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

Abstract

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