A formal test of the hypothesis that idiopathic calcium oxalate stones grow on Randall's plaque.
OBJECTIVE
To confirm that more than half of all idiopathic calcium oxalate (CaOx) stones grow on interstitial plaque, as CaOx stones can grow attached to interstitial apatite plaque but whether this is the usual mechanism of stone formation is uncertain.


METHODS
In nine idiopathic CaOx stone formers (ICSF) undergoing percutaneous nephrolithotomy or ureteroscopy all accessible renal papillae were endoscopically imaged using a digital endoscope. All stones were removed intact, and recorded by the operating surgeon as being attached or unattached; for all attached stones the surgeon determined if the site of attachment was to plaque. This determination was further verified by reviewing the intraoperative video record, and only instances where plaque was reliably seen on video were used for analysis. Surgical observations were further validated by a combination of microcomputed tomographic analysis and papillary biopsy. The results were analysed statistically using fixed-sample testing and group sequential sampling.


RESULTS
The nine patients had a total of 115 stones, primarily CaOx; 90 stones were attached. Of these, 81 were attached to plaque; surgeons could not visualize the site of attachment with sufficient clarity to judge in the other nine cases. Based on these data, the final point estimate for the number of stones attached to plaque was 0.754 (95% confidence interval 0.575-0.933; P = 0.013).


CONCLUSIONS
In ICSF most stones grow attached to papillae, on plaque, so growth on plaque is the main mechanism for stone formation in this very common group of patients.
Miller
Nicole L
NL
Department of Urologic Surgery, Vanderbilt University, Nashville, TN, USA. nicole.miller@Vanderbilt.edu
Gillen
Daniel L
DL
Williams
James C
JC
Evan
Andrew P
AP
Bledsoe
Sharon B
SB
Coe
Fredric L
FL
Worcester
Elaine M
EM
Matlaga
Brian R
BR
Munch
Larry C
LC
Lingeman
James E
JE
D000328:Adult; D000368:Aged; D002129:Calcium Oxalate / Q000032:analysis*; D005260:Female; D006801:Humans; D007669:Kidney Calculi / Q000737:chemistry / Q000209:etiology* / Q000601:surgery; D007679:Kidney Medulla; D008297:Male; D008875:Middle Aged; D009403:Nephrostomy, Percutaneous; D014741:Video Recording
D002129:Calcium Oxalate