Clinical Radiology (1990) 41, 86 91
Computed Tomography of Folded Lung P. M. C A R V A L H O and D. H. C A R R
Department o f Diagnostic Radiology, The Brompton Hospital, Fulham Road, London S W 3
Computed tomography (CT) scans of 22 examples of folded lung in nine patients were reviewed. The most important CT criteria of folded lung are the presence of vessels and bronchi running in a smooth curvilinear fashion towards a peripheral mass with an ill defined central edge associated with pleural thickening. These features were seen in all 22 examples. The lesions are frequently multiple (eight out of nine patients). When these features are present the diagnosis can be made without recourse to biopsy or thoracotomy. Enhancement with intravenous contrast medium is unnecessary and does not provide any extra useful information. Various other previously described criteria such as air bronchograms are not necessary for the diagnosis.
The folded lung syndrome was first described by Blesovsky (1966) who presented three cases of peripheral pulmonary mass lesions which were initially diagnosed as bronchial neoplasms and at thoracotomy were found to represent benign lesions. Since then there have been several studies (Hanke and Kretzschmar, 1980; Schneider et al., 1980; Mintzer et al., 1981; Payne et al., 1980) on the plain radiographic and tomographic appearances of this condition which has gone undei~ several synonyms (Blesovsky's Syndrome, pulmonary pseudotumours, round atelectasis). Tylen and Nylssen (1982) described the CT appearances of folded lung in twelve patients and stressed asbestos as a causative factor, but indicated that thoracotomy was still necessary in some cases in excluding neoplastic lesions. Doyle and Lawler (1984) established eight major criteria for the CT diagnosis of folded lung in a study in three patients, but stated that needle biopsy was still reassuring in helping to exclude neoplasms. More recently Taylor (1988), in a study with three patients found that folded lung enhances with intravenous contrast medium, but believed that this does not help in differentiating it from neoplastic lesions.
METHODS Nine patients with folded lung examined by CT over a 4 year period were identified from the patient records. All of the patients bar one were examined because of a mass or masses visible on the chest radiograph which were regarded as suspicious of malignancy. One patient was examined because of increasing left basal pleural thickening together with a clinical suspicion of a mesothelioma. Ten millimetre contiguous slices were performed on an E L S C I N T 2002 scanner. Scans were examined at both lung and mediastinal window settings. In two patients, in whom interstitial lung disease was suspected, 3 mm high
Correspondence to: Dr P. Carvalho, Department of Diagnostic Radiology, The Brompton Hospital, Fulham Road, London SW3.
resolution scans with bone algorithm reconstruction were also performed. Two patients were examined with dynamic i.v. contrast enhancement using 100 ml of Iohexol (Omnipaque 300, Nycomed). The diagnosis of folded lung was confirmed by thoracotomy in two patients. One of these one had a coexisting lingular squamous cell carcinoma diagnosed by bronchoscopy; the second patient underwent thoracotomy because the benign nature of the lesion was not recognised pre-operatively, a fine needle biopsy was inconclusive and a neoplastic lesion was suspected. Six patients were followed up for at least two years with no increase in size of the original lesion. One patient has been followed up for 9 months only so far; the radiographic appearances are characteristic and consistent with previous descriptions of folded lung.
RESULT S /
Twenty-two cases of folded lung in nine patients were identified over a 4 year period. Their CT features and their frequency are tabulated in Tables 1 and 2. Features seen in all 22 lesions included a peripheral location (defined as a lesion with its outer edge not more than 2 cm from the pleura), the presence of smoothly curved bronchi and vessels around the lesion and a centrally directed ill-defined or blurred edge to the lesion
Table 1 -Frequency of CT signs in 22 cases of folded lung in nine patients
CT signs The mass has a peripheral site Curved vessels and bronchi directed towards mass The mass has a centrally directed (towards the hilum) indistinct margin Mass incompletelysurrounded by lung Air bronchogramwithin mass The mass forms an acute angle with the pleura The mass has at least two sharp margins Spherical mass Wedge or other shaped mass Calcified mass
Number of lesions
Percentage
22
100
22
100
22 19 12
100 86 55
10 8 10 12 8
45 36 45 55 36
Table 2-CT signs in nine patients with folded lung
CT signs
Patients
Percentage
Pleura1 thickening More than 1peripheral lesion Calcified pleural plaques Displaced main bronchi Pleural effusion Pulmonary fibrosis
9 8 5 4 2 2
100 88 55 44 22 22
87
CT OF FOLDED LUNG
(a)
(b)
(e)
(a)
Fig. 1-(a) Chest radiograph showing bilateral lower lobe masses (arrows). CT shows (b) bilateral pleurally based areas of folded lung with (c) a centrally directed indistinct edge and (d) curved vessels and bronchi directed towards them.
