Should An Ankle Purple Birthmark Be Treated By Medication Or Removed Surgically?

My son was born with a purple birthmark on his ankle and I was told that in time it would disappear. He is now 15 and the birthmark is still visable and has become crusty over the years. Sometimes bits of the crust will fall off or when he plays sport his sock gets caught on the birthmark and causes the crust to fall off and the wound will bleed.It hasnt got any bigger in size but it hasnt shrunk either. Should he get this removed or is their any medication/creams that will help.