Testicle hurts and the veins are swollen?

Varicocele: Most common cause of swollen testicular veins. Almost always on the left side of scrotum. Feels like a "bag of worms" when subject is standing and virtually disappears when lying down, sometimes associated by dull aching pain & sometimes left testicle smaller than right. Due venous back pressure from lack of or incompetence of spermatic vein valves preventing venous back-flow. Consult urologist.