Varicoceles are enlarged veins of the pampiniform plexus of veins of the spermatic cord within the scrotum. These veins can enlarge when their valves become incompetent and fail to prevent blood from flowing properly. The left testicle may be commonly involved in patients with varicoceles.
If you or someone you know thinks they have a testicular mass, you should be seen by your primary care provider to determine if the mass is a varicocele or another more serious process.
For more information about varicoceles, you can review information from the U.S. National Library of Medicine at:
http://www.ncbi.nlm.nih.gov/pubmedhealth/PMH0002263/