MECHANISM OF STONE FORMATION

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Urinary stone disease has afflicted humankind since antiquity. A bladder stone was found in an Egyptian skeleton more than 7000 years old.8 Urolithiasis is a common disorder affecting 1% to 5% of the population in industrialized countries with a lifetime risk of 20% in white men and 5% to 10% in women.37 The recurrence rate without treatment for calcium oxalate renal stones is 10% at 1 year, 35% at 5 years, and 50% at 10 years.53 In the United States, urolithiasis accounted for 0.9% of hospital discharges with a mean stay of 3 days, costing 1.83 billion dollars in 1993.4 An understanding of the mechanism of stone formation helps to manage patients better, thereby significantly reducing the morbidity and health care costs associated with urolithiasis. In this article the authors discuss the physical basis of stone formation followed by the pathophysiology of the various types of urinary stones.

Section snippets

PHYSICAL CONCEPTS

Urolithiasis is a consequence of complex physical processes. The major factors are supersaturation and crystallization, inhibitors, complexors, promotors, and matrix. The sequence of events leading to urinary stoneformation is as follows: saturation → supersaturation → nucleation→crystal growth or aggregation → crystal retention → stone formation

MECHANISM OF FORMATION OF VARIOUS TYPES OF STONES

The various types of urinary stones and their incidence in United States are listed in Table 2. The pattern of urolithiasis shows significant geographic variation. For instance, close to 90% of urinary stones in India are pure calcium oxalate, whereas only 14% of urinary stones are pure calcium oxalate in Israel.8

CONCLUSION

Urolithiasis causes significant morbidity to patients in addition to adding substantially to health care costs. Remarkable advances have been made in understanding urolithiasis during the last 200 years, yet clinicians are far from curing patients of their urinary stone disease. The basis of urolithiasis is crystal formation, retention, and growth. When the urine is supersaturated with a stone-forming substance, it forms crystals in the presence of other favorable factors, namely pH, promotors,

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    Address reprint requests to K.C. Balaji, MD, Division of Urology, Department of Surgery, University of Massachusetts Medical Center, 55 Lake Avenue North, Worcester, MA 01655

    *

    From Division of Urology, Department of Surgery, University of Massachusetts Medical Center, Worcester, Massachusetts

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