Case of the Month—December 2003

Thyroid Cancer

History
A 50-year-old female with a history of papillary carcinoma of the thyroid presented with an elevated thyroglobulin (Tg) of 12. The patient is status post total thyroidectomy and I-131 ablation. Recent CT of the neck and whole body I-131 scan were negative.

Findings
PET FDG whole-body scan demonstrates a focus of increased uptake in the right neck. It is likely a level III cervical lymph node. This finding is consistent with metastastic disease.

How Did PET Help?
PET identified metastasis that was not evident on conventional imaging studies. The PET findings may change the patient’s clinical management from I-131 ablation to external beam radiation or surgery.

clinical image

Coronal
projection

Transaxial projection

Sagittal
projection

Discussion
Recently, CMS has approved the coverage for FDG PET scanning in patients with thyroid cancer of follicular origin (including papillary, follicular, and Hurthle cell cancer) who have a high or increasing serum Tg level >10 µg/l and no evidence of tumor on I-131 whole-body scan. Finding of persistent or recurrent thyroid cancer with FDG PET is important because it may be amenable to surgical or external beam radiation treatment. Studies have shown that FDG PET is a very accurate and cost-effective method of identifying residual/recurrent differentiated thyroid cancer not visualized by whole-body I-131 scan. Research shows that giving patients thyroid stimulating hormone (rhTSH) also has the effect of increasing the sensitivity of FDG PET to detect metastastic lesions.

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