Ultrastructure and pathogenesis of human urinary calculi.

The ultrastructure of human urinary calculi was studied using scanning and transmission electron microscopy. The hydroxyapatite constituent of the stones was often present in the form of sperical aggregates of the minute apatite crystallites (1 to 10 mu in diameter). In most cases, the sperical apatite deposits consisted of concentric lamellae of crystallites. The spherical apatite deposits, described in detail for the first time in urolithiasis, were similar to those found in a variety of calcified tissues including nephrocalcinosis and malakoplakia.