Structural changes of the intravesical ureter in children with vesicoureteral reflux-does ischemia have a role?

Previous studies have revealed structural and metabolic changes in the distal most ureter, impairing its contractile properties, and, thus, having a role in the pathogenesis of vesicoureteral reflux. Musculature and nerves are replaced by interstitial collagen, while matrix degrading enzymes are over expressed. We investigated the microvessel architecture of the ureterovesical junction to elucidate further the pathophysiology of vesicoureteral reflux.

Ureteral endings were obtained from 28 children during antireflux surgery. Ureteral tissue from 14 age matched autopsy specimens served as control. Routine histological paraffin embedded sections were immunostained, detecting CD31 as an endothelial marker as well as vascular endothelial growth factor. Microvessel density and vascular endothelial growth factor expression were investigated based on computer assisted high power field magnification analyses. The t test and the Spearman rho test were applied for statistical evaluation.

Overall, microvessel density was significantly reduced in cases of vesicoureteral reflux. While reflux grade and age were not correlated with microvessel density, it was particularly decreased in regions lacking smooth musculature. Vascular endothelial growth factor was observed in smooth muscle, endothelial and connective tissue cells. Additionally, cellular vascular endothelial growth factor expression was markedly abridged in cases of vesicoureteral reflux compared to healthy controls.

Overall microperfusion is supposed to be impaired, leading to tissue ischemia due to reduction of vascular endothelial growth factor expression and subsequent microvessel density. Diminished ureteral perfusion is likely to induce and support smooth muscle dysfunction as well as subsequent extracellular matrix remodeling, including increased collagen deposition. These ongoing functional and structural alterations may further deteriorate the active valve mechanism of the ureterovesical junction, causing vesicoureteral reflux.