Clinical Presentation
A 40-year-old woman with a history of papillary thyroid carcinoma, 5 years status post thyroidectomy and radioiodine ablation, now presents with rising serum thyroglobulin levels.
(A) Whole-body iodine 131 scintigraphy demonstrates no abnormal I131-avid lesion. Enteric, urinary, and faint salivary (circle) physiologic activity is present. (B) PET/CT demonstrates three abnormal FDG-avid lesions in the neck (circle).
Differential Diagnosis
All three will be FDG-avid and negative on I131. However, the typical location and history make recurrent thyroid cancer the most likely etiology.
• Metastatic dedifferentiated thyroid carcinoma: In the setting of a rising serum thyroglobulin (Tg) level after thyroidectomy and radioiodine (RAI) ablation and a negative I131 scan, FDG-avid lesions are most consistent with this diagnosis.
• Hodgkin lymphoma: This can look very similar to dedifferentiated thyroid carcinoma on FDG-PET, but the history, including the Tg value, is much more suggestive of recurrent thyroid carcinoma.
• Head and neck carcinoma:
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