Endoscopic and histologic images of Randall’s plaques in CaOx patients. In (a), an example of a papilla from a CaOx-stone former that was video recorded at the time of the mapping is shown. Several sites of Randall’s plaque (arrows) appear as irregular white areas beneath the urothelium in the CaOx patient. In addition, a plaque site was noted that lacked a urothelial layer and is thought to be a site where a stone had been attached to the side of the papilla (arrowhead). In (b), a low-magnification light-microscopic image of a papillary biopsy specimen from a CaOx patient is shown; the sites of calcium deposits (arrows) were stained black by the Yasue metal substitution method for calcium histochemistry. (c) A light micrograph shows large regions of crystal deposits in the interstitial tissue surrounding the ducts of Bellini (arrowhead), proceeding to the urothelium of the papillary tip (arrow), and progressing up the inner medulla. (d) A transmission electron micrograph shows the crystalline material (arrow) comprising Randall’s plaque to be normally covered by a complete layer of urothelium, making the plaque a suburothelial structure. Magnification, ×100 (b); ×600 (c); ×6,000 (d).