Microscopic Appearances:

The tissue between the cysts consists of connective tissue and a few atrophic tubules lined by low cuboidal epithelium. The glomeruli exhibit various stages of sclerosis. Some tubules contain pus. The interstitium contains foci of chronic inflammatory cells, and the small blood vessels show benign hypertensive changes. The appearances are diagnostic of acute-on-chronic pyelonephritis (inflammation of the kidney tubules, interstitium and renal pelvis) in a polycystic kidney.