British Journal of Industrial Medicine 1992;49:862-868

Chest x ray films from construction workers:International Labour Office (ILO 1980) classificationcompared with routine readings

M Albin, G Engholm, K Frostrom, S Kheddache, S Larsson, L Swantesson

AbstractThe extent of agreement between Inter-national Labour Office (ILO) and clinical read-ings of chest x ray films from constructionworkers was studied. From a survey of 5898workers 258 subjects with a profusion of smallopacities of > Il1 and a stratified sample ofsubjects with profusion <1/1 were selected.Only41% ofthefilms classifiedasILOprofusioncategory > 1i1 were clinically recorded as non-

normal for the parenchyma. The proportion offilms recorded as pneumoconiotic (or possiblyso) was especially low for irregular opacities(22%), but increased with the profusioncategory (both rounded and irregular) as wellas with the size of rounded opacities (p 3/11, q12/25, r 3/4). Only with the profusion category> 2/1 were most of the films recorded as

pneumoconiotic. The specificity and sensitivitywere highest in the geographical areas where a

few clinical readers had assessed many filmseach. The proportion of false negative clinicalreports was low for circumscribed pleuralthickening ofthe chest wall (9%) and diaphrag-matic pleural thickening (6%). For calcifiedpleural changes and for the combination ofdiffuse pleural thickening and obliteration ofthe costophrenic angle, false negative reportswere absent. The present study shows an unsat-isfactory sensitivity for clinical compared with

Department of Occupational and EnvironmentalHealth, Lund University, Lund, SwedenM AlbinThe Construction Industry's Organisation for Work-ing Environment, Safety and Health, Stockholm andGothenburgG Engholm, K Frostrom, L SwantessonDepartment of Radiology, Sahlgrenska HospitalS KheddacheDepartment ofLung Medicine, Renstrom's Hospital,GothenburgS Larsson

ILO readings as a means for screening theparenchyma of workers with a risk ofpneumoconiosis.

Workers exposed to fibrogenic dust such as asbestosor quartz are in many countries subject to periodicmedical examinations aiming primarily at earlydetection of pneumoconioses to prevent furtherpotentially deleterious exposure. It also allows thedetection of other pulmonary diseases that mightmake the worker more vulnerable to exposure todust. Accuracy (sensitivity, specificity) is necessary toachieve these aims. Failure is costly for the worker atrisk in terms of impaired health or loss of job and forsociety in terms of non-optimal allocation of resour-ces for diagnostic procedures and improvement ofworking conditions. The evaluation of the effective-ness (for protection ofhealth) ofcurrent programmesfor medical surveillance ofworkers exposed to asbes-tos or quartz was recently described as an unresolvedissue "that deserves careful scrutiny."'

In Sweden, periodic medical examinations arestatutory for workers with appreciable exposure toasbestos or quartz. Consequently, some 4000 con-struction workers have been examined with chest xray films each year through the Construction Indus-try's Organisation for Working Environment, Safetyand Health.

Chest x ray films from periodic examinations ofconstruction workers have been read both routinelyby a physician (radiologist or chest physician), and inaccordance with the ILO (1980) classification2 by apanel, to evaluate the present routines. The resultsare presented here.

Materials and methodsChest x ray films from periodic examinations of6049construction workers were assessed using the fullInternational Labour Office (ILO) (1980) classifica-tion. By extension ofthe classification, pleural strands(separate, convergent, or forming atelectasis) werecoded as additional symbols. The panel consisted of15 members (lung physicians, specialists inoccupational medicine, occupational health doctors,and nurses). During a training session, each member

862

copyright. on F

ebruary 14, 2020 by guest. Protected by

http://oem.bm

j.com/

Br J Ind M

ed: first published as 10.1136/oem.49.12.862 on 1 D

ecember 1992. D

ownloaded from

Chest x rayfilmsfrom construction workers: ILO 1980 classification compared with routine readings

of the panel read as many as possible of 450 films,sampled from the total material of constructionworkers, and was continuously provided with tabula-tions ofhis own readings in relation to the ones madeby the others. Of the training films, 197 were chosento be "trigger films".As well as the mentioned films, 131 films from white