(a)
(b)
Fig. 2 - (a) Bilateral midzone masses (arrows), in a 49-year-old male. (b) On CT the right upper lobe mass is lenticular, not pleurally based, has no air bronchograms, but does have vessels and bronchi curving towards it and has a centrally directed indistinct edge.
88
CLINICAL RADIOLOGY
(a)
(b)
(Figs 1-6). In all patients there was at least a moderate degree of pleural thickening in the ipsilateral lung. Other features frequently but not invariably seen included an air bronchogram within or at the periphery of the lesion (Fig. 3b) and at least two sharp margins to the lesion. These features were seen in 55% and 36% of the lesions respectively. Wide window settings (around C -400 U W 1400 U) were particularly useful in demonstrating the smoothly curved bronchi and vessels and the air bronchograms. Folded lung may calcify and abut calcified pleural plaques (Fig. 4). The shape of the folded lung was roughly spherical (Fig. le) in 10/22 lesions (45%), and of a wedge (Fig. 5b), lentiform or irregular shape (Fig. 4) in 12/22. Six of nine patients (66%) had a firm occupational history of asbestos exposure and all had CT evidence of pleural calcification. Of the three patlents without evidence of asbestos exposure, one developed folded lung following Dressler's syndrome related to cardiac surgery. Fifteen lesions (68%) were in the lower lobes, six (27%) occurred in the anterior segments of the upper lobes and one was in the middle lobe. Lesions were often multiple (8/9 patients) with the additional sites of folded lung revealed by CT often not being visible on the chest radiograph. The two patients who received intravenous contrast medium both showed homogenous enhancement of the folded lung, confirming the findings of Taylor (1988) but this feature did not help in the differentiation from neoplastic lesions. Serial CT scans were available for three patients, with intervals of 4 years, 2 years and 8 months respectively. No increase in size was seen within these time periods (Figs 3 and 4). In two patients the lesions were stable and in one, there was a decrease in size after a two year interval (Fig. 4). In two patients additional sites of folded lung developed several years after the original lesions. The interval was 3 years in case 5 and 6 years in case 3. Thin section scans performed on two patients suspected of having interstitial lung disease demonstrated both thickening of some bronchial walls as they approached the folded lung and air bronchograms (Fig. 3) rather better than did 10 mm sections, but did not provide any other additional diagnostic features in these two patients.
DISCUSSION
(e) Fig. 3-(a) Chest radiograph showing left pleural thickening. (b) CT demonstrates folded lung with air bronchograms. (e) HRCT 4 years later shows no increase in size, but does demonstrate some peribronchial thickening near the lesions.
Doyle and Lawler (1984) described eight major CT signs of folded lung. 1 A rounded peripheral lung mass never completely surrounded by lung. 2 A mass which is most dense at its periphery. 3 A mass which forms an acute angle with the pleura. 4 Pleural thickening. 5 Vessels and bronchi which curve towards the mass. 6 At least two sharp margins. 7 A blurred centrally directed edge. 8 An air bronchogram. All these criteria were present in their patients. However, several of these features, including air bronchograms, a round shape, an acute angle with the pleura and incomplete surrounding of the lesion by lung were absent in many of our cases (Figs 2-4). It is important to be aware that all the described signs are not invariably present and their absence should not result in needle biopsy, which often provides scanty inconclusive tissue;
89
CT OF FOLDED LUNG
(a)
(b)
(c)
(d)
Fig. 4 - (a) Bilateral midzone masses (arrows) on the chest radiograph of a 52-year-old male with asbestosis. (b, c) CT demonstrates folded lung in the anterior segments of both upper lobes. These lesions are irregular and have adjacent curved bronchovascular structures. (d) Two years later the left upper lobe lesion is smaller.
(a)
(b)
Fig. 5 - (a) Bilateral midzone masses (arrows) on the chest radiograph of a 76-year-old male. (b) CT shows the right midzone mass as a wedge shaped arec of folded lung abutting a calcified pleural plaque. Another lesion is present in the left lower lobe.
