[Clinical study of pneumoconiosis featuring small nodules and without large opacities on high-resolution CT]

High-resolution CT (HRCT) was performed in 25 patients with pneumoconiosis diagnosed as category 1 or 2 according to the ILO radiographic classification. The small opacities shown on HRCT images were classified as small branching structures (SBS) or small rounded opacities (SRO). Patients in these two groups were compared with respect to the distribution of small nodules, pulmonary function, arterial blood gas analysis, degree of exertional dyspnea, and alteration ratio of the lung field CT numbers between maximum inspiration and maximum expiration (%(I-E)). The small nodules in all patients of the SBS group were classified as type p. SBS were distributed evenly throughout the lungs, while SRO were mainly localized in the upper middle lobe. Pulmonary emphysema was observed in patients with SBS and was particularly common among patients in this group with an irregular septum (IS). No emphysematous lesions were detected in the SRO group. RV/ TLC was higher and exertional dyspnea was more severe in the SBS group than in the SRO group. It was considered that an increase of RV/TLC resulted in worsening of exertional dyspnea in the patients with SBS. The % (I-E) value was significantly lower in the SBS group than in the SRO group.