Kidney, Renal Tubule - Vacuolation, Cytoplasmic

Cytoplasmic vacuolation is characterized by the presence of clear vacuoles in renal tubule epithelium in the absence of any morphologic changes associated with degeneration (Figure 1). Cytoplasmic vacuoles are normally present in the outer cortical tubules of male mice in certain strains, but are not typically present in female mice or rats. Abnormal, or pathologic, vacuolation may be seen anywhere along the various tubule segments and collecting ducts. It is more commonly observed in the proximal convoluted tubule epithelium. Vacuolation may be associated with single, larger vesicles (macrovesicular) or may be associated with several smaller vesicles (microvesicular). Osmotically active compounds such as some sugars often result in "osmotic nephrosis," which appears as cytoplasmic vacuolation. Cytoplasmic vacuolation of renal tubule epithelium may also be seen with phospholipidosis-inducing chemicals, cyclodextrins, and other chemicals that induce vacuolation through phagolysosomes. Cytoplasmic vacuolation, in most cases, is reversible. Artifactual vacuolation, related to autolysis or poor fixation, is frequently observed in animals either dying on test or sacrificed in a moribund state. Often it becomes problematic to separate tubule toxicity from artifact.