Value of FDG PET imaging in the management of patients with thyroid, neuroendocrine, and neural crest tumors.

OBJECTIVES: The purpose of this study was to evaluate the value and impact on management of FDG PET imaging in patients with biopsy-proved neuroendocrine and neural crest tumors, as well as thyroid carcinoma of various types.

MATERIALS AND METHODS: This is a retrospective review of imaging and clinical data of 60 consecutive patients presenting for evaluation of suspected recurrence who underwent FDG PET imaging between August 1993 and February 2002. All patients were referred for PET because of equivocal findings on conventional evaluation (most often increasing tumor markers and negative conventional workup) or for restaging. The final diagnosis was established with pathology (n = 19) or at least 6 months of follow-up (n = 41). The FDG images were acquired 1 hour after the intravenous administration of 10 mCi FDG with 1 of 2 dedicated PET tomographs (Siemens ECAT 933, CTI, Knoxville, TN; and GE Advance, General Electric Medical Systems, Milwaukee, WI).

RESULTS: Thirty-four patients had recurrent disease and 26 had no evidence of recurrence. FDG PET imaging revealed at least as many focal abnormalities as concurrent CT, magnetic resonance, or other nuclear imaging modalities in 46 of 60 patients (77%). There were 17 patients (28%) in whom FDG PET found abnormalities not seen with other modalities. In the small group (n = 18) of cases of carcinoid, pheochromocytoma, Merkel cell tumor, and neuroblastoma, all cases were true positive (T+) or true negative (T-). In the group of 42 cases of thyroid carcinoma, the sensitivity was 67%. There were 16 T+, 18 T-, and 8 false-negative (F-) cases. Six F- cases presented with increasing thyroglobulin levels and negative whole-body I-131 scans. Four of these 6 F- cases were proved by surgery, 1 by a positive post I-131 therapy scan, and 1 by normalization of thyroglobulin levels after I-131 therapy. Two of the 8 F- PET cases had a positive I-131 scan. FDG PET imaging had an impact on the management of 13 of 60 of these patients (22%) by demonstrating extensive metastases and cancelling surgery (n = 2), and by detecting recurrence and guiding surgery (n = 5) or radiation therapy (n = 6).

CONCLUSIONS: FDG PET is helpful in the evaluation of thyroid, neuroendocrine, and neural crest tumors. Although the sensitivity was only 76%, there were no false-positive findings, and FDG PET findings changed the management of 22% of the patients.