Despite all the national and international energies devoted to their prevention, pneumoconioses are still very present both in industrialized and developing countries, and are responsible for the disability and impairment of many workers. This is why the International Labour Office (ILO), the World Health Organization (WHO) and many national institutes for occupational health and safety continue their fight against these diseases and to propose sustainable programmes for preventing them. For instance, the ILO, the WHO and the US National Institute for Occupational Safety and Health (NIOSH) have proposed in their programmes to work in cooperation on a global fight against silicosis. Part of this programme is based on medical surveillance which includes the reading of thoracic radiographs to help diagnose this pneumoconiosis. This is one example which explains why the ILO, in cooperation with many experts, has developed and updated on a continuous basis a classification of radiographs of pneumoconioses that provides a means for recording systematically the radiographic abnormalities in the chest provoked by the inhalation of dust. The scheme is designed for classifying the appearances of posterio-anterior chest radiographs.
The object of the classification is to codify the radiographic abnormalities of pneumoconioses in a simple, reproducible manner. The classification does not define pathological entities, nor take into account working capacity. The classification does not imply legal definitions of pneumoconioses for compensation purposes, nor imply a level at which compensation is payable. Nevertheless, the classification has been found to have wider uses than anticipated. It is now extensively used internationally for epidemiological research, for the surveillance of those industry occupations and for clinical purposes. Use of the scheme may lead to better international comparability of pneumoconioses statistics. It is also used for describing and recording, in a systematic way, part of the information needed for assessing compensation.
The most important condition for using this system of classification with full value from a scientific and ethical point of view is to read, at all times, films to be classified by systematically referring to the 22 standard films provided in the ILO International Classification set of standard films. If the reader attempts to classify a film without referring to any of the standard films, then no mention of reading according to the ILO International Classification of Radiographs should be made. The possibility of deviating from the classification by over or under reading is so risky that his or her reading should not be used at least for epidemiological research or international comparability of pneumoconioses statistics.
The first classification was proposed for silicosis at the First International Conference of Experts on Pneumoconioses, held in Johannesburg in 1930. It combined both radiographic appearances and impairment of lung functions. In 1958, a new classification based purely on radiographic changes was established (Geneva classification 1958). Since, it has been revised several times, the last time in 1980, always with the objective of providing improved versions to be extensively used for clinical and epidemiological purposes. Each new version of the classification promoted by the ILO has brought modifications and changes based on international experience gained in the use of earlier classifications.
In order to provide clear instructions for the use of the classification, the ILO issued in 1970 a publication entitled International Classification of Radiographs of Pneumoconioses/1968 in the Occupational Safety and Health Series (No. 22). This publication was revised in 1972 as ILO U/C International Classification of Radiographs of Pneumoconioses/1971 and again in 1980 as Guidelines for the use of ILO International Classification of Radiographs of Pneumoconioses, revised edition 1980. The description of standard radiographs is given in table 1.