90
CLINICAL RADIOLOGY
(a)
(b)
(c)
(d)
(e) Fig. 6-(a) Chest radiograph showing a left pleural effusion with a left lower lobe mass (arrow). c T shows (b, c) two areas of folded lung, with (d, e) a left pleural effusion and pleural thickening.
indeed in one study (Tylen and Nylssen, 1984), out of six needle biopsies performed in patients subsequently found to have folded lung, five yielded undiagnostic material and one case was erroneously diagnosed as a malignancy. As asbestos exposure predisposes to both bronchial
carcinoma (Selikoff, 1977) and folded lung (Mintzer et al., 1982), the two conditions may occur together, as in case 1, and the recognition of folded lung is also important in allowing potentially curative surgery. It has been suggested that high resolution CT is helpful
CT OF FOLDED LUNG
in differentiating pleural plaques in the oblique or accessory fissures from indeterminate lung nodules (LynCh et al., 1989). We have not found this necessary and have found it easy to identify fissural plaques on conventional 10 mm scans using the following criteria. Firstly they can be seen to follow the fissure in contiguous sections and secondly because of the obliquity of the fissures concerned, partial volume effect causes the fissural plaques to be of low density compared to other solid lung structures. Two main theories exist concerning the cause of folded lung. Hanke and Kretzschmar (1980) postulated that these lesions occur secondary to pleural effusions causing passive atelectasis of the underlying lung which then adheres to parietal pleura, and as the effusion recedes and the central atelectatic lung re-expands the peripheral collapsed adherent lung cannot re-expand and folds into a ball. Tylen and Nilsson (1984) have suggested that peripheral pleural fibrous contracture is the primary cause: in favour of this theory was the frequent occurrence of pleural plaques and parenchymal fibrosis in their series of 12 patients. These authors also state that free pleural fluid has seldom been demonstrated prior to the development of folded lung. In one of our patients we documented a left pleural effusion occurring prior to the development of folded lung in the left lower lobe (Fig. 6), apparently supporting Hanke's theory. However the not infrequent occurrence (29%) of folded lung in the upper lobes and the occurrence of folded lung next to pleural plaques (Fig. 4), in our series, is more in favour of pleural fibrous contracture. We suggest that both theories can be unified and that in some patients with inflammatory pleural effusions there develops a fibrosing pleuritis as described by
91
Buchanan et al. (1988) leading to pleural fibrous contracture and folded lung. In summary, we confirm that the most important criteria for the diagnosis of folded lung are vessels and bronchi curving towards a peripheral mass which has a centrally directed indistinct edge and that folded lung can be diagnosed with CT confidently and without recourse to needle biopsy or thoracotomy. REFERENCES
Blesovsky, A (1966). The folded lung. British Journal of Diseases of the Chest, 60, 19 22. Buchanan, R, Johnston, IDA, Kerr, IH, Hetzel, MR, Coffin, B & Turner-Warwick, M (1988). Cryptogenic bilateral fibrosing pleuritis. British Journal of Diseases of the Chest, 82, 186-193. Doyle, TC & Lawler, GA (1984). CT features of rounded atelectasis of the lung. American Journal of Roentgenology, 143, 225 228. Hanke, R & Kretzschmar, R (1980). Rounded atelectasis. Seminars of Roentgenology, 15, 174-182. Lynch, DA, Gamsu, G, Ray, CS & Aberler DR (1988). Asbestos related focal lung masses: Manifestations on conventional and high resolution CT scans. Radiology, 169, 603-607. Mintzer, RA, Gore, RM, Vogelzang, RL & Holz, S (1981). Rounded atelectasis and its association with asbestos-induced pleural disease. Radiology, 139, 567-570. Payne, CR, Jaques, P & Kerr, UH (1980). Lung folding simulating peripheral pulmonary neoplasm (Blesovsky's Syndrome). Thorax, 35, 12, 936. Schneider, HF, Felson, B & Gonzalez, LL (1980). Rounded atelectasis. American Journal of Roentgenology, 134, 225-232. Selikoff, IJ (1977). Cancer risk of asbestos exposure. In Origins of Human Cancer,eds Hiatt, HH, Watson, JD, Winstein, JA, pp. 17651784 Cold Spring Harbour Laboratory, New York. Taylor, PM (1988). Dynamic contrast enhancement of asbestos-related pulmonary pseudotumours. British Journal of Radiology, 61, 10701072. Tylen, U & Nilsson, U (1982). Computed tomography in pulmonary pseudotumors and their relation to asbestos exposure. Journal of Computer Assisted Tomography, 6, 229-237.
