Structure of uric acid concretion developed around a catheter.

A uric acid concretion formed round a catheter (JJ stent) in the bladder and removed intact from the body together with the catheter was studied using an electron scanning microscope. The concretion was composed of anhydrous uric acid, some uric acid dihydrate (< 5 wt.%) and individual particles of calcium oxalate monohydrate. The stone interior was porous with frequent occurrence of differently sized cavities that were either empty or partially filled with particles of uric acid and/or calcium oxalate monohydrate. Calcium oxalate particles were not of crystalluria origin but developed in the cavity. The succession of processes leading to the stone formation was deduced from its inner structure. The stone was formed due to a crystalline growth with minor, if any, participation of sedimentation. The estimated average rate of the calculus development, 2 x 10(-9) m/s, confirms the predominant role of crystalline growth in stone formation and indicates a relatively low urinary supersaturation with respect to uric acid prevailing during the period of calculogenesis.