Eggshell
Calcifications
in Coal and Metal Miners
By GEORGE JACOBSON, M.D., BENJAMIN FELSON, M.D., EUGENE P. PENDERGRASS, M.D., ROBERT H. FLINN, M.D., AND WILLIAM S. LAINHART, M.D.
E
CALCIFICATIONS in the lymph nodes of the mediastinum and hila of th’e lungs in silicotics were first described by Sweany in 19336.11Although occasionally they occur in the absence of exposure to dust, eggshell calcifications may be assumed to be due to pneumoconiosis when there is accompanying pulmonary nodulation and/or a history of industrial exposure. The United States Public Health Service has recently concluded extensive surveys of pneumoconiosis in coal miners” and metal miners” in the United States. When the roentgenograms of these two groups of miners were examined, a number of instances of eggshell calcifications were noted, In the present report, criteria for the recognition of this roentgen sign are defined, and its prevalence among the coal and metal miners is presented. Most of the calcifications in lymph nodes are the result of infections such as tuberculosis, histoplasmosis or, occasionally in the southwestern part of the United States, coccidioidomycosis. The calcification is usually distributed in an irregular fashion throughout the lymph node, although it may be deposited as a central nodule, in concentric rings, or in the periphery of the node. In the latter case, the calcification may be shell-like and indistinguishable from that seen in the pneumo’coniotic.1,4,5.” No satisfactory explanation for this variation in distribution is available, nor is there any known reason for the predilection of the peripheral form in pneumoconiosis. Eggshell calcifications have also been reported in patients with sarcoidosis.l” Each roentgenogram in the surveys was classified according to the United States Public Health Service (U.S.P.H.S.) modification of the International Labour Organization ( I.L.O. ) Classification of the Pneumoconioses (page 222) .9 To avoid over-reading of the incidental circumferential concentrations of calcium and to eliminate confusion with the ring shadows of bronchi on end, we formulated the following criteria for eggshell calcifications: GGSHELL
From the U. S. Depurtment of Health, Education, and Welfare, Public Health Service, Rurzau of Diszzse Prevention and Environmental Control, Nutional Center for Urban and Industrial Health, Occupatianal Health Program. GEOHGZ JACOBSON, 51.D.: Professor and Chairman of Radiology, University of Southern California School of Medicine; Chief Radiologist Los Angeles County Hospital, Los Angeles, M.D.: Professor and Director, Department of Radiology, BEXJAMIX FELSON, California. Cincinnati, Ohio. EUGENE P. PENDERGRASS, University of Cincinnati School of Medicine, M.D.: Emeritun Professor of Radiclogy, School of Medicine of the University of PennsylS1.D.: Medical Director, United ‘ROBERT H. FLINN, Gania, Philadelphia, Pennsylvania. States Public Heal% Service (Retired), Santa Barbara, California. WILLIAM S. LAINHART, M.D.: Chiej Ale&Cal O@cer, Epidemiology and Field Studies, Occupationul Health Progrum, Natiowl Center for Urban and Industrial Health, Public Health Service, Cincinnati, Ohio. Please send requests for reprints to Dr. Wm. S. Lainhart, 1014 Broadway, Cincinnati, Ohio 45202. 276
EGGSHELL
CALCIFICATIONS
277
IN MINERS
Fig. I.-U.S.P.H.S. Classification 3nC, es, em (3n=very numerous small opacities 3 mm. np to and including 1 cm. in diameter; C=large opacities whose combined area exceeds one-third of the visible right lung field; es=eggshell calcifications; and emzemphysema). See pages 222-223.
1. Shell-like calcifications measuring up to 2 mm. in thickness must be present in the peripheral zone of at least two lymph nodes. 2. The calcifications may be solid or broken. 3. In at least one of the lymph nodes, the ring-like shadow must be complete. 4. The central portion of the lymph node may show additional calcifications. 5. 0ne of the affected lymph nodes must be at least 1 cm. in its greatest diameter. Typical eggshell calcifications are illustrated in Figures 1, 2, and 3, with and without
pulmonary
nodulation. RESULTS
There were 68 individuals 16$05
miners,
a prevalence
with
eggshell calcifications
of 0.4 per cent. As shown
encountered in Table
among
1, the preva-
Fig. 2.-(A, left). U.S.P.H.S. Classification 2q, es, cn (2qznumerous small opacities 1.5 up to and including 3 mm. in diameter; es=eggshell
calcifications; enlargement
and cn=calcifications of small opacities. (B, right). of the right hilar area of (A). See pages 222-223.
