Calcium oxalate crystals in the lungs.

A 67-year-old man who had been prescribed prednisolone for 20 months consulted our department due to repeated episodes of pneumonia. Computed tomography showed a large cavity in the apex of the right lung (Picture A, arrow). A fungal culture of a sample aspirated from the cavity revealed black-colored colonies (Picture B), which were later confirmed to be Aspergillus niger. A Grocott’s methenamine silver-stained section of the lung biopsy sample revealed branched septate hyphae (Picture C), with evident crystallization (Picture D) under polarized light microscopy. The common pathogen of chronic pulmonary aspergillosis is Aspergillus fumigatus, whereas Aspergillus niger is seldom detected in such cases (1). Oxalic acid is produced by Aspergillus niger as a mycotoxin and subsequently forms