Routine analysis of urinary calculi by scanning electron microscopy.

Analysis of 529 urinary calculi by SEM(EDXA) and following x-ray diffraction in nearly all cases of oxalate-rich stones reveals a certain content of calcium phosphate, which in more than 75% can be related to the central core. This confirms the idea of a primary nidus at the beginning of stone formation. The abundant appearance of Ca-phosphate bearing microspherules both in urinary calculi and in urine of known stone formers as well as the presence of similar spherules in human kidney tissue leads to a conception of the physico-chemical nature of this nidus. A proposed model about the first steps of stone formation combines the two main theories of genesis of urinary calculi, which so far have been considered contradictory.