What could the mass be?

Nine months ago I found a mass about two-three inches above the back of my left knee.  Palpable more now than before.  Size and shape is similar to a walnut.  Texture is firm but rubbery.  No pain when palpating however, pressure applied for any length of time causes purple mottling effect to lower limb with decreased sensation, numbness/tingling, and foot becomes cold to the touch.  Three questions...  What do you believe the mass may be?  Is the numbness, mottling, and coldness due to the mass compressing on nerves and vessels thereby cutting/slowing the circulation to my lower extremity?  Should I be seriously concerned?

[caregiver222]

It sounds like a vascular problem, rather than a tumor. Phlebitis, perhaps. Perhaps a prolapsed valve and a vein engorged with blood. On the other hand these things have to be checked out a physician, M.D. type, in person.

I don't believe you have a life-threatening situation, but you need to get into the system and have it properly diagnosed.

Generally resolution is surgical.