Scanning electron microscopy of calcium oxalate crystal formation in experimental nephrolithiasis

The formation of calcium oxalate crystals was induced in rat kidneys by intraperitoneal injections of sodium oxalate. After varying lengths of time of sodium oxalate challenge the rat kidneys were fixed and prepared for scanning electron microscopy. Calcium oxalate crystals were found in the lumina of renal tubules and closely applied to the tubular epithelium. A number of proximal tubules exhibited considerable loss of brush border. Crystals were basically of two types. Calcium oxalate monohydrate crystals were more common, consisted of platelike crystallites, and revealed various shapes. The different shapes appeared to be the reflection of their growth pattern. Calcium oxalate dihydrate crystals, on the other hand, were tetragonal in habit and generally dipyramidal. Precipitation of oxalate crystals appeared to start with the formation of dihydrates, but later both types were formed simultaneously. No indications of solid phase transformation of dihydrate to monohydrate was found. However, the possibility of dissolution of dihydrate followed by the recrystallization as monohydrates cannot be ruled out.