Table 1. Description of standard radiographs
|1980 Standard radiographs showing||Small opacities||Pleural thickening|
|Technical quality||Profusion||Shape- size||Extent||Large opacities||Circum- scribed (plaques)||Diffuse||Diaphragm||Costo- phrenic angle obliteration||Pleural calcification||Symbols||Comments|
|0/0 (example 1)||1||0/0||–||–||No||No||No||No||No||No||None||Vascular pattern is well illustrated|
|0/0 (example 2)||1||0/0||–||–||No||No||No||No||No||No||None||Also shows vascular pattern, but not as clearly as example 1|
|1/1; p/p||1||1/1||p/p||R L x x x x x x||A||No||No||No||No||No||rp.||Rheumatoid pneumoconiosis in left lower zone. Small opacities are present in all zones, but the profusion in the right-upper zone is typical of (some would say a little more profuse than) that classifiable as category 1/1|
|2/2; p/p||2||2/2||p/p||R L x x x x x x||No||No||No||No||No||No||pi; tb.||Quality defect: radiograph is too light|
|3/3; p/p||1||3/3||p/p||R L x x x x x x||No||No||No||No||Yes R L x –||No||ax.||None|
|1/1; q/q||1||1/1||q/q||R L x x x x – –||No||No||No||No||No||No||None||Illustrates profusion 1/1 better than shape or size|
|2/2; q/q||1||2/2||q/q||R L x x x x x x||No||No||Yes R L x x width: a a extent: 1 1||No||Yes R L x x||No||None||None|
|3/3; q/q||2||3/3||q/q||R L x x x x x x||No||No||No||No||No||No||pi.||Quality defects: poor definition of pleura and cut basal angles|
|1/1; r/r||2||1/1||r/r||R L x x x x – –||No||No||No||No||Yes R L – x||No||None||Quality defect: subject movement. Profusion of small opacities is more marked in right lung|
|2/2; r/r||2||2/2||r/r||R L x x x x x x||No||No||No||No||No||No||None||Quality defects: radiograph too light and contrast too high. The heart shadow is slightly displaced to the left|
|3/3; r/r||1||3/3||r/r||R L x x x x x x||No||No||No||No||No||No||ax; ih.||None|
|1/1; s/t||2||1/1||s/t||R L x – x x x x||No||No||No||No||No||No||kl.||Quality defect: cut bases. Kerley lines in lower right zone|
|2/2; s/s||2||2/2||s/s||R L – – x x x x||No||No||No||No||No||No||em.||Quality defect: distortion of bases due to shrinking. Emphysema in upper zones|
|3/3; s/s||2||3/3||s/s||R L x x x x x x||No||No||Yes R L x x width: a a extent: 3 3||No||No||No||ho; ih; pi.||Quality defect: radiograph is too light. Honeycomb lung appearance is not marked|
|1/1; t/t Costophrenic angle obliteration||1||1/1||t/t||R L – – x x x x||No||No||Yes R L x x width: a a extent: 2 2||No||Yes R L x –||Yes R L – x extent: 2||None||This radiograph defines the lower limit for costophrenic angle obliteration. Note shrinkage in lower lung fields|
|2/2; t/t||1||2/2||t/t||R L x x x x x x||No||No||Yes R L x x width: a a extent: 1 1||No||No||No||ih.||Pleural thickening is present in the apices of the lung|
|3/3; t/t||1||3/3||t/t||R L x x x x x x||No||No||No||No||No||No||hi; ho; id; ih; tb.||None|
|1/1; u/u 2/2; u/u 3/3; u/u||–||–||–||–||–||–||–||–||–||–||–||This composite radiograph illustrates the mid-categories of profusion of small opacities classifiable for shape and size as u/u.|
|A||2||2/2||p/q||R L x x x x x x||A||No||No||No||No||No||No||Quality defects: radiograph is too light and pleural definition is poor|
|B||1||1/2||p/q||R L x x x x x x||B||No||No||No||No||No||ax; co.||Definition of pleura is slightly imperfect|
|C||1||2/1||q/t||R L x x x x x x||C||No||No||No||No||No||bu; di; em; es; hi; ih.||The small opacities are difficult to classify because of the presence of the large opacities. Note the left costophrenic angle obliteration. This is not classifiable because it does not reach the lower limit defined by the standard radiograph 1/1; t/t|
|Pleural thickening (circumscribed)||–||–||–||–||–||Yes||No||No||No||No||The pleural thickening present face on, is of indeterminate width, and extent 2|
|Pleural thickening (diffuse)||–||–||–||–||–||No||Yes||No||No||Yes||The pleural thickening present in profile, is of width a, and extent 2. Not associated small calcifications|
|Pleural thickening (calcification) diaphragm||–||–||–||–||–||No||No||Yes||No||Yes||Circumscribed, calcified pleural thickening of extent 2|
|Pleural thickening (calcification) chest wall||–||–||–||–||–||Yes||No||No||No||Yes||Calcified and uncalcified pleural thickening present face on, is of indeterminate width, and extent 2|
ILO 1980 Classification
The 1980 revision was carried out by the ILO with the cooperation of the Commission of the European Communities, NIOSH and the American College of Radiology. The summary of the classification is given in table 2. It retained the principle of former classifications (1968 and 1971).