Computed Tomography of Folded Lung P. M. C A R V A L H O and D. H. C A R R
Department o f Diagnostic Radiology, The Brompton Hospital, Fulham Road, London S W 3
Computed tomography (CT) scans of 22 examples of folded lung in nine patients were reviewed. The most important CT criteria of folded lung are the presence of vessels and bronchi running in a smooth curvilinear fashion towards a peripheral mass with an ill defined central edge associated with pleural thickening. These features were seen in all 22 examples. The lesions are frequently multiple (eight out of nine patients). When these features are present the diagnosis can be made without recourse to biopsy or thoracotomy. Enhancement with intravenous contrast medium is unnecessary and does not provide any extra useful information. Various other previously described criteria such as air bronchograms are not necessary for the diagnosis.
The folded lung syndrome was first described by Blesovsky (1966) who presented three cases of peripheral pulmonary mass lesions which were initially diagnosed as bronchial neoplasms and at thoracotomy were found to represent benign lesions. Since then there have been several studies (Hanke and Kretzschmar, 1980; Schneider et al., 1980; Mintzer et al., 1981; Payne et al., 1980) on the plain radiographic and tomographic appearances of this condition which has gone undei~ several synonyms (Blesovsky's Syndrome, pulmonary pseudotumours, round atelectasis). Tylen and Nylssen (1982) described the CT appearances of folded lung in twelve patients and stressed asbestos as a causative factor, but indicated that thoracotomy was still necessary in some cases in excluding neoplastic lesions. Doyle and Lawler (1984) established eight major criteria for the CT diagnosis of folded lung in a study in three patients, but stated that needle biopsy was still reassuring in helping to exclude neoplasms. More recently Taylor (1988), in a study with three patients found that folded lung enhances with intravenous contrast medium, but believed that this does not help in differentiating it from neoplastic lesions.
METHODS Nine patients with folded lung examined by CT over a 4 year period were identified from the patient records. All of the patients bar one were examined because of a mass or masses visible on the chest radiograph which were regarded as suspicious of malignancy. One patient was examined because of increasing left basal pleural thickening together with a clinical suspicion of a mesothelioma. Ten millimetre contiguous slices were performed on an E L S C I N T 2002 scanner. Scans were examined at both lung and mediastinal window settings. In two patients, in whom interstitial lung disease was suspected, 3 mm high
Correspondence to: Dr P. Carvalho, Department of Diagnostic Radiology, The Brompton Hospital, Fulham Road, London SW3.
resolution scans with bone algorithm reconstruction were also performed. Two patients were examined with dynamic i.v. contrast enhancement using 100 ml of Iohexol (Omnipaque 300, Nycomed). The diagnosis of folded lung was confirmed by thoracotomy in two patients. One of these one had a coexisting lingular squamous cell carcinoma diagnosed by bronchoscopy; the second patient underwent thoracotomy because the benign nature of the lesion was not recognised pre-operatively, a fine needle biopsy was inconclusive and a neoplastic lesion was suspected. Six patients were followed up for at least two years with no increase in size of the original lesion. One patient has been followed up for 9 months only so far; the radiographic appearances are characteristic and consistent with previous descriptions of folded lung.
RESULT S /
Twenty-two cases of folded lung in nine patients were identified over a 4 year period. Their CT features and their frequency are tabulated in Tables 1 and 2. Features seen in all 22 lesions included a peripheral location (defined as a lesion with its outer edge not more than 2 cm from the pleura), the presence of smoothly curved bronchi and vessels around the lesion and a centrally directed ill-defined or blurred edge to the lesion
Table 1 -Frequency of CT signs in 22 cases of folded lung in nine patients
CT signs The mass has a peripheral site Curved vessels and bronchi directed towards mass The mass has a centrally directed (towards the hilum) indistinct margin Mass incompletelysurrounded by lung Air bronchogramwithin mass The mass forms an acute angle with the pleura The mass has at least two sharp margins Spherical mass Wedge or other shaped mass Calcified mass
Number of lesions
Percentage
22
100
22
100
22 19 12
100 86 55
10 8 10 12 8
45 36 45 55 36
Table 2-CT signs in nine patients with folded lung
CT signs
Patients
Percentage
Pleura1 thickening More than 1peripheral lesion Calcified pleural plaques Displaced main bronchi Pleural effusion Pulmonary fibrosis
9 8 5 4 2 2
100 88 55 44 22 22
87
CT OF FOLDED LUNG
(a)
(b)
(e)
(a)
Fig. 1-(a) Chest radiograph showing bilateral lower lobe masses (arrows). CT shows (b) bilateral pleurally based areas of folded lung with (c) a centrally directed indistinct edge and (d) curved vessels and bronchi directed towards them.
