The fine structure of prostatic
calculi has not been elucidated yet, although the chemical components were reported in detail. We studied the primary or endogenous
calculi removed from eight human prostates by secondary scanning electron microscopy, backscattered electron imaging, energy-dispersive X-ray microanalysis and X-ray diffraction. The primary
calculi containing Mg, Zn and S, besides Ca and P were basically classified into four stone groups (I-IV) by fine structure and
mineral components. Stone I had the core deposits of calcospherites showing concentric rings and the laminated deposits concentrically around the core. Their deposits were identified as
apatite. Stone II was occupied with the calcospherite deposits of
apatite although the stone growth showed a rough concentric formation. Stone III contained the core of calcospherites and concentric laminated structures, similar to a smaller type of group I, whereas the wider peripheral region was deposited with needle-like structures, identified as
calcium oxalates. Stone IV had the core deposits containing small hexahedral structures, identified as
whitlockite, which were surrounded with several incompletely concentric laminated bands of
apatite.
Whitlockite crystals were also found between the fused large
calculi. The initial and formative
calculi were basically observed as the deposition of mineralizing spherical structures suggesting variously sized corpora amylaceous bodies. Thus, the primary prostatic
calculi of stones I-III will begin from the mineralization of amylaceous bodies as a core, while the organic substances, which form stone IV, might be derived from the simple precipitation of prostatic secretion.