Hello - thanks for asking your question.
You may be describing what is known as a
varicocele. A varicocele is caused by dilatation of the spermatic veins. It is present in 15 to 20 percent of post-pubertal males, occurring in the left hemiscrotum in the vast majority of cases. The venous complex in the scrotum dilates and produces anything from minimal fullness on Valsalva maneuver (i.e. when bearing down) to a large soft scrotal mass ("bag of worms") that decompresses and disappears in the recumbent position.
In any case, I would schedule an appointment with your personal physician for a scrotal ultrasound to exclude other causes of scrotal swelling (i.e. cancer, masses or cysts).
A referral to a urologist is strongly recommended as varicoceles are associated with infertility.
I strongly suggest followup with your personal physician.
I stress that this answer is not intended as and does not substitute for medical advice - please see your personal physician for further evaluation of your individual case.
Thanks,
Kevin, M.D.