I know this thread is pretty old, but I am experiencing the EXACT same thing. It came out of nowhere and was noticed when I was stretching my arms up while standing in the kitchen. Definitely sore to the touch and aggravated by stretching movement. I would appreciate any one sharing any information. I have a Dr appt on Monday, but I am a little freaked out and trying not to self diagnose from the internet is hard.
I have the same thing and no one knows what it is. I thought it was a lymph vessel or tissue next to the chest muscle. But, my DR. thinks I'm nuts. Did you find out what it is?
I can't imagine any large blood vessels on the chest that would appear near the surface of the skin across the chest and abdomen that would be visible like that. I'm rather pale and I can see some blood vessels snaking across my chest but they are no different than what I see on my arm. Nothing sinew-like as you described.
Hi, you may not see much confirming of this issue on this board, as it's a heart rhythm board. try googling with search terms like "map veins and arteries"