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The ultrasound appearance of asbestos-related pleural plaques
ClinicalRadiology (1991) 44, 413-416
The Ultrasound Appearance of Asbestos-Related Pleural Plaques R. A. M O R G A N , F. E. P I C K W O R T H , P. A. DUBBINS* and C. R. McGAVIN1-
Department of Radiology, Derriford Hospital, Department of*Ultrasound and tChest Clinic, Freedom Fields Hospital, Plymouth Twenty-five patients with a history of asbestos exposure and radiological evidence of pleural plaques were examined by ultrasound (US). Non-calcified pleural plaque appeared as a regular area of echo-poor tissue which was well defined adjacent to the diaphragm or lateral chest wall, and varied in thickness from 5 mm to 12 mm. Calcified plaques had echogenic and irregular anterior margins with acoustic shadowing beyond. They were associated with characteristic comet tail and straight line artefact. Morgan, R.A., Pickworth, F.E., Dubbins, P.A. & McGavin, C.R~ (1991). Clinical Radiology 44, 413-416. The Ultrasound Appearance of Asbestos-Related Pleural Plaques
The association between asbestos and pleuro-pulmonary disease is well known. Pleural plaques are frequently found in patients living in dockyard towns. They are not themselves premalignant but are a marker of previous exposure to asbestos and indicate risk of morbidity from other asbestos-related diseases (Harber et al., 1987). Diaphragmatic pleural plaques are often visualized during abdominal ultrasound (US) scanning as an incidental finding in our hospitals. Operators in US unfamiliar with their appearance may mistake them for pathological masses. The US appearances of asbestosrelated pleural plaques have not previously been described. This report presents the US findings in 25 patients with radiological evidence of pleural plaques. PATIENTS AND M E T H O D S A study was performed on 25 patients recruited from the Plymouth Chest Clinic. All had documented exposure to asbestos and had characteristic pleural plaque (either chest wall, diaphragmatic or both) on their PA chest radiograph, but no evidence of other asbestos-related disease, or of other pulmonary or pleural pathology. All patients were examined by one of two radiologists with an Acuson 128 machine using 3 M H z sector and 5 M H z or 7 MHz linear array transducers. Examination of the diaphragmatic pleura was performed with the patient in the supine position. A 3 M H z sector transducer was used, scanning in the parasaggital plane in the subcostal region during deep inspiration. The sound beam was directed upwards through the liver and spleen using these organs as acoustic windows, so that the sound beam was perpendicular to the diaphragm. Where there was chest wall plaque on the chest radiograph, scans were also performed of the chest wall using a linear array 5 MHz transducer aligned between the ribs along the axis of the intercostal space. Scans of the chest wall were performed during quiet respiration so that the interface between the lung and pleura could be localized. Occasionally scans were also performed in the sagittal plane.
Correspondence to: R. A. Morgan, Department of Radiology, Derriford Hospital, Plymouth.
During chest wall scanning the supine oblique position was adopted with the arm abducted. Alternatively, scans were performed with the patient in the sitting position with the arm behind the head, so that the intercostal spaces were widened, thereby improving access. The position adopted depended upon the location of the plaque, ease of localization and patient comfort.
RESULTS Twenty-five patients were examined. Pleural plaque could be identified with US both adjacent to the chest wall but more particularly in the juxta-diaphragmatic location. Juxta-hepatic plaque was more easily visualized than juxta-splenic plaque. The appearances were largely dependent on the presence or absence of calcification. Non-calcified Plaque Non-calcified plaque in both chest wall and juxtadiaphragmatic locations was hypoechoic with an echogenie surface. It was well defined with smooth, even contours.
Chest wall Small chest wall plaques were elliptical in shape (Fig. 1). More extensive chest wall plaque appeared as an additional layer deep to the intercostal muscles (Fig. 2). Chest wall plaque was echo-poor relative to the neighbouring muscles. Plaque was based on the parietal, as opposed to the visceral, pleura. This was confirmed by scanning during quiet respiration when the plaque, stationary on the parietal pleura, was easily delineated from the mobile lung and its reverberation shadow.
D~phragm Diaphragmatic plaque was recognized as thickening of the normally thin diaphragmatic layer, typically visualized immediately superior to the liver on US scans (Fig. 3). When present, the mirror image layer (Lewandowski and Winsburg, 1983) was also correspondingly thickened. Plaque thickness was 5-12 mm (mean 8.5 mm).