An
$ g 2-i
EGGSHELL
CALCIFICATIONS
IS
MINERS
Fig. 3.-U.S.P.H.S. Classification 0, es (O=no roentgenographic evidence coniosis in the lung fields; and es=eggshell calcifications). See pages 222-223.
279
of pneumo-
lence of eggshell calcifications was almost three times as high among coal miners as among metal miners, i.e., 0.8 as compared to 0.3 per cent. Of those with less than 20 years mining history, eggshell calcifications were seen in none of the coal miners and in only 7 of the 10,840 metal miners. Beyond this period, the prevalence of eggshell calcifications increased considerably, so that it reached 2.9 per cent in coal miners and 2.3 per cent in metal miners who had had 30 years or more experience. Table 2 relates the prevalence of eggshell calcifications to the severity of pneumoconiosis as determined roentgenographically. Eggshell calcifications were encountered in the absence of visible nodulation in 2 coal miners and 6 metal miners ( .05 per cent). Of the 724 miners with definite roentgen evidence of pneumoconiosis, eggshell calcifications occurred in 46, or 6.3 per cent (6.0 per cent of 248 coal miners and 6.5 per cent of 476 metal miners). Eggshell calcifications were more frequent in both coal and metal miners with suspected pneumoconiosis than in those with simple pneumoconiosis. These differences were not, however, statistically significant. The prevalence rose sharply in complicated pneumoconiosis (progressive massive fibrosis) and
280
JACOBSON,
Table
l.-Eggshell
Calcifications COAL
Years in Mining Less than 10 years lo-19 years 20-29 years 30 years and over
Eggshell
Related
2504 METAL
2 5 14 25
TOTAL
to Years
46-1.
FLINN,
LAINHART
in Mining
MINERS
21
Less than 10 years lo-19 years 20-29 years 30 years and over
PENDERGRASS,
No Eggshell 536 599 733 636
2 19
TOTAL
FELSON,
Total 536 599 735 655
% with Eggshell 0.0 0.0 0.3 2.9
2525”
0.8
MINERS
6514 4319 2111 1086
6516 4324 2125 1111
0.04 0.1 0.7 2.3
14,030
14,076
0.3
*Four were excluded because of unknown exposure history. -l-One was excluded because of unknown exposure history. Table
.%--Eggshell
Calcifications
Related COAL
Roentgen Diagnosis No pneumoconiosis Suspected pneumoconiosis Simple pneumoconiosis Complicated pneumoconiosis TOTAL
Eggshell 2 4 3 12 21
TOTAL
Diagnosis
of Pneumoconiosis
MINERS
No Eggshell 2144 131 169 64 2508
METAL
No pneumoconiosis Suspected pneumoconiosis Simple pneumoconiosis Complicated pneumoconiosis
to Roentgen
Total 2146 135 172 76 2529
% with Eggshell 0.1 3.0 1.7 15.8 0.8
MINERS
6 10 9 22
13,424 160 296 149
13,430 170 305 171
0.04 5.9 3.0 12.9
47
14,029
14,076
0.3
was comparable in both groups of miners, 15.8 per cent in coal miners and 12.9 per cent in metal miners. DISCUSSIOS
Bellini and Ghislandi’ reported a 5 per cent prevalence of eggshe!l calcifications in individuals with silicosis, a figure consistent with that reported in our studies of American miners with pneumoconiosis. Also in Italian workers, Galassi’ found a prevalence of 3 per cent among 600 roentgenograms classified as showing silicosis. Viega de Macedo’” found 18 cases of eggshell calcifications among 1178 workers with various pneumoconioses, a prevalence of 1.5 per cent. The difference in frequency of eggshell calcifications between the two groups of miners in our study is relatively small. In fact, the similar prevalence of this
EGGSHELL
CALCIFICATIONS
281
IN MINER3
