Tip lesion in early FSGS

Light micrograph shows a tip lesion (arrow), which is considered to be an early change in primary focal segmental glomerulosclerosis (FSGS). This lesion is characterized by epithelial cell injury and foam cell accumulation; note the enlarged cells with foamy cytoplasm in the lumen of the affected capillary. The lesion occurs at the "tip" of the glomerulus near the beginning of the proximal tubule.

Light micrograph of a normal glomerulus. There are only one or two cells per capillary tuft, the capillary lumens are open, the thickness of the glomerular capillary wall (long arrow) is similar to that of the tubular basement membranes (short arrow), and the mesangial cells and mesangial matrix are located in the central or stalk regions of the tuft (arrows).