Renal parenchymal malakoplakia: ultrastructural findings in different stages of morphogenesis.

Light microscopic and ultrastructural findings in five cases of renal parenchymal malakoplakia detected in renal biopsy specimens (four cases) or observed at autopsy (one case) are reported. The spectrum of ultrastructural changes ranging from lamellar and microvesicular phagolysosomal inclusions arranged in a biphasic pattern to fully developed Michaelis-Gutmann bodies is described. In three of the biopsy cases the lesions appeared to represent early stages of malakoplakia lacking classic Michaelis-Gutmann bodies. Especially in this phase of disease, ultrastructural investigation can distinguish between this condition and other histiocytic interstitial renal processes. The findings show that focal cytoplasmic degeneration and autophagolysosomal processes observed in macrophages could precede the disturbance in the process of bacterial breakdown that is responsible for the peculiar granuloma-like inflammatory histiocytic reaction.