[A case of rush dust (IGUSA-SENDO) pneumoconiosis with a large conglomerate mass shadow].

A 61-year-old woman, who had engaged in "tatami" mat production for 20 years, showed a gradually increasing large conglomerate mass shadow associated with small irregular opacities on chest X-ray film. Transbronchial lung biopsy revealed findings consistent with pneumoconiosis, with no suggestion of pulmonary tuberculosis or lung cancer. After 6 years' observation, right upper lobectomy was performed because the mass shadow was still increasing in size. Histological examination revealed a well-defined large mass composed of numerous macrophages containing abundant silicate minerals and fibroblasts proliferating in storiform fashion. No evidence of tuberculosis or malignancy has ever been detected. These findings are compatible with the previously reported pathological findings of "IGUSA-SENDO" pneumoconiosis; however, PR4 type "IGUSA-SENDO" pneumoconiosis has never been previously reported. This is the first reported case of PR4 type "IGUSA-SENDO" pneumoconiosis.