Endocapillary hypercellularity

A normal appearing glomerulus (left) compared to a glomerulus with endocapillary hypercellularity (right). Note the hypercellular capillary loop (red arrow) compared to the normal capillary lumens (black arrows). This histologic feature can be seen in several glomerular disorders, including IgA nephropathy, post-infectious glomerulonephritis, lupus nephritis, and C3 glomerulopathy. Images courtesy of Patrick Walker, MD.

Acute tubular necrosis

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.