struma ovarii struma ovarii a struma ovarii (literally: goitre of the ovary) is a rare form of monodermal teratoma that contains mostly thyroid tissue, which may cause hyperthyroidism. struma ovariimicrograph of a struma ovarii. characteristic thyroid follicles are seen on the right, and ovarian stroma on the left. h&e stain.specialtyoncology despite its name, struma ovarii is not restricted to the ovary. the vast majority of struma ovarii are benign tumours; however, malignant tumours of this type are found in a small percentage of cases. radiologic findings the ultrasound (us) features of struma ovarii are nonspecific, but a heterogeneous, predominantly solid mass may be seen. us demonstrates a complex appearance with multiple cystic and solid areas, findings that reflect the gross pathologic appearance of the tumor. magnetic resonance imaging findings may be more characteristic: the cystic spaces demonstrate both high and low signal intensity on t1- and t2-weighted images. some of the cystic spaces may demonstrate low signal intensity on both t1- and t2-weighted images due to the thick, gelatinous colloid of the struma. no fat is evident in these lesions. additional images low magnification high magnification