Chest
Volume 102, Issue 1, July 1992, Pages 251-260
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The Significance of Irregular Opacities on the Chest Roentgenogram

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Scanty irregular opacities are not uncommonly observed on the chest roentgenogram in the absence of interstitial fibrosis of the lungs. In such circumstances the irregular opacities, when present, tend to be relatively scanty and seldom, if ever, exceed an ILO category of 1/1. They are found in association with cigarette smoking, especially when emphysema is also present. The development of irregular opacities is also related to exposure to various mineral and other dusts, and although their prevalence increases with cumulative dust exposure, in general the type of dust, whether fibrogenic or relatively inert, seems to be of little moment. The presence of irregular opacities remains a troublesome confounding factor in epidemiologic studies of both dust-exposed and nonexposed populations. The morbid anatomic changes that occur in the lungs of nondust-exposed workers and which are responsible for the development of irregular opacities in the chest roentgenogram remain unknown. (Chest 1992; 102:251–60)

Section snippets

RADIOGRAPHIC TECHNIQUE

Commonplace defects in the chest roentgenogram may cause overreading or underreading.11,12 Also influencing the interpretation of roentgenograms for pneumoconiosis are an inadequate inspiration, bodily habitus, in particular excessive weight or height, and sundry technical factors. In obese subjects and in those who have not taken a full breath, the basal markings are often accentuated due to crowding together of the airways and vessels and appear as scanty irregular opacities. Furthermore, the

OBESITY

The presence of large pectoral muscles, gynecomastia, or excessive chest wall fat often leads to the assignment of a higher category for pneumoconiosis than that which is present and in some instances leads to pneumoconiosis being diagnosed when it is absent.1,15 This is especially true for persons who are markedly obese. The effect of obesity on the reading of films for pneumoconiosis was investigated by Musch et al15 and was shown to cause increased interobserver variation and overreading. In

AGE

The older the subject, the more likely that irregular opacities will be present in the chest x-ray film. Unfortunately, the effect of age is difficult to quantify, because as a subject ages, so does dust response increase and, in a smoker, so also do pack-years. Increasing age is likewise often associated with a gain in weight, which has been demonstrated to have an effect on the interpretation of films for pneumoconiosis.15 While it is often maintained that the use of multiple regression

CIGARETTE SMOKING

It has been established that cigarette smoking is associated with the presence of irregular opacities.6,9,17,18 These opacities for the most part are found in the lower zones of the lungs, are of scanty profusion, ranging mostly from 0/1 to 1/1, and when present are frequently associated with some degree of airways obstruction. Such opacities may be present in the absence of dust exposure and have been shown to be present in female smokers.17 In this study the chest roentgenograms were not

COAL

The hypothesis has been put forward that irregular opacities are related to the inhalation of coal dust and are a manifestation of CWE6 It was further suggested that in coal miners the presence of such opacities is associated with the presence of emphysema and that the latter can be a consequence of exposure to coal dust.

Ryder and colleagues19 published a survey correlating the pathologic, physiologic, and radiologic findings of emphysema in 247 deceased miners and ex-miners. These had been

SILICA

A number of studies have shown that workers exposed to silica may develop irregular opacities. Theriault et al31 in their study of Vermont granite-shed workers, showed a relationship between rounded opacities and dust exposure, but such a relationship was not evident for irregular opacities. The presence of irregular opacities was strongly related to the presence of smoking, with 29 percent of their cohort showing irregular opacities. The increased RV noted in some of the granite-shed workers

CIGARETTE SMOKING AND ASBESTOS EXPOSURE

There have been a number of reports which have suggested that smoking is associated with a greater prevalence of irregular opacities than is present in nonsmokers. This problem was thoroughly reviewed by Weiss.9 He pointed out that in 1963, Auerbach and colleagues34 carried out a large study of the histologic appearances of pulmonary tissue from over 1,000 autopsies in a VA hospital. The smoking, occupational, and residence histories were obtained from relatives, but the specimens were examined

ALUMINUM

A cross-sectional study of 788 male employees from an aluminum production company examined the relationship of radiographic abnormalities to smoking and dust exposure from the refining of bauxite to alumina.45 All of the roentgenograms were read by two B-readers without any knowledge of the smoking history or dust exposure. The predominant radiographic abnormality noted was the presence of small irregular opacities situated mainly in the lower zones and of limited profusion. The presence of

MAN-MADE MINERAL FIBERS

Weill and colleagues46 described a study of the respiratory health of workers exposed to man-made mineral fibers. Of the 94 x-ray films that were categorized as having a profusion greater than 0/1, some 55 were read by at least two interpreters as having irregular opacities and 15 as having rounded as the primary opacity. Of the remaining 24, the two readers disagreed according to shape. Among current cigarette smokers the prevalence of small irregular opacities increased with length of

KAOLIN

An increased frequency of small irregular opacities has been noted among china clay workers in Cornwall. This was noted by Oldham47 and more recently by Ogle and co-workers.48 The prevalence of irregular opacities was increased in cigarette smokers and ex-smokers, although dust may have also contributed. Similar findings have been described in kaolin workers from east central Georgia.49 In this instance, dust exposure could not be shown to be related to the occurrence of small irregular

DISCUSSION

The presence of small irregular opacities on the chest roentgenogram is associated with a number of factors, including age, cigarette smoking, and dust exposure. The majority of the evidence suggests that exposure to dust is associated with the development in low profusion of small irregular opacities. This appears to be a nonspecific effect in that it has been associated with exposure to a number of dusts, including coal, kaolin, bauxite, silica, and that generated during the production of

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    Manuscript received July 2; revision accepted November 1.

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