collar workers, supposedly unexposed to harmfuldusts, were included in the study. These films were allobtained from what will be referred to as geographicarea A. The films were organised in batches, eachcontaining 100 films plus 10 trigger films. Onlyposterior-anterior films were read, each batchindependently by three readers. For small opacities,individual readers agreed (+ 1 subcategory) for 92 6to 96-6% of the films compared with the medianreadings. The individual biasis (overreadings-underreadings/total readings) ranged from -3 0 to+ 5.4%.3All films read as a profusion ofsmall opacities > 1/2

by the panel (n = 34; 26 finally included in our study,see later), have been subject to a special study byStjernberg and co-workers. One of the cases, anelectrician classified as 3/3 by the panel, had, accord-ing to the medical records, an advanced sarcoidosisthat probably explained his pronounced paren-chymal changes (N Stjernberg, personal commun-ication). For the others, no intercurrent diseasescould fully explain their parenchymal changes.Ofthe 5898 films classifiable for profusion of small

opacities (film quality 1 or 2) 258 had a median ILOreading of profusion of small opacities category) 1/1. These workers were selected for the presentstudy together with a sample of258 workers who hada film classified as profusion <1/1, individuallymatched for age and geographical area.The original routine radiological reports were

retrieved; 237 cases and 248 referents remained afterexclusion ofpersons in whom the x ray film was takenfor reasons other than periodic medical examina-tions, or when the original radiological report couldnot be found. Each original radiological report waswritten by one physician. They were grouped intothree geographical areas: region A (239 films), B (106films), and C (140 films). The films from regionsAandB had been assessed by a few physicians (region Ausually one out oftwo), whereas the films from regionC were assessed by several physicians, consequentlyreading few films each.The routine radiological reports from the periodic

medical examinations were coded in a standardisedway for the present study (separately for parenchymaand pleura) as reporting either normal, suspectedpathological, or pathological findings. They werefurther subdivided for the parenchyma as changesclassified as pneumoconiosis (including descriptionsof changes compatible with pneumoconioses) or asshowing findings other than pneumoconiosis. For the

pleura, positive findings were grouped as pleuralplaques (including suspected ones), other specifiedpleural changes, or pleural unspecified changes.Radiological reports with no comment on the state ofthe parenchyma (n = 153) or the pleura (n = 182)were handled as normal in the analysis.This coding was performed independently by two

investigators (usually one radiologist or chestphysician) blinded as to the case or referent state.Discrepancies in the coding between these two weresolved through a master reading by two to four oftheother investigators. The coded version of the originalradiological report was compared with the medianILO reading of the same film. Overweight wasestimated by the ponderosity-(Quetelet) index, cal-culated as weight (kg)/(height (m) ).2 In the process-ing of the data in this descriptive analysis, tabulationswere made disregarding the individual matching offilms with profusion < 1/l and >1/1.

ResultsPARENCHYMAL CHANGESIn the original radiological reports, 98 (41%) of thefilms classified as profusion of small opacities > 1/1were recorded as having any type of certain (27%) orsuspected (14%) pathological changes of the paren-chyma. The parenchymal changes were described aspneumoconiotic or as showing unspecified paren-chymal changes compatible with pneumoconiosis for56 films.Of the films classified as < 1/1, 201 (81%) were

classified as normal. Two of the films (with a panelreading of ILO category 0/0 and 1/0 respectively)were described in the original reports as showingparenchymal asbestosis, eight as having unspecifiedparenchymal changes compatible with pneumocon-iosis, none as having silicosis.A positive association was seen between the

proportion of films classified in the routine

°°or-

75

E0= 50

z

-225

o All types* Pneumoconiosis* Other

0

0

0

0

* t9

S0

U

I .

Profusion 0/0 0/1 1/0 1/1 1/2 2/1 2/2Number 159 66 23 210 14 5 7

Figure 1 Proportion offilms recorded as abnormal in routineradiological reports v the profusion category (ILO 1980)assessed by a panel.

863

copyright. on F

ebruary 14, 2020 by guest. Protected by

http://oem.bm

j.com/

Br J Ind M

ed: first published as 10.1136/oem.49.12.862 on 1 D

ecember 1992. D

ownloaded from

Albin, Engholm, Frostrom, Kheddache, Larsson, Swantesson

radiological reports as having any abnormality in theparenchyma and the category of profusion of smallopacities according to the ILO classification (fig 1).The association was most striking when onlypneumoconiosis (certain or suspected) was con-sidered. The proportion of other disease was roughlyconstant over the ILO categories.

