Acute tubular necrosis (ATN). Note the tubules are not back-to-back due to interstitial edema (Masson trichrome staining, not shown, did not show appreciable fibrosis). There is blebbing and sloughing of tubular epithelial cells (black arrows) with loss of the brush border, as well as flattening of the renal tubular epithelium (black arrowhead) due to tubular dilation.

Image courtesy of Joseph Gaut, MD PhD.