Microstructural matrix-crystal interactions in calcium oxalate monohydrate kidney stones

The role of the proteinaceous matrix in the formation of calcium oxalate kidney stones is still not well understood. Simple scanning electron microscopy (SEM) has been of somewhat limited value in visualizing the organic and inorganic microstructure due to difficulties in obtaining detailed structural information for cut or fractured surfaces. To help clarify matrix-crystal microstructure, serial sections from 10-20 mm calcium oxalate calculi were partially demineralized with ethylenediamine tetraacetic acid (EDTA) and examined by SEM. Sections etched by EDTA showed a radial crystal structure composed of "microcrystal" subunits. Sections simultaneously EDTA etched and fixed with glutaraldehyde to insolubilize all matrix mucoprotein showed interesting forms of matrix structure: an amorphous sometimes membrane-like material, and a fibrous material that exhibited an apparent affinity for the inorganic crystalline phase. These observations give evidence for a more important etiological and structural role for the matrix than may be suggested by the relatively low matrix concentration in stones (2-6 wt. %).