Small pneumoconiotic opacities on U.S. coal worker surveillance chest radiographs are not predominantly in the upper lung zones.

Background: Radiographic shadows of coal workers' pneumoconiosis (CWP) are commonly described as predominantly in the upper lung zones.

Methods: We evaluated the lung distribution of small opacities on surveillance chest radiographs (CXRs) taken between 1981 and 2010 among 2,467 underground US coal miners. All had evidence of pneumoconiosis (category ≥1/0), based on the contemporary International Labour Office Classification of Radiographs of Pneumoconioses.

Results: Small opacity involvement was approximately equal over all lung zones, with 30.7% of the total involvement reported in the upper zones, 37.1% in the middle zones, and 32.1% in the lower zones. Primarily rounded opacities were seen in 62.1% of miners and primarily irregular opacities were seen in 37.9%. Miners with primarily rounded opacities had a distribution with moderate upper zone predominance (upper = 36.8%, middle = 36.5%, and lower = 27.2%). In contrast, miners with primarily irregular opacities showed a lower zone preponderance (upper = 20.5%, middle = 38.4%, and lower = 41.1%).

Conclusion: The distribution of small pneumoconiotic opacities on surveillance CXRs of working US coal miners is not consistent with the conventional expectations of upper lung zone predominance.