I developed bulging varicose veins after riding a couple of years on the inside of the left leg just below the knee. Doesn't bother me riding but I had to ask my doctor, who happens to be a vein specialist unbeknown to me, should I be worried. He asked if it hurt. I said no. He said, nothing to worry about. Come see me if it starts to hurt.
I did not dare tell him I take a perverse pleasure in hurting my legs climbing hills I could avoid.
But why in one leg I wonder? An imbalance somewhere (shorter or longer leg), a jacked back? I'm resigned to another fact of life that is likely to remain a mystery. Like balancing on a bike or slipping away each night into a coma, called sleep, or dying -- all mysteries, amazing mysteries.