<s>[INST] I had a sting like feeling on my scrotum on the left side. Inspection of the skin shows a vessel that is bright blue/purplish. The vein itself, almost like a blocked vessel. The sting is lengthy and just irritating. What could this be? No problems on the penis itself. [/INST] Greetings Sir. It's unfortunate that you got this problem. All your description confirm and suggestive of a condition called 'Varicocele'(a scrotal abnormality defined by elongated, dilated and tortuous veins that drain the testicle).Note:Best advise is to go a doctor and get yourself a Physical examination, in order to find the nature and grade of your problem so that further complication can be prevented.  He may advise you surgery which is absolutly necessary in order to avoid INFERTILITY. Reasons for Varicocele Repair The reasons to fix a varicocele include:1) An adolescent with a large varicocele & of a smaller testis on the side of the varicocele.2) For varicocele-induced scrotal pain 3) For correction of male factor infertility 4)To raise mildly low testosterone levelsHope it helped. </s>