Kidney - Nephropathy, Obstructive

Obstructive nephropathy may result from inflammation associated with deposition of crystals, retrograde nephropathy, or a lower urinary tract outflow blockage. Whatever the cause, similar morphologic changes can be observed. Retrograde (reflux) nephropathy, a form of obstructive nephropathy, is related to a backflow phenomenon characterized by small clusters of dilated tubules that ascend from the papilla to the cortex and are due to increased urine reflux resulting from changes in the lower urinary tract (Figure 1 and Figure 2). Lesions of the lower urinary tract contributing to obstructive nephropathy may not always be detected microscopically,and thus the pathogenesis may remain unclear. Tubule features often include foci or areas of cortical basophilic tubules with distal tubule and collecting duct dilation (Figure 3 and Figure 4). Intraluminal inflammatory cells or an accompanying ascending pyelonephritis may or may not be present. Resolving lesions may result in tracts of fibrosis.