large clot

[Rakay Dance]

I have a personal question for the venous specialists out there.  My 24 year old son has a clot in his Right leg from the iliac vein to his ankle and in the L leg from above the knee to the ankle.  We have no idea of the cause—Any ideas??  Also how is the rest of the country treating this problem?  Any help would be appreciated.     RaKay