These veins in the back of the thigh are either nonsaphenous tributaries or tributaries of the small saphenous system. Either way, you need to have a DUplex vein scan in an accredited vascular lab under the directionof a vein specialist and the decision can be made if you need ablation of the small SV in conjunction with sclerotherapy or sclerotherapy alone. See an ABVLM certified vein specialist. Dr H Karamanoukian
As doctor Landi wrote;Do dupplex ultrasound to rule out underlying truncal (GSV, SSV, etc) veins disorder, if negativeFoam sclerotherapy will clean up those veins nicely.Make sure to chose accredited vascular lab for dupplex and experienced, ABVLM-certified physician for your injection