In the routine readings, only 20% (41/210) inprofusion category 1/1 were reported as showingpneumoconiosis. More than half of the films wererecorded as any parenchymal abnormality (certain orsuspected) only when the ILO reading was profusioncategory 1/2 or higher (26 cases). For pneumocon-iosis, the corresponding ILO reading was as high as2/1 or more (12 cases).The proportion of films with profusion category1 /1 classified as pneumoconiotic (or compatible

with pneumoconiosis) varied with type and size ofsmall opacities (232 films classifiable for median typeand size). The proportion was much higher forrounded (7/11, 64%), than for irregular (37/192,19%) opacities, with an intermediate proportion forthe ones with both rounded and irregular opacities(11/29, 38%). The fraction increased with the size ofthe rounded opacities (p 3/11, 27%; q 12/25, 48%;r three out of four diagnosed as silicosis, one assarcoidosis (not in fig)). Among the irregularopacities, there was no such trend (s (smallest) 13/38,34%; t 35/183, 19%; no median reading of u by thepanel). Only one film had a median reading positive

100r-

for large opacities (type B). It was diagnosed assilicotic in the clinical reading.

Differences were seen between the geographicalareas in the extent to which the routine readingsagreed with the ILO readings (fig 2). Generally, overthe ILO categories, reports from area A had thehighest fraction of positive pneumoconiotic findingsand area C the lowest.The sensitivity of the clinical reports, tentatively

using the classification by the panel as the "goldstandard," was generally low (fig 3). The specificitywas high.

INFLUENCE BY CONCOMITANT FEATURESThere was no major difference between films classifiedas > 1 / 1 and < 1 /1 in the proportion ofpersons with aponderosity index on the top quartile (index > 28: 29and 22% respectively).The routine readings reported parenchymal

features other than pneumoconiosis (tuberculosis,sarcoidosis, cardiac incompensation, chronic obs-tructive lung disease, poor breath) among profusioncategories > 1/1 for 51 films (22%), and for 42 films(17%) in profusion categories < 1/1. Thus thesecharacteristics cannot explain the discrepancies inthe reading of pneumoconiosis in the routine v theILO readings.

PLEURAL CHANGESIn the total material, 233 (48%) of the films were

80 H

mPneumoconiosis

Other

60 H

40

20

0

Number 673953 431310 11210 1054857 6 2 6 3 2 0 4 0 3Profusion 0/0 0/1 1/0 1/1 1/2 2/1 2/2

Figure 2 Proportion offilms classified as abnormal in three geographical areas (A, B, C) by profusion category.

16E0

0z0-

864

copyright. on F

ebruary 14, 2020 by guest. Protected by

http://oem.bm

j.com/

Br J Ind M

ed: first published as 10.1136/oem.49.12.862 on 1 D

ecember 1992. D

ownloaded from

Chest x rayfilmsfrom construction workers: ILO 1980 classification compared with routine readings

| 3Pneumoconiosis []Other I

C

:

True positive False positive

B

A

70 60 50 40 v

Figure 3 Discrimination between < 1/1 and > 1/1 inroutine radiological reports using the classification by a panelas a standard.

classified according to ILO (1980) as showing pleuralthickening ofthe chest wall (diffuse or circumscribed)and 66 films (14%) pleural thickening of the dia-phragm. Generally, a high proportion of these chan-ges was reported in the routine readings (table). Thusa high proportion of films with ILO readings ofpleural thickening of the diaphragm were describedas showing suspected or definite pleural plaques in theclinical readings (unilateral 43/51, 84%; bilateral14/15, 93%); and so was circumscribed pleuralthickening of the chest wall (unilateral 34/47, 72%;bilateral 69/77, 90%).The proportions of reported pathological or sus-

pectedpathological pleural findings for diffuse pleuralthickening were 70% for both unilateral (39/67) and

bilateral (32/46) changes. All films with diffuse pleuralthickening of the chest wall combined with oblitera-tion of the costophrenic angle (1 1/1 1) were reportedas having a definite pathological pleura.The proportion of clinical readings without recor-

