Concretions in renal basement membranes.

A study of 196 renal biopsies was carried out by electron microscopy. In 78 cases concretions were detected, which x-ray microanalysis (EDAX) proved to be calcium phosphate deposits. Concretions always occurred in damaged basement membranes, especially in the basement membranes of Bowman's capsules and of proximal convoluted tubules. They were frequently also found in sclerotic foci. Both nephrotic syndrome (through hypercholesterolaemia) and progressive sclerotic processes seem to play a role in the pathogenesis of concretion formation. Concretions are considered to represent early dystrophic calcification.