What Causes Prominent Vein Over The Top Of Ribs?

I have had what seems to be a vein over the top of my ribs on the right side that has been enlarged to a little larger than a pencil for over a week now. For the first several days it was sore to the touch but now its not but it is harder now than before. I m a 40 year old male in good shape with only mild hypertension and reflux both controlled with med. Thanks for any insight.