F-18 FDG PET in insular thyroid cancer.
OBJECTIVE
Insular thyroid cancer (ITC) is known to be a rare subtype of follicular thyroid carcinoma showing poor differentiation and an unfavorable prognosis. The authors evaluated the use of F-18-fluorodeoxyglucose (FDG) positron emission tomography (PET) for restaging and follow-up in ITC.


METHODS
Five patients (2 male, 3 female) with elevated thyroglobulin levels (mean, 86 ng/mL; range 1.3-180 ng/mL) during follow-up underwent FDG PET (Siemens ECAT Exact 47). PET results were correlated to histopathologic and radiologic findings as well as to the results of whole-body radioiodine scintigraphy. In 1 patient a series of 4 PET scans was done.


RESULTS
FDG PET showed a total of 10 tumor sites, at least 1 in each patient. Four of those lesions were detected by computed tomography (CT) as well, which in addition revealed 3 lesions that had normal glucose consumption. Five PET lesions were missed by the CT scan because they were found outside the examined volume of CT. Only 1 PET-positive lesion was also radioiodine positive. Three radioiodine-positive lesions with normal glucose metabolism were detected.


CONCLUSIONS
As known for well and poorly differentiated thyroid cancer of the follicular epithelium, ITC may also show discordance between radioiodine studies and FDG-positive lesions. Given their initially poor differentiation, the ITC clearly showed the expected dominance of less well-differentiated, FDG-positive lesions. Therefore, FDG PET seems to be a very useful tool for the staging and restaging of such tumors.
Diehl
Michaela
M
Department of Nuclear Medicine, Hospital of Johann Wolfgang Goethe University, Frankfurt, Germany. m.diehl@em.uni-frankfurt.de
Graichen
Sinikka
S
Menzel
Christian
C
Lindhorst
Elmar
E
Grünwald
Frank
F
D018263:Adenocarcinoma, Follicular / Q000000981:diagnostic imaging* / Q000628:therapy; D000368:Aged; D005260:Female; D019788:Fluorodeoxyglucose F18; D006801:Humans; D008297:Male; D008875:Middle Aged; D009367:Neoplasm Staging; D019275:Radiopharmaceuticals; D012189:Retrospective Studies; D013964:Thyroid Neoplasms / Q000000981:diagnostic imaging* / Q000628:therapy; D014055:Tomography, Emission-Computed; D014057:Tomography, X-Ray Computed
D019275:Radiopharmaceuticals; D019788:Fluorodeoxyglucose F18