Table 2. ILO 1980 International Classification of Radiographs of Pneumoconioses: Summary of details of classification
|2||Acceptable, with no technical defect likely to impair classification of the radiograph of pneumoconiosis.|
|3||Poor, with some technical defect but still acceptable for classification purposes.|
|Small opacities||Profusion||The category of profusion is based on assessment of the concentration of opacities by comparison with the standard radiographs.|
|0/- 0/0 0/1 1/0 1/1 1/2 2/1 2/2 2/3 3/2 3/3 3/+||Category O—small opacities absent or less profuse than the lower limit of category 1. Categories 1, 2 and 3—increasing profusion of small opacities as defined by the corresponding standard radiographs.|
|Extent||RU RM RL LU LM LL||The zones in which the opacities are seen are recorded. The right (R) and left (L) thorax are both divided into three zones—upper (U), middle (M) and lower (L). The category of profusion is determined by considering the profusion as a whole over the affected zones of the lung and by comparing this with the standard radiographs.|
|Shape and Size|
|Rounded||p/p q/q r/r||The letters p, q and r denote the presence of small, rounded opacities. Three sizes are defined by the appearances on standard radiographs: p = diameter up to about 1.5 mm q = diameter exceeding about 1.5 mm and up to about 3 mm r = diameter exceeding about 3 mm and up to about 10 mm|
|Irregular||s/s t/t u/u||The letters s, t and u denote the presence of small, irregular opacities. Three sizes are defined by the appearances on standard radiographs: s = width up to about 1.5 mm t = width exceeding about 1.5 mm and up to about 3 mm u = width exceeding 3 mm and up to about 10 mm|
|Mixed||p/s p/t p/u p/q p/r q/s q/t q/u q/p q/r r/s r/t r/u r/p r/q s/p s/q s/r s/t s/u t/p t/q t/r t/s t/u u/p u/q u/r u/s u/t||For mixed shapes (or sizes) of small opacities, the predominant shape and size is recorded first. The presence of a significant number of another shape and size is recorded after the oblique stroke.|
|Large opacities||A B C||The categories are defined in terms of the dimensions of the opacities. Category A – an opacity having a greatest diameter exceeding about 10 mm and up to and including 50 mm, or several opacities each greater than about 10 mm, the sum of whose greatest diameters does not exceed about 50 mm. Category B – one or more opacities larger or more numerous than those in category A whose combined area does not exceed the equivalent of the right upper zone. Category C – one or more opacities whose combined area exceeds the equivalent of the right upper zone.|
|Chest wall||Type||Two types of pleural thickening of the chest wall are recognized: circumscribed (plaques) and diffuse. Both types may occur together|
|Site||R L||Pleural thickening of the chest wall is recorded separately for the right (R) and left (L) thorax.|
|Width||a b c||For pleural thickening seen along the lateral chest wall the measurement of maximum width is made from the inner line of the chest wall to the inner margin of the shadow seen most sharply at the parenchymal-pleural boundary. The maximum width usually occurs at the inner margin of the rib shadow at its outermost point. a = maximum width up to abut 5 mm b = maximum width over about 5 mm and up to about 10 mm c = maximum width over about 10 mm|
|Face on||Y N||The presence of pleural thickening seen face-on is recorded even if it can be seen also in profile. If pleural thickening is seen face-on only, width cannot usually be measured.|
|Extent||1 2 3||Extent of pleural thickening is defined in terms of the maximum length of pleural involvement, or as the sum of maximum lengths, whether seen in profile or face-on. 1 = total length equivalent up to one quarter of the projection of the lateral chest wall 2 = total length exceeding one quarter but not one half of the projection of the lateral chest wall 3 = total length exceeding one half of the projection of the lateral chest wall|
|Diaphragm||Presence||Y N||A plaque involving the diaphragmatic pleura is recorded as present (Y) or absent (N), separately for the right (R) and left (L) thorax.|
|Costrophrenic angle obliteration||Presence||Y N||The presence (Y) or absence (N) of costophrenic angle obliteration is recorded separately from thickening over other areas, for the right (R) and left (L) thorax. The lower limit for this obliteration is defined by a standard radiograph|
|Site||R L||If the thickening extends up the chest wall, then both costophrenic angle obliteration and pleural thickening should be recorded.|
|Pleural calcification||Site||The site and extent of pleural calcification are recorded separately for the two lungs, and the extent defined in terms of dimensions.|
