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1.Large testis after an infection remains large, needs to be evaluate the cause.
2.The possible causes could be inflammatory / infective causes with old healed granulomas, calcifications.
3.Could be collection of the fluid -
hydrocele, thickened chord, dilated venous channel.
4.
Ultrasound scrotum will help in evaluation of testicular size, blood supply, presence of fluid and other possibilities.
5.Mass lesion can not be ruled out - ultrasound will evaluate.
6.So if you want to be confident before starting relationship - get a scan done, that will give possible causes. Good luck.
Hope i have answered your query.
Any thing to ask do not hesitate. Thank you.