414
CLINICAL RADIOLOGY
Calcified Pleural Plaques Calcified plaques in both locations had the following characteristics: echogenic anterior margins with acoustic shadowing beyond; irregular margins in contrast to the smooth outline of non-calcified plaque. Diaphragmatic calcified plaque had additional characteristics: comet tail or ring down artefact (Fig. 4); straight line artefactual echoes at right angles to the sound beam directed away from the plaque (Fig. 5). Comet tail artefact was more c o m m o n than the straight line artefact. In both locations, when the plaque was heavily calcified it was difficult to visualize. In one case the thickened calcified juxta-hepatic plaque distorted liver shape, simulating hepatic pathology (Fig. 6). DISCUSSION The pleura is one of the main target organs for asbestos. Either isolated plaques or diffuse pleural thickening may occur_ The association between asbestos and pleural disease was first reported in a study of talc workers
(b)
le layer
Pleura plaque
J
Reverberation shadow
Lung
(c) (a)
Fig. 1 - (a) Smooth chest wall non-calcified pleural plaque. (b) and (e) Ultrasound appearances and diagrammatic representation.
415
US APPEARANCEOF ASBESTOS-RELATEDPLEURAL PLAQUES
(a)
Pleural layer+ plaque
~
Liver
Mirror imageartefact
(a)
Fat Lung
~
"
"
Musclelayer
Parietal pleura
Thick plaque -
-
Visceralpleura
/
v [ ~ Acousticshadow (b)
__
Reverberation shadow
Fig. 3 (a) Longitudinal scan and (b) diagrammatic representation showing juxta-hepatic diaphragmatic plaque with a small area of calcification.
Lung
(~) Fig. 2 Smoothnon-calcifiedchest wall plaque. (a) Ultrasound appearances and (b) diagrammatic representation.
in the 1940s (Porro et al., 1942; Siegal et al., 1943). Workers with a history of exposure to asbestos and radiological evidence of pleural plaque can claim compensation through the courts approximately £1000 (Seaton, 1990). The first report of the use of US in the chest was by Pell (1964) on a patient with massive pleural effusion. During sonography of the normal chest wall the pleura is too thin to be seen. The US appearance of the normal right hemidiaphragm has been stated to consist of three lines in 80% of patients, forming two layers (Lewandowski and Winsberg, 1983). The inferior layer represents the liver capsule, diaphragm and pleural cavity, while the superior layer represents a mirror image artefact_
Fig. 4 - Longitudinal sgan through the liver showing comet tail artefact (arrow) associated with calcified plaque.
416
CLINICAL RADIOLOGY
Fig. 5 - Longitudinal scan through spleen (S) showing straight line artefact (arrow) associated with calcified plaque.
further study, two fibrous benign plaques were also echogenic ( F a t a a r , 1988). In neither study was asbestos i m p l i c a t e d as an etiological factor, n o r was there evidence o f calcification within the plaques, either r a d i o l o g i c a l or on US. I n all the patients in this study, pleural p l a q u e was h y p o e c h o i c c o m p a r e d to the liver, spleen a n d intercostal muscles. Non-calcified p l a q u e was well defined, straight in outline, elliptical a n d arising f r o m the p a r i e t a l pleura. T h e U S a p p e a r a n c e o f small calcified d i a p h r a g m a t i c p l a q u e s was characteristic. T h e c o m e t tail artefact a n d the straight line artefact were seen in no o t h e r types o f plaque. Small calcified plaques were irregular, in c o n t r a s t to the s m o o t h outlines o f non-calcified plaque. W e have described the U S characteristics o f asbestos related pleural plaques in o r d e r to aid in the correct identification o f pleural based masses. P l e u r a l p l a q u e in some cases, if sufficiently thick, can actually d i s t o r t the liver or spleen causing altered shape a n d m i m i c k i n g p a t h o l o g y . R e c o g n i t i o n o f this artefact by s o n o g r a p h e r s , p a r t i c u l a r l y in an at-risk p o p u l a t i o n , will allow p r o p e r i n t e r p r e t a t i o n o f U S a p p e a r a n c e s . F u r t h e r m o r e , identific a t i o n o f these features o f pleural p l a q u e in a patient p r e s e n t i n g for u p p e r a b d o m i n a l u l t r a s o u n d for a n o t h e r cause s h o u l d p r o m p t an enquiry into h i s t o r y o f possible asbestos exposure.
