Kidney stones can vary in size and texture and are made up of calcium layers, similar to other sedimentary deposits in nature.
They affect more men than women; more than 10 percent of men develop them, compared with 7.1 percent of women.
Passing kidney stones can be extremely painful. The stones are primarily made of a substance called calcium oxalate, which was believed — until now — to be insoluble in the kidney.
However, new research suggests that this may not be the case. Drawing knowledge from the fields of geology, microscopy, and medicine and using many advanced technologies, a new study finds that kidney stones can and do, in fact, dissolve.
The new findings reveal additional information about the nature and composition of kidney stones, running against the understanding of kidney stones that has prevailed for centuries.
Mayandi Sivaguru, an associate director at the Carl R. Woese Institute for Genomic Biology at the University of Illinois at Urbana-Champaign, is the first author of the paper, now published in the journal Scientific Reports.
'A minute-by-minute record of kidney health'
Sivaguru and colleagues used a combination of the latest optical techniques to study thin sections of kidney stones.
They explain that many of the visualization techniques used in this study are common in geology and geobiology but have never been used to examine mineralizations in vivo.
One technique used — super-resolution nanometer-scale auto-fluorescence microscopy — allowed the researchers to view slices of kidney stones at a resolution of 140 nanometers. A nanometer is a billionth of a meter.
The analysis revealed that kidney stones are made of "alternating organic matter- and mineral-rich nano-layers" of crystals. Moreover, these layers are "strikingly similar" to other ancient sedimentary deposits, such as "marine stromatolites, ooids, and oyster shells and pearls," among others.
Co-lead study author Bruce Fouke, a professor of geology and microbiology from the University of Illinois, explains what the findings mean, saying, "In geology, when you see layers, that means that something older is underneath something younger. One layer," he states, "may be deposited over the course of very short to very long periods of time."
So, "Instead of being worthless crystalline lumps, kidney stones are a minute-by-minute record of the health and functioning of a person's kidney," adds Prof. Fouke.
"[J]ust one rock represents a whole series of events over time that are critical to deciphering the history of kidney stone disease."
Dissolving stones 'right in a patient's kidney'
Importantly, the study also revealed that some of these layers had degraded, uncovering "disrupt crystals." The images showed that new crystals had started to develop, suggesting that kidney stones "undergo multiple events of dissolution as they crystallize and grow within the kidney."
In other words, kidney stones cyclically dissolve and grow back, says co-lead study author Jessica Saw, an M.D. student at the Mayo Clinic School of Medicine in Rochester, MN, and a Ph.D. student at the University of Illinois.
"Before this study," she claims, "it was thought that a kidney stone is just a simple crystal that gets bigger over time. What we're seeing here is that it's dynamic. The stone is growing and dissolving, growing and dissolving. It's very rich with many components. It's very much alive."
This contradicts a belief that has been held for centuries: that kidney stones are homogenous and essentially insoluble in vivo.
"Contrary to what doctors learn in their medical training, we found that kidney stones undergo a dynamic process of growing and dissolving, growing and dissolving," Prof. Fouke explains.
"This means that one day we may be able to intervene to fully dissolve the stones right in the patient's kidney, something most doctors today would say is impossible."
Prof. Bruce Fouke
"These observations," conclude the researchers, "open a fundamentally new paradigm for clinical approaches that include in vivo stone dissolution."