Role of organic matrix in urinary stone formation: An ultrastructural study of crystal matrix interface of calcium oxalate monohydrate stones

Human calcium oxalate monohydrate (COM) urinary stones were decalcified by treatment with a mixture of ethylenediaminetetraacetic acid (EDTA) solution and Karnovsky's fixative after embedding in bactoagar. Decalcified stones were examined by light microscopy, and also by scanning and transmission electron microscopy. Stones had distinct nuclei that were occupied by amorphous or apatitic calcium phosphate or aggregates of spherulitic COM crystals. EDTA insoluble matrix was ubiquitous in stones and consisted largely of finely matted fibrous material. It was organized in concentric laminations in the peripheral area of the stone but appeared highly disorganized in the stone center. Crystals were replaced by crystal ghosts. Organic matrix was present both inside the crystals and in the intercrystalline spaces. The study indicates a very close association between crystals and organic matrix. The relationship appears to begin early in crystal formation and persists throughout the formative and growth phases of the urinary stones.