|Chest wall||R L|
|Other||R L||“Other” includes calcification of the mediastinal and pericardial pleura.|
|Extent||1 2 3||1 = an area of calcified pleura with greatest diameter up to about 20 mm, or a number of such areas the sum of whose greatest diameters does not exceed about 20 mm. 2 = an area of calcified pleura with greatest diameter exceeding about 20 mm and up to about 100 mm, or a number of such areas the sum of whose greatest diameters exceeds about 20 mm but does not exceed about 100 mm. 3 = an area of calcified pleura with greatest diameter exceeding about 100 mm, or a number of such areas whose sum of greatest diameters exceeds about 100 mm.|
|It is to be taken that the definition of each of the symbols is preceded by an appropriate word or phrase such as “suspect”, “changes suggestive of”, or “opacities suggestive of”, etc.|
|ax||Coalescence of small pneumoconiotic opacities|
|ca||Cancer of lung or pleura|
|cn||Calcification in small pneumoconiotic opacities|
|co||Abnormality of cardiac size or shape|
|di||Marked distortion of the intrathoracic organs|
|es||Eggshell calcification of hilar or mediastinal lymph nodes|
|hi||Enlargement of hilar or mediastinal lymph nodes|
|ih||Ill-defined heart outline|
|kl||Septal (Kerley) lines|
|od||Other significant abnormality|
|pi||Pleural thickening in the interlobar fissure of mediastinum|
|Presence||Y N||Comments should be recorded pertaining to the classification of the radiograph, particularly if some other cause is thought to be responsible for a shadow which could be thought by others to have been due to pneumoconiosis; also to identify radiographs for which the technical quality may have affected the reading materially.|
The Classification is based on a set of standard radiographs, a written text and a set of notes (OHS No. 22). There are no features to be seen in a chest radiograph which are pathognomonic of dust exposure. The essential principle is that all appearances which are consistent with those defined and represented in the standard radiographs and the guideline for the use of the ILO International Classification, are to be classified. If the reader believes that any appearance is probably or definitively not dust related, the radiograph should not be classified but an appropriate comment must be added. The 22 standard radiographs have been selected after international trials, in such a way as to illustrate the mid-categories standards of profusion of small opacities and to give examples of category A, B and C standards for large opacities. Pleural abnormalities (diffuse pleural thickening, plaques and obliteration of costophrenic angle) are also illustrated on different radiographs.
Discussion in particular at the Seventh International Pneumoconioses Conference, held in Pittsburgh in 1988, indicated the need for improvement of some parts of the classification, in particular those concerning pleural changes. A discussion group meeting on the revision of the ILO International Classification of Radiographs of Pneumoconioses was convened in Geneva by the ILO in November 1989. The experts made the suggestion that the short classification is of no advantage and can be deleted. As regards pleural abnormalities, the group agreed that this classification would now be divided into three parts: “Diffuse pleural thickening”; “Pleural plaques”; and “Costophrenic angle obliteration”. Diffuse pleural thickening might be divided into chest wall and diaphragm. They were identified according to the six zones—upper, middle and lower, of both right and left lungs. If a pleural thickening is circumscribed, it could be identified as a plaque. All plaques should be measured in centimetres. The obliteration of the costophrenic angle should be systematically noted (whether it exists or not). It is important to identify whether the costophrenic angle is visible or not. This is because of its special importance in relation to pleural diffuse thickening. Whether plaques are classified or not should be merely indicated by a symbol. The flattening of the diaphragm should be recorded by an additional symbol since it is a very important feature in asbestos exposure. The presence of plaques should be recorded in these boxes using the appropriate symbol “c” (calcified) or “h” (hyaline).
A full description of the classification, including its applications and limitation is found in the publication (ILO 1980). The revision of the classification of radiographs is a continuous ILO process, and a revised guideline should be published in the near future (1997-98) taking into account the recommendations of these experts.