My 4 Year Old Son Has A Vein That Bulges

My 4 year old son has a vein that bulges out on the lower right side -- I think it's his Brachiocephalic vein -- when he talks loudly or yells. It kind of "pops" out, then disappears. I've noticed it for some time but it seems to be more pronounced lately. He is a super skinny kid with little body fat/ lots of muscle. Is this anything to be worried about?