Department of Radiology, Kagoshima University Graduate School of Medical and Dental Sciences, Kagoshima, Japan.
Department of Pathology, Kagoshima University Graduate School of Medical and Dental Sciences, Kagoshima, Japan.
Medicine (Baltimore). 2022 Jul 1;101(26):e29282. doi: 10.1097/MD.0000000000029282.
I-131 radioiodine false-positive findings in postoperative patients with differentiated thyroid cancer (DTC) should be recognized to avoid unnecessary therapies.
A 50-year-old man underwent I-131 therapy 3 times, including the initial ablative therapy after total thyroidectomy for papillary thyroid cancer. The initial I-131 posttherapeutic whole-body scintigraphy showed 2 cervical and one superior mediastinal focal I-131 positive uptake lesions. The serum thyroglobulin level was negative every time when the radioiodine therapy was performed. Although the 2 cervical positive uptake lesions disappeared after the second therapy, the superior mediastinal I-131 positive uptake persisted even after the third therapy, and this lesion was suspicion of I-131 therapy-resistant node metastasis.
The lesion was resected, and the pathological diagnosis with immune-histochemical analysis was a thymic cyst with thymic epithelial cells having a weak expression of the sodium-iodide symporter (NIS).
The false-positive result may be attributed to the NIS expression in the thymic cyst epithelial cells. It is necessary to include a thymic cyst in the differential diagnosis, when I-131 uptake is noted in the superior mediastinal region on I-131 posttherapeutic scans of patients with postoperative DTC. Although the I-131 positive uptake in a thymic cyst may be influenced by the I-131 administered dose and scan timing after I-131 administration, the NIS expression may be essential to the false-positive uptake in a thymic cyst.
术后分化型甲状腺癌（DTC）患者的 I-131 放射性碘假阳性结果应得到识别，以避免不必要的治疗。
一名 50 岁男性，因甲状腺乳头状癌行甲状腺全切除术后接受了 3 次 I-131 治疗，包括初始清除治疗。初始 I-131 治疗后全身闪烁扫描显示 2 个颈部和 1 个上纵隔局灶性 I-131 摄取阳性病变。每次进行放射性碘治疗时，血清甲状腺球蛋白水平均为阴性。尽管第 2 次治疗后 2 个颈部摄取阳性病变消失，但上纵隔 I-131 摄取阳性病变仍持续存在，甚至在第 3 次治疗后也如此，该病变被怀疑为 I-131 治疗抵抗的淋巴结转移。
切除病变，行病理诊断和免疫组化分析，诊断为胸腺囊肿，其内胸腺上皮细胞弱表达钠碘同向转运体（NIS）。
假阳性结果可能归因于胸腺囊肿上皮细胞中的 NIS 表达。当术后 DTC 患者的 I-131 治疗后扫描发现上纵隔区域有 I-131 摄取时，需要将胸腺囊肿纳入鉴别诊断。尽管胸腺囊肿中的 I-131 摄取阳性可能受到 I-131 给药剂量和给药后扫描时间的影响，但 NIS 表达可能是胸腺囊肿中假阳性摄取的关键。
