What is significance of small bilateral renal cortical cysts if renal function tests are normal?

Not much, but. Need a follow up ultrasound in a few years to see if increasing suggestive of polycystic kidney disease (pkd). If this is the case there is a chance to lose kidney function over long years. It is not a cancer. But increasing cysts number and size can overtake kidneys. Chances are, none of that will happen to you. But, better safe than sorry. Pkd is a benign and slow condition but may cause failure.