Abstract
The study of 4 cases of Xantogranulomatous Pyelonephritis (X. P.) and a review of the literature lead to the conclusions that X. P. is not an autonomous disease, but simply a stage in the development of subacute or chronic suppurative pyelonephritis. It depends on difficulty of drainage of necrotic material with increased cellular breakdown and liberation of lipids. These lipids are partly phagocitized by histiocytes, which become foamy as a result. At the same time the presence of this foreign material give rise to the formation of a granulomatous tissue. Further evolution towards fibrosis does not occur simultaneously throughout the kidney so that a mixed morphological picture can result. Xantogranulomas can coexist with suppurative areas or with completely sclerotic ones. In the end, when the replacement by connective tissue is completed, the morphological picture will be the same as with a common pyelonephritic atrophy. On the basis of this interpretation it is possible to suggest a convincing explanation about the low incidence of X. P., the absolute rarity of autoptic cases, the near constant localization in one kidney and the absence of changes in general lipid metabolism in every case where they have been thought.