form of calcification in these two groups of miners, its reported frequency in other occupations where silicosis is known to occur, and its apparent absence in individuals exposed to other types of dust, such as asbestos, beryllium and talc, all suggest that the finding is related to the deposition of silica. It is of interest that pleural calcification was not noted among the miners with eggshell calcifications. We are in the process of studying the relationship of eggshell calcifications to calcification in the small intrapulmonary nodules, In the absence of other chest roentgen findings, the occurrence of eggshell calcifications in miners cannot be taken to indicate a certain diagnosis of pneumoconiosis. The relationship might be purely coincidental in these individuals. Only 8 such examples were encountered among 16,000 miners in our series and, as noted earlier, eggshell calcifications are also encountered in the absence of dust exposure. However, we suspect that most of the 8 have silicosis. The prevalence of the finding among a group of unexposed healthy individuals would be of interest. When roentgen signs are suggestive of pneumoconiosis, the presence of eggshell calcifications adds considerably to the likelihood of pneumoconiosis. If the calcifications are associated with small pulmonary nodules or localized areas of fibrosis, the diagnosis of pneumoconiosis can be considered established. SUMMARY
AND
(=~NCLUSIONS
Specific criteria are described for the diagnosis of eggshell calcifications in the lymph nodes of the mediastinum and hila of the lungs. In roentgen surveys of pneumoconiosis in the metal and coal mining industries, eggshell calcifications were seen in less than 1 per cent of the miners. However, an increasing number of miners showed the calcifications as the duration of the mining exposure increased. Furthermore, the prevalence of eggshell calcifications among miners with other roentgen evidence of pneumoconiosis was over 6 per cent. This figure rose to above 13 per cent in those miners who showed complicated pneumoconiosis. No striking difference was noted in the prevalence of eggshell calcifications among the coal and metal miners. Although the presence of eggshell calcifications in the lymph nodes cannot be considered diagnostic of pneumoconiosis, it raises the possibility of this diagnosis. If there is also a history of dust exposure, the likelihood of pneumoconiosis is enhanced. If roentgen evidence of nodulation is present, the diagnosis of pneumoconiosis can be considered established. REFERENCES 1. Ealestra, C.: Le calcificazioni a guscio d’uovo sono patognomoniche della silicosi? Radiol. Med. 38:829-836, 1952. 2. Bellini, F. and Ghislandi, E.: Calcificazioni “a guscio d’uovo” a sede extrailare in silica-tubercolotico. bled. d. Lavoro 51:600606, 1960. 3. Brown, M. C.: Pneumoconiosis in bituminous coal miners. Mining Congress J.
51:44-48, 1965. 4. Eggenschwyler, H. : Schalenformige Hilusverkalkungen ohne Silikose, Radial. Clin. 19:77-81, 1950. 5. Felson, B.: In Rabin, C. B. (Editor): Rcentgenology of the Chest. Philadelphia, Charles C Thomas, 1958 (p. 262 ). 6. Flinn, R. H., Brinton, H. P., Doyle, H. N., Cralley, L. J., and Harris, R. L.:
282
JACOBSON,
Silicosis in the l
FELSON,
PENDERGRASS,
FLINN,
LAINHART
9. Pendergrass, E. P., Felson, B., Jacobson, G., Flinn, R. H., and Lainhart, W. S.: Use of the IL0 Classification in the study of silicosis. Arch. Envir. Health 10:776-785, 1965. 10. Shanks, S. C., and Kerley, P.: A TestBook of X-ray Diagnosis, Vol. II. Philadelphia, W. B. Saunders Co., 1962 (pp. 432433). 11. Sweany, H. C.: Patholomgic interpreLations of roentgenologic shadows in pneumoconixis. J.A.M.A. 106:1959-1965, 1936. 12. Viega de Macedo, A.: Image en “coquille d’oeuf” thoracique, abdominale et susclaviculaire bilaterale dans la silicotuberculose. Revue Tuberc. 28:373-374, 1964.