(a)
(b)
Fig. 2 - (a) Bilateral midzone masses (arrows), in a 49-year-old male. (b) On CT the right upper lobe mass is lenticular, not pleurally based, has no air bronchograms, but does have vessels and bronchi curving towards it and has a centrally directed indistinct edge.
88
CLINICAL RADIOLOGY
(a)
(b)
(Figs 1-6). In all patients there was at least a moderate degree of pleural thickening in the ipsilateral lung. Other features frequently but not invariably seen included an air bronchogram within or at the periphery of the lesion (Fig. 3b) and at least two sharp margins to the lesion. These features were seen in 55% and 36% of the lesions respectively. Wide window settings (around C -400 U W 1400 U) were particularly useful in demonstrating the smoothly curved bronchi and vessels and the air bronchograms. Folded lung may calcify and abut calcified pleural plaques (Fig. 4). The shape of the folded lung was roughly spherical (Fig. le) in 10/22 lesions (45%), and of a wedge (Fig. 5b), lentiform or irregular shape (Fig. 4) in 12/22. Six of nine patients (66%) had a firm occupational history of asbestos exposure and all had CT evidence of pleural calcification. Of the three patlents without evidence of asbestos exposure, one developed folded lung following Dressler's syndrome related to cardiac surgery. Fifteen lesions (68%) were in the lower lobes, six (27%) occurred in the anterior segments of the upper lobes and one was in the middle lobe. Lesions were often multiple (8/9 patients) with the additional sites of folded lung revealed by CT often not being visible on the chest radiograph. The two patients who received intravenous contrast medium both showed homogenous enhancement of the folded lung, confirming the findings of Taylor (1988) but this feature did not help in the differentiation from neoplastic lesions. Serial CT scans were available for three patients, with intervals of 4 years, 2 years and 8 months respectively. No increase in size was seen within these time periods (Figs 3 and 4). In two patients the lesions were stable and in one, there was a decrease in size after a two year interval (Fig. 4). In two patients additional sites of folded lung developed several years after the original lesions. The interval was 3 years in case 5 and 6 years in case 3. Thin section scans performed on two patients suspected of having interstitial lung disease demonstrated both thickening of some bronchial walls as they approached the folded lung and air bronchograms (Fig. 3) rather better than did 10 mm sections, but did not provide any other additional diagnostic features in these two patients.
DISCUSSION
(e) Fig. 3-(a) Chest radiograph showing left pleural thickening. (b) CT demonstrates folded lung with air bronchograms. (e) HRCT 4 years later shows no increase in size, but does demonstrate some peribronchial thickening near the lesions.
Doyle and Lawler (1984) described eight major CT signs of folded lung. 1 A rounded peripheral lung mass never completely surrounded by lung. 2 A mass which is most dense at its periphery. 3 A mass which forms an acute angle with the pleura. 4 Pleural thickening. 5 Vessels and bronchi which curve towards the mass. 6 At least two sharp margins. 7 A blurred centrally directed edge. 8 An air bronchogram. All these criteria were present in their patients. However, several of these features, including air bronchograms, a round shape, an acute angle with the pleura and incomplete surrounding of the lesion by lung were absent in many of our cases (Figs 2-4). It is important to be aware that all the described signs are not invariably present and their absence should not result in needle biopsy, which often provides scanty inconclusive tissue;
89
CT OF FOLDED LUNG
(a)
(b)
(c)
(d)
Fig. 4 - (a) Bilateral midzone masses (arrows) on the chest radiograph of a 52-year-old male with asbestosis. (b, c) CT demonstrates folded lung in the anterior segments of both upper lobes. These lesions are irregular and have adjacent curved bronchovascular structures. (d) Two years later the left upper lobe lesion is smaller.
(a)
(b)
Fig. 5 - (a) Bilateral midzone masses (arrows) on the chest radiograph of a 76-year-old male. (b) CT shows the right midzone mass as a wedge shaped arec of folded lung abutting a calcified pleural plaque. Another lesion is present in the left lower lobe.
