Hi and welcome to HCM.
Thanks for the query.
If this was there for 10 years then this is obviously some of the benign testicular lesions such as epydidimal cyst
so you dont have to be worried. However,to confirm my diagnosis you can do ultrasound
and further tests if neccessary but if there is no pain and fast growth then possiblity of tumor
is negligible. But in some cases testicle may become torsioned around cyst and then it must be urgently managed,but in this case you would have symptoms such as rapid testicle swelling,redness
and pain. WIsh you good health. Regards