ded pleural changes decreased with increasing extentand width of pleural thickening of the chest wallaccording to the ILO readings (table). Thus all filmswith pleural thickening width > 10 mm were repor-ted as definite pleural plaques, compared with half ofthe films with width < 5 mm. All films with pleuralcalcification (n = 35) were reported as definitelypathological, all but one showing definite or suspec-ted pleural plaques. No trends were found betweenthe proportion offalse negative reports and Quetelet-index for diffuse or circumscribed pleural thickeningof the chest wall. Pleural strands (separate, conver-

gent, or forming an atelectasis) were recorded in 24clinical readings and in 23 readings by the panel (onlythree concordant positive).The proportion of films with certain or suspected

pathological pleural changes according to the clinicalreadings was similar among subjects with paren-chymal changes > 1/1 and < 1/1 (48 v 45%). In theILO readings, pleural thickening of the chest wallwas more often recorded for profusion ) 1/1 (54%)than < 1/ 1 (42%), but distributions of width, extent,and type (circumscribed, diffuse) for recordedchanges were similar between the two groups.

DiscussionPARENCHYMAThe proportion of films classified in routineradiological reports as pneumoconiotic, or even as

Relations between ILO and clinical readings for pleural changes in 5898 construction workers

Clinical readings ofpleuraTotal Not normal Suspected plaques Plaques

ILO readings No No(%) No(%) No(%)

Pleural thickening:Diaphragm 66 62 (94) 2 (3) 55 (83)

Chest wall*Circumscribed only 96 87 (91) 6 (6) 76 (79)Circumscribed and diffuse 5 5 (100) 1 (20) 3 (60)Diffuse only 73 51 (70) 13 (18) 22 (30)

Extent:t< 1/4 (1) 96 57 (59) 11 (11) 37 (39)<1/4and <1/2 (2) 109 93 (85) 14(13) 65 (69)> 1/2 (3) 28 27 (96) 4 (14) 16 (57)

Width:t<5mm (A) 140 92 (66) 20 (14) 50 (36)> 5 and 10mm (B) 79 73 (92) 8 (10) 58 (73)> 10 mm (C) 5 5 (100) 0 5 (100)

Pleural calcification:Chest wall 15 15 (100) 2 (13) 13 (87)Diaphragm 28 28 (100) 1 (4) 26 (93)Other sites 2 2 (100) 0 2 (100)

*Left side.tMaximum extent/width of pleural thickening; lateral chest wall, either side.

865

copyright. on F

ebruary 14, 2020 by guest. Protected by

http://oem.bm

j.com/

Br J Ind M

ed: first published as 10.1136/oem.49.12.862 on 1 D

ecember 1992. D

ownloaded from

Albin, Engholm, Frostrom, Kheddache, Larsson, Swantesson

having any pathological findings, was low amongcases with profusion category 1/1 or more. Theproportion of false positive readings was also low.The relations found indicate that in routine

radiological reports, the level for classifying a film aspneumoconiotic or compatible with pneumocon-iosis, either suspected or certain, is in fact aroundILO category 2/1. A difference existed, however,between different hospitals with one centre, servingarea A generally recording more findings. The dif-ferences in proportion of positive clinical readingsbetween the areas probably reflects, at least in part,differences in the number of films read by eachradiologist or lung physician.The differences may, however, also represent dif-

ferent policies in dealing with the problem of falsenegatives or positives. When subtle changes are moreoften classified as pathological, the burden on thediagnostic resources will increase, not only frompneumoconiotic subjects, but also healthy ones, whowill suffer from "needless fear and perceivedincapacity."4 Our results show that the detectionlimit in the routine readings was higher than wouldbe desirable.An increasing sensitivity was found with the size of

rounded opacities and the lowest sensitivity wasfound for irregular ones. A similar finding was madeby Gaensler et al.' This might be because irregularopacities with a low profusion category are more non-specific for dust exposure (increasing with age,6 withsmoking,78 (although contested by Kilburn et al9),and ponderosity'°) than the rounded ones. Thus sucha conservative reading of films from workers exposedto dust is beneficial in reducing the number of falsepositive readings, but at the same time potentiallydangerous, as it may delay further diagnosticprocedures, appropriate removal from furtherexposure to dust, and general measures to reduce thedust exposure at the workplace. It may still beimportant to detect irregular opacities, however.Although handling of asbestos is heavily restricted,exposures of concern do remain among severalgroups, such as asbestos demolition workers, work-ers exposed to minerals contaminated with tremolitefibres, and possibly also among workers exposed tocrystalline fibres other than asbestos. The low sen-sitivity in the routine readings is in agreement withthe findings of an earlier study (30% false negativereadings, pleura and parenchyma)."There was probably no major systematic observa-

