Accurately localizing the thyroid tissue in mature cystic teratoma of ovary by single-photon emission computerized tomography/computerized tomography

A 30-year-old woman was using propylthiouracil for 3 years due to hyperthyroidism. Although increased thyroid function was found, the gland was normal in ultrasonography (USG). Abdomen USG detected a cystic pelvic mass in left ovary. Magnetic resonance imaging showed 60 mm × 45 mm cystic mass in left ovary. Radioiodine uptake (10 µCi) and thyroid scintigraphy with 185 MBq (5 mCi) Tc-99m was also normal. A whole-body scan was performed 48 h after oral ingestion of 29.6 MBq (0.8 mCi) iodine-131 (I-131) capsule revealed a round structure located to the left lower abdomen. Iodine uptake was detected in this cyst that was compatible with functional thyroid tissue demonstrated by single-photon emission computerized tomography/computerized tomography (SPECT/CT) [Figure 1]. Left salpingo-oophorectomy was done with frozen section. Histopathology confirmed mature cystic teratoma that was containing thyroid follicles [Figure 2]. The euthyroid state was achieved. Struma ovarii is rare and usually benign ovarian teratoma, which consist of thyroid tissue in the ovarian mass. Most of these tumors are associated with hyperthyroid disease in 5–20%.[1] Clinical features may resemble ovarian malignancy and rarely can be metastatic.[2345] Typically presents as a multicystic mass with lobulated surface and thickened septic or cyst walls with some solid components. High attenuation areas and calcifications in the solid components are common findings on CT images.[6] Scintigraphy with Tc-99m pertechnetate, I-123, and I-131 was used for diagnosing a hyperfunctioning struma ovarii on the basis of higher uptake of the radionuclide with planar images.[2345] If the clinicians or nuclear medicine physician does not consider the extrathyroidal tissue as a result of hyperthyroidism patient's diagnosis cannot be made by the other nuclear medicine test such as I-131 uptake and thyroid scintigraphy. So, the extrathyroidal cause of hyperthyroidism can lead to the dilemma in nuclear medicine. In our patient, an I-131-thyroid uptake was in normal ranges, and a Tc-pertechnetate scan of the thyroid showed normal distribution. I-131 whole-body scan identified the cause of hyperthyroidism. Further, SPECT/CT localized the thyroid tissue in large pelvic mass accurately.

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Figure 1

A whole-body scan was performed 48 h after oral ingestion of 29.6 MBq (0.8 mCi) I-131 sodium iodide capsule revealed a focal uptake. (a) Planar image shows focal iodine uptake located to the left lower abdomen. In single-photon emission computerized tomography/computerized tomography images this focal uptake was corresponding to the solid components of the large cyst which is containing calcification (arrow). (b) Low dose unenhanced computerized tomography without intravenous contrast images. (c) Axial fusion single-photon emission computerized tomography/computerized tomography images. (d) Coronal fusion single-photon emission computerized tomography/computerized tomography images

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Figure 2

(a) Mature cystic teratoma of ovary. (b) Macroscopic photo of an opened ovarian cyst with hairs and greasy sebaceous material. This teratoma contains thyroid tissue (blue arrow). (c) Microscopic photo showing bone, thyroid tissue, a cystic spaces lined with smooth membrane and mucous glands (H and E, ×40). (d) Microscopic photo showing benign thyroid tissue and sebaceous glands in cystic wall of a benign multiloculated ovarian mature cystic teratoma cyst (H and E, ×100). (e) Microscopic photo showing benign thyroid tissue and cartilage in cystic wall of lesion (H and E, ×100)

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