Positron emission tomography for detecting iodine-131 nonvisualized metastasis of well-differentiated thyroid carcinoma: two case reports.
To investigate the usefulness of positron emission tomography (PET) in detecting I-131 nonvisualized metastatic foci of well-differentiated thyroid carcinoma (WDTC), 2 patients with papillary and follicular thyroid carcinoma respectively, were studied with I-131 total body scan, thallium-201 scan, Tc99m bone scan and [18F]-2-deoxy-2-fluoro-D-glucose (FDG) PET. Case 1 showed no metastatic lesion in I-131 (up to 150 mCi) total body scan, 1 anterior mass in thallium-201 scan, none in Tc99m bone scan and 7 including the main anterior mediastinal mass in FDG-PET. Case 2 showed 2 metastatic lesions in I-131 (150 mCi) total body scan, 11 bony metastatic lesions in Tc99m bone scan and 13 in FDG-PET. However, lower extremities were not scanned in FDG-PET. Tumor/background ratio of 1.5 or above is needed to be visualized grossly. The FDG-PET tumor/background ratios are higher than those of thallium-201 except in one site. In conclusion, I-131 scintigraphy is still the first line method to use in detecting WDTC recurrence and metastasis, as I-131 has the advantage of being both a therapeutic and imaging agent. For I-131 nonvisualized metastasis of WDTC, thallium scintigraphy and FDG-PET may be considered. Even though FDG-PET has better sensitivity, resolution imaging and spatial localization, this has to be balanced with its higher cost when compared with thallium scintigraphy.
Department of Internal Medicine, College of Medicine, National Taiwan University, Taipei, Taiwan.
T S
TS
Huang
P U
PU
Chieng
C C
CC
Chang
R F
RF
Yen
D018263:Adenocarcinoma, Follicular / Q000000981:diagnostic imaging; D000368:Aged; D002291:Carcinoma, Papillary / Q000000981:diagnostic imaging; D005260:Female; D019788:Fluorodeoxyglucose F18; D006801:Humans; D007457:Iodine Radioisotopes; D008297:Male; D009362:Neoplasm Metastasis / Q000000981:diagnostic imaging*; D019275:Radiopharmaceuticals; D013667:Technetium; D013794:Thallium Radioisotopes; D013964:Thyroid Neoplasms / Q000000981:diagnostic imaging*; D014055:Tomography, Emission-Computed
D007457:Iodine Radioisotopes; D019275:Radiopharmaceuticals; D013794:Thallium Radioisotopes; D019788:Fluorodeoxyglucose F18; D013667:Technetium