Ultrastructure of selected calcium oxalate-containing urinary calculi fromdogs

Objective-To elucidate the ultrastructural details of calcium oxalate-conta ining urinary calculi from dogs. Sample Population-38 specimens selected from a collection of 8,297 oxalate- containing urinary calculi from dogs: 22 specimens composed of calcium oxal ate (calcium oxalate monohydrate [COM], caicium oxalate dihydrate [COD], or COM and GOD) and 16 specimens composed of calcium oxalate with amorphous c alcium phosphate. Procedure-Analyses of specimens included use of plain, reflected, and polar ized light microscopy. X-ray diffractometry, scanning electron microscopy ( SEM) with backscattered electron (BSE) imagery, and electron microprobe ana lysis. Results-Four texture types were observed in calcium oxalate calculi; 4 text ure types of calcium oxalate-calcium phosphate-mixed calculi were recognize d. Texture types were delineated through differences in calcium oxalate cry stal sizes, which were affected by urine supersaturation and abundance of c rystal nucleation sites. Segregation of calcium oxalate from caicium phosph ate indicated they do not precipitate under the same conditions. Deposition of calcium phosphate between calcium oxalate crystals decreased the volume of pore spaces within calculi. Porosity was observed along boundaries betw een COM and GOD. Minute pores increased the surface area of caiculi exposed to urine, and this increase in liquid-solid interface promotes interaction of crystals with the surrounding urine. Conclusions and Clinical Relevance-Calcium oxalate urolithiasis is of major concern, because it is often a recurrent disease among dogs, principally t reated by surgical removal of calculi, with few effective dissolution strat egies. Understanding the ultrastructure and mineralogic content of calcium oxalate and its association with amorphous calcium phosphate is a step towa rd the solution of this increasingly important medical problem.