Radioiodine concentration by the thymus in differentiated thyroid carcinoma: report of five cases

Abstract

The radioactive iodine has been used with great value as a diagnostic and therapeutic method in patients with differentiated thyroid carcinoma previously submitted to total thyroidectomy. False-positive whole-body scans may occur due to misinterpretation of the physiologic distribution of the radioisotope or lack of knowledge on the existence of other pathologies that could eventually present radioiodine uptake. Thymic uptake is an uncommon cause of false-positive whole-body scan, and the mechanism through which it occurs is not completely understood. The present paper reports five cases of patients with differentiated thyroid cancer who presented a mediastinum uptake of radioiodine in a whole-body scan during follow-up. The patients had either histological or radiological confirmation of the presence of residual thymus gland. It is very important to know about the possibility of iodine uptake by the thymus in order to avoid unnecessary treatment, such as surgery or radioiodine therapy. Arq Bras Endocrinol Metab. 2009;53(7):874-9. KeywordsThyroid neoplasms; thyroid gland; thymus gland; iodine isotopes; radionuclide imaging resumo O iodo radioativo tem sido utilizado com grande valia como método diagnóstico e terapêutico em pacientes com carcinoma diferenciado de tireoide previamente submetidos à tireoidectomia total. Resultados falso-positivos na pesquisa de corpo inteiro (PCI) podem ocorrer por má interpretação da distribuição fisiológica do radioisótopo ou por não conhecimento da existên-cia de outras patologias que podem eventualmente captar o radioiodo. Captação pelo timo é uma causa incomum de resultado falso-positivo e o mecanismo pelo qual ocorre não é totalmente esclarecido. O presente trabalho relata cinco casos que apresentaram PCI positiva em mediastino durante o seguimento, com comprovação histológica ou tomográfica sugestiva de timo. Ressalta-se a importância do conhecimento dessa possível causa de falso-positivo a fim de se evitar tratamentos desnecessários. Arq Bras Endocrinol Metab. 2009;53(7):874-9.

Radioiodine uptake in A Renal CYST in A Patient with Papillary Thyroid Carcinoma

“…However, tracer uptake has also been reported less commonly in nonthyroidal tissues, including thymus and breast, in areas of inflammation, and in cases of spina bifida, ovarian teratomas, and cysts, raising suspicion of possible metastasis (7)(8)(9)(10)(11)(12)(13). Multiple theories to explain this phenomenon of tracer uptake have been suggested, with the earliest being a possible connection between the cyst and the renal pelvicalyceal system.…”

Fixation inhabituelle au balayage à l’iode-131 : un textilome !

“…Il a également été décrit des fixations du radioiode au niveau d'un kyste lymphoépithélial à localisation médiastinale, au niveau d'hydrocèle chronique ainsi que sur des brûlures du derme [12]. D'autres fixations à mécanisme non encore expliqué sont aussi rapportées [7,13]. Par exemple, la fixation thymique a été décrite et son mécanisme est mal connu.…”

Incidentally Visualization of the Thymus on Whole-Body Iodine Scintigraphy

“… 2 , 3 The whole body scan (WBS) with 123 I or 131 I is the gold standard imaging for the detection of thyroid remnant and regional or distant metastases, thus being routinely used for evaluation before and after radioiodine therapy. 4 – 7 However, false-positive WBS may occur because of radioiodine uptake by normal or pathological tissues that are not related to the thyroid tissue. This could lead to unsuitable therapy, such as unnecessary surgery or administration of 131 I.…”

“…There are many normal tissues that commonly accumulate iodine, such as breasts, salivary glands, gastrointestinal, and urinary systems. 4 , 5 In addition, pathological uptake has been reported in neoplastic diseases or pulmonary inflammatory, sinusitis, pericardial effusions, esophagus pathologies, urinary tract diseases, ovarian cysts or tumors, and traumatic lesions. 5 – 8 Radioiodine uptake by normal thymus is an uncommon reason of false-positive WBS that might be considered as lung or mediastinal nodes metastases.…”

“…5 – 8 Radioiodine uptake by normal thymus is an uncommon reason of false-positive WBS that might be considered as lung or mediastinal nodes metastases. 4 , 9 – 12 It should be borne in mind to recognize this condition in order to facilitate distinction between this normal variant and metastases. We present two patients with DTC, who underwent total thyroidectomy and 131 I therapy that had 131 I concentrate in the mediastinum during the follow-up, and provide a review of the latest insights.…”