss of the adjacent mediastinal silhouette. (b) Negative silhouette sign. Ultrasound image of the same patient as in (a), showing an encysted right pleural effusion (located posteriorly) to be the cause of the opacity in the radiograph. A posterior pleural lesion/abnormality will not abut the mediastinum and hence will not cause loss of silhouette.
Sail sign The ‘sail sign’ describes the appearance of the right lobe of the normal thymus in infancy in a frontal chest radiograph and helps to rule out other causes of superior mediastinal widening (Fig. 11).
Silhouette sign When a soft tissue border that is normally outlined by air in the adjacent lung is abutted by soft tissue/fluid, there is a ‘loss of silhouette’ of that particular border.1 This sign is most frequently applied with respect to mediastinal borders and diaphragm, and is helpful in diagnosing collapse of various lung lobes (Fig. 12a,b). The silhouette sign also helps to localise a mediastinal lesion seen on frontal chest radiograph as anterior or posterior mediastinal (Fig. 13a,b).
Fig. 14. Snowman heart. Frontal chest radiograph of a patient with total anomalous pulmonary venous drainage. The mediastinal silhouette has the shape of a snowman, shown in the cartoon at right.
© 2013 The Authors Journal of Medical Imaging and Radiation Oncology © 2013 The Royal Australian and New Zealand College of Radiologists
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Fig. 15. S sign of Golden. Frontal chest radiograph of patient with a right hilar mass illustrates the two curves of the ‘S sign of Golden’. The lower curve (thin arrow) is the mass and the upper curve (thick arrow) is the inferior margin of the collapsed right upper lobe. Please note that the two curves together actually form a ‘reverse S‘.
Fig. 16. Third Mogul. Frontal chest radiograph of a patient with mitral stenosis. The third bump on the left cardiac border (arrow) is due to left atrial appendage enlargement. These bumps resemble the bumps – ‘moguls’ – seen on ski slopes (image at right, arrow).
The cervicothoracic sign and thoracoabdominal signs are also based on the principle of the silhouette sign.
Thoraco-abdominal sign
Snowman heart The configuration of the heart shadow in instances of total anomalous pulmonary venous drainage via a left vertical vein flowing into the left innominate vein resembles the profile of a snowman (Fig. 14), hence the name of this sign. The left upper border of the cardiovascular silhouette is the large vertical vein and the right upper border, the enlarged superior vena cava.
A sharply marginated mediastinal mass visible through the diaphragm on either a chest or an abdominal radiograph implies that it is in contact with air, and therefore must lie at least partly within the thorax. To understand this better, it must be recalled that the posterior basal lung extends more caudally than the anterior basal lung. Convergence of the inferolateral border of the mass towards the spine suggests that the mass is probably entirely intrathoracic (Fig. 17a,b), whereas lack of convergence or divergence indicates a segment silhouetted by the soft tissue density of the abdomen – the thoracoabdominal sign.
S sign of Golden This refers to the particular appearance of a combination of right upper lobe collapse and a central mass causing the obstructive lobar collapse1 (Fig. 15).
The third mogul Classically described for left atrial appendage enlargement, this sign refers to the third bump along the ‘ski slope’ of the left cardiac border, the first and second bumps being the aortic knuckle and a prominent pulmonary artery, respectively (Fig. 16). The ‘third mogul’ may also be seen with double left atrial appendage, cardiac aneurysm, cardiac/pericardial tumour or cyst, coronary artery aneurysm/fistula, corrected transposition, or normal thymus.1
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Vanishing tumour A loculated pleural effusion can simulate a mass in the lung (Fig. 18a,b). However, once the pleural effusion has resolved, follow-up chest radiographs will show that the apparent tumour has ‘vanished’, hence the name of this sign.
Conclusion In this pictorial essay, we have revisited classic chest radiographic signs and endeavoured to reiterate their continuing usefulness in present-day radiologic practice. We hope that our readers, especially new radiologists and radiology residents, will benefit from this review.
© 2013 The Authors Journal of Medical Imaging and Radiation Oncology © 2013 The Royal Australian and New Zealand College of Radiologists
‘Felson Signs’ revisited
Fig. 17. (a) Frontal chest radiograph of a patient shows an apparent mediastinal mass with its border visible through the diaphragm. The infero-lateral border of the mass converges towards the spine, suggesting that it is intrathoracic (negative thoraco-abdominal sign). (b) CT scan image of the same patient as in Figure (a) shows the mass lying in the posterior costophrenic recess, almost entirely outlined by air in the right lower lobe. Hence, the chest radiographic appearance.
© 2013 The Authors Journal of Medical Imaging and Radiation Oncology © 2013 The Royal Australian and New Zealand College of Radiologists
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PP George et al.
References 1. Felson B. Chest Roentgenology. W.B. Saunders Co., Philadelphia, 1998. 2. Webb WR, Higgins CB. Consolidation and Atelectasis. Thoracic Imaging: Pulmonary and Cardiovascular Radiology. 2, revised. Lippincott Williams & Wilkins, Philadelphia, 2010; 37. 3. Burgener F, Kormano M, Pudas T. Pulmonary Edema and Symmetrical Bilateral Infiltrates. The Chest X-Ray. 2, illustrated, revised. Thieme, Stuttgart, 2006; 143–56. 4. Parker MS, Chasen MH, Paul N. Radiologic signs in thoracic imaging: case-based review and self-assessment module. AJR Am J Roentgenol 2009; 192 (3 Suppl.): S34–48.
Fig. 18. (a) Chest radiograph of a patient shows an apparent right lung mass, or ‘tumour’. (b) CT scan image of the patient in (a) shows a pleural effusion loculated in the right major fissure, and simple left pleural effusion. When the effusion resolves, the apparent ‘tumour’ disappears, hence the ‘vanishing tumour’ sign.
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© 2013 The Authors Journal of Medical Imaging and Radiation Oncology © 2013 The Royal Australian and New Zealand College of Radiologists
