Hi Chroma- the clots were actually found because they blocked the vein completely. I felt a twinge in my bicep and immediately could feel my forearm swelling. I looked down and could see it expanding. I checked my arm in the mirror and saw 2 large blue spots on my bicep. I pushed on them to see if they were bruises, but they didn't hurt. My entire arm started swelling and turning red/purple. By 4 minutes my arm was swollen 3 times and blue from fingers to shoulder. I don't have cervical ribs- it was my first rib compressing. My vascular surgeon determined TOS by the CT scan. He could see the interscalene triangle was too small. (Where first rib, clavicle and scalene muscle cross.) Hope this helps.