Localized deposition of calcium oxalate around a pulmonary Aspergillus niger fungus ball

A case of pulmonary Aspergillus niger fungus ball is presented. Crystals of calcium oxalate, presumably derived from oxalic acid produced by the fungus, were deposited in tissues around the fungus ball. The crystals were identified by x-ray diffraction analysis. Histochemical technics for the identification of calcium oxalate were applied, and evaluation of those showed Yasue's silver nitrate-rubeanic acid method to be the most satisfactory. More frequently used methods for identifying calcium salts in tissues may give equivocal reactions. Oxalic acid may cause localized tissue damage, and if this affects blood vessels severe hemorrhage may follow.