FDG PET of recurrent or metastatic I-131-negative papillary thyroid carcinoma

This study reports on the use of FDG PET in the follow-up of papillary thyr oid cancer patients with negative findings on I-131 total body scans and el evated levels of thyroglobulin after total thyroidectomy. Methods: Eleven a symptomatic patients with previous papillary thyroid cancer, total thyroide ctomy, I-131 ablation, and treatment of ail known metastases had negative f indings on I-131 total body scans after therapy but persisting elevations o f thyroglobulin when not receiving thyroid hormone. All imaging before PET failed to show persisting tumor. FDG PET was performed on ail patients whil e receiving full thyroid hormone replacement, except for the repeated scan of I patient (patient 6). After the PET scan, all patients were referred fo r supplementary CT, sonography, or biopsy of lesions in the neck. Results:A ll 11 patients showed FDG uptake in the neck or upper mediastinum-in the in itial scan in 10 and in a repeated scan in 1. Sonographically guided biopsy confirmed malignancy in 6, was nondiagnostic in 2, and showed normal findi ngs in I, In 2 patients, the sonographic results were normal and no biopsy was attempted. FDG imaging redirected the treatment of 7 patients, resultin g in surgery and external beam radiotherapy in 3, surgery in 1, and externa l beam radiotherapy in 2. One patient declined further recommended surgery. The other 4 patients remain under observation. Surgical histopathology con firmed thyroid tumor in ail 4 surgically treated patients. Retrospective re view of the original histopathology slides showed no preponderance of aggre ssive histology. Conclusion: FDG PET is able to guide further evaluation of thyroid cancer patients who have elevated thyroglobulin levels and normal findings on I-131 whole-body scanning.