tion bias in the ILO readings by the panel. Thus inthe material from white collar workers assessed bythe panel in the original study 11% had a medianreading of > 1/0 and 5% of ) 1/1. This is within therange of previously published reference populations(4 to 18% in category > 1/0)679 Assuming that thefilms from white collar workers are representative ofan unexposed population and that no changes clas-

sifiable as small opacities are present in such apopulation, our results indicate that whendichotomising between 1/0 and 1/1 the proportion offalse positive readings by the panel using the ILOclassification is roughly 5%. This is close to thecommonly used procedures for establishing a normalrange in which findings exceeding two standarddeviations (2 5%) are classified as pathological. Animportant difference between an ILO reading and atraditional radiological report is that the first istechnically descriptive and based on posterior-anterior projections only, whereas the second isdiagnostic and includes clinical data as well as furtherprojections. Moreover, only six out of 15 members inthe panel had had a formal training in thoracicradiology. These differences would all tend to make itmore difficult for the panel than for the clinicalradiologist to discriminate between pneumoconioticand non-pneumoconiotic changes.

Analysis of our data, accounting for the possibleinfluence on the readings of parenchymal changesfrom other concomitant diseases, pleural changes,and overweight, did not explain the differences bet-ween the ILO and the routine readings, althoughslightly higher proportions of these characteristicswere found for high profusion categories. Age andfilm technique might bear upon the reading of smallopacities. Age was matched for in sampling films< 1/1 and > 1/1, and so was region. Within regions Aand B, film technique was similar. Thus age and filmtechnique is (roughly) accounted for in comparisonsstratified by region, and dichotomised at 1/1, whereasanalysis by profusion category could be biased;however, as the results were similar for both types ofanalyses uneven distributions of age and film tech-nique over profusion categories could not create thediscrepancies between the ILO and the clinicalreadings.The ILO classification is a useful tool. It was

designed mainly for evaluation of effects of exposureto dust in groups of workers in scientific studies, andin occupational health. The classification has alsobeen recommended, however, for use in periodicmedical examinations'2 to select individual workersfor whom further diagnostic procedures should beinitiated.We used 1/1 as a cut off between normal subjects

and cases (suspected and certain) ofpneumoconiosis.This is the action level recommended in Sweden bythe National Board of Health and Welfare.'3 It hasbeen claimed that in current practice an ILO grade of< 1/0 makes asbestosis unlikely,'4 although 10-16%of the patients with histopathologically provedfibrosis have been shown to have false negativeradiographs.'5"6 In silicosis, the problem with falsenegative radiographs is less.5 Coal miners in theUnited States are given the option of transfer at anagreed reading of profusion category > 1/0.17

866

copyright. on F

ebruary 14, 2020 by guest. Protected by

http://oem.bm

j.com/

Br J Ind M

ed: first published as 10.1136/oem.49.12.862 on 1 D

ecember 1992. D

ownloaded from

Chest x rayfilmsfrom construction workers: ILO 1980 classification compared with routine readings

PLEURAThere was a reasonably good sensitivity in theroutine reports on pleural changes. The proportionof false negative clinical reports was low for circum-scribed pleural thickening of the chest wall anddiaphragmatic pleural thickening; and virtuallyabsent for calcified pleural changes and the combina-tion of diffuse pleural thickening and obliteration ofthe costophrenic angle. Only diffuse pleural thicken-ing of the chest wall, without obliteration of thecostophrenic angle, and circumscribed changes withminimal width and extent, had > 30% falsenegatives. This is remarkable, especially when com-pared with the proportion of false negative readingsof parenchymal changes. The good agreement oncircumscribed pleural thickening could partly be dueto the widely circulated diagnostic criteria for pleuralchanges (for compensation purposes), initiallyproposed by Thiringer et al,8 and later confirmed inrecommendations issued by the National SwedishBoard of Health and Welfare (requesting width> 5 mm for chest wall and > 3 mm for diaphragmaticuncalcified pleural thickening).'3 These criteria are,however, not entirely congruent with the ILOclassification.The high sensitivity for the combination of diffuse

pleural thickening and obliteration of the costo-phrenic angle is especially gratifying, as this typeof pleural changes (even without parenchymalfibrosis) is associated with impairment of the lungfunction. 1-22

