Epidermoid cyst and teratoma of the testis: sonographic and histologic similarities

The classic sonographic description of an epidermoid cyst is a mass with a target or onion ring appearance of alternating rings of hyperechogenicity and hypoechogenicity. This study presents a pathologic-sonographic assessment of classic and nonclassic appearances of an epidermoid cyst of the testis and reports the possible similarity between a classic epidermoid cyst and a teratoma on sonography.

We reviewed the sonographic and histologic features of 8 testicular tumors that either had a classic onion ring pattern or were found at pathologic examination to be epidermoid cysts but did not have the classic sonographic pattern.

Three epidermoid cysts had a typical onion ring appearance. Histologic sections of these tumors revealed a squamous epithelial layer lining the cyst and multiple concentric laminated layers of keratin. Two tumors did not have a typical sonographic appearance of epidermoid cysts but were found to be epidermoid cysts at pathologic examination. One was homogeneously hypoechoic, and the other had irregular cystic and solid components, but neither had a target or onion ring appearance. Histologically, both of these tumors consisted of cystic cavities lined by squamous epithelium and contained desquamated keratinized epithelium. Notably, 3 other tumors pathologically diagnosed as teratomas had a sonographic appearance of classic epidermoid cysts. These tumors contained layers of keratin, but the cyst was lined by both squamous cells (ectodermal origin) and cylindrical epithelium (endodermal origin), thereby precluding the diagnosis of epidermoid cysts.

There is considerable overlapping of the sonographic appearances of teratomas and epidermoid cysts of the testis. Although the onion ring appearance of an intratesticular tumor is suggestive of an epidermoid cyst, this appearance may also be found in cases of a teratoma. Whereas the former condition can be treated by local enucleation, the latter requires radical orchiectomy.