Vascular anatomy, leg swelling - question for Christine

I'm thinking about pelvic vasculature as a suspect for my left leg edema. I've had chronic swelling of the left leg for 4 or 5 years and they cannot tell me why. They cannot even tell me if it is lymph insufficiency or venous insufficiency. I've had basic tests covering the acute bad stuff, and they ruled it all out. (Kidneys, heart, liver, DVT, tumors, etc.)

The swelling responds profoundly to steroids and anti-inflammatories. Since I also have an unrelated autoimmune disease, this has led me (and my doctors) to conclude the left leg swelling might be some localized vasculitis, or other autoimmune inflammation. Not wanting to do invasive biopsies or dye-injected radiographs, we've treated it conservatively.

But I don't want to stay on strong anti-inflammatories long term so I'm continuing to pursue a diagnosis. The kidney doctor, after ruling out kidney disorder, suggested maybe my uterine prolapse is "compressing a vein" in my pelvis. I poo-poo'd that suggestion, saying that if anti-inflammatories make the swelling go down, how could the cause be MECHANICAL?

Well I am not one to leave any stone unturned, so I googled vessel compression ad nauseum and low and behold I come up with a syndrome called May-Thurner disease, which results in swelling of only the left leg. The right iliac artery normally crosses over the left iliac vein, as they both branch out to the two legs, right about the level of the pelvic inlet. In people with May-Thurner, the artery compresses the vein against the vertebrae, causing reduced blood flow to the left leg. This in turn causes insidious swelling in only the left leg. Most cases go undiagnosed until the patient develops a DVT in that leg due to sluggish venous return, throws the clot and has a pulmonary embolism, OR the clot obliterates the iliac vein at the point of narrowing, causing the leg to become massively swollen, purple, and excruciatingly painful. This is a vascular emergency. Since this is a less common incident, they say it's possible many of us have May-Thurner's that will never be diagnosed.

Still, if that is mechanical, why would anti-inflammatories resolve my swelling... when to my shock, I read that as the artery pulses against the vein, it causes the two interior sides of the vein to rub together, irritating them, and causing them to become inflamed! Wow... maybe the kidney doctor was partially right after all... a mechanical compression COULD create a condition anti-inflammatories might treat. But still, it seems unlikely to me that the uterus is the culprit. Unless... the uterus pulls or tugs it's blood vessels and by turn the upward vessels they're connected to, changing the relationship and causing a venous compression.

Or at lower levels, where the vein further branches to the leg, or, lymph vessels - could the uterus, or any of the structures or tissues, be applying direct pressure, or tugging, in such a way as to block or narrow a vessel? Have you ever heard of this, thought about it or come up with any theories? And more broadly, what are your thoughts about lymphedema of the leg in general? (Or venous insufficiency - varicose veins would be related.) When it doesn't have an obvious cause, like surgery (BY THE WAY permanent lymphedema is another terrible side effect of pelvic surgery! You don't have to have a lymph node dissected for cancer either, regular pelvic floor repair, hysterectomy, or simple c-section can cause this!) But since "idopathic" lymphedema is so common in middle aged woman, have you come across any theories from the non-western sources about causes and natural treatments? Right now I'm seeing a lymphedema therapist who is treating with massage, exercise, and gentle compression bandages. I'm finding it very effective, and much preferable to drugs.