[An architectural study of mixed uric acid and calcium oxalate stones by polarized light microscopy of thin section]

The architecture of mixed uric acid and calcium oxalate stones was studied by polarized light microscopy. Some uric acid stones contained calcium oxalate stones (whewellite or weddellite) as a nucleus. Other uric acid stones contained calcium oxalate crystals in the nucleus or inner portion. A uric acid stone covered with layers of calcium oxalate was also found. In the mixed stones, nuclei of randomly mixed fine grained whewellite and uric acid were seen and both crystals appeared in alternating sequence in the outer layers. Weddellite crystals dissolved layers of uric acid and invaded into them in the nuclear or peripheral zones. Whewellite may precipitate in the same or a similar condition as uric acid precipitates, whereas weddellite may precipitate in a different condition. We discussed the pathogenesis of mixed uric acid and calcium oxalate stones, heterogeneous nucleation and epitaxial growth based on a morphologic study of the mixed stones.