ABSTRACT
BACKGROUND: FDG-PET has been suggested to have a supplementary role in localizing recurred sites of differentiated thyroid carcinoma. This study was performed to show whether FDG-PET is feasible as an alternative diagnostic modality for patients with I-131 scan negative thyroid carcinoma by verification of post-surgical pathology findings. METHODS: Eighteen patients of papillary thyroid carcinoma (M:F=4:14, age 41+/-16 year) who had total thyroidectomy and I-131 ablation therapy were included. All patients showed negative I-131 scan on therapeutic dose but they were suspected as disease recurrence because of elevated serum Tg or anti-Tg Ab during follow-up periods. FDG-PET was performed, and then cervical lymph node dissection on either side or both sides of the neck was done according to FDG-PET results. RESULTS: A total of 77 cervical lymph node groups were dissected in 18 patients; internal jugular chain 49, spinal accessory 9, jugulodigastric 5, anterior jugular 4, paratracheal 3, supraclavicular 2, and others 5. Forty eight lymph node groups revealed metastatic papillary carcinoma on pathology and their largest diameter ranged from 0.4 to 7.0cm (1.2+/-0.7cm). All patients had at least one malignant lymph node group. FDG-PET detected 37 among 48 malignant lymph nodes (sensitivity 77%), and their count ratio ranged 1.7-31.1 (6.1+/-6.3). Among the 30 malignant lymph nodes less than 1cm, FDG-PET detected 20 lymph nodes. Of the 29 lymph node groups without malignant cells, FDG-PET was also negative in 24 groups (specificity S3%). Positive predictive value of FDG-PET on I-131 scan negative differentiated thyroid carcinoma was 88%; negative predictive value was 69%. CONCLUSION: FDG-PET has been confirmed as a valuable diagnostic modality to detect cervical lymph nodes of differentiated thyroid carcinoma who are suspicious for recurrence but with negative I-131 scan, by pathologic findings.