Ultrastructural studies of renal stones from patients on continuous ambulatory peritoneal dialysis.

Patients on haemodialysis or peritoneal dialysis due to renal failure have an unusually high incidence of kidney stones (from 5 to 51% depending on methodology). However, there is a controversy on the composition of these stones - whether they are calcium oxalate stones or matrix stones. This paper presents ultrastructural evidence that these stones are in fact heterogeneous, ranging from calcium oxalate stones with little organic matrix component, through calcium oxalate and calcium apatite stones with substantial organic matrix component, to matrix stones with little inorganic material component. The correlative analytical methodology developed in this laboratory employing analytical scanning and transmission electron microscopy, electron and x-ray diffraction, as well as biochemistry, was reported previously. For the calcium oxalate stones, scanning electron microscopy showed that numerous small crystals of 1-3 micron in size were exposed to stone surfaces, apparently in an unorganized manner. However, transmission electron microscopy sections showed orderly stacking of crystals held together by organic matrix, just like bricks held together by mortar. For the matrix stones, scanning electron microscopy showed smooth stone surfaces while transmission electron microscopy sections showed focal areas of calcium oxalate or apatite deposits as identified by selected area electron diffraction.