Structural analysis of the formation of glomerular microaneurysms in the Habu venom model.

The goal of this study has been to characterize the process of glomerular microaneurysm formation and to separate it from capillary ballooning. In the Habu venom model glomerular capillary ballooning and glomerular microaneurysm formation are seen regularly. The sequence of glomerular lesions leading to a glomerular microaneurysm has been examined and it is clear that the process starts with local mesangiolysis. This may proceed to mesangial expansion and/or ballooning of glomerular capillaries but in contrast to ballooning the formation of a glomerular microaneurysm is based on endothelial defects. The process occurs as follows: once initiated by mesangial failure lesions extend along the mesangial axis. As long as the extension of the lesion encroaches on divergent capillary branches, capillary ballooning by "coalescence" is the result. This process comes to an end when convergent capillary branching is reached and two capillaries join. At this point endothelial disruptions occur, blood and mesangial spaces merge and a glomerular microaneurysm is established. Further growth of the microaneurysm occurs following damage spreading along the lobular axis. The entire process has been reconstructed and is presented in a three-dimensional model.