Epidermal cysts in the superficial soft tissue: sonographic features with an emphasis on the pseudotestis pattern

The purposes of this study were to report the sonographic features of superficial epidermal cysts with an emphasis on the characteristic pseudotestis appearance and to highlight the spectrum of ancillary findings.

The medical records and sonographic studies of all cases of surgically proven epidermal cysts (n = 42) from January 2005 through December 2009 were reviewed. Twenty-six epidermal cysts (62%) that appeared on sonography as ovoid nodules with homogeneous low to medium echoes, simulating a testicle, were included in the pseudotestis group. The other 16 epidermal cysts (38%) without the pseudotestis pattern were included in the nonpseudotestis group. The age, sex, lesion size, length to width ratio, sonographic appearances, and frequencies of rupture and infection were compared between the groups.

Epidermal cysts in the nonpseudotestis group presented as heterogeneously echoic or lobulated nodules or had a concentric ring or target appearance. There were no significant differences in the age, sex, lesion size, and length to width ratio between the groups. The pseudotestis group had significantly higher frequencies of intralesional bright echogenic reflectors and filiform anechoic areas than the nonpseudotestis group (P < .01). There were no significant differences in the associated ancillary sonographic features, including posterior acoustic enhancement, dermal attachment, focal dermal protrusion, and frequencies of rupture and infection between the groups.

In this study, two-thirds of the superficial epidermal cysts had a characteristic pseudotestis pattern on sonography, whereas the others could be suspected by recognition of the ancillary sonographic findings, including dermal attachment and focal dermal protrusion or a distinctive concentric ring or target pattern.