Epididymal cyst in a boy with a palpable scrotal mass. Longitudinal US scan shows a cystic lesion (C) that demonstrates increased sound transmission and replaces almost the entire epididymal head. This US appearance is indistinguishable from that of a spermatocele. T = testis.

http://radiographics.rsna.org/content/25/5/1197.figures-only