PROPOSALSA discussion is warranted on the present proceduresin Sweden for periodic medical examinations ofworkers exposed to fibrogenic dust. Coding of thex ray films according to the ILO classification bytrained readers as a complement to the traditionalclinical report, would be one possible way to improvethe sensitivity in the reading of parenchymalchanges.Temporal certification of readers is employed in

the United States to grant sufficient knowledge anduniformity in the use of the classification forsurveillance of coal miners. In scientific studies,uniformity and reproducibility in the readings is nowoptimised by the use of trigger films (films withpreviously agreed readings) throughout the studies.The use of these techniques and a centralisation to afew centres of the readings are possibilities to com-pensate for the decreasing amount of films withpneumoconiotic changes encountered by the generallung physician or radiologist.Another possibility to improve the diagnostics is

high resolution computed tomography, which hasbeen shown to correlate rather well with histopath-ologically proved asbestos disease,23 to detect earlysilicotic changes, and to reduce interreader

variability.24 A scoring system for asbestos relateddisease has recently been suggested.25 High resolu-tion computed tomography is, however, presentlyavailable for routine examination only at a fewcentres, and the dose of ionising radiation is higherthan with standard techniques. Thus, systematic useofthe ILO classification in the surveillance ofworkersexposed to fibrogenic dust is still to be recommended.

AddendumAfter we submitted this paper for publication, Hiltand co-workers published a paper in which 430radiographs clinically recorded as showing asbestosrelated parenchymal or pleural abnormalities, werereassessed using the ILO classification. As in ourstudy, they found a low sensitivity for parenchymal,and a high sensitivity for pleural, changes in theclinical readings. Contrary to our findings, thespecificity in the clinical readings of parenchymalabnormalities, was also low (Hilt B, Borgersen A,Lien JT, Langard S. Chest radiographs in subjectswith asbestos-related abnormalities: comparison be-tween ILO categorisations and clinical reading. Am JInd Med 1992;21:855-61).

The ILO readings were carried out by us (exceptGE), and by H'akan Arvidsson MD, Bengt FristedtMD, Ebba Granqvist, registered nurse, GunnarHillerdal MD, Kristina Jakobsson MD, Gerd Lin-den, registered nurse, Berit Salomon MD, NilsStjernberg MD, Jan Tollqvist MD and GoranTornling MD. The panel was trained by Charles ERossiter MA, DSc(Med), FFOM. Zoli Mikoczy BScproduced the graphs. The trial was initiated byAnders EnglundMD of the Construction Industry'sOrganization for Working Environment, Safety andHealth, and supported by a grant from the SwedishWork Environment Fund (AMF 596/88). This isgratefully acknowledged.

Requests for reprints to: Maria Albin, Department ofOccupational and Environmental Medicine, Univer-sity Hospital, S-221 85 Lund, Sweden.

1 Becklake MR. Evaluation of respiratory hazards in the workingenvironment through environmental, epidemiological andmedical surveys. In: Proceedings of the VIIth internationalpneumoconioses conference, Pittsburgh, 1988. Part 1, 1990;16-22. (DHHS (NIOSH publ No 90-108.)

2 International Labour Office. Guidelines for the use of ILOinternational classification of radiographs of pneumoconioses.Geneva: ILO, 1980 (Occupational safety and health series:No 22).

3 Rossiter CE, Stjernberg N, Linden G, Englund A. Bygghalsanstudy of construction workers exposed to silica dust and/orasbestos: chest x-ray reading trials. 23rd International congresson occupational health of the international commission onoccupational health, ICOH, Montreal, 1990. Book of abstracts1990; 251.

4 Weill H. Diagnosis of asbestos-related disease. Chest 1987;91:802-3.

5 Gaensler EA, Carrington CB, Couto RE, Tomasian A, HoffmanL, Smith AA. Pathological, physiological, and radiological

867

copyright. on F

ebruary 14, 2020 by guest. Protected by

http://oem.bm

j.com/

Br J Ind M

ed: first published as 10.1136/oem.49.12.862 on 1 D

ecember 1992. D

ownloaded from

Albin, Engholm, Frostrom, Kheddache, Larsson, Swantesson

correlations in the pneumoconioses. Ann NY Acad Sci1972;200:572-607.

