FDG PET of recurrent or metastatic 131I-negative papillary thyroid carcinoma.
This study reports on the use of FDG PET in the follow-up of papillary thyroid cancer patients with negative findings on 131I total body scans and elevated levels of thyroglobulin after total thyroidectomy.


METHODS
Eleven asymptomatic patients with previous papillary thyroid cancer, total thyroidectomy, 131I ablation, and treatment of all known metastases had negative findings on 131I total body scans after therapy but persisting elevations of thyroglobulin when not receiving thyroid hormone. All imaging before PET failed to show persisting tumor. FDG PET was performed on all patients while receiving full thyroid hormone replacement, except for the repeated scan of 1 patient (patient 6). After the PET scan, all patients were referred for supplementary CT, sonography, or biopsy of lesions in the neck.


RESULTS
All 11 patients showed FDG uptake in the neck or upper mediastinum-in the initial scan in 10 and in a repeated scan in 1. Sonographically guided biopsy confirmed malignancy in 6, was nondiagnostic in 2, and showed normal findings in 1. In 2 patients, the sonographic results were normal and no biopsy was attempted. FDG imaging redirected the treatment of 7 patients, resulting in surgery and external beam radiotherapy in 3, surgery in 1, and external beam radiotherapy in 2. One patient declined further recommended surgery. The other 4 patients remain under observation. Surgical histopathology confirmed thyroid tumor in all 4 surgically treated patients. Retrospective review of the original histopathology slides showed no preponderance of aggressive histology.


CONCLUSIONS
FDG PET is able to guide further evaluation of thyroid cancer patients who have elevated thyroglobulin levels and normal findings on 131I whole-body scanning.
Alnafisi
N S
NS
Department of Diagnostic Radiology, University of Western Ontario, London, Canada.
Driedger
A A
AA
Coates
G
G
Moote
D J
DJ
Raphael
S J
SJ
D000328:Adult; D002291:Carcinoma, Papillary / Q000175:diagnosis / Q000000981:diagnostic imaging* / Q000556:secondary / Q000628:therapy; D005260:Female; D019788:Fluorodeoxyglucose F18; D006801:Humans; D007457:Iodine Radioisotopes; D008297:Male; D008875:Middle Aged; D009364:Neoplasm Recurrence, Local / Q000000981:diagnostic imaging; D019275:Radiopharmaceuticals; D013954:Thyroglobulin / Q000097:blood; D013964:Thyroid Neoplasms / Q000175:diagnosis / Q000000981:diagnostic imaging* / Q000628:therapy; D014055:Tomography, Emission-Computed
D007457:Iodine Radioisotopes; D019275:Radiopharmaceuticals; D019788:Fluorodeoxyglucose F18; D013954:Thyroglobulin