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Background: The likelihood of a Randall's plug composed of calcium oxalate monohydrate (COM) forming by the free particle mechanism in a model of kidney with a structure recently described by Robertson was examined at the most favourable conditions for the considered mechanism., Methods: The Robertson model of the kidney is used in the following development. The classical theory of crystallization was used for calculations., Results: Initial COM nuclei were assumed to form at the beginning of the ascending loop of Henle where the supersaturation with respect to COM has been shown to reach the threshold level for spontaneous nucleation. Nucleation proceeds by a heterogeneous mechanism. The formed particles are transported in the nephron by a laminar flow of liquid with a parabolic velocity profile. Particles travel with a velocity dependent on their position in the cross-section of the nephron assumed to be straight tubule with smooth walls and without any sharp bends and kinks. These particles move faster with time as they grow as a result of being surrounded by the supersaturated liquid. Individual COM particles (crystals) can reach maximum diameter of 5.2 × 10 -6  m, i.e. 5.2 μm, at the opening of the CD and would thus always be washed out of the CD into the calyx regardless of the orientation of the CD. Agglomeration of COM crystals forms a fractal object with an apparent density lower than the density of solid COM. The agglomerate that can block the beginning of the CD is composed of more crystals than are available even during crystaluria. Moreover the settling velocity of agglomerate blocking the opening of the CD is lower than the liquid flow and thus such agglomerate would be washed out even from upward-draining CD., Conclusions: The free particle mechanism may be responsible for the formation of a Randall's plug composed by COM only in specific infrequent cases such as an abnormal structure of kidney. Majority of incidences of Randall's plug development by COM are caused by mechanism different from the free particle mechanism.

Background: Chemical composition of internally non-homogeneous phosphate stones should be related to the conditions prevailing during the formation of each individual part., Objective: The object of this paper was to provide a detailed study of phosphate stone composition on the micro- and macro-scales., Methods: Fine inner structure, chemical and phase composition of 10 phosphate calculi from different patients were determined by chemical (wet) analysis, observation by scanning microscope, semi-quantitative determination of Ca, Mg, P and C by energy dispersive X-ray and by X-ray diffraction. Results. Eight calculi are formed by amorphous calcium phosphate and two by hydroxyapatite. Magnesium was inversely related to Ca/P ratio. Point chemical composition of solid phase varies in wide limits, i.e. composition of calculus interior is highly inhomogeneous on the microscale. All studied calculi contained an abundance of organic matter incorporated in their volume; the content of carbon was double the calcium content in molar quantities., Conclusions: Phosphate renal calculi with the low Ca/P molar ratio predominantly consist of amorphous calcium phosphate whereas those with a high Ca/P molar ratio are composed of poorly crystalline hydroxyapatite which can be partially carbonated. Magnesium may be an inhibitor of HAP formation from urine. Abundant organic matter incorporated into the calculus volume indicates its decisive role at stone formation. Variable point composition of stones implies widely varying conditions during their 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., (Copyright 2001 S. Karger AG, Basel.)

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.

Density and content of mineral constituents were determined for 33 human calcium oxalate monohydrate (hereafter COM) uroliths whose external appearance and inner structure were described in part I and II respectively. Studied stones contained 0.13-0.42 wt.% of struvite, 0.68-4.12 wt.% of hydroxyapatite, 73-96 wt.% of COM and 3-10 wt.% of water unbound in a crystallohydrate 10 to 20 wt.% of calculus mass is not accounted for by chemical analysis. Density of COM calculi varying between 1.67 and 2.06 g cm-3 is not a function of any single stone parameter. Around 30% of stone volume is not occupied by crystalline components. The mulberry stones of sedimentary origin contained higher amount of organic matter than papillar and mulberry stones displaying site of attachment to epithelium.

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.

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.

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.

Possible effects of crystal agglomeration on the early stages of calcium oxalate papillar stone formation are evaluated. The collecting ducts are filled with liquid that flows laminarly as established through hydrodynamical and physicochemical considerations. Under such conditions, agglomeration due to laminar shear forces proceeds. Agglomeration of calcium oxalate monohydrate crystals present in urine at a concentration typical for clinically observed crystalluria cannot result in the formation of a particle sufficiently large enough to be retained in the Bellini's duct and become a papillar stone nidus (nucleus). Formation of such an aggregate during the passage time of urine through the duct requires an unrealistically high concentration of crystals in urine, one that exceeds the normal content of urinary oxalate by several orders of magnitude. Aggregates obstructing the Bellini's duct as assumed in the free particle theory cannot represent a major factor in stone formation. This conclusion is corroborated by experimental results and other observations.

A new technique simulating some of the conditions experienced by papillar and caliceal oxalocalcic stones during the early stages of their generation was developed. This technique enables the study of how conditions prevailing at calculogenesis, such as pH, composition of urine and presence of admixtures, influence the rate of formation and development, the crystalline texture and the composition of the concretion formed. Results achieved with this technique demonstrate that: (1) an appropriate substrate always gives rise to a crystalline concretion if it is in contact with supersaturated urine; (2) primary agglomeration plays a significant role in concretion development whereas secondary agglomeration is of minor importance; and (3) citrate and pyrophosphate exert a considerable influence on the shape and composition of particles constituting the concretion.

Fine structure, location and size of the core of 12 calcium oxalate monohydrate (COM) papillar calculi from different 'idiopathic' stone-formers were studied by an optical and scanning electron microscope equipped with the EDAX analytical device. Each individual core exhibited a unique overall structure composed of loosely arranged twined and intergrown crystals of plate-like and/or columnar shape and particles of 'rosette' structure with considerable void space among crystals in some cases or compact structure in others. Crystals were covered by a thin layer or organic material mostly invisible to the microscope. Sometimes debris of organic origin in a core was observed. A substantial amount of organic matrix appeared at the core boundary, often in the form of amorphous plates. The outer striated layer of COM stone consisting of tightly packed columnar crystals originated on this matrix. The stone core was located near the stone surface that was attached to the kidney wall and contained foreign particles that act as heterogeneous nucleants of calcium oxalate crystals.

Based on reconsideration of the contemporary knowledge on calcium oxalate urolithiasis a feasible mechanism of calculi generation is suggested. Experimental findings and clinical aspects supporting the suggested mechanism are presented. The ways of urolithiasis treatment and areas of future research are indicated.

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 under conditions closely simulating the early stages of renal stone formation. Among the studied admixtures, citrate was determined as the most effective substance preventing the phosphate particle formation. Indeed, in the presence of citrate, some calcium oxalate monohydrate crystals were found. Pyrophosphate induced the formation of calcium oxalate dihydrate crystals. Phosphate crystals appeared at pH 6 and never at pH 5. The easy formation of phosphate particles supports the hypothesis that these crystals represent a very important heterogeneous nucleus-initiating oxalocalcic calculus formation in the kidney. Reported results also indicated uric acid as a significant heterogeneous nucleus of calcium oxalate monohydrate crystals at urinary pH equal or lower than 5 and the important role of bacteria in increasing the organic detritus deposited on the solid surfaces.