New studies on papillary calculi.

Five hundred spontaneously passed stones were collected during a three-year period in an outpatient clinic. They were studied under a stereoscopical optical microscope. Complementary analyses were performed with infrared spectroscopy, scanning electron microscopy and EDAX. There were 142 true papillary stones (28.4%). The rest (71.6%) showed different non-papillary patterns. Papillary stones, type 1 (61 calculi), had an apatite plaque of intrapapillary origin of which 14 showed calcified tubules. Type 2 showed other substances, presumably due to crystalluria but not to an interstitial papillary process (28 stones). Type 3 showed no plaques in their concave faces (53 stones). In types 1 and 2 whewellite is a secondary growth, the plaque acting as a trigger for the development of calcium oxalate. The possibility of hidden Randall's plaques is discussed. Stones with papillary patterns are not as rare as hitherto considered and merit microscopical study.