Scanning electron microscopy images of sections of COM papillary calculi from patient 1. (a, b) A type I calculus, in which COM columnar crystals started to develop in the concave zone in close contact with papillary tissue. (c, d) A type II calculus with a hydroxyapatite core (arrow) in or near the concave zone. (e, f) A type III calculus that developed on the papilla tip, with its concave zone containing hydroxyapatite, calcified tissue and calcified tubules (arrow). (g, h) A type IV calculus in which the core, situated near the concave zone (arrow), was formed by the intergrowth of COM crystals and organic matter.
Grases et al. BMC Urology 2013 13:14 doi:10.1186/1471-2490-13-14