Architecture of calcium oxalate monohydrate urinary calculi.

We have developed a partial dissolution method which enabled us to observe the internal architecture of urinary calculi. Using this method with improved organic matrix fixative, we studied the architecture of small calcium oxalate monohydrate urinary calculi with special attention to crystal-matrix interrelations. Calculi, we have observed, are invariably composed of 3 distinct zones. A core area is composed of randomly aggregated plate-like crystals with tendency of rosette formation. This core area is surrounded by an intermediate layer which shows prominent radial striations. This layer is composed of radially arranged piles of sheet-like crystals which extend beyond many layers of lamination. This layer gradually shifts to a peripheral layer where concentric laminations are prominent and each layer of lamination is composed of minute crystals which have lost radial arrangement. The organic matrix is observed only at the outside of the crystals, and matrix-rich crystal-poor bands separate each layer of concentric lamination. The concentric lamination seems to be a manifestation of the altered density of organic matrix which encrusted on the developing calculi and offered a milieu for crystal growth within.