Randall’s Plaques

Abstract

First described by Alexander Randall in the 1930s, carbapatite plaques formed in the interstitium of the inner medulla are now a major cause for calcium oxalate stone formation in western countries. At least 50% of all calcium stone formers (and even more than 75% of patients in the United States) exhibit such calcified deposits beneath and at the surface of the papillary epithelium as observed by endoscopic examination of kidney papillae. On the other hand, a majority of spontaneously passed calcium oxalate monohydrate stones exhibit a peculiar morphology suggestive of stone nucleation from a Randall’s plaque. The stones developed from a papillary plaque are easily identified by microscopic examination due to the presence of a concave, depressed zone (“umbilication”) at their surface, which corresponds to the attachment site at the tip of the papilla. The origin of the calcified deposits is the basement membrane of the deep thin Henle’s loops. Calcium phosphate then spreads out through the interstitium of the inner medulla. The mechanisms involved in the formation of these plaques are not yet entirely clarified. Metabolic examination of urine suggests a predominant role of hypercalciuria in concordance with a high urine pH and a high phosphate concentration in the interstitium and a possible link with diet. Low diuresis is another factor often found in patients who exhibit stones developed from a Randall’s plaque. As observed by electron microscopy from both tissue and stones, it appears that Randall’s plaques may extend around the vasa recta and collecting ducts, which may be pulled out of the tissue when the stone breaks away from the papilla.