O. Söhnel

Phosphates precipitating from artificial urine and fine structure of phosphate renal calculi

Phosphates precipitating from artificial urine in the pH range 6-8 were identified using X-ray diffraction, chemical analysis and scanning electron microscopy. The influence of magnesium and citrate on phases precipitating from urine was established. From urine containing a normal quantity of magnesium (around 70 ppm), brushite accompanied by hydroxyapatite (HAP) precipitated at pH < or = 7.0 and struvite with HAP at pH > 7.0. HAP was formed exclusively from magnesium deficient urine at pH 7.0. Newberyite, octacalcium phosphate and whitlockite were not identified. The chemical and phase composition and inner fine structure of 14 phosphate calculi were studied. Three types of stones were distinguished based on their magnesium content: (i) stones rich in magnesium composed of struvite, hydroxyapatite and abundant organic matter, (ii) stones with low magnesium content constituted by calcium deficient hydroxyapatite, up to 5% of struvite, considerable amount of organic matter and occasionally brushite, and (iii) calculi without magnesium consisting of brushite, hydroxyapatite and little organic matter. Conditions prevaling during stone-formation assessed for each type of stone were confirmed by corresponding urinary biochemical data and corroborate the in vitro studies of phosphates precipitation.

Study on concretions developed around urinary catheters and mechanisms of renal calculi development

Aims: To study the structure and composition of encrustation and concretions developed on urinary catheters to better understand their formation mechanism to be able to prevent them. Methods: The surface of catheters was studied by direct and scanning electron microscopy observation. In vitro formation of encrustations was performed in synthetic urine. Results: The surface of catheters was covered by a continuous layer of organic matter, on which a thin scale consisting of crystals of calcium oxalate monohydrate (COM), uric acid anhydrous or calcium phosphate developed. Encrustations observed on catheters generally exhibited the same composition as the previously developed renal calculi. In catheters collected from patients without previous episodes of renal calculi or with previous episodes of infected renal calculi in which infection was afterwards eradicated, on the first organic layer, in that case plate-like COM crystals forming a columnar layer were observed. In vitro experiments demonstrated that COM columnar structures were only formed when normocalciuric urine containing organic matter was used, and the presence of crystallization inhibitors, as phytate, notably delayed their formation. Conclusion: Calcium oxalate was the main crystalline phase developed on catheters inserted in patients, specially in the absence of urinary infection or urinary pH values <5.5 and high urinary uric acid levels. Thus, prophylaxis of encrustations may consist of preventive measures usually applied in cases of recurrent idiopathic calcium oxalate urolithiasis.

Renal Stone Formation and Development

A concise account of formation mechanisms of attached (papillary) and unattached renal stones is presented. Urinary conditions prevailing at least during the stone forming period are indicated. Ten main categories of renal stones, covering over 95% of all conceivable calculi, are distinguished based on their composition and structure. Aetiologic factors leading to stone formation of every category are specified and general outlines of recommended treatment procedures indicated.

The influence of crystal morphology on the kinetics of growth of calcium oxalate monohydrate

The growth of several calcium oxalate monohydrate seeds in the presence and absence of additives (phytate, EDTA and citrate) has been followed by potentiometry measurements. Growth rates have been calculated from precipitate curves by a cubic spline method and represented in logarithmic plots versus supersaturation. Crystal growth kinetics were found to be dependent on crystal morphology, crystal perfection and degree of aggregation. Some seeds were dissolving in supersaturated solutions. Other seeds showed an initial growth phase of high-order kinetics. The effect of the additives was also different on each seed. Three alternative mechanisms for calcium oxalate crystal growth are proposed.

Artificial Simulation of Renal Stone Formation

The effect of natural admixtures occurring in human urine (citrate, pyrophosphate and glycosaminoglycans) on the precipitation of stone-forming compounds was studied. Experiments were carried out unde

Inhibition of calcium oxalate monohydrate crystal growth in high and low ionic strength solutions

The effect of additives on the kinetics of growth of calcium oxalate monohydrate crystals has been studied. Conductivity and potentiometry measurements have been compared. Growth rates were calculated from precipitate curves by a cubic spline method. An approach consisting on the calculation of rate constants and orders of reaction from logarithmic plots of growth rate versus supersaturation has been followed to study crystal growth kinetics. This method revealed that the presence of additives is causing not only a decrease on the rate constant but an increase on the order of reaction as well. The effect of additives (EDTA, citrate and phytate) was considerably weaker in high ionic strength media. Phytate produced a complete blockage of crystal growth in concentrations as low as 2 × 10 -6 mole/L in both methods.

A Study on Calcium Oxalate Monohydrate Renal Uroliths II. Fine Inner Structure

The inner fine structure of 30 human uroliths composed predominantly of calcium oxalate monohydrate was studied in detail. Each type of stone distinguished on the basis of qualitative parameters, viz. M1, M2, S1 and S2 (see Part I), exhibited a specific and characteristic inner structure different in several well-defined aspects from the other types. The inner structure suggests a sedimentary origin of the M1 type stone whereas the fixed particle origin of the M2, S1 and S2 stones, 3 types of core on which M2, S1 and S2 calculi developed were identified. The A type was represented by a void cavity with walls covered by an organic matter, the B type was formed by loosely arranged COM crystals and the C type was represented by a layer of an organic matter. Clinical observations lend support to the sedimentary origin of the M1 stones.

Role of Agglomeration in Calcium Oxalate Monohydrate Urolith Development

Formation of agglomerates of calcium oxalate monohydrate (COM) crystals on semi-batch precipitation performed at conditions relevant to urolithiasis (37 degrees C, pH = 6, initial ratio [Ca]/[Ox] = 10), but without any specific admixture, was followed by both optical and electron microscopy. COM crystals formed on precipitation developed into large agglomerates consisting of intergrown crystals by a mechanism of primary agglomeration. Primary agglomeration of COM crystals represents an important mechanism of COM renal calculi growth.

Study on calcium oxalate monohydrate renal uroliths. I. Qualitative properties.

Shape, colour, surface features and external appearance were determined from 33 human uroliths composed predominantly of calcium oxalate monohydrate (COM). Based on these properties COM renal stones were classified into mulberry (M) and spheroid (S) type, each of which was further divided into two well defined subtypes, M1-fused globules, M2-loose globules, S1-corrugated surface and S2-even surface. This classification indicates that only specific combinations of external characteristics could occur on COM renal uroliths. No apparent correlation between the stone type and respective biochemical urinary data transpired from available information.

Calcium oxalate monohydrate renal calculi. Formation and development mechanism

Available information relevant to stone genesis on both calcium oxalate monohydrate crystallization and fine inner structure of papillary calculi is reviewed. Integration of attained facts facilitated formulating a feasible mechanism of papillary calculi formation and development. Medical implications of this mechanism are assessed.