Calcium Oxalate Calculi Found Attached to the Renal Papilla: Preliminary Evidence for Early Mechanisms in Stone Formation

Background: Calculi are commonly found attached to the renal papilla in calcium oxalate (CaOx) stone formers, but the mechanisms by which stones form in this manner are not well established. Materials and Methods: Data are presented from three attached stones collected from different patients. Stone morphology and composition were determined using micro computed tomography (CT) and infrared microspectrometry. Results: One of the stones was composed of CaOx with a peripheral region of apatite, such as might have come from a Randall's plaque. Another stone was covered with large CaOx crystals but contained at least two layers of apatite, with no apatite regions exposed at the surface. The third stone contained CaOx with inclusions of apatite and more apatite on its surface, along with a substantial volume of poorly mineralized material that could not be identified. Conclusions: The complexity of these stones and their differing morphologies do not by themselves allow inference of the mechanism of stone formation. Future work will require the careful documentation of attached stones on the papilla, as well as study of the papilla after the stone has been removed, before it can be determined whether such diverse CaOx stones originate from the same or different underlying etiologies.