Physicochemical mechanisms of stone formation

In this article, the term physicochemical mechanism is defined as a sequential series of steps culminating in the formation of a renal stone. Distinctions are drawn between physicochemical prerequisites for urinary supersaturation, crystallization, and stone formation. In particular, attention is focussed on the transition from crystal to stone. Emphasis is laid on crystal retention being the fundamental mechanism by which stones are formed, and mention is made of the different ways in which it can be achieved. The processes which dictate crystal-size enlargement, either during free particle flow or during fixed particle entrapment, are described. Modulators of these processes are classified in terms of their mode of action on particular steps in the mechanism rather than on their molecular weight or size. Three different approaches for describing stone formation mechanisms are summarized. These involve mathematical models, qualitative step-by-step pathways, and qualitative non-schematic descriptions. It is suggested that although physicochemical mechanisms are crucially involved in stone formation, they do so in concert with numerous other mechanistic processes, all of which are dictated by their own specific conditions.