Acknowledgements. We are grateful to Karen Creed for the typing and to Sallie Waring and Trevor McCausland for their work in Medical Photography.
REFERENCES
Fig. 6 Longitudinal scan through the liver demonstrating large irregular calcified plaque, with comet tail (arrowhead) and straight line (arrow) artefact, causing hepatic distortion and mimicking hepatic pathology Several studies have d e s c r i b e d the s o n o g r a p h i c a p p e a r ances o f p l e u r a l - b a s e d masses b u t there are n 9 r e p o r t s o f the s o n o g r a p h i c a p p e a r a n c e o f pleural plaques caused by asbestos. In one s t u d y o f 56 patients with pleural opacities, 13 p a t i e n t s h a d pleural fibrous plaques, o f which three were echo free a n d 10 were echogenic with m u l t i p l e internal echoes ( I c h i k a w a et al., 1985). I n a
Fataar, S (1988). Ultrasound in chest diseases. 1. Pleura. Australasian Radiology, 32, 295 301. Harber, P, Mohsenifar, Z, Oren, A & Lew, M (1987). Pleural plaques and asbestos-associated malignancy. Journal of Occupational Medicine, 29, 641-644. Ichikawa, Y, Mitutake, Y, Hayashi, S, Yano, T, Fujino, K, Matsumato, T et al. (1985). The observation of pleural opacities by B mode ultrasonogram. Kurome Medical Journal, 32, 141 146. Lewandowski, BJ & Winsberg, F (1983). Echographic appearance of the right hemidiaphragm. Journal of Ultrasound Medicine, 2, 243-249. Pell, RL (1964). Ultrasound for routine clinical investigations. Ultrasonics, 2, 87. Porro, FW, Patton, JR & Hobbs, AA (1942). Pneumoconiosis in the talc industry. American Journal of Radiology, 47, 507 524. Seaton, A (1990). Asbestos disease and compensation-by way of advising patients to sue. British Medical Journal, 301, 453-454. Siegal, W, Smith, AR & Greenburg, L (1943). The dust hazard in tremolite talc mining, including roentgenologic findings in talc mining_ Ameriean Journal of Radiology, 49, 11 29.
The Ultrasound Appearance of Asbestos-Related Pleural Plaques R. A. M O R G A N , F. E. P I C K W O R T H , P. A. DUBBINS* and C. R. McGAVIN1-
Department of Radiology, Derriford Hospital, Department of*Ultrasound and tChest Clinic, Freedom Fields Hospital, Plymouth Twenty-five patients with a history of asbestos exposure and radiological evidence of pleural plaques were examined by ultrasound (US). Non-calcified pleural plaque appeared as a regular area of echo-poor tissue which was well defined adjacent to the diaphragm or lateral chest wall, and varied in thickness from 5 mm to 12 mm. Calcified plaques had echogenic and irregular anterior margins with acoustic shadowing beyond. They were associated with characteristic comet tail and straight line artefact. Morgan, R.A., Pickworth, F.E., Dubbins, P.A. & McGavin, C.R~ (1991). Clinical Radiology 44, 413-416. The Ultrasound Appearance of Asbestos-Related Pleural Plaques
The association between asbestos and pleuro-pulmonary disease is well known. Pleural plaques are frequently found in patients living in dockyard towns. They are not themselves premalignant but are a marker of previous exposure to asbestos and indicate risk of morbidity from other asbestos-related diseases (Harber et al., 1987). Diaphragmatic pleural plaques are often visualized during abdominal ultrasound (US) scanning as an incidental finding in our hospitals. Operators in US unfamiliar with their appearance may mistake them for pathological masses. The US appearances of asbestosrelated pleural plaques have not previously been described. This report presents the US findings in 25 patients with radiological evidence of pleural plaques. PATIENTS AND M E T H O D S A study was performed on 25 patients recruited from the Plymouth Chest Clinic. All had documented exposure to asbestos and had characteristic pleural plaque (either chest wall, diaphragmatic or both) on their PA chest radiograph, but no evidence of other asbestos-related disease, or of other pulmonary or pleural pathology. All patients were examined by one of two radiologists with an Acuson 128 machine using 3 M H z sector and 5 M H z or 7 MHz linear array transducers. Examination of the diaphragmatic pleura was performed with the patient in the supine position. A 3 M H z sector transducer was used, scanning in the parasaggital plane in the subcostal region during deep inspiration. The sound beam was directed upwards through the liver and spleen using these organs as acoustic windows, so that the sound beam was perpendicular to the diaphragm. Where there was chest wall plaque on the chest radiograph, scans were also performed of the chest wall using a linear array 5 MHz transducer aligned between the ribs along the axis of the intercostal space. Scans of the chest wall were performed during quiet respiration so that the interface between the lung and pleura could be localized. Occasionally scans were also performed in the sagittal plane.