6 Epstein DM, Miller WT, Bresnitz EA, Levine MS, Gefter WB.Application of ILO classification to a population withoutindustrial exposure: findings to be differentiated frompneumoconiosis. AmJ Roentgenol 1984;142:53-8.

7 Weiss W. Smoking and pulmonary fibrosis. J Occup Med1988;30:33-9.

8 Weiss W. Cigarette smoking and small irregular opacities. Br JInd Med 1991;48:841-4.

9 Kilburn KH, Lilis R, Anderson HA, Miller A, Warshaw RH.Interaction of asbestos, age and cigarette smoking in produc-ing radiographic evidence of diffuse pulmonary fibrosis. Am JMed 1986;80:377-81.

10 Stjernberg N, Rossiter CE, Englund A. Effect of body mass onradiographic appearances. 23rd international congress onoccupational health of the international commission onoccupational health, ICOH, Montrial, 1990. Book of abstracts1990; 272.

11 Sheers G, Rossiter CE, Gilson JC, Mackenzie FAF. UK navaldockyards asbestosis study: radiological methods in thesurveillance of workers exposed to asbestos. Br J Ind Med1978;35: 195-203.

12 International Labour Office. Safety in the use of asbestos: An ILOcode ofpractice. Geneva: ILO, 1984.

13 Diagnostik av dammlunga fororsakad av kvarts och asbest.Allmanna rddfrdn Socialstyrelsen 1987:4, Stockholm 1987. (InSwedish.)

14 Gefter WB, Conant EF. Issues and controversies in the plain-film diagnosis of asbestos-related disorders in the chest.J Thorac Imaging 1988;3:11-28.

15 Epler GR, McLoud TC, Gaensler EA, Mikus JP, CarringtonCB. Normal chest roentgenograms in chronic diffuse infil-trative lung disease. N Engl J Med 1978;298:934-9.

16 Gaensler EA, Carrington CB. Open biopsy for chronic diffuseinfiltrative lung disease: Clinical, roentgenographic, andphysiologic correlations in 502 patients. Ann Thorac Surg1980;30:41 1-26.

17 Federal Register 1979;44(76):23084-5.18 Thiringer G, Blomqvist N, Brolin I, Mattsson SB. Pleural

plaques in chest x-rays of lung cancer patients and matchedcontrols (Preliminary results). Eur JRespir Dis 1980;61 (suppl107):1 19-22.

19 Wright PH, Hanson A, Kreel L, Capel LH. Respiratory functionafter asbestos pleurisy. Thorax 1980;35:31-6.

20 McLoud TC, Woods BO, Carrington CB, Epler GR, GaenslerEA. Diffuse pleural thickening in an asbestos-exposed popula-tion: prevalence and causes. Am J Roentgenol 1985;144:9-18.

21 Hillerdal G, Malmberg P, Hemmingsson A. Asbestos-relatedlesions of the pleura: parietal plaques compared to diffusethickening studied with chest roentgenography, computedtomography, lung function, and gas exchange. Am J Ind Med1990;18:627-39.

22 Kouris SP, Parker DL, Bender AP, Williams AN. Effects ofasbestos-related pleural disease on pulmonary function. ScandJ Work Environ Health 1991;17:179-83.

23 Akira M, Yamamoto S, Yokoyama K, Kita N, Morinaga K,Higashihara T, Kozuka T. Asbestosis: high-resolution CT-pathologic correlation. Radiology 1990;176:389-94.

24 &gin R, Ostiguy G, Fillion R, Colman N. Computed tomo-graphy scan in the early detection of silicosis. Am Rev RespirDis 1991;144:697-705.

25 Al Jarad N, Wilkinson P, Pearson MC, Rudd RM. A new highresolution computed tomography scoring system for pulmon-ary fibrosis, pleural disease, and emphysema in patients withasbestos related disease. Br J Ind Med 1992;49:73-84.

Accepted 16 March 1992

868

copyright. on F

ebruary 14, 2020 by guest. Protected by

http://oem.bm

j.com/

Br J Ind M

ed: first published as 10.1136/oem.49.12.862 on 1 D

ecember 1992. D

ownloaded from