Thank you for asking the query:
The swelling appears to be a condition called varicocele. A varicocele is caused by dilatation of the pampiniform plexus of 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.
Unfortunately without a clinical examination and Ultrasound of scrotum we cannot confirm the diagnosis. So I recommend you to visit a Surgeon or Urologist for further evaluation and a ultrasound scan.
This is not a life – threatening problem. Most of the cases the varicoceles are harmless. But in certain cases it may lead on to infertility and pain. So it is prudent to evaluate the mass and get treated.
Hope this helps. Please feel free to ask follow-up query.