One of the most common causes of kidney swelling, called hydronephrosis, is a condition known as acute unilateral obstructive uropathy, states Healthline. This condition occurs when a blockage suddenly develops in one of the ureters.
An obstacle in one of the ureters causes urine to travel back to the kidneys, leading to swelling. Kidney stones are the most common cause of ureter blockages, explains Healthline, but scarring and blood clots can also be causes. A kink in the ureteropelvic junction, tumors in or near the ureter, and narrowing of the ureter as a result of an injury or birth defect also leads to ureter blockages and, in turn, swelling of one or both kidneys.