Correspondence to: R. A. Morgan, Department of Radiology, Derriford Hospital, Plymouth.
During chest wall scanning the supine oblique position was adopted with the arm abducted. Alternatively, scans were performed with the patient in the sitting position with the arm behind the head, so that the intercostal spaces were widened, thereby improving access. The position adopted depended upon the location of the plaque, ease of localization and patient comfort.
RESULTS Twenty-five patients were examined. Pleural plaque could be identified with US both adjacent to the chest wall but more particularly in the juxta-diaphragmatic location. Juxta-hepatic plaque was more easily visualized than juxta-splenic plaque. The appearances were largely dependent on the presence or absence of calcification. Non-calcified Plaque Non-calcified plaque in both chest wall and juxtadiaphragmatic locations was hypoechoic with an echogenie surface. It was well defined with smooth, even contours.
Chest wall Small chest wall plaques were elliptical in shape (Fig. 1). More extensive chest wall plaque appeared as an additional layer deep to the intercostal muscles (Fig. 2). Chest wall plaque was echo-poor relative to the neighbouring muscles. Plaque was based on the parietal, as opposed to the visceral, pleura. This was confirmed by scanning during quiet respiration when the plaque, stationary on the parietal pleura, was easily delineated from the mobile lung and its reverberation shadow.
D~phragm Diaphragmatic plaque was recognized as thickening of the normally thin diaphragmatic layer, typically visualized immediately superior to the liver on US scans (Fig. 3). When present, the mirror image layer (Lewandowski and Winsburg, 1983) was also correspondingly thickened. Plaque thickness was 5-12 mm (mean 8.5 mm).
414
CLINICAL RADIOLOGY
Calcified Pleural Plaques Calcified plaques in both locations had the following characteristics: echogenic anterior margins with acoustic shadowing beyond; irregular margins in contrast to the smooth outline of non-calcified plaque. Diaphragmatic calcified plaque had additional characteristics: comet tail or ring down artefact (Fig. 4); straight line artefactual echoes at right angles to the sound beam directed away from the plaque (Fig. 5). Comet tail artefact was more c o m m o n than the straight line artefact. In both locations, when the plaque was heavily calcified it was difficult to visualize. In one case the thickened calcified juxta-hepatic plaque distorted liver shape, simulating hepatic pathology (Fig. 6). DISCUSSION The pleura is one of the main target organs for asbestos. Either isolated plaques or diffuse pleural thickening may occur_ The association between asbestos and pleural disease was first reported in a study of talc workers
(b)
le layer
Pleura plaque
J
Reverberation shadow
Lung
(c) (a)
Fig. 1 - (a) Smooth chest wall non-calcified pleural plaque. (b) and (e) Ultrasound appearances and diagrammatic representation.
415
US APPEARANCEOF ASBESTOS-RELATEDPLEURAL PLAQUES
(a)
Pleural layer+ plaque
~
Liver
Mirror imageartefact
(a)
Fat Lung
~
"
"
Musclelayer
Parietal pleura
Thick plaque -
-
Visceralpleura
/
v [ ~ Acousticshadow (b)
__
Reverberation shadow
Fig. 3 (a) Longitudinal scan and (b) diagrammatic representation showing juxta-hepatic diaphragmatic plaque with a small area of calcification.
Lung
(~) Fig. 2 Smoothnon-calcifiedchest wall plaque. (a) Ultrasound appearances and (b) diagrammatic representation.
in the 1940s (Porro et al., 1942; Siegal et al., 1943). Workers with a history of exposure to asbestos and radiological evidence of pleural plaque can claim compensation through the courts approximately £1000 (Seaton, 1990). The first report of the use of US in the chest was by Pell (1964) on a patient with massive pleural effusion. During sonography of the normal chest wall the pleura is too thin to be seen. The US appearance of the normal right hemidiaphragm has been stated to consist of three lines in 80% of patients, forming two layers (Lewandowski and Winsberg, 1983). The inferior layer represents the liver capsule, diaphragm and pleural cavity, while the superior layer represents a mirror image artefact_
Fig. 4 - Longitudinal sgan through the liver showing comet tail artefact (arrow) associated with calcified plaque.
