Testicular epidermoid cysts: sonographic features with histopathologic correlation.

Testicular epidermoid cysts are rare, accounting for 1% of all testicular tumors. We present the sonographic appearances of epidermoid cysts in 3 cases, together with the histopathologic correlation. In case 1, sonography showed an intratesticular hypoechoic mass with a well-defined echogenic rim; the mass measured 1.8 x 1.5 x 1.5 cm, and there was no evidence of calcification. In case 2, sonography showed a well-circumscribed mass measuring 1.3 x 1.3 x 1.0 cm, with alternating hypoechoic and hyperechoic rings (onion-ring appearance) and no calcifications. In case 3, sonography showed a 2.4- x 2.3- x 2.3-cm, well-circumscribed, oval mass with a heterogeneous echotexture and an outer hypoechoic halo. The mass contained plaque-like regions of increased echogenicity, with peripheral acoustic shadowing from refraction artifact. Hypoechoic clefts were visualized posterior to the plaque-like areas. The triad of findings-sonographic appearance of an onion ring, avascularity on Doppler sonography, and negative results of tumor marker studies-is highly suggestive of an epidermoid cyst.