Ultrastructural studies of crystal-organic matrix relations in renal stones

Biochemically the organic matrix of kidney stones contains mucoproteins, mucopolysaccharides, inorganic material and bound water. Morphologically, the organic matrix exists as either amorphous or fibrous forms. We have attempted to critically evaluate results from analytical and morphological studies on stone matrices using light microscopy, histochemistry, x-ray diffraction, scanning electron microscopy, x-ray energy dispersive spectrometry, transmission electron microscopy and selected area electron diffraction. On the surface of calcium oxalate stones, there are usually large masses of randomly deposited calcium oxalate crystals each coated with organic matrix. Transmission electron microscopy shows these large surface crystals are composed of rows of smaller crystallites interleaved by organic matrix in a fairly orderly manner suggesting the crystallites are held together by organic matrix. In the core of a calcium containing stone, the organic matrix frequently exists as concentric laminations alternating as calcium apatite covered fibrous matrix layers and amorphous matrix layers. Transmission electron microscopy suggests that the fibrous area is probably just an area heavily populated by calcium apatite crystallites which give the fibrous appearance while the amorphous area is sparsely populated. Organic matrix richness in stones can be associated with infection and calcium apatite crystal deposition is favored in infection stones.