416
CLINICAL RADIOLOGY
Fig. 5 - Longitudinal scan through spleen (S) showing straight line artefact (arrow) associated with calcified plaque.
further study, two fibrous benign plaques were also echogenic ( F a t a a r , 1988). In neither study was asbestos i m p l i c a t e d as an etiological factor, n o r was there evidence o f calcification within the plaques, either r a d i o l o g i c a l or on US. I n all the patients in this study, pleural p l a q u e was h y p o e c h o i c c o m p a r e d to the liver, spleen a n d intercostal muscles. Non-calcified p l a q u e was well defined, straight in outline, elliptical a n d arising f r o m the p a r i e t a l pleura. T h e U S a p p e a r a n c e o f small calcified d i a p h r a g m a t i c p l a q u e s was characteristic. T h e c o m e t tail artefact a n d the straight line artefact were seen in no o t h e r types o f plaque. Small calcified plaques were irregular, in c o n t r a s t to the s m o o t h outlines o f non-calcified plaque. W e have described the U S characteristics o f asbestos related pleural plaques in o r d e r to aid in the correct identification o f pleural based masses. P l e u r a l p l a q u e in some cases, if sufficiently thick, can actually d i s t o r t the liver or spleen causing altered shape a n d m i m i c k i n g p a t h o l o g y . R e c o g n i t i o n o f this artefact by s o n o g r a p h e r s , p a r t i c u l a r l y in an at-risk p o p u l a t i o n , will allow p r o p e r i n t e r p r e t a t i o n o f U S a p p e a r a n c e s . F u r t h e r m o r e , identific a t i o n o f these features o f pleural p l a q u e in a patient p r e s e n t i n g for u p p e r a b d o m i n a l u l t r a s o u n d for a n o t h e r cause s h o u l d p r o m p t an enquiry into h i s t o r y o f possible asbestos exposure.
Acknowledgements. We are grateful to Karen Creed for the typing and to Sallie Waring and Trevor McCausland for their work in Medical Photography.
REFERENCES
Fig. 6 Longitudinal scan through the liver demonstrating large irregular calcified plaque, with comet tail (arrowhead) and straight line (arrow) artefact, causing hepatic distortion and mimicking hepatic pathology Several studies have d e s c r i b e d the s o n o g r a p h i c a p p e a r ances o f p l e u r a l - b a s e d masses b u t there are n 9 r e p o r t s o f the s o n o g r a p h i c a p p e a r a n c e o f pleural plaques caused by asbestos. In one s t u d y o f 56 patients with pleural opacities, 13 p a t i e n t s h a d pleural fibrous plaques, o f which three were echo free a n d 10 were echogenic with m u l t i p l e internal echoes ( I c h i k a w a et al., 1985). I n a
Fataar, S (1988). Ultrasound in chest diseases. 1. Pleura. Australasian Radiology, 32, 295 301. Harber, P, Mohsenifar, Z, Oren, A & Lew, M (1987). Pleural plaques and asbestos-associated malignancy. Journal of Occupational Medicine, 29, 641-644. Ichikawa, Y, Mitutake, Y, Hayashi, S, Yano, T, Fujino, K, Matsumato, T et al. (1985). The observation of pleural opacities by B mode ultrasonogram. Kurome Medical Journal, 32, 141 146. Lewandowski, BJ & Winsberg, F (1983). Echographic appearance of the right hemidiaphragm. Journal of Ultrasound Medicine, 2, 243-249. Pell, RL (1964). Ultrasound for routine clinical investigations. Ultrasonics, 2, 87. Porro, FW, Patton, JR & Hobbs, AA (1942). Pneumoconiosis in the talc industry. American Journal of Radiology, 47, 507 524. Seaton, A (1990). Asbestos disease and compensation-by way of advising patients to sue. British Medical Journal, 301, 453-454. Siegal, W, Smith, AR & Greenburg, L (1943). The dust hazard in tremolite talc mining, including roentgenologic findings in talc mining_ Ameriean Journal of Radiology, 49, 11 29.