90
CLINICAL RADIOLOGY
(a)
(b)
(c)
(d)
(e) Fig. 6-(a) Chest radiograph showing a left pleural effusion with a left lower lobe mass (arrow). c T shows (b, c) two areas of folded lung, with (d, e) a left pleural effusion and pleural thickening.
indeed in one study (Tylen and Nylssen, 1984), out of six needle biopsies performed in patients subsequently found to have folded lung, five yielded undiagnostic material and one case was erroneously diagnosed as a malignancy. As asbestos exposure predisposes to both bronchial
carcinoma (Selikoff, 1977) and folded lung (Mintzer et al., 1982), the two conditions may occur together, as in case 1, and the recognition of folded lung is also important in allowing potentially curative surgery. It has been suggested that high resolution CT is helpful
CT OF FOLDED LUNG
in differentiating pleural plaques in the oblique or accessory fissures from indeterminate lung nodules (LynCh et al., 1989). We have not found this necessary and have found it easy to identify fissural plaques on conventional 10 mm scans using the following criteria. Firstly they can be seen to follow the fissure in contiguous sections and secondly because of the obliquity of the fissures concerned, partial volume effect causes the fissural plaques to be of low density compared to other solid lung structures. Two main theories exist concerning the cause of folded lung. Hanke and Kretzschmar (1980) postulated that these lesions occur secondary to pleural effusions causing passive atelectasis of the underlying lung which then adheres to parietal pleura, and as the effusion recedes and the central atelectatic lung re-expands the peripheral collapsed adherent lung cannot re-expand and folds into a ball. Tylen and Nilsson (1984) have suggested that peripheral pleural fibrous contracture is the primary cause: in favour of this theory was the frequent occurrence of pleural plaques and parenchymal fibrosis in their series of 12 patients. These authors also state that free pleural fluid has seldom been demonstrated prior to the development of folded lung. In one of our patients we documented a left pleural effusion occurring prior to the development of folded lung in the left lower lobe (Fig. 6), apparently supporting Hanke's theory. However the not infrequent occurrence (29%) of folded lung in the upper lobes and the occurrence of folded lung next to pleural plaques (Fig. 4), in our series, is more in favour of pleural fibrous contracture. We suggest that both theories can be unified and that in some patients with inflammatory pleural effusions there develops a fibrosing pleuritis as described by
91
Buchanan et al. (1988) leading to pleural fibrous contracture and folded lung. In summary, we confirm that the most important criteria for the diagnosis of folded lung are vessels and bronchi curving towards a peripheral mass which has a centrally directed indistinct edge and that folded lung can be diagnosed with CT confidently and without recourse to needle biopsy or thoracotomy. REFERENCES
Blesovsky, A (1966). The folded lung. British Journal of Diseases of the Chest, 60, 19 22. Buchanan, R, Johnston, IDA, Kerr, IH, Hetzel, MR, Coffin, B & Turner-Warwick, M (1988). Cryptogenic bilateral fibrosing pleuritis. British Journal of Diseases of the Chest, 82, 186-193. Doyle, TC & Lawler, GA (1984). CT features of rounded atelectasis of the lung. American Journal of Roentgenology, 143, 225 228. Hanke, R & Kretzschmar, R (1980). Rounded atelectasis. Seminars of Roentgenology, 15, 174-182. Lynch, DA, Gamsu, G, Ray, CS & Aberler DR (1988). Asbestos related focal lung masses: Manifestations on conventional and high resolution CT scans. Radiology, 169, 603-607. Mintzer, RA, Gore, RM, Vogelzang, RL & Holz, S (1981). Rounded atelectasis and its association with asbestos-induced pleural disease. Radiology, 139, 567-570. Payne, CR, Jaques, P & Kerr, UH (1980). Lung folding simulating peripheral pulmonary neoplasm (Blesovsky's Syndrome). Thorax, 35, 12, 936. Schneider, HF, Felson, B & Gonzalez, LL (1980). Rounded atelectasis. American Journal of Roentgenology, 134, 225-232. Selikoff, IJ (1977). Cancer risk of asbestos exposure. In Origins of Human Cancer,eds Hiatt, HH, Watson, JD, Winstein, JA, pp. 17651784 Cold Spring Harbour Laboratory, New York. Taylor, PM (1988). Dynamic contrast enhancement of asbestos-related pulmonary pseudotumours. British Journal of Radiology, 61, 10701072. Tylen, U & Nilsson, U (1982). Computed tomography in pulmonary pseudotumors and their relation to asbestos exposure. Journal of Computer Assisted Tomography, 6, 229-237.
