"Onion skin" sign in an ovarian mucinous cyst.

The sonographic "onion skin" sign was initially described as concentric echogenic layers in mucinous tumors unrelated to the female reproductive system. Typically, the sonographic appearance of ovarian mucinous cystadenoma includes numerous septa and fine, gravity-dependent echoes. We present a case of the "onion skin" sign in a mucinous ovarian tumor.