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SUN-349 Rising Serum Thyroglobulin After Resection Of Papillary Microcarcinoma Leading To Discovery Of Benign Struma Ovarii

Year: 2025
Type: article
Abstract: Disclosure: R. Wang: None. M. Djekidel: None. S. Khutti: None. C. Taneja: None. Background: Struma ovarii is a rare ovarian teratoma consisting of more than 50% thyroid tissue, accounting for 1% of all ovarian tumors. Pre-operative diagnosis is challenging due to non-specific symptoms and difficulty to distinguish from other types of ovarian tumors. We present a unique case of benign struma ovarii discovered due to rising serum thyroglobulin (Tg) during surveillance after total thyroidectomy in a patient with papillary microcarcinoma. Case presentation: A 67-year-old female with hyperthyroidism secondary to Graves’ disease was noted to have bilateral thyroid nodules on sonography. FNA of dominant nodule showed atypia of undetermined significance (Bethesda III), with Afirma Gene Expression Classifier showing ‘suspicious’ nodule with approximately 40% risk of malignancy. She underwent total thyroidectomy which revealed unifocal 0.7 cm follicular variant papillary thyroid cancer (PTC) with negative margins, no angio-lymphatic invasion or extrathyroidal extension. She had detectable serum Tg (35 ng/mL) post-surgery, which was attributed to likely thyroid remnant from large substernal goiter and underlying Graves’ disease. No additional therapy was planned given the very low-risk intrathyroidal microPTC. Over the next 2 years, her Tg remained stable and surveillance neck ultrasounds showed no evidence of recurrence. Subsequently, a significant increase in Tg was noted (Tg 63, 147 and 609 ng/mL at 24-, 34- and 37-months post-surgery) without identifiable structural disease. She was treated with 142 mCi of I-131, with post-therapy scans showing intense iodine uptake in a complex cystic multiloculated mass in the right peri-adnexal region (17.5 x 10.2 cm). Resection of the mass revealed a cystic tumor with areas of hemorrhage and scattered atrophic tubules/follicles with small foci of atypia. Extensive metaplastic changes were present, true papillary structures were absent, and atypia appeared degenerative. Due to the presence of large areas of hemorrhage with mucinous and squamous lining epithelium, differential included endometrioma and teratoma. However, the rising Tg levels prompted immunohistochemical staining for thyroid markers, and microfollicles were highlighted by PAX8, TTF1 and Tg. The final diagnosis was benign struma ovarii with marked reactive and metaplastic changes. The patients Tg at 8 weeks post-resection of adnexal mass decreased to <0.2 ng/mL, indicating complete resection of the struma ovarii.Conclusion: This case highlights a unique etiology of rising Tg after total thyroidectomy for low-risk microPTC unrelated to thyroid cancer recurrence. Struma ovarii may demonstrate rapid growth and rapid Tg doubling time as an incidentally noted concerning feature. Rare diagnoses such as struma ovarii should always be considered in patients with unexplained rising Tg after total thyroidectomy, especially if noted to have an adnexal mass. Presentation: Sunday, July 13, 2025
DOI: 10.1210/jendso/bvaf149.2362
Language: English
Field: Medicine
Open Access status: gold
Estimated APC paid: $3,255
OpenAlex ID: W7093364906
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