Cystic struma ovarii: imaging findings.

We report three cases of cystic struma ovarii not associated with any solid component. One case was a thin-walled unilocular mass, and the other two cases were multilocular cystic masses. An area of signal void on T2-weighted images and intermediate intensity on T1-weighted images was noted in the two multilocular cases. Preoperative diagnosis was difficult in each case, but struma ovarii should be included in differential diagnoses even in the case of a completely cystic ovarian mass.