Tubular vacuolization in renal allografts can be related to calcineurin inhibitor toxicity, ischemic injury though other less commonly recognized conditions exist.
Osmotic nephrosis is caused by administration of many
agents such as sucrose, dextran, maltose and contrast media. In renal allografts, it can occur as the result of IVIG administration in acute rejection because IVIG preparation may contain sucrose or maltose. The term seems to be a misnomer because the etiology is not the accumulation of water due to different osmotic gradient. The pathogenesis involves pinocytosis of the causative molecules by the proximal tubular cells, then the molecules fuse with lysosomes to form vacuoles. The high concentration of these agents administered to the patients with impaired renal function (impaired lysosomal clearing function) in a relatively short period of time results in massive accumulation of the vacuoles and further impairs renal function.
Histologically the proximal tubular cells show clear cell transformation due to accumulation of vacuoles. The vacuolated tubular cells are often seen side by side with the normal ones. This change is sometime difficult to differentiate with acute calcineurin inhibitor in allograft biopsy.
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