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Indian J Nucl Med
Indian J Nucl Med
IJNM
Indian J Nucl Med
Indian Journal of Nuclear Medicine : IJNM : The Official Journal of the Society of Nuclear Medicine, India
0972-3919
0974-0244
Wolters Kluwer - Medknow India

IJNM-39-210
10.4103/ijnm.ijnm_24_24
Case Report
Delusory Radioiodine Uptake in Endometriotic Ovarian Cyst
Farhoudi Farinaz
Student Research Committee, School of Medicine, Shiraz University of Medical Sciences, Shiraz, Iran
Address for correspondence: Dr. Farinaz Farhoudi, Student Research Committee, School of Medicine, Shiraz University of Medical Sciences, Shiraz, Iran. E-mail: farhoudif.ff@gmail.com
May-Jun 2024
17 8 2024
39 3 210212
24 2 2024
12 3 2024
01 4 2024
Copyright: © 2024 Indian Journal of Nuclear Medicine
2024
https://creativecommons.org/licenses/by-nc-sa/4.0/ This is an open access journal, and articles are distributed under the terms of the Creative Commons Attribution-NonCommercial-ShareAlike 4.0 License, which allows others to remix, tweak, and build upon the work non-commercially, as long as appropriate credit is given and the new creations are licensed under the identical terms.
A 25-year-old woman with a known case of papillary thyroid carcinoma conventional type referred to our center for treatment with radioactive iodine after total thyroidectomy. She received 200 mCi of radioiodine, and in the whole-body scan 1 week after the radioiodine therapy, an area of increased absorption was seen on the right side of the pelvis, which was diagnosed as an endometriotic ovarian cyst in the follow-up examinations.

Endometriotic ovarian cyst
false-positive radioactive iodine uptake
I-131 whole-body scan
ovarian cyst
==== Body
pmcIntroduction

The management of patients diagnosed with differentiated thyroid carcinoma typically involves the surgical removal of the entire thyroid gland, followed by the administration of radioactive iodine therapy. To evaluate the possible presence of metastasis to the neck and other parts of the body, a whole-body scan and measurement of blood serum thyroglobulin level are used.[1] Understanding the underlying factors contributing to the erroneous uptake of radioactive iodine is crucial for preventing unnecessary additional examinations. Here, we report a case of false-positive radioiodine uptake in an endometriotic cyst of the right ovary.

Case Report

A 25-year-old woman, known case of papillary thyroid carcinoma conventional type, has been referred to this center for treatment with radioactive iodine after total thyroidectomy. She received 200 mCi of radioiodine for the second time due to rising thyroglobulin levels (Tg>500ng/ml) and in the scan 1 week after the radioactive iodine therapy, an area of radioiodine accumulation was seen on the right side of the pelvis [Figure 1]. To rule out the possibility of metastasis in the pelvic cavity, single-photon emission computed tomography (CT)-CT was done in which radioiodine accumulation was localized in a cystic lesion in the right adnexa, in favor of an ovarian cyst [Figure 2]. Further evaluation with magnetic resonance (MR) images before and after intravenous gadolinium administration revealed a cystic lesion in the right adnexa measuring 19 mm, which shows hyperintensity on T1-weighted images and hypointensity (shading) on T2-weighted images. The shading sign is a characteristic pattern of endometriotic cysts at MR imaging [Figure 3].

Figure 1 Anterior (blue arrow) and posterior (red arrow) views of whole-body scan one week after radioiodine therapy showing radioiodine accumulation in the right side of the pelvic cavity

Figure 2 Single-photon emission computed tomography (CT)-CT (blue arrow) images showing I-131 uptake localizing to a cystic lesion in the right adnexa

Figure 3 A cystic lesion is noted in the right adnexa measuring 19 mm, which shows hyperintensity on coronal T1-weighted image (a) and hypointensity (shading) on coronal T2-weighted image (b). The shading sign is a characteristic pattern of endometriotic cysts at magnetic resonance imaging. Coronal T1-fatsat sequence after the administration of intravenous gadolinium (c)

Discussion

Following a complete removal of the thyroid, patients undergo an I-131 whole-body scan to detect any remaining thyroid tissue or signs of cancer spread. Posttreatment whole-body scans may reveal more areas of radioactive iodine uptake compared to the initial diagnostic scan in 6% to 13% of cases.[1] The sodium iodide symporter (NIS) is a strong transporter of iodine, responsible for concentrating radioiodine into the active thyroid tissue.[23] NIS is also found in salivary glands and gastric mucosa,[4] resulting in the uptake of radioactive iodine at these locations. Iodine is eliminated through the urinary system, resulting in physiological absorption in the kidneys and bladder. In addition to these physiological locations, some nonthreatening conditions may also exhibit higher RAI avidity, including blockage of the nasolacrimal duct, thymus, Meckel’s diverticulum, cysts in the liver and kidneys, adrenal adenoma, vascular aneurysms, and nabothian cysts.[256] While uncommon, the literature has documented instances of RAI uptake in different types of ovarian cysts, including endometrioid cysts, mucinous ovarian cystadenomas, dermoid cysts, and simple ovarian cysts.[7891011] Receiving the lowest dose rate is one of the most important concerns in iodine therapy[12] so it is crucial to distinguish between these noncancerous conditions and metastases to prevent unnecessary treatments and exposure to radioactive iodine.

Declaration of patient consent

The authors certify that they have obtained all appropriate patient consent forms. In the form, the patient(s) has/have given his/her/their consent for his/her/their images and other clinical information to be reported in the journal. The patients understand that their names and initials will not be published and due efforts will be made to conceal their identity, but anonymity cannot be guaranteed.

Financial support and sponsorship

Nil.

Conflicts of interest

There are no conflicts of interest.
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