대한흉부영상의학회 Korean Society of Thoracic Radiology

Discussion

Diagnosis With Brief Discussion

Diagnosis

Pneumoconiosis (Radiographic type p)

Radiologic Findings

Magnification view from posteroanterior chest radiograph shows fine miliary nodules in left lung.
HRCT scans through the upper, middle and lower lung zones, respectively, show tiny centrilobular nodules and branching opacities.
Centrilobular opacities can be divided into two types according to size.
The larger ones are seen as sharply demarcated, rounded nodules and the smaller ones, more frequent in number, are seen as relatively ill-defined nodular or branching opacities.
These opacities are distributed fairly uniformly throughout the lungs. Subpleural nodules are also seen.

Brief Review

The International Labor Office (ILO) classification of radiographs of pneumoconiosis is now used worldwide. The opacities caused by dust inhalation are divided according to whether they are round or irregular in shape. Those that are round are classified according to size as p, q, or r (p, up to 1.5 mm in diameter; q, 1.5 ~ 3 mm; r, 3 ~ 10 mm). Those classified as irregular are designated as fine, medium, or coarse, using the letters s, t, and u, respectively. As might be expected, the interobserver variability in categorizing small opacities is great.
On CT, nodules of the q and r types were characterized by sharply demarcated, rounded nodules or irregular, contracted nodules that are centrilobular or subpleural in distribution. Nodules are present diffusely and bilaterally, but upper lobe and posterior predominance of nodules is often visible on CT. Nodules occurring in relation to thickened interlobular septa can be seen. In contrast, Akira et al. reviewed the HRCT scans in 55 patients with radiographic type p pneumoconiosis. In those patients with radiographic type p pneumoconiosis, HRCT showed ill-defined centrilobular opacities, sometimes having the appearance of small branching structures or a few closely spaced dots. In 21 of the 55 patients, nonperipheral, small areas of low attenuation with central dot were found. On the basis of CT-pathologic correlation, these centrilobular opacities and areas of low attenuation corresponded to irregular fibrosis around and along the respiratory bronchiole and to focal-dust emphysema, respectively. On HRCT, therefore, type p pneumoconiosis could be considered in the differential diagnosis for disease entities manifesting as bronchiolitis. In our case, centrilobular opacities were present as a mixed pattern consisting of the nodules of p type and of q type. However, nodules of the p type were, on the whole, more predominant.
In summary, HRCT appearance of radiographic type p pneumoconiosis is different from that of type q or r pneumoconiosis consisting of distinct rounded opacities. In contrast, radiographic type p pneumoconiosis is characterized by tiny centrilobular opacities and frequent areas of low attenuation on HRCT. These centrilobular opacities are pathologically regarded as lesions of respiratory bronchiole.


PATIENT'S CLINICAL COURSE AND DIFFERENTIAL DIAGNOSIS

This patient, a 46-year-old farmer, presented to a hospital other than ours with hematuria. He was diagnosed as having bladder cancer on the basis of clinical and cystoscopic findings in that hospital, where he did not receive any treatment. He was subsequently transferred to our hospital for treatment. On admission, he showed no symptoms and signs except intermittent hematuria. Because miliary pattern was found on routine preoperative chest radiograph, he underwent chest HRCT scanning for evaluation of miliary disease. We thought the lung lesions were less likely to be miliary tuberculosis because fever, a very common sign of miliary tuberculosis, was not present recently and miliary nodules were less numerous on HRCT in this case than in patients with typical miliary tuberculosis. The possibility of hematogenous metastasis could not be ruled out at that time because of the presence of multiple, sharply demarcated, small nodules on HRCT. He eventually underwent thoracoscopic lung biopsy after a nondiagnostic transbronchial biopsy.
On pathologic examination, there were multiple dense fibrotic nodules in lung specimens. These nodules were composed of whorled collagen and reticulin centrally, with surrounding fibroblast, lymphocytes, and macrophages containing dust particles. Refractile particles could be seen at the center of lesions. These histologic features corresponded to the silicotic nodules; there was no evidence of caseating or noncaseating granulomas or malignant tumor. After the pathologic diagnosis was made, careful questioning of the patient revealed that he had worked underground in a mine for 12 years from 22 to 33 years old.
In this case, the differential diagnosis includes miliary tuberculosis, metastasis, pneumoconiosis, and sarcoidosis. In miliary tuberculosis, the size of nodules are relatively uniform throughout the lungs and the number of those are usually more numerous than in our case. Additionally, patients with miliary tuberculosis commonly have a fever. In hematogenous metastasis, metastatic nodules are usually smooth, well-defined and round in shape except for hemorrhagic tumor. They are usually variable in size and do not show ill-defined, fine centrilobular nodular or branching opacities. In contrast to miliary tuberculosis and metastasis spreading through the bloodstream, sarcoidosis is characterized by noncaseating granulomas primarily distributed along the lymphatics. The characteristic HRCT abnormality of sarcoidosis is the nodular thickening of peribronchovascular interstitium. Interlobular septa and pleural surfaces are also frequently involved. When sarcoid granulomas involve the peribronchovascular interstitium of the lobular core, centrilobular nodules can be seen. However, these are not usually a predominant feature on HRCT.

References

1. ILO classification of radiographs of pneumoconiosis. International Labor Office. Geneva: ILO Publications, 1980.
2. Akira M, Higashihara T, Yokoyama K, et al. Radiographic type p pneumoconiosis: high-resolution CT. Radiology 1989; 171:117-123

Keywords

Lung, Inhalation and aspiration disease, Occupational lung disease,