I Have Had A Pulsating Vein In My Left Temple

I have had a pulsating vein in my left temple for a few years. It doesn't hurt at all but is most noticeable when at night when I am lying down. When I am quiet at night it seems to spread a little further and pulsates more! Nobody seems to know what this is. Would be grateful if a doctor could tell what it is and if it can be treated. Thank You