A case of nonfunctional struma ovarii preoperatively diagnosed by scin
tigraphy of the pelvis using I-123 NaI is reported. US, CT, and MRI re
vealed a multilobulated mass composed of cystic and solid components.
CT showed cystic components with slightly high density and MRI showed
various signal intensities on T1- and T2-weighted images. I-123-scinti
graphy of the pelvis showed uptake in the pelvic mass. Microscopic exa
mination revealed the histologic appearance of thyroid tissue accompan
ied by follicular adenoma. I-123 scintigraphy of the pelvis was useful
for reaching the correct preoperative diagnosis in this patient with
nonfunctional struma ovarii.