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Rebound Thymic Hyperplasia Detected by 18F-FDG PET/CT After Radioactive Iodine Ablation Therapy for Thyroid Cancer

 Jeon Tae Joo  ;  Lee Yong Sang  ;  Lee Jae-Hoon  ;  Chang Hang Seok  ;  Ryu Young Hoon 
 THYROID, Vol.24(11) : 1636-1641, 2014 
Journal Title
Issue Date
Ablation Techniques/adverse effects* ; Adolescent ; Adult ; Female ; Fluorodeoxyglucose F18* ; Humans ; Iodine Radioisotopes/adverse effects* ; Iodine Radioisotopes/therapeutic use ; Male ; Middle Aged ; Multimodal Imaging ; Retrospective Studies ; Thymus Hyperplasia/diagnostic imaging* ; Thymus Hyperplasia/etiology ; Thyroid Neoplasms/radiotherapy* ; Tomography, Emission-Computed ; Young Adult
Background: Rebound thymic hyperplasia (RTHP) is not an uncommon finding after radiation or chemotherapy in patients with various malignancies. However, there are limited case reports of this phenomenon after radioactive iodine ablation therapy (RIAT) in differentiated thyroid cancer (DTC). The goal of this study was to evaluate the incidence, patterns, and factors affecting RTHP after RIAT using 18F-FDG PET/CT.

Methods: The study design was a retrospective review of 2550 patients (568 men, 1982 women; age 13–79 years) who underwent FDG PET/CT imaging after total thyroidectomy and RIAT from June 2009 through June 2012. Patients were divided into four age-related subgroups. Overall incidence, age-related incidences, and sex distribution were evaluated in patients with thymic FDG uptake on PET/CT (RTHP+). The correlation between incidence of RTHP and age was assessed using the Cochran–Armitage trend test. The Wilcoxon rank–sum test and multiple regression were applied to investigate the effect of applied dose of radioactive iodine (RAI) and age on the incidence of RTHP. Correlations of standardized uptake value (SUV) and thymic volume with age and morphologic type were also evaluated.

Results: Overall incidence of RTHP after RIAT was 1.49%, and all of the RTHP+ patients except one were female. The Cochran–Armitage trend test revealed significantly decreased incidence from the second to fifth decade (8.84%, 1.74%, 0.98%, and 0.39% respectively; p<0.001). In each age-related subgroup, the RAI dose was significantly higher in the RTHP+ than RTHP− group (p<0.001), while there was no difference in RAI dose in RTHP+ patients among age-related subgroups (p=0.838). SUVmean and SUVmax of RTHP revealed no meaningful correlation with RAI dose or age. There were no differences among morphologic patterns of RTHP in age distribution and ablation dose.

Conclusions: RTHP after RIAT showed a strong female predominance, despite the higher administration dose of RAI in male patients. Although the decreased incidence of RTHP after RIAT with age is similar to the pattern of RTHP induced by other causes, the fact that older patients, even sixth decade patients, can present with RTHP after RIAT is noteworthy in the management of DTC.
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1. College of Medicine (의과대학) > Dept. of Nuclear Medicine (핵의학교실) > 1. Journal Papers
1. College of Medicine (의과대학) > Dept. of Surgery (외과학교실) > 1. Journal Papers
Yonsei Authors
Ryu, Young Hoon(유영훈) ORCID logo https://orcid.org/0000-0002-9000-5563
Lee, Yong Sang(이용상) ORCID logo https://orcid.org/0000-0002-8234-8718
Lee, Jae Hoon(이재훈) ORCID logo https://orcid.org/0000-0002-9898-9886
Chang, Hang Seok(장항석) ORCID logo https://orcid.org/0000-0002-5162-103X
Jeon, Tae Joo(전태주) ORCID logo https://orcid.org/0000-0002-7574-6734
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