MSRA-2439

A 25-year-old man presents to the GP with a swelling in his scrotum. He is feeling well otherwise. Upon examination, there is a soft swelling on the right side of the scrotum that is painless and illuminates brightly with a pen torch. The swelling is localized to the scrotum, and the rest of the scrotum can be palpated above the mass. The testicle is palpable with no apparent mass. The patient is particularly concerned about the possibility of having testicular cancer.

What is the most probable diagnosis?