Figure 14. Surgically proved intratesticular epidermoid cyst in a 21-year-old man. Longitudinal US scan of left testis reveals a well-circumscribed hypoechoic mass with a concentric lamellar pattern (curved arrow) of alternating hyper- and hypoechoic rings. This US appearance is referred to as the onion-ring appearance and is characteristic of epidermoid cyst. (Reprinted, with permission, from reference 115.)