An 82-year-old asymptomatic woman with breast cancer underwent mastectomy and tamoxifen therapy. A transvaginal ultrasound was performed for endometrial evaluation 4 years after initiating tamoxifen. No vaginal bleeding or discharge was reported and the serum CA125 was normal. Magnetic Resonance (MR) imaging was then performed.
On transvaginal ultrasound, it was observed a right ovarian complex cystic lesion with a solid parietal component (red arrow) and multiple thick septa (yellow arrow) (Fig. 1).
On MR, a multi-loculated predominantly cystic mass with solid parts was identified. The cystic spaces demonstrate both high (red arrow) and low signal intensity (from gelatinous colloid - yellow arrow) on T2-weighted image (Fig 2). On T1-weighted image (Fig 3) the colloid areas are hyperintense (yellow arrow). Hypervascularized septa (yellow arrow) and solid component (red arrow) are seen on T1-contrast enhanced image (Fig. 4). The solid portion has low signal intensity at diffusion-weighted-imaging (Fig.5) obtained with a b value of 1000 sec/mm2 and showed a relatively intermediate apparent diffusion coefficient value (Fig.6), indicating unrestricted diffusion.
Total hysterectomy and adnexectomy were then performed. The histopathologic exam was compatible with cystic struma ovarii (presence of thyroid tissue, with positive tireoglobulin and TTF-1).
Struma ovarii is majority a benign and very rare ovarian tumour. It is a subtype of ovarian mature teratoma and the most common form of monodermal teratoma. The presence of macroscopic and histologically detectable thyroid tissue with variable-sized follicles with colloid material characterize this identity . It accounts for 0.3–1 % of all ovarian tumours . It presents generally with a peak of incidence in the 5th decade of life.
The clinical manifestations of an uncomplicated and non-functioning struma ovarii often overlap with those of other diseases. In the absence of thyrotoxicosis, most patients are asymptomatic or present with non-specific clinical features. The diagnosis is often delayed until the development of symptoms related to ovarian hyperthyroidism or ascites . When struma ovarii is not associated with hyperthyroidism, imaging does not allow the differentiation from other cystic masses.
CA125 is a tumour marker of ovarian carcinoma but it has little clinical value in struma ovarii patients because it can be elevated in both benign and malignant subtypes .
Histologically, the proportion of thyroid tissue present in struma ovarii lesion must be more than 50 % of the overall tissue . Struma ovarii does not demonstrate lipid material .
It usually presents as a unilateral multi-loculated cystic adnexal mass with solid components. Ascites is often present. Therefore, its imaging features usually overlap with those of malignant ovarian tumours. At ultrasound, struma ovarii usually manifests as non-specific heterogeneous multilocular cystic ovarian mass with solid components [1,4].
Computed tomographic findings are non-specific and it demonstrates a complex multiple cystic and solid lesion 
MR imaging is the more important technique used to characterize these lesions and it should include diffusion-weighted imaging. The typical MR imaging appearance of struma ovarii includes multiple intra-cystic solid components which represent thyroid tissue. The solid component presents with variable signal intensities and usually demonstrate low signal intensity on T2-weighted images and intermediate signal intensity on T1-weighted images. The cystic space demonstrates both high and low signal intensity on T1- and T2-weighted images. However, some cystic spaces may demonstrate low signal intensity on both T1- and T2-weighted images due to the presence of gelatinous colloid material. This variable signal intensity is highly characteristic of struma ovarii. Marked enhancement of the thickened septations and solid components is also seen. On diffusion-weighted images, the hyperintense solid components demonstrate restricted diffusion [1,6].
Treatment of struma ovarii is done with surgical resection.
 Dujardin M, Sekhri P, Turnbull L. (2014) Struma ovarii: role of imaging?. Insights Imaging 5:41–51 (PMID: 3948908)
 Clement PB, Young RH, Scully RE (1991) Clinical syndromes associated with tumors of the female genital tract. Semin Diagn Pathol 8:204–233. (PMID: 1759057)
 Willemse PH, Oosterhuis JW, Aalders JG et al (1987) Malignant struma ovarii treated by ovariectomy, thyroidectomy, and I131 administration. Cancer 60:178–182 (PMID 3297279)
 Outwater EK, Siegelman ES, Hunt JL (2001) Ovarian teratomas: tumor types and imaging characteristics. Radiographics 21:475–490(PMID: PMID: 11259710)
 Shen J, Xia X, Lin Y, Zhu W, Yuan J (2011) Diagnosis of struma ovarii with medical imaging. Abdom Imaging 36:627–631(PMID: 21104246)
 Matsuki M, Kaji Y, Matsuo M, Kobashi Y (2000) Struma ovarii: MRI findings. Br J Radiol 73:87–90. (PMID: 1072132)
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