The origins of urinary stone disease: upstream mineral formations initiate downstream Randall's plaque.
OBJECTIVE
To describe a new hypothesis for the initial events leading to urinary stones. A biomechanical perspective on Randall's plaque formation through form and function relationships is applied to functional units within the kidney, we have termed the 'medullo-papillary complex' - a dynamic relationship between intratubular and interstitial mineral aggregates.


METHODS
A complete MEDLINE search was performed to examine the existing literature on the anatomical and physiological relationships in the renal medulla and papilla. Sectioned human renal medulla with papilla from radical nephrectomy specimens were imaged using a high resolution micro X-ray computed tomography. The location, distribution, and density of mineral aggregates within the medullo-papillary complex were identified.


RESULTS
Mineral aggregates were seen proximally in all specimens within the outer medulla of the medullary complex and were intratubular. Distal interstitial mineralisation at the papillary tip corresponding to Randall's plaque was not seen until a threshold of proximal mineralisation was observed. Mineral density measurements suggest varied chemical compositions between the proximal intratubular (330 mg/cm3) and distal interstitial (270 mg/cm3) deposits. A review of the literature revealed distinct anatomical compartments and gradients across the medullo-papillary complex that supports the empirical observations that proximal mineralisation triggers distal Randall's plaque formation.


CONCLUSIONS
The early stone event is initiated by intratubular mineralisation of the renal medullary tissue leading to the interstitial mineralisation that is observed as Randall's plaque. We base this novel hypothesis on a multiscale biomechanics perspective involving form and function relationships, and empirical observations. Additional studies are needed to validate this hypothesis.
Department of Urology, School of Dentistry, University of California San Francisco, San Francisco, CA, USA.
Ryan S
RS
Hsi
Department of Urology, School of Dentistry, University of California San Francisco, San Francisco, CA, USA.
Krishna
K
Ramaswamy
Division of Biomaterials and Bioengineering, Department of Preventive and Restorative Dental Sciences, School of Dentistry, University of California San Francisco, San Francisco, CA, USA.
Sunita P
SP
Ho
Department of Urology, School of Dentistry, University of California San Francisco, San Francisco, CA, USA.
Marshall L
ML
Stoller
D002114:Calcinosis / Q000150:complications*; D006801:Humans; D007674:Kidney Diseases / Q000150:complications*; D007679:Kidney Medulla; D008903:Minerals; D014545:Urinary Calculi / Q000209:etiology*
D008903:Minerals
calcification; kidney; physiological; urinary tract physiology; urolithiasis